Notices by Daniel Swain (weatherwest@mastodon.social), page 2

Given combination of strong/damaging wind potential, & vegetation that will approach record-dry levels for early Jan date, "extremely critical" wildfire conditions are possible Tue-Thu. This is definitely one to watch, given magnitude & antecedents. #CAwx #CAfire [3/3]

A major offshore wind & fire weather event will develop this week across much of Southern California. Essentially no rain has fallen so far this season in SoCal, and a high-end "atmospheric blowdryer" wind event will greatly increase wildfire risk by Tue/Wed. #CAwx #CAfire [1/3]

New on Weather West : As pronounced CA precipitation dipole persists, a high-end offshore wind/fire weather event (including "extremely critical" conditions) may unfold in SoCal this week. More benign, but drier, pattern in NorCal. Read more: #CAwx #CAfire https://weatherwest.com/archives/43171

Busy week coming up! I'll have a new blog post Sat/Sun on major to extreme offshore wind/fire weather event in SoCal, then another focused on our new paper on global hydroclimate whiplash on Thu. I'll also have at least 2 YouTube livestreams (dates/times TBD)... #CAwx #CAfire

North of San Francisco, periodic minor to moderate flooding and mudslides have been common; in SoCal, an active fire season continues are damaging wildfires have occurred during nearly every offshore (Santa Ana) wind event up through Dec. #CAwx #CAwater #CAfire

Much of NorCal has seen more than 200% of average precip to date since Oct 1, while most of SoCal is under 10% of average. In fact, parts of Sonoma County are still near record-wet to date will much of SoCal is at or near record dry to date as of late Dec. #CAwx #CAwater #CAfire

As the new year approaches, the already remarkable season-to-date "precipitation dipole" in California has further intensified. Much of SoCal has still not received meaningful rain this season, while NorCal continues to get soaked on a recurring basis. #CAwx #CAwater #CAfire

This pattern is likely due to a combination of subseasonal tropical forcing (MJO-like teleconnections from warm West Pacific) plus #LaNina or La Nina-like forcing from central/east Pacific. There has been a lot of (mostly anticyclonic) Rossby wave breaking in NE Pacific... #CAawx

Also, an unusually strong jet stream over the northeastern Pacific Ocean, combined with unusually warm ocean temperatures in the same region, have generated a number of impressive individual storm systems as well (some with very strong winds/unusually much lightning). #CAwx

The proximal culprit has been persistent subtropical ridging over and west of SoCal since autumn. This has kept SoCal high and dry (and near record-warm, too), but directed a parade of mostly warm #AtmosphericRiver storms into PacNW and NorCal. #CAwx #CAwater #CAfire

Even in a region frequently characterized by dramatic precipitation contrasts, this is one of the most extreme north-south season-to-date precipitation disparities I've ever seen in CA. This is *not* simply the usual wet north/drier south partition! #CAwx #CAwater #CAfire

So, what's next? A 1-2 week period of stronger/more widespread West Coast ridging likely in early Jan, w/drier conditions in NorCal & PacNW. Unfortunately, little/no rain & warm temps continues in SoCal--fire weather season continues there until further notice. #CAwx #CAfire

What did the seasonal models get wrong? The region of recurring cyclogenesis west of WA/OR, which has kept not only PacNW quite wet but ALSO most of NorCal, esp. north of San Francisco. This is a known "predictive failure mode" during La Nina-influenced periods. #CAwx

Overall, the pattern so far is reminiscent of a slightly latitudinally shifted version of what the seasonal predictive models had indicated for Oct-Dec (see below). What did models get right? Broad anomalous subtropical ridging plus strong/northward-shifted storm track. #CAwx

The "Relative Nino Index" (helpful in a warming climate) suggests a stronger #LaNina influence than traditional measures would otherwise indicate (esp. strong/north-shifted NPAC jet), w/wet PacNW and dry SoCal: https://www.climate.gov/news-features/blogs/enso/can-little-la-nina-pack-big-precipitation-punch

Beyond that, seasonal models continue to indicate fairly strong tilt in the odds toward dry winter in SoCal & interior SW, w/weaker tilt toward dry into Central CA. To the north, PacNW looks quite wet & NorCal may be battleground as storm track shifts around. #CAwx #CAwater

It has been exceptionally wet in parts of northern California, and exceptionally dry across most of southern California--resulting in a remarkable north-south "precipitation dipole." Will this likely continue? In a word: yes. #CAwx #CAwater #CAfire https://weatherwest.com/archives/43161

3) Very strong shaking reported in a modest swath east of epicenter; some modest damage likely south of Eureka.

4) I just ended a ~70 minute livestream in which I discussed all of this in detail; check out the recorded version here:
https://www.youtube.com/live/4spsWH-v6mg?si=_JWguQfLGdTFIQSH
[3/3]

2) The Tsunami Warning that had been issued for NorCal Coast, including SF Bay Area, has been canceled. I suspect the warning was issued, somewhat precautionarily, because of shallow #earthquake depth & initial conflicting data indicating some vertical displacement (vs. pure strike-slip). [2/3]

A couple of follow-ups re: today's California #quakes:
1) There was actually only one significant quake as of 1pm PT--the M7.0 SW of Eureka. The far northern Sonoma County quake was actually ~M4.1 but initially registered higher due to conflicting data. [1/3]