Discover and read the best of Twitter Threads about #CAwx

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This was, by any quantitative measure, an extraordinary (and meteorologically extreme) lightning event across the southern half of California. But the societal impacts will be nowhere as severe as the dry lightning event in August 2020? Why? A brief thread: #CAwx #CAfire
First, & most importantly, the June 2022 thunderstorms were generally significantly wetter than the Aug 2020. Yesterday, most of these cells brought at least brief rains (and sometimes downpours). There were certainly dry strikes outside of rain cores, but most strikes were wet.
The June 2020, by contrast, were truly dry thunderstorms--many places only saw a trace of rainfall or nothing at all. Even a modest amount of rain co-occurring with lightning can greatly reduce (though not eliminate) the likelihood of a lightning-caused wildfire ignition.
Read 11 tweets
Some mixed news on CA weather front over next couple of weeks. First, by Monday, another "inside slider" system will bring another burst of cooler & winder conditions statewide. Once again, some Sierra snow showers are possible, but most places stay dry. #CAwx #CAwater
Midweek, however, an even colder airmass and associated low pressure center will slide down the coast slightly farther to the west. This system, although still quite dry, stands a better chance of bringing convective activity (scattered showers/isolated thunder) statewide. #CAWx
The biggest impact from this mid-week system, outside of some additional modest Sierra snow accumulations and a few pockets of accumulating small hail showers at lower elevations (like last week in SoCal), will be a dramatic shift toward much colder temperatures. #CAwx
Read 6 tweets
October and December were extremely wet in parts of California (record wet in some parts of NorCal). But the most recent ~45 day stretch (Jan 1-Feb 17) has been among driest mid-winter periods on record most of CA, NV, UT, and portions of adjacent states. #CAwx #CAwater (1/3) Image
This has yielded in a seasonal "percent of average" precipitation map that is pretty misleading. Most of CA has slipped slightly below avg precip for the season to date--except for narrow swath along I-80 corridor that experienced the extreme Oct #AtmosphericRiver. #CAwx (2/3) Image
Yet hydrologic/landscape conditions--inc. surface reservoirs, soil moisture, streamflow, & vegetation aridity--are at extremely dry levels for mid-winter. This is due to 1) ongoing long-term drought and 2) the recent 6+ week record dry/warm & windy spell. #CAwx #CAWater (3/3) Image
Read 3 tweets
Very dry conditions will continue through end of month, bringing record dry January to some portions of Central & interior Northern CA/western NV. Multi-model ensembles are suggesting a subtle westward shift in Pacific blocking ridge in early February. However... #CAwx #CAwater
However, that while westward shift in ridge axis may be enough to bring some colder & unsettled conditions, it's unlikely to be enough to offer more than light precip in most spots. And pattern shift may be short-lived, with ridging shifting back toward coast by mid Feb. #CAwx
This is another good meteorological example of why only considering individual "operational" weather model output can be misleading in broader context. The "op member" (e.g., left) is presently much wetter than the ensemble mean (e.g., right) from the same model... #CAwx #CAwater
Read 3 tweets
We have just released the 2021 Annual U.S. Climate Report. Follow this thread for details, and read more online: #StateOfClimate Map of US with NCEI logo with text "2021 Annual U.S. Cl
The 2021 contiguous U.S. average temperature was 54.5°F, 2.5°F above average, the fourth-warmest year on record. #StateOfClimate 2021 Mean Temperature Departure from Average U.S. Map
RECORD WARM FOR THE MONTH: December contiguous U.S. temperature was 39.3°F, 6.7°F above average, exceeding the previous record set in December 2015. #StateOfClimate Map of December 2021 U.S. Statewide Average Temperature Rank
Read 10 tweets
Enfin une « bonne » nouvelle en provenance des États-Unis 🇺🇸 : La #sécheresse en partie résorbée en #Californie après plusieurs épisodes d’#intempéries ces dernières semaines. L’État de l'Ouest #américain était en proie à une sécheresse historique à l’automne dernier. #Thread 🧵 Image
📈Contexte : Les #USA contigus ont connu un été météorologique (Juin-Août) 2021 record 🌡, l’un des plus chaud jamais enregistré, à égalité avec l’été 1936. Sur la période Janvier-Août 2021, les températures sur tout l’ouest américain ont été bien au-dessus des normales. @NOAA ImageImage
Zoom 🔎 sur l’Ouest américain : Tout simplement l’été météorologique le plus chaud depuis le début des relevés en 1895. Près de 3°C au-dessus de la normale 🥵 (1901-2000). Du jamais vu !

Source : @NOAA ImageImage
Read 36 tweets
Downtown Sacramento has observed 7.72" of rain since the start of new Water Year.

The entire last Water Year only recorded 7.87".

Expect the current water year rain total in Sacramento to exceed all of last year by Sunday afternoon or Sunday night. #CAwx #CArain
Note that Water Years run from October 1 to September 30.
Redding airport still has a bit more to go to in order surpass last WY's total of 14.24". Current WY total is 8.51".
Read 3 tweets
📰 Hot off the press! Check out the #snow forecast via our cross sections for I-80, Highway 50, and other impacted highways. Be prepared for difficult to impossible mountain travel. #CAwx #CAsnow ImageImageImageImage
More highway snow forecasts fresh off the press: ImageImageImageImage
And a few more: ImageImageImageImage
Read 4 tweets
Time for a 🧵

A hazy view from the nest cam in the City this morning as a temperature inversion continues to trap pollutants near the surface. Now is a good a time as any to do a deep-dive into the science behind these set ups. #CaWx
It is important to highlight that when we talk about pollution we are often referring to two key particulates: PM and Ozone. Both tend to be emitted 🏭 from a wide arrange of emission sources and spread outward into the lower levels of the atmosphere. PM and Ozone
Normally, these pollutants get transported away from their original sources, but this transport gets halted as soon as we A) have a temperature inversion over us and B) are sitting under a stable air mass. Infographic on temperature inversions.
Read 8 tweets
Last I checked, our city of Richmond has accumulated nearly 5 inches of rainfall, which is higher than most other East Bay cities. But this presents massive problems considering our dynamics. Many unsheltered folks for one, and the topography of the landscape, from east hills.
This is content captured by my bruh @Dennykpt as he was making way back from Marin County, back into North Richmond/San Pablo are.
The big rig had been pushed over by windy and rainy conditions on the Richmond bridge. #CAwx
This was captured by my other homie, mobbin down San Pablo Ave. Poor and exhausted infrastructure. Nearby is wildcat creek, which is not afforded appropriate protection and restoration to help regulate flow in general. Today’s extreme hydrologic event is very bad. #CAwx
Read 6 tweets
California, on statewide basis, is now experiencing its worst drought in observational record going back to late 1800s--narrowly beating out peak of last drought in 2014-15 (as measured by PDSI, a metric that takes into account both precip & temperature). #CAwx #CAfire #CAwater
There is a clear trend toward increasing aridity in California--and yet little trend in mean precipitation. How can this be? A very strong warming trend due to #ClimateChange means same the amount of water falling from sky just doesn't go as far as it used to. #CAwx #CAwater
We explored this phenomena in research published in 2015 (finding that rising temps are the main factor behind increasing CA drought severity):…

and 2018 (increasing "precip whiplash" despite little change in mean):…
#CAwater #CAwx
Read 5 tweets
Dry lightning event of *some* magnitude is now looking increasingly likely across *some portions* of CA on Sun/Mon. Details to come. But first, some thoughts on potential wildfire risks posed if this comes to fruition. (Thread) #CAwx #CAfire
Usually, fewer than 1 in 10 lightning strikes actually ignites a wildland fire. These numbers can be higher if lightning is not accompanied by precip, or if lightning occurs under unusually dry conditions in dense vegetation. But in general, lightning ignition *rate* is low-ish.
A big problem thus arises when there are a very large number of dry lightning strikes. This occurred during the extraordinary and historic Aug 2020 event in Northern CA, where 10,000+ strikes were observed (and subsequently *hundreds* of fires were ignited).
Read 12 tweets
While we're having fun being exasperated by the heat. We want to put it into context. The Rogue Valley is forecast to see max Temps at or above 100 degrees for 9 days in a row (starting yesterday). There have been only 3 times in our history (since 1911) where this has happened.
Two of the streaks reached 10 days (August 1967 and July 1962). The 3rd reached 9 days (August 1990). The other important part of this, is that our overnight low temperatures will only reach into the mid to upper 60s to 70s. This does not give people a chance to recover at night.
Please check in on your neighbors and friends throughout this heat wave. If you know someone who has a broken A/C (or no A/C), invite them over for a cold beverage (be safe with COVID, please). If you're working outside, take frequent breaks in A/C.
Read 5 tweets
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
Fire danger spiking again: after a barely 24-36 hr dip in ERC values from spotty precip/cooler temps last weekend, levels have shifted quickly back to near max high values (extremely dry). Bay marine region 3A in Summer/Fall like values (1/2) #CAwx #FireWx ImageImageImageImage
In retrospect the signs of an early fire season start have been there for awhile. Spring fuel moisture values tracking near or at record lows vs. what should’ve been seasonal highs. Extreme drought cause and effect. (2/2) #CAwx #FireWx @nbcbayarea…
Ignore the fact it’s early May, conditions are Summer dry already esp. hills, parched by drought and above average temps. Add wind and you’ve got a Fire Weather Watch for interior NorCal starting Sunday. Important messaging by @NWSSacramento #CAwx #FireWx Image
Read 3 tweets
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…
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:… (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… (3)
Read 18 tweets
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
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
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
1/_ Interactive #GIS map showing risk of #DebisFlow for wildland fires. For the legend and to get the most benefit from the map, please click “Map tips” in upper left corner. To search on address click Menu > Search. #CAwx

Open #GISsurfer map: Image
2/_ The map opens at the #CZULightningComplex. You can pan the map to other 2020 fires and see the same type of data. Be patient! The map might be slow to refresh. It depends in part on how much other work the GIS server is doing.
3/_ The map can display the risk of debris flow for fires back to 2017. Here is one way to make a map to see the risk of debris flow for a fire prior to 2020:
A. Click the basemap button and look under the “Overlays” heading
B. Click “Turn off all overlays”
Read 12 tweets
First, some good news: NorCal seems to have made through initial (extreme wind) phase of this critical fire weather event relatively unscathed. Few new small fires, but nothing unmanageable. A few thoughts as to why this was the case: #CAwx #CAfire
Very strong to extreme winds and exceptionally low humidity did materialize, despite an initial delay. A peak Bay Area gust of 89mph (with fairly widespread gusts above 50-60 mph), and peak Sierra Nevada gusts well over 100mph, were recorded. #CAwx #CAfire
In some spots, extreme winds did indeed mix down to low elevations (interior North Bay Valleys; Oakland Airport; San Francisco; Half Moon Bay). But some locations closer to sea level saw little wind,so sea level gusts were somewhat less widespread than initially anticipated.#CAwx
Read 6 tweets
Folks: major wind/extreme low humidity/fire weather event is still coming--it just might be slightly delayed (by a couple hours or so in SF Bay Area). Very surprised to hear that PG&E is cancelling some of the planned PSPS with strong winds still inbound?? #CAwx #CAfire
Are @NWSBayArea or @NWSSacramento aware of any major forecast changes that would explain why PG&E is claiming that conditions will no longer justify a PSPS (at least in portions of East Bay Hills and Sierra foothills)? I certainly am not...
cc @RobMayeda @psuweatherman I am genuinely baffled here.
Read 4 tweets
Confidence increases regarding a significant offshore flow event late in the weekend - not just strong winds, but the very dry airmass with it. Comparing offshore gradients SFO-WMC. (1/4)
2017 Wine Country Fires -17.8mb
2019 Kincade -16.3mb
2020 Model Fcst Sunday night -18 -20mb
Regarding the model forecast - I've seen this before where the models put out -20mb, but verify closer to the upper teens. That was the case 2017. Here's a look at the wind anomaly - wish there was a 925 mb layer as that is a key level for the Bay Area. (2/4)
More wind info from ECMWF Extreme Forecast Index 0.5 to 0.8 is an unusual pattern and >0.8 is very unusual. In other words on the extreme end. (3/4).
Read 4 tweets
This is the fire weather forecast I was hoping wouldn't come to pass, given all that has already transpired in 2020: Very strong offshore winds, coupled w/exceptionally low humidity & record-dry vegetation, will bring extremely critical wildfire risk Sun/Mon. 1/3 #CAwx #CAfire Image
This will likely be strongest & most widespread offshore wind event of season, & is reminiscent of extreme events in 2019 & 2017. Hardest-hit areas appear to be west slopes of Sierra Nevada (gusts of 70+mph) & SF Bay Area (widespread gusts 40-50mph; higher in hills). #CAwx Image
Exceptionally low atmospheric humidity (relative humidity of 5% or less and dewpoints below zero F) will accompany these strong winds. This will be a *cold* offshore wind event, and temperatures will drop precipitously (especially in mountains). #CAwx ImageImage
Read 4 tweets

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