Introduction: Transmogrification in California

We need a new word to describe this. Forgive those who sense that we have entered some sort of space-time warp, when two locations and microclimates separated by just a few miles could experience such radically different atmospheres, as if they were worlds apart. But it also seems unthinkable that such remarkable changes could occur within any specific region within just one year, challenging us again to check our calendars. Old descriptors for our once more dependable seasons and weather patterns have been evolving toward unfamiliar, unlikely, exceptional, and unprecedented. Comparing the final months of the calendar years 2024 and 2025 unveils a topsy-turvy environment that repeatedly produced chaotic scenes more common to a science fiction movie. Exceptional pattern anomalies amplified again through and beyond the first month of 2026.

Several years of stories on this website have documented widely researched seasonal disorders that have made news headlines each month … and they only seem to be getting weirder and more impactful. We are, at this time in this state, perfectly situated to explore and learn from these upheavals as our unparalleled diversity of microclimates, ecosystems, and landscapes continue calling out to us.

Calendar Contrariness

One year ago, our stories led you through the unprecedented weather patterns that set the stage for catastrophic historic and deadly wildfires which eventually consumed entire Southern California communities. We examined the momentous drought that left only around 1/10^th of an inch of rain in the SoCal coastal plains from spring into mid-January (the middle of our rainy season). This year stood out in stark contrast as many of those same locations had already equaled or exceeded half their average annual precipitation totals by mid-November, long before what are usually the wettest months of the rainy season. But as we advanced into November, 2025, nature performed another dramatic switch. Persistent weather patterns locked into place into mid-December and they were all powerfully connected: SoCal’s seemingly endless sun and above-average temperatures in the 80s versus consecutive days of record cold, dank, and dreary valley fog; merciless warm atmospheric rivers (ARs) from the tropics that produced record catastrophic flooding in Washington contrasted with arctic blasts that plunged the upper Midwest and East Coast into the deep freeze. Yet another radical shift near the end of December (and into 2026) brought powerful storms and flooding atmospheric rivers across California during the holiday season. Another reversal to persistent, resilient high-pressure systems and winter storm blockades dried out the entire West Coast through January while historic Arctic deep freezes paralyzed the continent east of the Rockies all the way to the Eastern Seaboard. The spectacular diversity of conditions and their theatrical impacts on us and our landscapes have ranged from astounding to unnerving. There’s so much going on in this story that should keep curious observers on the edge of their seats.  

Episode One: Odd Cutoff Lows Spin Their Moisture Magic

Some of the blame for these multiple twists of fate (sometimes coined weather whiplash) started with a series of odd early-season cold and unstable upper-level low-pressure troughs that dug down from the north and broke off from general circulation patterns. November’s cutoff low repeat performers skimmed down the West Coast, mostly whirled and sprinkled through Northern California, taking the bulk of their moisture and energy with them. Then, the pesky, reenergized storms anchored and spun their turbulence over waters just off the Southern California Bight, entrained Pacific moisture, and tossed it inland. Give the National Weather Service credit for warning us about these cutoff lows that remain a weather forecaster’s woe.

As hours ticked into days, trains of steady showers circulated from Mexico up through and past Santa Barbara County. When the unstable moisture was lifted up the Transverse Ranges, heavier orographic precipitation watered the slopes and snuffed out the fire season. Soils became saturated, seasonal streams resumed flowing early, fresh green spouts appeared everywhere, and premature weeds erupted in our gardens. Since the showers were mostly beneficial and steady rather than sporadic downburst gulley washers, we were first spared the worst of flooding and debris flows that could have coughed out of our burn scars. Observers were wondering how it was possible that the hills were so alive just one calendar year after debilitating drought and Santa Ana winds had primed these same landscapes for their dehydrated fiery destruction. One of the wettest starts to our rainy season this year had transposed last year’s driest into our rear-view mirrors.

Ocean Current Mysteries

Augmenting the improbability of these captivating whodunnits, all this early-season atmospheric chaos was raining down during the start of a weak La Niña year, when cooling water currents in the tropical East Pacific might be expected to result in more stable air and a relatively dry SoCal rainy season. Here’s more proof that the El Niño/La Niña Oscillations we research as ENSO cycles (such as in previous stories on this website) and their effects have NOT been as dependable or predictable during this century compared to late last century. We are reminded that we are observing and researching targets that are constantly moving and evolving.

A possible less-understood culprit for the October-December 2025 SoCal wetness could have been the now infamous North Pacific “blob” that peaked in September and circulated through the end of the year. This giant marine heat wave (which has reappeared in some form during recent years) expanded to 5,000 miles across the Northern Pacific Ocean until sea surface temperatures maxed out at a record 68°F (20°C). In addition to ongoing climate change, research suggests that recent decreases in air pollution (particularly sulfur dioxide) from cleaner shipping and Chinese sources have helped to clear Pacific air masses of reflective aerosols, allowing more direct solar radiation to heat ocean surfaces. Regardless, such a mysterious warm blob throws another complicating variable into our understanding of ocean-atmosphere interactions that could be responsible for these historic anomalies.

Episode Two: High Pressure Heat Versus Cold Fog

As if to keep us on our toes and our eyes on the skes, nature abruptly and dramatically flipped the switch again after mid-November. Massive high-pressure systems took control, building and oscillating off the Southern California coast and over the Southwest States into Mexico. The strength and extent of these tall, heavy domes of stacked air challenged seasonal records and eventually dominated the entire state. As air descended out of the monstrous fair-weather storm blockers, clear and dry became the latest curious forecast fads across most of the state, lasting an entire month through mid-December, a period which normally marks the annual start to our seasonal rains. The November air columns started out cool, but days of dry offshore flow and compressional heating pushed temperatures into the 80s along the SoCal coast and into the upper 80s in the inland valleys right into mid-December. Weather stations in the Coast Ranges (such as in the Santa Cruz Mountains) and Sierra Nevada foothills recorded high temperatures well into the 70s in the clear, dry, sinking air. Adding an additional layer of complexity, another conspicuous exception developed and stubbornly held out as the antithesis to the warm and dry: historic valley fog episodes.

Epic Fog Traps

The same powerful high pressure that squeezed Southwest air columns toward the surface for a month also capped a shallow layer of cold air that settled and pooled in Northern and Central California inland valleys like dense water in a vast bathtub. I’ve written on this website and in my latest California Sky Watcher book about how our Great Central Valley is the perfect winter laboratory to make valley fog (AKA as tule fog or radiation fog), which forms in place as cold, dense, heavy air often settles down to the lowest flatlands and becomes trapped for 400 miles from Redding to Bakersfield. In this latest classic episode, the valley floor had been moistened by those earlier October/November rain events; then, the air just sat down there below the inversion with little or no circulation as leftover heat radiated out, gradually cooling the air toward its dewpoint. Once the late-night air chilled to near 100% relative humidity, the moist haze turned to cold fog. Now, we have a saturated pool of air trapped in the confines of our natural oval-shaped beaker, with the Coast Ranges on one side and the Sierra Nevada Mountains on the other.

With such short daylight hours and low sun angles, weak sunlight struggled to boost temperatures above dewpoints, allowing the winter fog to further thicken during long nights until it didn’t even “burn off” during the daytime. This tule fog enshrouded the valley from late November well into mid-December, 2025. It became the star of conversations, news headlines, and memes as the cold and gray bled west through the Carquinez Strait to invade the Bay Area. As valley temperatures stalled in the 40s, Bay Area residents shivered through consecutive hazy and foggy days that could barely warm into the 50s. The dull creepy mist also condensed in other inland valleys through Central and Northern California, from wine country, to the Trinity, Klamath, and Eel River Basins. Such a remarkable and historic prolonged exaggeration of the annual valley fog doldrums was capable of depressing the most upbeat Pollyanna to beg for mercy in the form of some clear-sky relief.

To be or not to be Fog

Though we call it “fog”, this particular weeks-long episode often formed as low stratus cloud ceilings a few hundred feet above the ground. Visibilities near the ground (and below the thicker hovering blanket) were often measured at around a mile or so, decreasing at night and slightly improving again each afternoon. Just above the inversion, at around 2,000 feet above sea level, temperatures warmed well into the 70s each day thanks to dry, sinking air and unlimited visibilities. Some mountain and foothill communities could only look down through their pristine ether toward the distant layers of thick silver cotton below. In contrast, that same descending air often scoured out any inversions trying to form in SoCal. When the high pressure strengthened overhead, the Southland enjoyed a string of iconic warm and crystal-clear December days. When the resilient high weakened or drifted a bit, a shallow marine layer was enabled to spread night and morning fog into coastal valleys. During those days, most California coastal and valley communities were mired below stagnant inversions that forced air quality management districts to issue alerts and enforce no burn days: no chestnuts roasting on open fires to belch smoke that quickly gets trapped below shallow choking anvils.

Pollution and Fog Partnerships

Recent research shows that the frequency of cold valley fog events in California was increasing each decade into the 1980s, most likely because of increasing air pollution. Droplets of water are more likely to condense around certain particulate matter, known as cloud condensation nuclei. As emissions from fuels combustion and farm operations increased, fog episodes became thicker and more frequent. After the 1980s, as air pollution controls took effect and emissions decreased, so has the frequency of dense fog. Indeed, there is an exact correlation between NOx pollution (nitrogen oxides) content in valley air and fog density and frequency, measured both from the ground and satellite imagery. This could explain why the more recent thickest “fog” actually formed a few hundred feet above sea level, leaving the higher fringes of the valley shrouded while residents at lower elevations were looking up toward the grayest low blanket. Gradual climate change could also be playing a role when today’s warming surface temperatures remain just a degree or two above valley dew points.

Essential Fog

These might seem like foggy details, but they are important for a number of reasons, far beyond casting our brooding moods; here are two. First, transportation is often crippled by dense valley fog. There is a long history of deadly California accidents caused by low visibilities, followed by scenes of multiple mangled vehicles once the mysterious murk finally begins to clear. Surviving commuters have been caught in hours of gridlock on shrouded highways and narrow serpentine detour routes. Air traffic is often diverted and delayed when even the most experienced pilots with highly sophisticated cockpit instruments are challenged while attempting to take off or land through such dense curtains of potential aviation disasters. Second, the foggy winter chill deposits some moisture and may shield valley fruit and nut trees from direct sunlight during dormant periods of rest, which eventually increases annual production of these multi-billion-dollar agricultural products. (Before native plant communities were plowed, grazed, and developed into history, winter fog played an essential role in nurturing vast valley prairies that some coined California’s Kansas.)

Tule fog’s malaise is finally broken up when restraining high pressure eases or moves away and when turbulent instability sweeps in from the Pacific, allowing wind currents to scour down to valley floors. Regardless, this latest misty atmospheric quagmire kept millions of acres and millions of Californians from the Central Valley to the Bay Area enveloped throughout a remarkable string of consecutive clammy days and nights with temperatures stuck in the 40s F.

Episode Three: Catastrophic Floods and Frigid East Coast Connections

We can also recognize how our resilient high-pressure blocker was part of a larger pattern that dominated weather across the continent. As air descended out of our massive high, its winds were turned to the right by the Coriolis force, creating those familiar clockwise pinwheel circulations common to all high-pressure systems that often span thousands of miles in the Northern Hemisphere. These gyrating winds curved toward big, cold low-pressure systems spinning counterclockwise in the Gulf of Alaska. Strong pressure gradients and powerful air streams grew along narrow battlefronts between the highs and lows to drive abundant moisture and embedded disturbances flowing across the Pacific within atmospheric firehoses; a parade of rainmakers were directed north, up and over California’s tall stacks of fair weather and into the stormy Pacific Northwest.

The resulting archetypal atmospheric rivers (ARs) had sources so distant and farther south of Hawaii that Mango Express replaced the more familiar Pineapple Express monikers. The prolonged invasions of unusually warm moist air strengthened to attack the Pacific Northwest. Snow levels were so high, almost all the precipitation fell as torrential mountain rain that had to runoff somewhere. Rivers surged over their banks in December until record stream gauge heights sent catastrophic flooding across landscapes and into neighborhoods from north of Portland into Canada.

Amplified Waves Make West Coast-East Coast Connections

How is this connected to the December artic blasts that dropped clippers of snow, ice, and wind storms across the upper Midwest until temperatures plunged below zero F and wind chills could freeze flesh within a few minutes? Once that same stream of air arched up and over our West Coast high pressure ridge, it came diving down its opposite (east) side and into the middle of the continent. This downstream trough opened the door for arctic air to race directly out of Canada and all the way to the East Coast, proving how all of these pattern shifts and winds are connected. And these high-amplitude waves in the upper-level winds are just what computer models have warned us about. As the Arctic has warmed faster than most other locations on our planet, temperature gradients and pressure gradients between warmer air to the south and cool air to the north are decreasing. The jet stream that forms between these contrasting air masses tends to slow down and form large meanders (Rossby waves) of upper-level troughs and ridges that get stuck in place and that’s exactly what happened through mid-December. Two more powerful connections in one paragraph!      

Episode Four: Atmospheric Rivers Bring More Winds of Change 

Later in December, yet another major weather pattern whiplash changed everything again. The stubborn Southwest high-pressure system finally began weakening and drifting away, allowing that historic atmospheric river to gradually, mile by mile, sag south as pressures dropped. As it shifted south, the AR whipped back and forth, targeting most of California through the holiday season. To keep your attention and prove how these winter AR storms mean business in Northern California’s high country, consider this NWS forecast on December 23, 2025 for Mount Shasta:

“Snow. The snow could be heavy at times. Low around 13. Wind chill values as low as -13. Windy, with a south wind 85 to 95 mph increasing to 100 to 110 mph after midnight. Winds could gust as high as 115 mph. Chance of precipitation is 100%. New snow accumulation of 41 to 47 inches possible.” 

Unfortunately, snow levels remained very high especially early during most of these AR onslaughts, adding snowpacks only to the highest elevations, often above resort levels. A low-pressure trough forming off the coast finally bent the AR into a more southwest-northeast oriented arc to circulate copious amounts of rain and high-elevation snow into the state. As air pressure continued to drop offshore, fears of a “bomb cyclone” event grew, while pulses of damaging winds, thunderstorms, and other severe weather swung across California’s Central and North coast during the holidays.

And as the bullseye finally migrated into Southern California, this AR was following recent patterns, behaving much like computer models have also warned: as global temperatures increase, warmer water can evaporate into warmer air that has the capacity to hold more water vapor. These trends are loading ARs with moisture and energy since the air can hold about 7% more water vapor for every 1°C increase in temperature (about 4% more water vapor for each 1°F). Recent single AR events have produced more than a foot of rain as they get lifted over higher terrain. In this holiday episode, such orographic effects dumped more than a foot of water into rain gauges from north of Santa Barbara along the Transverse Ranges into the San Gabriel Mountains. Where ARs had stalled over them, some weather stations had already received their average annual rainfall totals even before the two normally wettest months (January and February) of the season. As expected, flooding and debris flows belched out of the mountains, particularly below recent burn scars. The resort communities of Wrightwood and Lytle Creek in the San Gabriel Mountains earned most of the media attention for mudflow destruction (see links to videos following these essays). With a few exceptions, many of these fitful storms lost much of their punch while trying to slip south toward San Diego County, bringing mostly lighter and beneficial precipitation there.  

Reiterating the power of atmospheric connections (again), upper-level winds dipping around the low-pressure trough that directed firehoses to blast California through the Christmas season were forced to turn back north over a massive high-pressure ridge dominating the central US. Air descending out of this monster dome of high pressure set countless records for both the hottest high and highest low temperatures ever recorded during the holiday season, from Arizona, Utah, and New Mexico, across the Rocky Mountains, through the Plains and Midwest and into the southern US. Temperatures peaked at 20-35°F above the average in many of these regions (high temperatures in and around Oklahoma City made it past 80°F) while some Californians were getting washed out.  

It would be difficult to overstate the difference between the start of last year’s rainy season and this 2025-2026 season, especially in Southern California. (The official water season begins on October 1 each year.) The parade of holiday storms continued across California through the first few days of January, raining on the Rose Parade for the first time in 20 years and cancelling celebrations into the New Year’s Weekend. Contrast this year’s drought-breaking and eventual deadly inundations with virtually no rain by this time last year and the deadly fires that followed. On January 1 alone, more than one inch of rain fell from Oxnard to Long Beach, setting new records for the date. By early January, 2026, numerous locations from north of Orange County to the Central Coast Ranges had already equaled or exceeded their average annual rainfall totals, just as the two traditionally wettest months of the year were to begin. Some stations (such as in Santa Barbara County) experienced their wettest start just after last year’s record driest start to any rainy season. On the first days of January this year, freshwater runoff coincided with another astronomical King Tides event, causing historic shoreline flooding (such as around the Bay Area), when the tides combined with low pressure, onshore winds, and storm surges. You can see why we can only guess what surprises to expect in the long run, so stay tuned.  

Epilogue: Following the Science that Connects the Dots to our Future

This story’s roller-coaster ride analysis of interconnected phenomena guides us into 2026, as we hope to settle back into more seasonable expectations; but nature likely has other plans. If you want to imagine 2026 and beyond, click back to some of 2025’s extreme weather events, such as those analyzed in our other recent website stories (rogue storms, Texas flash floods, SoCal wildfires, etc.). What do they all have in common? Though we were warned a few days ahead by remarkably accurate forecasts from the National Weather Service, the deadly catastrophes went on to destroy too many lives and too much property, often because local officials failed to properly prepare and respond.

We have learned that anything goes as we anticipate beyond those seven- and ten-day forecasts, and the mysteries grow as we look further into the next year. So, we wonder why, at this critical time when we must better comprehend the science behind what is rocking our world, the US Government is cutting the heart out of the very scientific organizations that help us make sense of these changes and anticipate what might be next. As I write this, the latest victim to be thrown on the chopping block is the National Center for Atmospheric Research (NCAR) in Colorado. Should we lose this and other vital agencies that objectively and efficiently guide us through the science of change and warn us what to anticipate, we all become victims. What took us decades to build and nurture may be lost forever. Such short-sided penny-wise and pound-foolish irreversible policies are certain signs of a less developed society in decline, a culture that celebrates ignorance only to suffer the long-term consequences.    

We could be forgiven for behaving like the frogs in the pot parable, except these are not gradual changes; they’re slapping our faces and kicking our butts every season. Changes that have always ruled our world have been growing in intensity and duration and these coalescing change agents are calling out for our immediate attention. Like uninvited intruders in our homes, such massive experiments are repeatedly and more frequently transforming our environments and our lives to remind us that we ignore them—and nature—at our peril.

For you dedicated weather enthusiasts and researchers who are hungry for even more discussion and details, continue on past this brief list of links, where you will find a chronological sequence of dynamic images from the last months and days of 2025. We then carry you through the next weather whiplash that delivered another record-breaking West Coast dry spell which coincided with the historic (and connected) cold waves of deadly ice and snow storms that froze the Midwest and East Coast through January 2026.       

California Current Marine Heatwave Tracker

Atmospheric Rivers Science

Mud and Debris Flow Videos from Wrightwood and Nearby High Desert:

https://www.facebook.com/watch/?v=4259235981063913

https://www.facebook.com/watch/?v=1576524737019441

Lytle Creek Mudflows

King Tides During the Storms Videos

Daniel Swaine’s Weather West year-end summary, including late December storms

Defunding National Center for Atmospheric Research

A History of Winter Dry Spells from Golden Gate Weather Services (and thanks to Bill Patzert)

By late January, 2026, the early warm storms followed by mid-season drought sounded alarms across the West as snowpacks dwindled.

The latest maps.

Trapped under another round of resilient high-pressure systems, dangerous tule fog episodes returned to California inland valleys through January.

The series of warm, sunny days that followed early-season heavy rains produced a premature season surprise desert bloom (in January!) at places such as Anza Borrego. This story explores the mysteries behind Joshua Tree early bloomers at higher desert elevations.

A wealth of additional images (from the ground and from space) and maps follows, carrying you through some of the more memorable and dynamic weather events and colorful scenes from late 2025. Captions are limited, but they are also in chronological order. This journey (we could consider it an appendix or addendum) incudes some details that should interest meteorologists and climatologists AND instruct newer students and casual observers. We will make it all the way to the start of 2026 and a break in the stormy weather, ending our photo ops with sunsets, moon rises, flowers, and feathered friends. Finally, our January 2026 epilogue II (a necessary addition) displays images and weather maps showing how the West Coast suddenly dried out as the Midwest and East Coast were experiencing their epic prolonged cold snap. Such connected West Coast/East Coast opposites extremes would play out into February.  

Revisiting Episode One (October-November, 2025): Odd Cutoff Lows Spin Their Moisture Magic

Revisiting Episodes Two and Three (December 9-10): High Pressure, Dry Heat Versus Cold Fog AND Catastrophic Floods Versus Frigid East Coast Connections

Revisiting Episode Four (December 20, 2025-early January, 2026): Atmospheric Rivers Bring More Winds of Change

Follow Us to the End-of-Story Bonus Colors: Rainbows, Trash, Cloud Murals, Sunset, Wetlands, Flowers, Birds, and the Return of El Sol.     

The rain paused and clouds parted just enough by the afternoon of January 1, 2026 to encourage a long walk (the next six photos) at Bolsa Chica Wetlands in Orange County …   

January into February, 2026 (Epilogue II): Yet Another Historic Weather Whiplash

January 2026 brought yet another meteorological shift that will go down in the record books. As if to mimic another movie sequel, a giant high-pressure system formed over California; but this time, it eventually elongated all the way up past the Canadian border. The big storm blocker kept California dry for weeks during the middle of the rainy season and left some Pacific Northwest locations (such as Seattle) with their longest period without precipitation during any January in history. And in what has become a familiar twist of weather pattern whiplash fate, upper-level winds that curved north of the West Coast and into Canada then made drastic U-turns to plunge toward the middle of the continent. These same winds raced south from the Arctic, driving temperatures below zero Fahrenheit into the Midwest, spreading historic freezing ice and snow storms across the continent to the East Coast, prompting deep freeze news stories that lasted through much of January. It was yet another example of how West Coast-East Coast antithetic extremes become connected by high-amplitude upper-level waves that seem to get stuck in place. The following images illustrate some of January’s weather dramas.    

The following photos were taken in mid-January, 2026, as the record-breaking arctic cold snap was freezing the Midwest and East Coast. By contrast, this was Southern California during the same time, a few weeks following those premature heavy rains, and during the unusually long winter warm spell when afternoon temperatures peaked well into the 80s.   

THE END … for now.

The post What a Difference a Year Makes first appeared on Rediscovering the Golden State.

For now, we can learn from the images prepared by David Gomberg as the rainy season ended in May. David is Lead Forecaster/Fire Program Manager at the L.A./Oxnard  National Weather Service office and he shared his work during a workshop organized for college educators by Senior Meteorologist Todd Hall, with contributions from other meteorologists there. We are reminded again that all U.S. weather information and forecasts originate from the National Weather Service. These dedicated scientists use their knowledge of the complex physical laws that rule our atmosphere to prepare each day’s forecast. Without their technologies and expertise, weather forecasting would be unreliable guesswork. NWS original forecasts are then distributed to the public where commercial apps and self-appointed gatekeepers filter out the substance and relay their versions that will entertain the masses and increase ratings. To bypass this media fluff, you can go directly to the source of the forecast. Just click your region and let the real learning begin: https://www.weather.gov/ Thank you National Weather Service professionals!

The images that follow are presented in chronological order as the season progressed. Various NOAA satellite imagery was used along with weather maps from San Francisco State University to display and explain evolving weather patterns. These 500mb charts are used to show upper level patterns and winds that often dictate weather conditions on the ground.

After a dry October, powerful autumn storms began to form in the north Pacific and aim at the Golden State. Atmospheric rivers seemed to be setting up ahead of these incoming low pressure systems until the lowest sea level pressure ever observed in California was recorded at Crescent City in late November.  By December, we seemed well on our way toward what would be another banner water year.        

By January, upper level patterns were shifting dramatically toward drought and by February, those ridiculously resilient ridges were locking in place over us, right in the middle of what should have been our wettest months of the year. Huge swaths of California from the coast to the Sierra Nevada received no measurable precipitation in February for the first time since recording began, following an unusually dry January. And for most stations in central and northern California, March was also disappointing. Stations around and beyond the San Francisco Bay Area into the Central Valley and along the central Coast received no precipitation in February. These included San Francisco, Oakland, San Jose, Sacramento, Salinas, Big Sur State Park, and Paso Robles. Southern California stations also recorded well below average precipitation in February (L.A. experienced its 10th driest on record) and most of the state was left at less than 5% of its average for the normally wettest months of January and February combined.

Just when it seemed too late to salvage this rainy season, nature delivered some March and April miracles to southern California that would miss many locations to the north. They arrived as a series of odd upper level lows that became cut off from general circulation patterns. Some of them drifted inland to the north as dry inside sliders and then retrograded southwest back over the ocean to pick up moisture off of southern California. Others spun right down the coast, mostly missing the north and then wandering and wobbling, again, southwest of southern California. As they finally drifted inland from northern Baja or across the southern California bight, these relatively small systems delivered soaking rains throughout southern California and well into the Desert Southwest.

During April, southern California caught up to its average or surpassed the seasonal precipitation totals, while northern California was left stranded in a serious drought year. As an example, Los Angeles accumulated 140% of its average precipitation for November and December, only 8% for January and February, and then 130% for March and April, while central and northern California missed most of those spring downpours. These cutoff lows became much more than the typical weather forecasters’ woes in the spring of 2020.

Though the late rains brought spring wildflower displays to the deserts and tempered what would have been a horrendous early fire season in southern California, they kept northern and central California on the dry side. As if the state had become meteorologically inverted, many southern California coastal stations ended up with twice as much rainfall as San Francisco and other stations around the Bay Area. The state’s northern and central snow packs and runoff into reservoirs (sources for most of California’s water projects) resembled some of the record lows experienced during our recent severe droughts that were finally doused by more recent record wet years. 

And so, as this is written in mid July, our spring has turned to summer as a series of high amplitude high pressure ridges and low pressure troughs have been migrating over us, bringing periods of extreme heat, followed by refreshing cool spells, punctuated by high winds . These erratic weather patterns leave us all wondering what is next, knowing that another fire season looms ominous. Will some summer monsoon moisture sneak in from Arizona and Mexico to briefly quench inland southern California and the southern Sierra Nevada? Will Pacific Northwest troughs be strong enough to usher in cool air masses over our state? How long will we have to wait into autumn before the next rainy season returns to snuff out this year’s fire season? If you are reading this several months later, you may already know the answers to these annual scientific guessing games that have become more challenging with our changing climates.

After reviewing this story, you might be interested in comparing this year’s weather events to the average trends during the last century or so. Go to our next story about climate trends in southern California that was inspired by National Weather Service Senior Meteorologist Todd Hall.

The post Another Bizarre California Rainy Season: 2019-2020 first appeared on Rediscovering the Golden State.

Our weather science story begins when summer turns to autumn. Land masses in the Basin and Range and Desert Southwest begin cooling much faster than the ocean surface. Summer’s less dense, expanding air masses in the thermal low pressure that has dominated over land are replaced with cooler, denser, sinking air masses in the Basin and Range during many fall and winter days and especially colder nights. The thermal low that was sucking in summer’s sea breezes from the coast is replaced by the cooler Great Basin High surface pressure that forms in this frigid air of fall and winter. As heavy, dense air settles out of this high pressure system, the wind flows away from the high and toward now relatively low pressure near the coast. The Coriolis effect spins this land breeze a little to its right as it flows over California. These cooler air masses are forced to compress and squeeze through California’s mountain passes and canyons on their way toward sea level and the coast. This compression heats an already dry continental air mass as it cascades into inland and coastal valleys on the ocean sides of the mountains. Relative humidities can drop well below 10%.           

Whether you call them Santa Ana (southern California) or Diablo (northern California) winds, they announce fall’s arrival. Each year, we witness a competition that will determine the severity of our state’s fire season. Will the first weather fronts drop down from the Pacific to bring quenching rains to a state parched by several months of summer drought? Or will the dry winds come first, blowing across fire-adapted pant communities and baked soils that haven’t yet received the season’s first showers? Every year is different. In the fall of 2017 and 2018, brutal winds arrived before the rains, following especially long, hot, dry summers. Relative humidities dropped below 10% in the compressionally heated winds that fanned epic firestorms of death and destruction.

The accompanying weather maps (thanks again to NOAA’s National Weather Service) display some specifics from the most deadly days of November 2018. The surface map shows a steep pressure gradient from inland to the coast. And this event had the upper atmosphere support that is so important in bolstering the offshore winds so that they howl throughout the day and night. Note the 500mb map that shows air pressure and wind flow patterns approximately half way up through our atmosphere, around 18,000 feet (5,600 meters). Here, you see a large ridge of high pressure over the eastern Pacific that extends above the California coast. This shows upper level support that encourages a stronger offshore flow. Upper level winds will blow roughly parallel to the lines on this isoheight map (this map showing the height of 500mb) as those meandering winds flow west to east around the globe. You might be familiar with the upper level jet stream that can be embedded within these air flow patterns.

Just as these upper level winds curve up toward the north and over the ridge, they then meander back down south, toward the adjacent trough. This upper level motion causes the stream of air to slow down and become denser and heavier just east of the ridge, similar to how traffic on the freeway slows and bunches up behind various obstructions. Here is where negative vorticity advection and anticyclonic flow usually dominates. This denser air sinks, fortifying high pressure at the surface. It’s the combination of this upper level support on top of the already cold, dense high pressure at the surface that creates the strongest offshore winds. Winds blow out of this strong surface high pressure and toward lower pressure near the coast or out into the ocean. The Coriolis effect pulls the winds slightly to their right, spinning the air clockwise out of the high, resulting in strong surface winds that may gradually shift from north to northeast to east over days as the high pressure slowly migrates farther east. Eventually, the pressure gradients ease as the pressure cells change and migrate; the offshore event ends.

The good news is the fires are contained in the relative calm aftermath. The bad news may be displayed in layers of residual smothering smoke that hover over and downwind of the fires in the stable air. This air quality problem that takes us full circle to the start of our fire essays earns one more lesson in weather science. After the high pressure responsible for these offshore winds weakens and/or moves east, normally migrating northern hemisphere pressure systems and their shifting winds often disperse the smoke and may even deliver precious moisture to parched landscapes as winter’s storms begin to drop south and clear the air. In other cases, the weather patterns may briefly stall, leaving a stable, stagnant atmosphere lacking the winds necessary to disperse smoke from the fires.

The later was the case on November 10, 2018, the day after the Woolsey Fire erupted in southern California as the L.A. Basin was shrouded in orange and red. Dangerous air quality was measured until another Santa Ana event scoured out the basin on the next day.  Still, one week after the Paradise Fire erupted and was being successfully contained, a veil of toxic smoke from that blaze had covered the Sacramento Valley and drifted all the way over the Bay Area. Schools were closed, athletic events were canceled, and officials discouraged any outdoor activities from the Sacramento Valley through the Bay Area. Even The City’s iconic cable cars were shut down. 

How bad was it? We can start with the gone-viral photo taken by editor David Little and published by the Chico Enterprise Record just as the Camp Fire was spreading terror and death. As the winds gradually subsided, so did the air masses, allowing the accumulating smoke clouds to creep across the Sacramento Valley until they were finally strangling the Bay Area. Six days after the Camp Fire started, air quality was still some of the worst ever recorded in the region, the accumulated smoke capped by a ridge of high pressure overhead. More than 35 micrograms of small particulate matter per cubic meter are considered unhealthful by federal standards. But monitors around Chico and Gridley were recording more than 300 micrograms and one temporary station between Chico and Paradise recorded dangerous amounts over 900 micrograms per cubic meter. These microscopic particles of ash can lodge deep within the lungs, causing serious health problems.   

So these latest nightmares started with the dreaded National Weather Service wind advisories and red flag warnings for November 9, 2018 that turned out to be spot on. They included those NWS warning maps covering an area from the coastal ranges across the Central Valley and well into the Sierra Nevada foothills. At the same time, another NWS map displayed high wind or red flag warnings for all southern California mountains and coastal valleys. As was feared, apocalyptic firestorms swept through both regions. One week later, the maps forecast the dangerous air quality that spread into the Bay Area as responders dug through the ashes in Paradise hoping not to find the remains of hundreds of people still missing. Luckily, most were finally found alive, except for the 85 victims who perished. Our mission and responsibilities couldn’t be clearer or more urgent: our efforts to better understand the forces of nature and our interactions with them, and our abilities to anticipate what comes next require our immediate attention.       

The National Weather Service is the original source of all weather forecasting information in the United States.

The post Weather Science Behind the Firestorms first appeared on Rediscovering the Golden State.

These eastern slopes that face inland are dominated by continental air masses. Summer’s daytime heat yields to some of the coldest temperatures in the nation at night, thanks to the thin, dry air. Temperatures at select locations (often high-altitude basins where cold air masses can pool) drop well below 0 degrees F during winter. Hardy species that can withstand such extremes mix together in resilient communities that may be more familiar to the Rocky Mountains. Add accessible water and you will find some of the finest displays of autumn colors in the state when trees such as cottonwoods (often at lower elevations), willow, and the rarer aspen ((Populus tremuloides) often found at higher elevations) lose their chlorophyll greens and turn dormant to signal winter’s approach. In some cases, these locations were within view of the magnificent glaciers that reworked eastern Sierra Nevada landscapes during hundreds of thousands of years of cooler and wetter glacial periods.

Thousands of years ago, as climates warmed and the glaciers retreated, plant communities were left to evolve in drier climates. We find their stranded remnants as relicts snaking mostly along riparian woodlands in protected canyons or clustered around springs where they have access to precious water. And if you were wondering why these landscapes aren’t blanketed with the seemingly endless fall colors that spread from New England to Appalachia each season, you forgot the magic limiting factor here: water. Only about 1% of Basin and Range landscapes are riparian habitats. Soils, fires, microclimates, slope exposure, and climate change and other human impacts also help determine the nature of these communities.

So it is here that we take you on a journey to find California’s spectacular autumn colors among native plant communities most people might not include in their stereotyped California landscapes. The time is late October 2018, when the majority of leaves have lost their chlorophyll, but haven’t fallen off the deciduous trees. Our search leads us toward the West Walker River and East Walker River headwaters near the Nevada border southeast of Lake Tahoe, where streams feed the upper Walker River Basin. And once again, we quickly discover that these landscapes have plenty of concomitant stories to share.

In this case, we see how two different drainages start in spectacular mountain scenery and then cascade off the eastern slopes of the Sierra Nevada to deliver precious water to high desert landscapes below. Both rivers turn north, separated on opposite sides of the Sweetwater Mountains before flowing out of California and into Nevada.  And as is common with so many streams in the West, human demands (mostly for agriculture) are often greater than the discharge from these rivulets.

The familiar results are less water for downstream ecosystems and users as the West and East Walker Rivers flow into Nevada and finally merge. By the time what’s left of the Walker River makes an abrupt right turn south and struggles toward Walker Lake in Nevada, there is little or nothing left, except during flood years. By then, free-flowing water must have survived abuse from a variety of stakeholders through several jurisdictions and land uses. Especially during dry years, downstream fish, wildlife, and entire riparian ecosystems struggle along with the humans who depend on these water diversions for survival.

So this starts out as a simple story about how a history of water, fire, and ice have combined to produce some of the state’s most spectacular fall colors. It quickly becomes a more complex drama that involves water diversion and water rights among multiple stakeholders and between bordering states and Indian reservations. Issues involving groundwater access and quality, irrigation for agriculture, domestic water quality, fishing and other ecotourism, watershed and ecosystem management and restoration, and sustainable land uses all float to the surface. It finally ends well beyond the boundaries of our California project in a threatened and protected Lake Walker, a terminal lake in Nevada’s high desert. During more than 100 years of human diversions, lake levels dropped 160 feet and total dissolved solids increased ten times up to 2010 in this water that often began as crystal clear Sierra Nevada snowmelt.

All of these undercurrents lurk among the relatively remote small town America landscapes and cultures near Hwy. 395 where the ever-changing weather and climate, the best fishing holes, and the tastiest homemade pies might dominate local conversations.         

Our images begin just south of and then around Twin Lakes near the headwaters of the East Walker River. We will then explore the West Walker River as it cascades through its gorge and then spreads into its Antelope Valley. 

We end by skipping south and away from these watersheds to find color in Round Valley just above and northwest of Bishop and below the lateral and terminal moraines left by glaciers similar to those mentioned earlier, a rangeland on the northern edge of an Owens Valley with a very different, but epic water rights story of its own.

Highway 395 is the remarkable thread that ties these images together, since all of these locations are conveniently accessible, especially by adding a short drive or hike up a local canyon. The colors get easier to find north of Bishop. Additional patches of fall colors can be found in canyons and on slopes near Hwy. 395 north of Reno, into more remote northeastern California. This would make a good excuse for another autumn excursion into the colors of the Warner Mountains.

Autumn Colors

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The post Searching for Autumn Colors in the Eastern Sierra Nevada first appeared on Rediscovering the Golden State.