Posting as heads-up to weather modeling world (not as a realistic prediction of future conditions): the (new) GFS has occasionally been spitting out completely absurd surface temperatures for CA's Central Valley. 18z run today shows 128-130F. Anyone know what's up? Image
An intense and very possibly record-breaking heatwave is indeed possible in that interval, but not "hottest temperature in modern history" hot. I'm assuming it's the surface scheme, but then again, the 850mb temps are absurdly high also (though maybe feedback from sfc?). Image
Seems as if the ECMWF is now doing something similar. Either both models share some kind of similar surface scheme bias/error that involves sporadic positive/self-reinforcing surface temp feedback during extreme events (still by far most likely), or...hmm.
Paging anyone in numerical weather modeling world who has insights, esp. folks at @NOAAResearch, @NWSWPC, @NWSEMC, etc. This is turning into a potential public communications problem, especially because there could actually be very high-impact heat event buried in these errors.

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More from @Weather_West

7 Jun
Correction to give more accurate context: vegetation dryness & flammability metrics (1000hr fuel moisture & ERC, respectively) are indeed exceeding record levels for *calendar* date over most of Sierra Nevada, but *not* records for *any date.* (Phew!) (1/4) #CAwx #CAfire
For those interested, the confusion apparently arose due to a differing period of record for NorCal vs. SoCal data via the NorthOps/SouthOps GACCs. In SoCal, period of record is only ~10 years, so "any date" records less meaningful. So: data not wrong, but context is missing.
This really doesn't change the overall picture: there's still an exceptionally severe drought across all of Northern California and vegetation is still exceptionally dry--even relative to extreme values of recent years. But it's important to get the details right! (3/4)
Read 4 tweets
27 May
@MichaelWWara @jtemple As I've been emphasizing recently, the *predictable* aspects of Fire Season 2021 (soil moisture/vegetation dryness) are as bad or worse as any observed historically. The level of landscape flammability--especially in denser brush & forests--is genuinely scary. BUT... (1/2)
@MichaelWWara @jtemple ...A big part of what makes certain fire seasons exceptionally severe (from lives lost, homes burned, & ecosystems damaged perspective) has substantial random component. Do ignitions primarily occur during extreme fire wx? Do we see many heatwaves/wind/dry lightning events? (2/3)
@MichaelWWara @jtemple Latter aspects are largely not predictable in advance (except perhaps frequency of heatwaves--which are indeed expected to be elevated). In 2020, we were very unlucky w/all the unpredictable elements. I hope we won't be in 2021...but that's not a good management plan! (3/3)
Read 4 tweets
2 Mar
My perspective piece, "A shorter, sharper rainy season amplifies California wildfire risk," is now out in GRL. I discuss recent findings pointing toward shortening & sharpening wet season, & implications for ecology/wildfire. (1/17) #CAwx #CAfire #CAwater agupubs.onlinelibrary.wiley.com/doi/abs/10.102…
This perspective is in response to a recent analysis led by Jelena Luković showing that seasonal onset of CA precipitation has become progressively delayed (by ~1 month) in recent decades, w/ shorter but sharper rainy season. Underlying paper: agupubs.onlinelibrary.wiley.com/doi/full/10.10… (2)
Record heat, plus late arrival of seasonal rains, have played a key role in CA's extremely severe wildfire seasons in recent years. Autumn 2020 exemplified this trend: vegetation conditions were, by a wide margin, the most flammable on record.#CAfire agupubs.onlinelibrary.wiley.com/doi/abs/10.102… (3)
Read 18 tweets
1 Mar
March 1st update: 2020-2021 "wet season" in California remains dismally dry in most places. In fact, wide swaths of both NorCal & SoCal are well under 50% of average precipitation. It has also been a warmer than average winter overall, despite some cold interludes. #CAwx #CAwater
Statewide average snowpack has quickly fallen from late January highs (around 70-75% of average for the date) to around 61% of average for the date as of Mar 1. #CAwx #CAwater
Outside of a brief period of possible showers across coastal SoCal on Wednesday, the next ~5 days still look very dry across most of CA. #CAwx
Read 5 tweets
18 Feb
PSA: Relatively low-latitude, even sub-tropical, locations in central & eastern portions (but less frequently western portions) of continents can occasionally experience severe winter cold spells--like Texas is currently enduring. But how, & why this longitudinal asymmetry?(1/17)
Well, water has a tremendous ability to buffer against thermal extremes. This is because H20 has high heat capacity--around 4x that of land! This means that it takes around 4 times as much energy to raise the temperature of a given mass of water the same amount as land. (2/17)
An intuitive consequence is that regions near large bodies of water are usually milder than landlocked areas at a similar latitude. This is also why dry places have much larger diurnal temperature ranges than humid places. (3/17)
Read 17 tweets
26 Jan
Thread on very strong inbound CA storm. A cold & clear morning will quickly give way to increasing clouds, NorCal valley rain & snow down to 1,500-2,000 ft (locally lower) later this PM. Current satellite imagery shows this strengthening system off the coast. (1/10) #CAwx
Tonight, a rapidly intensifying cold front will sweep across NorCal. This front will be unusually well defined, for a CA winter storm, and will replace an already cold airmass with...another cold airmass! (2/10) #CAwx
The cold frontal passage is expected to be quite dramatic across NorCal in the overnight hours. A convective "narrow cold frontal rainband" (NCFR) will likely develop, which could bring a period of torrential rain or snow to many areas, as well as possible lightning. (3/10) #CAwx
Read 11 tweets

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