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Live from La Farine: The Second California Storm of This Winter's Rainy Season Approaches..,

Daniel Swain: After another extraordinary mid-winter dry spell, major atmospheric river to soak NorCal later this week : California Weather Blog: "California has experienced some serious ‘weather whiplash’ over the past several months.... Extremely dry conditions heading into the early fall months gave way to a relatively brief ~2 week period of extremely heavy precipitation throughout much of coastal Northern California in early December, shattering local calendar date rainfall records in many places and even approaching all-time daily/December monthly records in a few spots... courtesy of a series of ‘atmospheric rivers’ (the emerging technical term for narrow corridors of very high atmospheric water vapor transport, typically associated with mid-latitude storms).... Then... the spigot shut off.... January 2015 was an extraordinarily dry month across most of California. Across the northern 2/3 of the state, there was almost no precipitation to speak of.... Numerous locations set new records for the lowest January precipitation ever recorded.... The culprit: a persistent, strong region of high pressure anchored over the northeastern Pacific/West Coast of North America has deflected Pacific storm systems to the north of California–just like last year. In fact, the similarity of the large-scale atmospheric wave pattern between January 2014 and January 2015 is extraordinary....

At this point, it almost goes without saying that January 2015 was extremely warm throughout California....

As seems to have become the theme over the past few years, an intense precipitation event now appears likely to immediately follow an extraordinary dry spell across Northern California. Confidence has been growing in recent days that another extremely moist plume of subtropical moisture will take aim at NorCal during the first week in February, bringing heavy to excessive precipitation to at least the far northern part of the state.... Places at least as far south as the Bay Area are likely to see significant precipitation over the next 7-10 days.... Someone along the West Coast is going to get a serious soaking.... Simulated rain totals for a ~7 day precip event have been very impressive for the North Coast, actually exceeding 20-25 inches of liquid in a couple of recent GFS runs....

In great contrast, the southern 1/3 of the state is likely to remain completely dry (and very warm–perhaps near 80 F!) for the duration of this storm sequence. Also, it’s worth noting that sea surface temperatures immediately offshore of California remain extremely elevated–and are locally more than 3-4 F above average for this time of year. These near-record temperatures could provide some extra moisture to the incoming storm systems, as occurred during the December storm sequence in NorCal....

Numerical model solutions currently disagree regarding the persistence of this wet pattern–certainly realizations suggest that this could be a ‘one-and-done’ storm sequence over 4-5 days, and other suggest a continuing parade of moist/warm atmospheric rivers through mid-February...

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