Discover and read the best of Twitter Threads about #CAwater

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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
Interesting new analysis led by @ame_kaminari and co-authors including @epispheric demonstrating observed increases in hydroclimatic variability in California. *Increasing* 90th percentile in winter, but decreasing variability in autumn.… #CAwater
This offers some observational confirmation of climate model projections, which suggest that winter wet extremes will increase substantially with #ClimateChange even as shoulder season precipitation decreases and overall variability increases. #CAwater…
Another reflection on @ame_kaminari's analysis: it is striking how many statistically robust changes are occurring to variability & seasonality of both precip & streamflow even when mean annual values change little. Yet another example of why averages can be misleading...#CAwater
Read 3 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
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
In case you missed it: a "thread of threads" highlighting some of our collaborative research from 2020. How are wildfires, atmospheric rivers, floods, and other extreme events changing in a warming #climate (and in California specifically)? Read on for details: (1/8) #CAwater
A general-audience primer on the rapidly advancing science of "extreme event attribution." How do scientists approach question of whether #ClimateChange is affecting likelihood and/or severity of extreme weather events? (2/8) @ClimateChirper @danielletouma
Our deep dive into extreme #AtmosphericRiver storms in California and how they are likely to warm & intensify considerably due to #ClimateChange. (3/8) @xingyhuang @ProfAlexHall
Read 8 tweets
New research led by @ggpersad & featuring @PabloWater. Using downscaled climate model simulations, we show that there is unexpectedly high inter-model agreement re: increasing extremity of California hydroclimate due to #ClimateChange. (1/n)… #CAwater
In general, climate models agree than an increasing fraction of California's overall precipitation will become concentrated into the most intense events--and that the most extreme precip events will themselves be substantially more intense. (2/n)… #CAwater
There is also agreement that CA's already pronounced precipitation seasonality will become even sharper--with more rain concentrated into winter months at expense of the autumn & spring. Consider the wildfire season implications... (3/n)… #CAwater #CAfire
Read 8 tweets
The Central Valley Regional @CaWaterBoards has reported that a recent collection of water samples from cyanobacteria #AlgalBlooms along the #Stockton waterfront contain microcystins up to 220 times higher than the “danger” level.

Read more: #CAWater
Our ED: “We are grateful that the @CaWaterBoards continue to make water quality testing a priority throughout the #SFBayDelta and along the #Stockton waterfront, the most populated urban area within the Delta with CA’s largest #environmentaljustice community percentage-wise. (1/
"We are, however, deeply disappointed in decisions being made by @CA_DWR because none of their plans for the Delta or #cawater management include solving the HABs issue for our region or for Northern California tribal communities suffering with the same water quality problem. (2/
Read 8 tweets
New work led by Xingying Huang on extreme #AtmosphericRiver storms in California in a warming climate is out today in @ScienceAdvances (open access)! A thread discussing our findings and their implications follows. #CAwx #CAwater #CAclimate (1/n)…
Top-level findings: we find that the most intense atmospheric river storms in California will be become considerably more intense as the climate warms, bringing substantially more precipitation overall as well as higher precipitation intensities. (2/n)…
We find that largest *absolute* increases in extreme AR precip occur where you might expect: along windward slopes of Sierra Nevada & Coastal Mountains. But...the largest *relative* increases occur in historically rain-shadowed areas--Central Valley & Sierra lee side. (3/n)
Read 13 tweets
Weather/climate programming note: (1/3)
Our extreme #climate event attribution piece will be out this Friday in @OneEarth_CP (expect a Tweetstorm, and brief discussion in an upcoming Weather West blog post!). #CAwx #CAwater
Then, in early July, our extreme California #AtmosphericRiver & #ClimateChange paper will be out in @ScienceAdvances (expect a dedicated Weather West blog post). #CAwx #CAwater (2/3)
In Aug/Sep, I'll have dedicated post discussing our recently published paper on #ClimateChange-caused increases in extreme CA wildfire conditions (& possibly also additional work, still in review, examining population exposure to public safety power shut-offs). #CAwx #CAfire(3/3)
Read 3 tweets
The Central Valley Flood Protection Board is floating a draft “statement of no objection” letter once again, without circling back to the #SFBayDelta community for full and robust input. #cawater Read more here:
The Board’s return to simply drafting language for approval tells us that public participation will require Delta residents once again having to rally to oppose state actions that fail to address Delta community needs... (1/2)
...rather than being given the time to give thoughtful input to the need for comprehensive levee protection in response to Delta sea level rise, storm surge, and river flooding concerns. (2/2)
Read 9 tweets
Our new work on #ClimateChange & autumn wildfire risk in California, led by Michael Goss, is out today in (open-access) ERL. We find that climate change has already doubled the frequency of extreme fire weather days since 1980s.(1/6) #CAwx #CAfire #CAwater… Image
Historical increases in autumn temperature & decreases in precipitation have led to increased number of days where aggregate Fire Weather Index (FWI) exceeds historical 95th percentile, which are strongly associated w/large wildfires.(2/6) #CAfire #CAwx… ImageImage
This historically observed increase in autumn wildfire risk in California is generally consistent with climate model projections for the same period. #CAwx #CAfire (3/6)… Image
Read 7 tweets
For those looking for some good news this week, I do have some from a California weather perspective: a sudden burst of potentially quite heavy Sierra Nevada snowfall (along with widespread rain elsewhere) is likely this weekend into early next week. (1/3) #CAwx #CAwater ImageImage
Over the next 5-7 days, a pretty broad swath of 2-3 foot snowfall is possible across Sierra Nevada. This will be a cold system, so accumulating snowfall possible down below 2,500 ft. Rainfall accumulations elsewhere will be fairly widespread and mostly moderate. (2/3) #CAwx ImageImage
Clearly, this is very good news! It is, however, still important to keep these numbers in perspective. Snowpack currently at only 38% of avg., & is "missing" ~24 *inches* of liquid SWE. Even after upcoming big snowfall, we'll still be massively behind. #CAwx #CAwater (3/3) Image
Read 3 tweets
New work led by @SciGibson @NASAJPL! We take a deep dive into northeastern Pacific high pressure ridging, including trends, implications for California drought, #AtmosphericRiver activity, and possible underlying physical mechanisms. (1/6) #CAwx #CAwater…
We find several distinct "flavors" of high pressure ridging that tend to recur historically. Each spatial configuration affects atmospheric river activity & western U.S. precipitation in a distinct manner. (2/6) #CAwx #CAwater #AZwx #ORwx #WAwx…
All three ridge types (north, west, and south-centered) are associated with drought in California and the Colorado River basin, but only "north-type" ridges are associated with drought in the Pacific Northwest. #CAwx #ORwx #WAwx #AZwx #UTwx #CAwater… (3/6)
Read 6 tweets
Light coastal rain showers (and mountain snow showers) are still expected to end prolonged dry spell in NorCal this weekend (finally!), although significant precip not expected. Then, early next week... 1/3 #CAwx #CAwater Image
Early next week, a stronger & dramatically warmer system is expected to affect SoCal. Widespread, locally heavy rainfall is likely from this warm/wet #AtmosphericRiver--but only in far SoCal. Very high snow levels due to subtropical airmass. 2/3 #CAwx #CAwater Image
Thereafter, there is uncertainty regarding how the pattern evolves. Best chance of additional precip is in SoCal; unfortunately, in parched NorCal, ensembles still suggesting continued below-average precip through mid-March. #CAwx #CAwater #CAfire Image
Read 3 tweets
Tonight we are at the last Delta Tunnel Scoping Meeting in Redding. @CaliSalmon and the @winnememwintu Tribe organized a rally beforehand. We will be live tweeting the meeting and comments. Image
A clip of the rally before the meeting.
More pictures of the rally walking into the scoping meeting. ImageImage
Read 53 tweets
More record high temperatures possible over the next few days across California. With ensembles projecting zero precipitation in San Francisco and Sacramento through Saturday evening, February 2020 now virtually certain to be driest in history across most of NorCal. #CAwx ImageImage
Models now suggesting Sunday system may be an "outside slider"--missing most of CA to the west and possibly leaving NorCal dry, cool, and windy. Scattered SoCal rain showers and Sierra Nevada snow showers still possible. #CAwx
Still some hints of the possibility of a wetter pattern by mid-March, but ensembles are mixed on this and would likely not occur until 2nd week in month or later. Based on current forecasts, I would not hold my breath for a "March Miracle" this year.... #CAwx #CAfire #CAwater ImageImage
Read 4 tweets
New research led by Xingying Huang on simulating extreme U.S. Pacific Coast #AtmosphericRiver storms. We found that our high resolution weather model configuration yielded substantial improvements in extreme precip representation. (1/3)… #CAwx #CAwater Image
We selected extreme AR events between 1980-2017, evaluating model performance specifically for the *most* intense precipitation in *wettest* regions. This modeling framework forms basis for forthcoming work on #AtmosphericRivers in warming climate. (2/3) #CAwater #CAwx Image
One selected storm was Dec. 12 1995 event in N. California, which brought a violent windstorm to portions of SF Bay Area (100+ mph gusts!). This was actually a formative weather event of my childhood--it's one of the reasons why I'm an atmospheric scientist today! (3/3) #CAwx Image
Read 5 tweets
New research led by @k_r_gonz points to striking #AtmosphericRiver warming trend along U.S. West Coast in recent decades. We found that ARs have already warmed by > 2°C (3.6°F) in some months--faster than previous #climate projections had suggested. (1/8)…
#AtmosphericRiver warming signal is robust in all regions during at least some months, including coastal Washington, Oregon, & California. But warming has been greatest in central & southern CA, especially during January & March. #CAwx #ORwx #WAwx (2/8)…
This #AtmosphericRiver warming appears to be driven by both local and geographically remote warming, but appears to scale most closely with near-shore ocean and local background (non-AR) temperature trends. (3/8)…
Read 8 tweets
A federal judge dismissed portions of a water lawsuit by the Agua Caliente tribe, ruling against its attempt to quantify its rights to groundwater.… @EvanWyloge
This decision comes after an earlier court ruling that the tribe holds groundwater rights dating back to the creation of its reservation in the 1870s.
That ruling by the Ninth Circuit Court of Appeals stands. But the federal judge ruled this time that the tribe “does not have standing to pursue its quantification and quality claims.”
Read 7 tweets

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