Daniel Swain
@weatherwest
Weather and climate scientist focused on extreme events like floods, droughts, & wildfires on a warming planet.
SE-to-NW monsoonal flow is in full effect across California this PM. There's also a notable remnant MCV (mesoscale convective vortex) currently over LA & moving NW-ward. This feature will potentially be the "trigger" for some dry thunderstorms to NorCal overnight into Mon. #CAwx
The abstract submission window for our Western United States-focused hydroclimate extremes session (GC-071) at the American Geophysical Union December meeting (in San Francisco) is now open! This year's invited speakers will be Adrienne Marshall & Dmitri Kalashnikov.
Notable, fast-moving #SummitFire now making hard upslope run amid hot, dry, and breezy conditions (and high grass fuel loading after recent wet years) in San Bernardino County mountains. This fire is moving *southward,* toward Wrightwood from the *north.*
Along the western flank of the gigantic interior west-central U.S. ridge, monsoonal moisture will surge northwestward across California and the Great Basin. This could bring some initially dry thunderstorms, including over parts of CA (slight chance coastal areas), Sun-Mon. #CAwx
Another month & another upward shift in predicted #ElNiño peak intensity (between Oct & Dec) in the multi-model ensemble median. The single most likely outcome is now a very strong ("Super") El Niño event; a record-breaking event is possible, but not guaranteed. Full steam ahead.
I just submitted my formal comment on the disastrous proposal to transform essentially all U.S. federal grantmaking--affecting every sector of American science, technology, education, & health--into an overtly partisan political process. Full text here: weatherwest.com/wp-c...
While this potential event is still 7-10 days in future, there is currently an unusually strong signal in multi-model ensembles pointing toward an intense-to-record event--rare at such a lead time. Notably, this would cause Mountain West wildfire situation to deteriorate further.
There are growing indications that large, intense, & perhaps record-breaking mid-atmospheric high pressure system (aka a "heat dome") will develop somewhere between Rockies & Central Plains by mid-Jul. This could bring a widespread & severe heatwave across much of the U.S.
Very active fire behavior continues on existing large fires across S. Rockies/Four Corners--some of which are directly threatening communities. Less windy weather to come, but also growing indications of major heatwave by mid-Jul (w/shift from wind-driven->plume-dominated fires).
The #AspenAcresFire, still burning quite actively along southern Colorado Front Range & having destroyed ~200 structures thus far, has become an exceptionally complex & challenging event from a firefighting perspective due to a confluence of climate, weather, & geography. [Thread]
However, in the meantime, unusually dry conditions across West will continue. It looks like we will trade anomalous wind (but relatively cool temps) for anomalous heat (but lighter winds). Wildcard will be risk of dry t-storms, which could spark new fires & spread existing ones.
Looking ahead toward mid-July, there are early signs of an amplifying Four Corners ridge/high pressure system. The ridge may be unusually strong on its western flank, potentially portending a new Western heatwave and potential (tentative) monsoonal moisture incursion from SE.
Despite modest temperatures, extreme wildfire risk in the interior Western U.S. will continue due to persistent winds, very low humidity, and record-dry vegetation amid extreme drought. After July 4, the Western trough will be replaced by a ridge (and Eastern ridge will weaken).
Cooler than average conditions will persist along the West Coast for a few more days. Meanwhile, the extreme humid heatwave in the Eastern U.S. will set countless daily, many monthly, and even some all-time temperature records. Elevated humidity will further amplify health risk.
Cooler-and-windier-than-average conditions will persist in the Western U.S. for a few more days as persistent and unusual summer troughing continues. Meanwhile, in the Eastern U.S., a genuinely extreme, and possibly historic, heatwave will build under an intense ridge. [Thread]
The wildfire situation in the Southern Rockies continues to escalate. A new and fast-moving wind-driven fire today southwest of Pueblo, CO (#AspenAcresFire, near Beulah, circled in yellow) is of particular concern, and is currently burning through populated areas. #COwx
The #GoldMountainFire near Ouray, CO (ignited yesterday) and the hours-old #WillowFire near Leadville, CO are both spreading rapidly and exhibiting extreme fire behavior and are burning mainly in high-elevation timber, with expanding evacuations in these areas. #COwx
Unfortunately the interior West wildfire outbreak has continued to intensify under "extremely critical" fire weather conditions today and record-dry vegetation in some areas. Existing fires have re-intensified, and there are 2 new fires of particular concern in Colorado. [Thread]
Why is the vegetation here so dry, including record low fuel moisture in heavier fuel types? Well, this region record-low snowpack in 2026 (and a record-warm winter) and is experiencing a severe-to-extreme multi-year drought. (See just-issued NIFC Fuels and Fire Behavior.)
Today and in coming days, highly anomalous strong southwesterly winds (gusting to ~50 mph, at surface) and low humidity are co-occurring in a region with near-record or record vegetation dryness. Gravity waves (indicative of strong winds aloft) are visible in smoke plumes.
NOAA once again highlighting a rare, highest-end "extremely critical risk" region today around Four Corners/CO Western Slope for exceptionally adverse fire weather conditions amid severe drought. Numerous lightning holdovers are popping up during unusual summer wind event.
Many new & fast-moving wildfires in UT, w/emergency evacuations ongoing in multiple communities tonight due to explosive growth on #CherryFire. Notably, this is occurring in bullseye of NOAA SPC "extremely critical" outlook & NWS Salt Lake "Particularly Dangerous Situation" RFW.