Strong storm across NorCal today; SoCal remains mostly dry

Filed in Uncategorized by on November 15, 2017 4,976 Comments

Intense burst of rain, wind likely across NorCal later today

A modest atmospheric river will be enhanced by a small surface low near North Coast. (NCEP via Scripps)

This will be a quick update (deadlines beckon). But the short, sharp burst of precipitation expected across NorCal later today is worth a brief discussion. This precipitation event was foreseen a week or more in advance by long-range weather models, but it’s only in the past 36 hours or so that it became clear that this would likely become a respectable storm for many of the urban areas near the I-80 corridor (including the Bay Area, Sacramento region, and even Lake Tahoe).

Why have expectations for this event been revised upward so sharply? A modest atmospheric river is currently aimed at the state, which will (slowly) sweep down the coast later tonight. But in general, an atmospheric river alone isn’t enough to produce heavy precipitation and strong wind outside of very specific mountain areas subject to dramatic “orographic enhancement.” For a significant storm in California’s lowlands, there needs to be some sort of “forcing mechanism” to generate upward vertical motion in the atmosphere and squeeze out all that water vapor present in even the most robust of atmospheric rivers. Until a couple of days or so ago, no such mechanism appeared to be in place–it looked like there would be a lot of water vapor transport but not much precipitation at the lower elevations. What changed? Now, a small surface low is expected to spin up later today west of the North Coast, bringing a burst of dynamic enhancement of the water vapor plume associated with this atmospheric river as it moves southward.

The Bay Area could experience pretty intense rainfall rates associated with cold front tonight. (NCEP via tropicaltidbits.com)

This storm, while not enormous, could nonetheless end up being fairly impressive for a narrow corridor near the Bay Area. Rainfall totals may be somewhat uniformly distributed across the region; while 1-3 inches is not too impressive in the coastal hills, that’s actually quite a lot in the urban areas and inland valleys. Moreover, most of this rainfall will fall over the course of just 3-6 hours–meaning that precipitation intensity could be quite high for a time later this evening. With strong vertical motion near the cold front, I would not even be surprised to see some reports of lightning associated with the heavy rain tonight across NorCal. Winds may also become strong and gusty in the typical spots, and while this is unlikely to become a major windstorm, the first wind event of the season typically brings down a disproportionate number of tree limbs and power lines. (Sierra snow levels will be relatively high, though some snow will be possible toward the end of the event at or below pass level).

 

Significant risk of flash flooding/debris flows in wildfire burn areas

While a storm of the magnitude expected to blow through tonight typically would cause only minor urban/small stream flooding issues, the recent wildfire burn scars in Northern California (especially the North Bay Fire region, including the Tubbs Fire near Santa Rosa) are extremely susceptible to sudden water runoff, ash-laden debris flows, and subsequent flash flooding. The rainfall rates with tonight’s system will be quite high for at least a brief period, and there have not yet been any heavy rainfall events in this region since the devastating October fires. Thus, for this event in particular (and to some extent for the rest of winter), folks in these regions should be prepared for more sudden and extensive flood issues than would typically be experienced during similar storm events.

 

Mixed signals for second system next week

A strong & persistent blocking ridge will continue over the North Pacific near Alaska. (NCEP via tropicaltidbits.com)

The models have been bouncing back and forth regarding the potential for a second system next week, which would likely take the form of a relatively weak but very warm atmospheric river with a subtropical tap. The instability in recent forecasts stems from the presence (and persistence) of a very high amplitude blocking ridge over the North Pacific over the past 30-40 days, and most forecasts suggest this will persist in some form for at least another 2-3 weeks. As previously discussed, downstream impacts over California can range from ridging (warm and dry) to deep troughing (cold and wet). At the moment, the “warm and dry ridging” still appears to be the more likely outcome (especially across SoCal), though that could change. For what it’s worth, both the GFS and ECMWF ensembles currently show a very warm and dry Thanksgiving across all of California next week.

Current indications are for a very warm and dry Thanksgiving across all of California. (NCEP via tropicaltidbits.com)

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  • AlTahoe
  • matthew

    A bit nippy at 6 degrees this morning. NWS had the Truckee airport at 3 earlier. Coldest of the season. On another note – Ridgezilla is looking downright scary. This is starting to concern me.

  • Howard Goodman

    In the 20’s here but the wind !! not in a hurry to go outside this morning

  • Admode (Susanville)
  • Howard Goodman

    It may be cold and windy but this photo just popped up on my facebook memories from 7 years ago , had to snow shoe 3 miles from there https://uploads.disquscdn.com/images/cb033ad940a19cb9af215f07452186c42f1bf25e8380e8d3aa8731c80ba2f0f8.jpg

    • Yolo Hoe

      That’s a great picture

  • AlTahoe

    It was dead calm this morning but the east winds have arrived. Pretty serious wind chill right now with temps in the teens and 30mph gust.

  • Fairweathercactus

    The 6z was a true dumpster fire. The 12z not finished but it looks about to the same.

  • Dry Bones

    All you guys posting near-zero morning temps, I’m just curious, what planet are you posting from? Can’t be the planet that SoCal is on.

  • Dry Bones

    Waiting to see if this big cool Santa Ana pans out. I am no longer living near the proverbial “canyons and passes” so we usually just get an hour or two of breezy wind gusts on the coastal plain, and then sit and bake in the single digit humidity and blasting sunshine for three days. I used to live in the Northridge/Granada Hills area, and we would get rippin Santa Anas up there. That was well on 15 years ago, though, when the climate was less abnormal.

  • tomocean

    Thought I’d jump in quickly to share some pics from this weekend “storm” (and post). Squeezed out .25″ in Auburn. Coldest morning of the season (35.4F) so far (but still haven’t had any frost).
    OK. Back to your regularly scheduled manic depression. Enjoy!https://uploads.disquscdn.com/images/696a85080cbb7bed331fa4255a6446a2cc2a558b1f1cfd6a07a512a5809e7cb5.jpg https://uploads.disquscdn.com/images/11c9bd51a3286e44c600c2d4378c05867b2f88970c129d9c44a1eae26f91159b.jpg https://uploads.disquscdn.com/images/0659ffcc40be3b7d2d06f7b22de3ea4482593fb814de1c9c96f994b016df7bbc.jpg

  • jstrahl

    This is a big factor behind our abnormal West Coast weather, as temps in Siberia are down to -60 deg F, way before the heart of winter. I’m guessing the polar vortex has been displaced. https://weather.com/news/weather/news/2017-11-28-siberia-colder-than-minus-60-degrees-in-november?utm_medium=social&utm_source=facebook&cm_ven=Facebook&cm_cat=www.facebook.com&cm_pla=fb_feed&cm_ite=fb_social_rec&fb_ref=ls_share

    • SoCalWXwatcher

      And it looks to keep getting displaced. If I were back East, I’d order extra heating oil.

      https://twitter.com/MJVentrice/status/937694315530289152

    • AlTahoe

      hmm all of our Arctic outbreaks usually start with an extreme cold pool over Siberia. I think we might still be on track for something crazy to happen in Jan or Feb.

  • redlands

    What’s happened to the moderate to strong Santa Anas that were predicted. We can’t have rain and snow, at least we could have is wind. The winds flopping out too

    • SoCalWXwatcher

      *Bust*!
      Just kidding. It looks like it won’t get underway until later today. I’m not sure we really want this to happen anyways, since we haven’t had a real storm yet this year, and if some power lines get blown down we could have some really destructive fires, even with a cold Santa Ana.

      • weathergeek100

        Hopefully, the winds won’t materialize.

    • Pfirman

      Up here in lower Sacramento Valley we are getting winds of 26 mph with gusts to 35 after the fine full moon last night. Not liking it at all. Otherwise clear and sunny.
      Damn wind is drying out what little rain we got.

      • Dry Bones

        That sure was a nice full moon though, even down here in the LA coastal basin.

    • SoCalWXwatcher
      • weathergeek100

        Why do you want wind? You want increased fire weather? Your region is suffering from record, extreme dryness and you want it to be EVEN dryer?

        • SoCalWXwatcher

          Who said I want wind? See my first reply to @disqus_4GKKrn6wAw:disqus.

          The only benefit I see from any of this is from colder night time low temps in the Mountain resorts, combined with low wet-bulb temps, which will be favorable for snow-making, especially since they won’t be seeing any natural snowfall up there before Christmas.

          • weathergeek100

            OOPS I meant to respond to Redlands not you!!! Apologies.

          • Pfirman

            That’s what I was thinking, so thanks for the heads up.

        • Bob G (Gustine)

          I always hate strong winds even when they are associated with wet weather, Prefer wet and calm

        • Hollow Scene (The Desert)

          No one wants fires, but Santa Ana winds are a normal part of our weather. They have been largely absent during the drought years. Yes, I want winds if it leads to a more progressive pattern

        • redlands

          Well since March 1st 2017 only 0.87 of rain.. If it doesn’t rain in December thats 10 months and not even 1 inch of rain.. I don’t want people’s houses to burn, however would be nice to have some change in the weather. Sunny and hot, with no rain daily gets boring, along with lots of plants n trees dying

    • Dry Bones

      The Santa Anas do seem to be flopping in the last several years, but the NWS forecast and the large and long package of warning products they’ve issued this time seem to indicate that at least the NWS thinks this one will be serious. The LA Times is also going on and on about this event, using the dubious term “strongest and longest” of the year.

    • AlTahoe

      Our East winds didn’t start up here until about 8am so I would imagine they might take a while to work down the state.

    • RunningSprings6250

      Keep the wind in redlands, don’t want it here not without having any solid rain or snow yet….hopefully we can get through unscathed as i have hopes the old adage will apply….

    • matthew

      Pretty interesting up here at 6100′ – there is virtually no ground-level nor treetop wind, but look up a few hundred feet and there are scattered clouds moving quickly from east to west.

    • Hollow Scene (The Desert)

      I was pretty impressed earlier. It’s supposed to get stronger later today

    • New post still forthcoming. Probably later today.

      • Bob G (Gustine)

        Looking forward to it even though I am expecting gloom and doom

        • It takes a broader perspective. For reference, posts usually take me 1-2 hours to write and edit. This one took 4 days…

          • Bob G (Gustine)

            Thanks. Look forward to it

          • Takes me about that long to post a comment. 🙂

          • Bombillo1

            Waiting with baited eyes. However, advancement of our understanding of our climate is very incremental as we are not likely to have a Watson and Crick moment. Just setting reasonable expectations.

    • Bob G (Gustine)

      Very concerning. This pattern looks stuck right now with strong ridge on west coast and big trough on east coast. Any rain December at all would be welcome but not expecting it. Can only hope we start seeing changes in the overall pattern heading into January

      • Bombillo1

        Even the Eastern trough is only impacting about 15% of the country. What really stands out to me is the quiescence of the entirety of continental U.S.

        • AlTahoe

          Yeah I have noticed that as well. I can’t ever recall the entire nation being that quiet for so long on model runs.

          • 805 Weather (Camarillo)

            Wave 5 pattern sitting at just the right position for that.

    • RunningSprings6250
      • Pfirman

        Too many kinds of war all messing up the atmosphere.

        • Bombillo1

          Somehow I do not picture you listening to this music too often and carrying a boombox. Message received however.

    • celo

      The polar ice cap is at an all time low for this time of year. In winter time, the polar cap can act as a stabilizing factor for the polar jet and therefore mitigating high and low amplitude jet patterns. If the polar cap was larger, colder air could migrate down from the polar regions easier and therefore lessening the amplitude of the jet, which would make breaking down persistent patterns easier. (The lack of ice especially around the bering straight and churchi sea are really problematic for western north america).
      The persistence of patterns will only be increased in the future as the polar region becomes more and more ice free. Warmer and dryer falls for the western north america, with more infrequent, but more intense, shorter duration winter and spring rainfall periods.
      Just my opinion
      Very hard to concentrate with weird Al below

    • AntiochWx

      I’d definitely say it’s related to the state of the arctic sea ice. However, what are the chances we could be entering a natural long term pattern change we haven’t observed in the last 100 years? Afterall, how did the past desert southwest drought pattern evolve 1,000s of years ago. I mean there is no denying our patterns are being enhanced by AGW, but could there be an underlying pattern we are entering into we haven’t seen in modern times?

  • SoCalWXwatcher

    If anyone is looking for some positive glimmer hope to grasp onto, read Howard’s latest update regarding hints of possible return of some wet weather during week 3. I guess we’ll know by Christmas.¯_(?)_/¯

    • Bob G (Gustine)

      I did. But way too soon. A glimmer of hope for me would be for some changes start showing up in the models with the ridge starting to move on along with the big east coast low. It appears for now that east coast low is going to remain for some time possibly into January, That is concerning

      • SoCalWXwatcher

        I’d love for Howard to be right with that week 3 call, but I sure don’t see it when looking at the GEFS and EPS Ensembles.

        • Bob G (Gustine)

          Me too but i just dont see it right now.

    • ” with this interseasonal pattern shift”
      Halloween to Christmas or Christmas to Easter?

      • SoCalWXwatcher

        Note he’s relying on the CFS’ depiction of the ridge shift during week 3/4. When we find our best hope is the CFS, it’s equivalent to the Dodgers handing the ball to Darvish.

    • thlnk3r

      Well PNA is looking (well forecasted) to head towards a negative phase. QBO though just doesnt want to budge: https://www.esrl.noaa.gov/psd/data/correlation/qbo.data https://uploads.disquscdn.com/images/3f3e9f18fc4a66aee1a6a5217f79482ee1b4ea49ff086ce6204e410c51ed8489.png

  • Windy as heck outside.

    • inclinejj

      Nothing here at all. Dead calm.

      • FolsomPrisonBlues

        Its been really windy out here all morning.

        • Jason Jackson Willamette

          And cold too. Brrrrr! Got some outdoors work to do. Maybe not….

    • Hollow Scene (The Desert)

      Down here it’s getting off to a good start. Lots of debris all over and blowing dust / sand.

  • Mario Gallegos

    https://uploads.disquscdn.com/images/2bac2848e632d8ae32bff8d2435e6d1005ca6e834e8f1a60701890f0d418e6ba.jpg
    Usually by now the san bernardino mountains look like that from the high desert in the victor valley but this year the mountains still look like mountains during the summer this is the first year that has happend even during our drought years they had a little snow on the tops incredible.

    • Pfirman

      When was that photo taken?

      • Mario Gallegos

        Around 2013-2014 fall winter season

    • Hollow Scene (The Desert)

      This is the driest fall I can remember in a long time

      • Mario Gallegos

        yea that year the other side of the mountains did not have any snow on top only on the high desert side. each year its getting disappointing for the ski resorts up there.

        • RunningSprings6250

          Yet the crowds and traffic get worse and worse…. ?

          • redlands

            Cause the normal non weather geeks like the Sunny and hot or hotter with no rain or snow daily

      • Charlie B

        San Diego NWS noted earlier that if this holds (likely) then they will see the second driest calendar fall ever at .02″. Driest is 1929.

        • Hollow Scene (The Desert)

          1929 recorded 12.50 in LA for the year, so the rain must have really ramped up at some point to be able to catch up that much. Interesting

        • redlands

          They need to go back to the correct July 1st rain start. It makes previous and future records meaningless. Can’t change the rules when the game is already started. Billboard did the same thing — changing rules to fit their desires and wants

      • Dan the Weatherman

        This is certainly the driest fall that we have had in quite some time. A couple of other dry falls over the last 20 years included 1995-96 and 1999-2000, but I don’t remember if they were as dry as this fall has been to date. Even the moderate La Nina of 1998-99 had a few storms in November.

    • Dan weather maniac (ORINDA)

      For Socal, the drought never ended though right? This is the cummulative extreme we are seeing I think.

  • gray whale

    The pithiest extended discussion i’ve ever seen. I’m going to try to enjoy the inconsequential weather while it lasts. Surf looks amazing for the next 10 days, maybe the family wants a little coastal getaway.Wish me luck.

    EXTENDED DISCUSSION (Friday THROUGH Monday)

    Little weather of consequence in the extended period as high
    pressure remains in control. This will continue dry and mild
    conditions with above normal temperatures during the day. Cool
    nights expected due to clear skies and light winds.

    • Pfirman

      Luck wished.

  • molbiol

    Let me get this straight: Synoptic scale Rossby waves typically loose energy or weaken as one moves toward the poles..however another type of Rossby wave created by topographical features can actually interact with Synoptic Rossby waves resulting in stable resonance with positive self reinforcing feedback? Hopefully the upcoming post will touch on this and whether climate change, arctic warming may be enhancing this. Looking forward to reading the next post…and then it’ll be time for a long break until a winter storm hits or the summer monsoon kicks in 😉

    • RanDog

      Interesting. I wonder if the opposite is also true, that they could interact and reinforce each other positively?

    • Are you referring to Mountain Torque?

      • molbiol

        I think mountain waves (which cause lenticular clouds and severe aircraft turbulence) would be examples of smaller scale gravity waves. Not sure how much those contribute, but I am NOT an expert in this field. Hopefully the next post addresses this

        • molbiol

          Case in point, I see now that mountain waves and mountain torque are two related but different features

        • SoCalWXwatcher
          • molbiol

            yup, just realized that. I should just stick with biology

          • SoCalWXwatcher

            That link doesn’t make it any easier either, LOL. There’s gotta be a good laymen’s source for this stuff somewhere.

          • molbiol

            “The impact of Titan’s large-scale topography and surface roughness on
            the atmospheric angular momentum budget is investigated by the Cologne
            Titan general circulation model that is run with and without topography
            constrained by Cassini. On seasonal timescales the angular momentum
            exchange is dominated by the friction torque, which oscillates
            semi-annually. Topography gives rise to a large diurnal and small
            seasonal mountain torque.”

            Yup, super easy 😉

          • SoCalWXwatcher

            I did a quick google search, and all the links I could find were similarly technical in nature. Couldn’t find any laymen-friendly ones. When I see a paper with more equations than illustrations, my eyes gloss-over. 😛

          • Dan the Weatherman

            I wish there were an introduction site on this information as well. I would probably be able to understand it at least somewhat if there were one.

          • SoCalWXwatcher

            If you’re reading a paper talking about mountain torque that mentions Titan & Cassini, it’s probably not even talking about this planet.

          • molbiol

            Titan has a Nitrogen/methane atmosphere but the same physical rules still apply

          • SoCalWXwatcher

            It has a very dense atmosphere, but I’d imagine it has a much weaker Coriolis effect, given it is tidally-locked to Saturn, much like our own moon is to the Earth, so it’s “rotation” rate about its axis is the same length as one complete revolution around Saturn. Not to go off on a tangent, but this is the same problem with most of those “habitable zone” planets being discovered – most circle dwarf stars, so the habitable zone is so close to their sun that they are tidally locked, one side permanently facing their sun, with almost no Coriolis effect.

          • molbiol

            which is why planet earth is a true freak of nature

          • Dan the Weatherman

            That’s true. That must be based on information that was sent back from the Cassini mission and the Huygens probe that landed on Titan’s surface.

  • Bartshe

    Northern Sierra snow level marching upward: “positive trend in snow level with a Thiel-Sen slope of 72 m year?1 ”

    http://www.mdpi.com/2073-4441/9/11/899

    Hatchett, B.J.; Daudert, B.; Garner, C.B.; Oakley, N.S.; Putnam, A.E.; White, A.B. Winter Snow Level Rise in the Northern Sierra Nevada from 2008 to 2017. Water 2017, 9, 899.

  • Jason Jackson Willamette

    Ridge firmly cemented in place. Anything that approaches it either gets shunted north or simply evaporates upon contact (southern jet/ subtropical moisture.)

    My head hangs down and I shuffle thru the day shielding my eyes from the unrelenting sun. No wait! that was this past summer. Welcome to the new normal. Please submit my complaint to management….

    http://www.ssd.noaa.gov/goes/west/nepac/flash-rb.html

  • Fairweathercactus
    • SoCalWXwatcher

      If it’s based on the comments section here, “Bust” and “RRR” should be on there multiple times.

    • molbiol

      You should make a heatmap of these phrases based on frequency of occurrence.

      • Fairweathercactus

        I will make a summer one.

    • Jason Jackson Willamette

      Haha, well done Cacti. I’ll take the third row down for $50.

    • Charlie B

      Which square has “alcohol?”

      • Fairweathercactus

        That will be added in the Spring or Summer list when no weather at all is going on.

      • Jason Jackson Willamette

        Column 1, row 3. On sale at Raley’s, $7.99 a sixer….

    • matthew

      Where is ChemTrails???

      • Jason Jackson Willamette

        Second column, row 4.

    • Dan the Weatherman

      Where is GFS Hour 384?

  • 805 Weather (Camarillo)

    Ok… The wind is getting violent out here.

    • SoCalWXwatcher

      Seems like it’s going to be even nastier in your area by tomorrow morning. Batten down the hatches! And be on the lookout for flying inflatable Christmas yard decorations!

      • Jason Jackson Willamette

        Whoa! Got lots of those in my neighborhood! Tethered to 100′ extension cords, whipping around and wrapping around the gawking neighbors necks.

      • 805 Weather (Camarillo)

        It’s a flipping tumbleweed congregation out there, some patches of them being stacked against fences 6 feet tall.

      • thlnk3r

        Record-breaking dry unprecedented conditions will continue through Friday. A significant amount of Christmas decorations flying through the air is possible. Extreme Christmas debris danger!

        • molbiol

          “Extreme Christmas debris Danger!”
          Thanks, that made me LOL

        • SoCalWXwatcher

          30% chance of heavy inflatable snowman showers.

          • Chris

            Now that’s funny!!!

    • molbiol

      Easterly winds in Lancaster are getting quite strong. That usually means that damaging winds are occurring in the more favorable locations

      • Pfirman

        Weird locution…..favorable.

    • Hollow Scene (The Desert)

      I had to tow a trailer earlier and I was dodging Palm fans all morning. I wouldn’t be surprised if there are downed trees after this is all over, since the last time we had winds this strong was about one year ago.

    • RandomTreeInSB

      Just a light breeze in Santa Barbara. We were supposed to get advisory-level sundowner winds last night but that never happened.

    • AntiochWx

      Going to get some good wind power generation today out in Altamont pass!

      • 805 Weather (Camarillo)

        Yep, this is the type of event that takes down the big Eucs… Hoping nobody is crushed this week.

  • Dan the Weatherman

    It has been breezy here in Orange this morning, but it has picked up a bit stronger over the last half hour or so.

  • 805 Weather (Camarillo)

    Santa Ana’s can make these graphics look incredibly strong, however when looking at them in the 80-meter to 900mb range where the winds are the strongest… That is why this graphic is startling –– It’s displaying 10-meter wind gusts typically only the higher elevations see and for this I am certainly not parking next to any trees over the next 24 hours… https://twitter.com/NWSLosAngeles/status/937770686701101057

  • Chris

    I coach a swim team in the morning.
    My thermometer read 32 degrees outside (Morgan Hill).
    So, I dressed in layers as I’ll be outside for the next 1.5 hrs.
    I arrive in San Jose and my thermotmeter reads 50 degrees with a light breeze!
    I’m overdressed! ?