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   Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:07 JST Daniel Swain

   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

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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:04 JST Daniel Swain

     in reply to

     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

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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:05 JST Daniel Swain

     in reply to

     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

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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:05 JST Daniel Swain

     in reply to

     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

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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:05 JST Daniel Swain

     in reply to

     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

     Bill repeated this.
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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:05 JST Daniel Swain

     in reply to

     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

     Bill repeated this.
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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:06 JST Daniel Swain

     in reply to

     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

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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:06 JST Daniel Swain

     in reply to

     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

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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:06 JST Daniel Swain

     in reply to

     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

     Bill repeated this.
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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:06 JST Daniel Swain

     in reply to

     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

     Bill repeated this.
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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:07 JST Daniel Swain

     in reply to

     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

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     Daniel Swain (weatherwest@mastodon.social)'s status on Saturday, 28-Dec-2024 02:05:07 JST Daniel Swain

     in reply to

     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