Figure 29: Broken Patterns. By late January, upper-level patterns had finally changed, blocking the atmospheric rivers. A Pacific ridge nudged near the West Coast, directing colder moisture-starved storms down troughs located farther inland. Source: National Centers for Environmental Prediction, Weather Prediction Center.
Figure 30. Cold Invasions. The break in relentless downpours was replaced by drier inside sliders and record cold air masses from the north, slipping down the east side of the ridge. Here in the water vapor image, a disturbance spins inland just north of Las Vegas while north winds dominate over California. Source: NOAA/National Weather Service.
Figure 31. Rippling with the Wind. During late January and early February, wet, stormy skies were often replaced with clouds shaped by cold upper-level northerly winds. Notice the ripples forming perpendicular to winds as vertical wavy motions develop and continue downstream, similar to an undulating roller coaster ride.
Figure 32. Cold Storm Organizes. By February 23, an exceptionally cold trough and its cyclone dropped along the Pacific Northwest coast. Instead of taking the drier inside track that had been established during recent weeks, it stayed out over the ocean. It continued drifting south, drawing in enough moist air to feed bands of precipitation toward the coast. Source: NOAA/National Weather Service.
Figure 33. Deep Trough Directs the Cold Train. This 500mb height contour map (about halfway up through our atmosphere) shows the cold upper-level trough digging in along the West Coast. Upper level winds flow roughly parallel to the contour lines. Note how frigid winds meander south from Alaska and directly over California as the trough intensifies. Source: National Centers for Environmental Prediction, Weather Prediction Center.
Figure 34. Following the Cold Trough. In this water vapor imagery, the storm spins off the Washington coast, circulating unstable convection into the Pacific Northwest. Parts of the coast, including Portland, would eventually be buried under record snowfall that crippled infrastructures. Winds within the massive, cold upper trough that dominated the west coast would steer the storm south. Source: NOAA/National Weather Service.
Figure 35. Catching Hail from Towering Turbulence. Exceptionally cold air was advected into upper altitudes by the late February storm, creating extremely steep environmental lapse rates (great differences between temperatures near the surface and aloft). Resulting instability erupted cloudbursts and thunderstorms that covered landscapes with graupel and hail down to sea level all the way into southern California. This individual cumulonimbus cloud spread pea-sized hail along a wide swath from the beaches into inland valleys. It delivered heavy snow squalls when it hit foothill and mountain slopes.
Figure 36. Record Snow Maker. By the next day (February 24), the center of the upper low had dropped off the coast of northern California and the trough had tilted out over the ocean, where it could entrain more moisture. California was on the stormy east side as the system gathered strength and continued digging south. Source: National Centers for Environmental Prediction, Weather Prediction Center.
Figure 37. Snow Accumulates at Low Elevations. By February 24th, the entire state was in the grips of this cold storm with its bands of heavy precipitation circulating counterclockwise around the low, now centered west of the Bay Area. Note how moist, unstable air is being drawn from the southwest and into the state to meet the cold core of air. Heavy snow at unusually low elevations spread from the Coast Ranges and Sierra Nevada into southern California. Source: NOAA/National Weather Service.
Figure 38. The Perfect Winter Storm. As the cyclone strengthened, it began to pull in a larger stream of moist air off the ocean. When air with high dew points and precipitable water encountered such cold air, rapid condensation and intense downpours paraded across the state. Source: NOAA/National Weather Service.
Figure 39. Formulated for Snow and Hailstorms. By February 25, the upper low was parked just west of Pt. Conception. This left southern California under a zone of upper-level divergence, where nature would put on an historic show. Source: National Centers for Environmental Prediction, Weather Prediction Center.
Figure 40. Coming Ashore, Sending the Turbulence East. The cold late February surface low circulated an intense frontal system, dragging the moisture and storminess across southern California. Northern California had already experienced snow down to sea level and it was now southern California’s turn. It was one more in a series of our storms that would be tracked east across the continent. Source: National Centers for Environmental Prediction, Weather Prediction Center.
Figure 41. Circulating Snowstorm History. Here, our frigid storm drags an intense cold front across southern California, circulating all the way up along the Sierra Nevada. Turbulent cloudbursts turned to record low-elevation snowfalls that piled higher on the Transverse Ranges, closed highways, and brought routine life to a standstill in mountain resorts. Note the popcorn cumulus clouds forming behind the front, in the cold unstable air over the ocean. Source: NOAA/National Weather Service.
Figure 42. Preparing for Landfall. By that February 25th date, only wraparound moisture was left streaming offshore in northern California. But southern California was in the bullseye of the storminess as the center of the cold low (the same low that spun down from the Canadian coast) drifted toward our coast. Source: NOAA/National Weather Service.
Figure 43. Unlikely Snowdrifts on the Hills. By late February, the historic cold storm had moved on, leaving jaw-dropping scenes of accumulated snow down near valley floors. These are the hills at the base of the Santa Susana Mountains just above the San Fernando Valley on February 26. Post-storm stratocumulus clouds pop up in moist midday updrafts.
Figure 44. Seattle Settles in California? Millions of Californians were treated to the sight of snow-clad hills above major population centers after the historic cold cyclone of late February, 2023. But this was only a brief break from the incessant parade of winter storms. Even periods between storms inevitably turned partly to mostly cloudy as moist air masses continued streaming overhead.
Figure 45. Drought-busting Water Delivery. By late February, soils were saturated and plant communities that had survived the great megadrought were soaked and shedding excess water. Here at the base of the San Gabriels, prickly pear cacti and chaparral plant communities prove we are still in California; but abundant water and impressive snowpacks hiding behind the clouds suggest we have moved to the Pacific Northwest.
Figure 46. Springing Back. Falls in San Gabriel Mountain’s Rubio Canyon sprang back to life in glorious fashion. This was just one example of rejuvenated streams and their falls that would swell to historically impressive discharges throughout the state, thanks to the long wet winter that slopped us into March, 2023.
Figure 47. Saving Californians. After historic rains that totaled more than 10 inches during individual storms upstream, the Rubio Debris Basin was doing its job, filling with sediment that would have cascaded through downstream neighborhoods. Can you see the difference between this March 2 image and our photo from two months earlier, before the big storms? Catch basins such as these saved thousands of residents from flooding and mudflows that would have devastated communities across California. Unfortunately, some other levees, debris basins, and infrastructure were finally overwhelmed, flooding thousands of residents out of their homes as storms continued to batter the state well into March.
Figure 48. Scenes from The Shining? Higher California elevations were buried in snow that accumulated in drifts over 20 feet high. By late February and early March, scenes from our mountain regions resembled snow seasons in the northern Rockies. Here, crews struggle to plow Hwy 50 near Echo Summit (south of Lake Tahoe), above 7,000 feet elevation. Source: Caltrans and the CHP.
Figure 49. Piling it on in Yosemite Valley. By late February, low snow levels had buried elevations that were not accustomed to such impressive accumulations. Yosemite Valley is only about 4,000 feet above sea level. It usually gets brief dustings of made-for-selfies snow near the cold back ends of winter’s storms and cold fronts. But this historic storm was all snow. Source: National Park Service.
Figure 50. Burying the National Park. Still wondering why they had to close Yosemite National Park on February 25? These tent cabins barely peeked above the snowpack at Curry Village… at 4,000 feet above sea level. Source: National Park Service.
Figure 51. Winter Wonderland. Historic winter storms have their advantages. Upslope fog cradles the base of Half Dome as snow accumulates on the valley floor during the memorable winter of 2023. Source: National Park Service.
Figure 52. AR Madness Returns. By March 10, yet another atmospheric river weather pattern had set up. Unlike the January storms, warmer subtropical air masses were streaming in from more southerly sources, such as near Hawaii. Source: NOAA/National Weather Service.
Figure 53. Flood Machines on Steroids. As if to duplicate January weather patterns, the familiar mother low off the Pacific Northwest Coast circulates counterclockwise. But this time, warmer atmospheric river air masses are drawn in from beyond Hawaii. Source: NOAA/National Weather Service.
Figure 54. Snow Melters. The low drifts inland on March 10, dragging the warm AR into the same parts of the state that were targeted by January storms. Warm rains at middle elevations begin melting record snow packs. Source: NOAA/ National Weather Service.
Figure 55. Déjà vu Weather Patterns. Compare this 500mb chart with our early January map (Figure 16). This is not a duplicate, but it is sometimes hard to tell. Exactly two months have passed, but similar upper pressure and air flow patterns are evident, helping to guide the atmospheric rivers. Source:National Weather Service/NCEP/Ocean Prediction Center.
Figure 56. From Hawaii to California. The warm southern source regions mark differences between the March and January ARs. These storms melted much of our snowpack water reservoirs, which we hoped would hold through spring. But the storm onslaught continued. Source: NOAA/National Weather Service.
Figure 57. Nature’s Repeat Performances. By mid March, another slug of moisture raced toward the Golden State. Like previous ARs, it would be wrung out, but now over completely saturated soils and warming snow packs. Some of the extreme runoff flooded infrastructures and communities on its way to the ocean. Source: NOAA/National Weather Service.
Figure 58. Broken Record Weather. Each shortwave disturbance organizes the AR into another flooding rainstorm and directs it into California. Weather history has been made in 2023. You get the picture and the routine by now. Spring starts the next week. Our rainy season usually ends in about a month. Super bloom season is just around the corner. Relentless storms take their final shots. Source: NOAA/National Weather Service.
Figure 59. The Improbable becomes Reality. On the calendar day when winter flipped to spring, the AR hits just kept on coming. This water vapor image shows yet another wet storm charging toward the state, but the subtropical jet stream and deeper AR moisture is directed more toward SoCal.
Figure 60. Charading as a Cold Hurricane. The center of another historic storm has arrived on the first full day of spring, intensifying and spinning as if to mimic a hurricane. Labelled by some as a bomb cyclone, its noticeable core rotates just west of the Golden Gate. It circulated pulses of instability and frontal bands with heavy rain, hail, and mountain snow across the state, spawning some funnel clouds and a tornado that touched down as far south as L.A. County. Winds topped 80 mph along the coast and 100 mph over some highlands. Source: NOAA/National Weather Service.
Figure 61. As if to compete with the season’s previous middle latitude and “bomb” cyclones, one more large, late-season cold, deep low dropped down from the Gulf of Alaska near the end of March. It swept its cold front across the state and blew more damaging winds over northern California. The front raced ahead and the mother low followed southeast, spinning more heavy rain, thunderstorms, and mountain snow statewide. Source: NOAA/National Weather Service.
Figure 62. By late March, incredible snow images were flooding out of the Sierra Nevada. More than 870 inches of snow had been recorded on Mammoth Mountain’s summit. Just below, the main lodge was buried by more than 695 inches of snowfall during this historic season. Both were all-time records. Photo Source: The Weather Channel.
By the first week of spring, many especially central California weather stations had recorded staggering precipitation totals for the season, more than double their annual averages, and some more than double the season’s totals in Washington and Oregon. Here are a few of the winners, all benefiting from some orographic effects. Far northern California stations were usually more distant from this season’s atmospheric river targets. Late March totals are shown in inches:
Big Basin Redwoods State Park: 83 Big Sur: 62 Santa Barbara: 41 Berkeley: 40 Sierra Nevada mountain and foothill locations include water equivalent snowfalls: Yosemite Valley: 67 water equivalent. Huntington Lake: 60 water equivalent. Mariposa: 52 water equivalent. Devil’s Postpile near Mammoth: 52 (with snow packs measuring over 180 inches). Central Sierra Snow Lab: 670 inches total snowfall by first week of spring. Mammoth: 695 inches snowfall at the main lodge, 870 inches at the summit, both all-time records.
Death Valley (demonstrating the most extreme rain shadow): 0.76 inches rain.
It is no surprise that historic floods were the result. You likely saw them earning lead stories in national media coverage, devastating mostly working-class communities. Dramatic videos from just two regions follow. We end with a quote inspired by a John Muir classic and written into the 2022 film, Infinite Storm, based on a true story. Near the end of the movie, the heroic rescuer and real life super hero, Pam Bales (played by Naomi Watts) declares, “Even in the storm, even in the pain, there is so much beauty. The whole universe appears as an infinite storm of beauty.”
Tule and Kern River Floods, March 2023:
Pajaro River Flood, March 13, 2023:
We leave you with two more detailed links that address specifics about this winter’s storms and the impacts they were having on our drought and our water projects, as winter turned to spring. For instance, this year lifted us out of a prolonged La Niña pattern and may have launched us into an El Niño phase. What might be the long-term consequences and how can we build more resilient water infrastructures that will get us through future droughts and flood years? www.youtube.com/watch?v=FW84W-Hh-OY
Here is an excellent summary of this stormy rainy season with some interesting specifics. It comes from Alex Tardy in the San Diego office of the National Weather Service. We will also end with a map from his presentation (see below), since it illustrates how the storms repeatedly aimed at that path from the Bay Area down to Santa Barbara County and then streamed over the Sierra Nevada and into the Great Basin. https://www.youtube.com/watch?v=QD0O_nlga-U
Stay tuned.
Figure 63. By April, the bizarre 2023 record rainy season’s die had been cast. Note how many weather stations in the path of the storms recorded 2X their average precipitation for January-March and some set all-time records. All this was at the end of an unusual three-year “triple-dip” La Niña. This wettest Jan-Mar period followed last year’s record driest Jan-Mar period at some of the same locations! These patterns offer countless opportunities for scientific research.
