As progressive ridge-trough pattern shifts toward more persistent ridging, rising heat in CA and the Southwest likely in late May
Recent conditions in California: Unsettled, though mostly drier and windier than average; temperatures mixed
The past month has brought a notable unsettled period of weather to much of California and the broader Southwest. Significant, and much-needed, precipitation fell across some portions of the interior Southwest (including northern Arizona and New Mexico), along with some rain-shadowed and desert portions of California east of the Sierra Nevada. Warmer than the recent (climate-warmed) average temperatures were generally the rule across most of the West during this period, with the notable exception of coastal California and the aforementioned portions of AZ and NM. Additionally, nearly zero precipitation fell during this period across the Pacific Northwest and southward into NorCal, which is unusual for this time of year. Overall, it was quite a windy period as well, with multiple moderate to strong north wind events in California causing some downslope/compressional heatwave conditions at times and driving relatively rapid drying of grasses in exposed areas, leading to some fire activity during windy periods.
The main driver of this overall quite changeable pattern was what’s known as a “progressive” pattern, characterized by a recurring ridge-trough-ridge sequence that allowed occasional low pressure disturbances to dive southward and bring occasional showers/wind but did not allow them to linger, and also allowed fairly strong but transient ridges to build in between. We’ll see another 4-5 days of this pattern continuing before a more persistent and pronounced ridge builds (see below).
One more “inside slider” low pressure system before broader and stronger ridging builds; high grassfire risk in some spots
One more “inside slider”-type low pressure system will affect California and the Great Basin this weekend, bringing widespread windy conditions late weekend into early next week. A few showers are also possible across the Sierra Nevada and northern mountains during this period (plus maybe an isolated thunderstorm), as well as a bit of coastal drizzle in parts of SoCal, but in general this system will be more notable for its wind than its rain or mountain snow. In fact, the NWS in Sacramento has already raised a Fire Weather Watch for the Sacramento Valley and adjacent lower hills during this period for an elevated risk of grassfires (specifically) during this period of strong winds and low humidity. This will not be an extreme or widespread fire risk day–it’s just not dry enough across most of NorCal yet–but in some places the grasses have started to cure and they will be plenty able to carry a wind-driven fire at lower elevations moving forward this season.
Substantial heatwave possible in 7-10 days across interior Southwest and inland portions of California
Once the Sun-Mon inside slider moves to the east, it looks like the rest of May will be dominated by a broadening ridge across most of the West. In the 7-10 day period, a fairly strong springtime ridge will build aligned with the interior SW–bringing a period of possibly notable heat across the Lower Colorado River Basin and also across CA’s Central Valley and inland valley/desert portions of SoCal. There are already some indications that temperatures in these areas could potentially approach daily record highs, at least, during this period; details remain TBD. But unlike other heatwaves so far this season, this one will not be especially brief. In fact, at the moment, all major modeling ensembles now agree that beginning 5-7 days from now and continuing for at least 10 days thereafter (and likely longer), Western U.S. weather will increasingly be characterized by persistently hotter than average conditions under a broad ridge of varying strength (but no longer interrupted by significant troughs). This means that the month of May will likely, in the end, indeed end up being much warmer than average and probably also drier than average across most or all of California–as had been foreseen in most seasonal outlooks.
All signs continue to point to a notably hot, and possibly fiery, summer ahead across most of the West (including CA)
For several months, there has been a notable strong signal in the global “super-ensemble” (i.e., the “ensemble of ensembles” including predictions from all major global modeling groups) that this summer may be exceptionally hot across the western U.S. (and, really, across most or all of North America). The latest May update is no exception, and continues to point to a summer than may be much hotter than even (exceptionally hot) recent ones across most of the Western U.S. (and beyond).
Two details are of note: 1) There is a very high likelihood that Jul-Sep temperatures may end up in the hottest 20% of recent summers (i.e., even accounting for our climate-warmed baseline) and that yet another record hot summer is entirely possible in some areas, and 2) The anomalous warmth, particularly later this year from July onward, may reach closer to the California coast than it has the past couple of summers due to expectations that ocean temperatures will not be below average (and may end up warming to above average levels later in the season). So while the coast (as always) will still be cooler than inland areas this year, the seasonal gradient may be less pronounced than recent summers where record inland heat has been in great contrast to chilly and foggy conditions along the coast. It’s worth noting that May Grey and June Gloom are still likely, but after that, I do think this summer may be different than recent ones.
Accordingly, NIFC predictive services are now explicitly forecasting an above average fire season across most of California (away from the immediate coast), especially from July onward, and also across the Pacific Northwest, central and northern Rockies, as well as the Four Corners region. In other words: there are some striking signals pointing to widespread risk of a very active fire season across most of the West. The reasons vary a bit from location to location–in some cases, severe multi-year drought is raising risk in forests (interior SW); in others, the wet-to-dry whiplash transition expected later this summer (from wet antecedent conditions in 2024 or earlier, causing abundant grass and brush growth, followed by a dry spring and perhaps exceptionally hot summer) could be of concern in non-forest settings. In the Sierra Nevada and other higher mountain regions (including much of Colorado, and the Cascades in the PacNW), winter snowpack was quite respectable but melted very quickly this spring–leaving these upper elevations at greater risk of significant fire activity than solid peak season SWE numbers might otherwise suggest (especially in the context, once again, of a notably hotter summer potentially on tap).
In the short term, there continue to be good prescribed burning windows across CA and much of the West as the spring-to-summer transition is still underway. But there are some pretty strong signs that this summer has the potential to be a very active one, wildfire-wise, across the West–and that may be compounded by non-weather/climate-related considerations (see below).
Alarming cuts to NOAA have now left CA’s entire Central Valley & adjacent mountains without 24/7 coverage by local NWS
If you’ve been following my YouTube livestreams, or the Weather West comments section, or my (increasingly stark) public statements to various media outlets in recent weeks, you are probably aware of the ongoing decimation of not only weather and climate research in the United States, but also of the paragon of applied meteorology that is the U.S. National Weather Service. I won’t go into details here–although if you want more information, I strongly encourage folks to check out my recent livestreams or other recent media coverage on this topic–but I did want to alert the Weather West audience to the now major and still-expanding negative consequences for California.
Yesterday, the Washington Post reported that a growing number of local NWS offices were so extremely understaffed that they are no longer operating 24 hours per day (i.e., they are completely shutting down at night). Additionally, far more offices are now understaffed to the point that most/all supervisory and coordinating science staff roles (including critical “Meteorologist In Charge” and “Warning Coordination Meteorologist” roles, as well as technical and repair staff roles (for weather radars and surface stations), are now vacant and cannot be filled (due to severe funding cuts as well as a total hiring freeze–even in emergencies).
In an extraordinary development, the list of NWS field locations no longer operating 24 hours per day includes two in California: the Sacramento and Hanford offices, which together serve not only the CA capital city but also the entire Central Valley and surrounding foothill/mountain regions, including the Sierra Nevada west of the crest.
For those wondering: yes, this is as bad as it sounds. While adjacent NWS offices are, undoubtedly, stepping in to help and gap fill wherever and whenever they can, it’s important to remember that most of those offices are now, too, understaffed. The NWS in California, and elsewhere, is now being stretched critically thin–and there is a growing risk of consequential mistakes being made during extreme weather events (including extreme fire weather events, like the historic Los Angeles event back in January amid which the NWS office in Oxnard played a pivotal and life-saving role). In California, the lack of 24/7 NWS field office operation across a vast region extending across much (or even most) of the California interior is, simply put, a ticking time bomb (and I don’t say that lightly). We’re now entering fire season, and the region above includes a large fraction of the most fire-prone regions of the state (outside of the SoCal coastal chaparral zone); it also includes nearly the entirety of the Sacramento and San Joaquin watersheds that drain into the Central Valley and ultimately into the Delta (which could become a major problem, beginning again in the fall and winter, should major flood risk arise), not to mention the vast majority of California’s most productive agricultural lands.
Together with the ongoing dismantling of disaster and emergency response capacity by the federal government–including FEMA and other relevant entities–my colleagues and I are alarmed that California, along with other states/regions, may be much more vulnerable to weather and wildfire-related hazards for the foreseeable future. My sincere hope is that, following increasing public outcry and dissension by Congress, there will be a rapid resolution to this developing crisis. But in the meantime, I’ll continue to keep folks updated as best I can as to developments at the federal level and what the weather, climate, wildfire, and general disaster-related implications may be for Californians.