Major storms approaching California; significant flooding possible

Filed in Uncategorized by on November 27, 2012 58 Comments

Overview

A dramatic change to an extremely active weather pattern is currently unfolding over the Eastern Pacific. The first in a series of powerful storm systems will approach the California coast tonight, bringing a brief period of heavy rain, high winds, and possibly thunderstorms Wednesday morning. Additional storms will continue to slam into the coast through the upcoming weekend, bringing additional periods of very strong winds and heavy rainfall. An atmospheric river event could bring extremely heavy precipitation to a relatively small area by this weekend, possibly resulting in significant flooding.

Short Term Discussion

A quick glance at satellite imagery appears to verify what the numerical models are currently depicting: a rapidly strengthening storm system 500-800 miles off the coast of California. The developing surface low is expected to move in a more northeastward fashion overnight as the associated cold front moves almost due east and approaches the coastline by dawn tomorrow. The models are projecting that this front will be quite intense as it moves ashore, accompanied by a burst of very heavy rain and a period of strong to very strong winds. There is already very strong dynamic lift along and just ahead of the front itself, and this is only expected to increase over the next 12 hours. Strong upper-level divergence, coincident with some rather impressive positive vorticity advection, support a fairly dramatic cold frontal passage tomorrow morning that may be accompanied by thunderstorms containing torrential rainfall and winds in excess of 50-60 mph.  850 mb wind fields are already quite strong–in the 50-70 kt range–so I would not be at all surprised to see some potentially damaging gusts over 60 mph gusts mix down to the surface in convection. Flooding is not a big concern with this first system since it will be very fast-moving, though that will change with subsequent storms later this week. Most of Thursday will be a “break” day except over the far north, though rain will return in earnest by evening.

Long Term Discussion

Even stronger and more impressive storm systems are slated to arrive by Friday and continue through at least Sunday. Friday’s storm will, of course, contain heavy rain and strong winds once again, but there indications that the synoptic scale feature may act on an existing plume of subtropical moisture (atmospheric river) to produce excessive rainfall in some part of Norcal on top of the intense cold frontal rains. The models have been struggling with the placement (and even existence) of this particularly enhanced band of precipitation, so there remains uncertainty regarding where it might fall and how much rain it might produce. Regardless…rainfall totals will really start to add up by Friday evening (and will probably be approaching double digits already in orographically-favored areas).

The Saturday-Sunday storm system, though, is the most concerning and potentially the strongest of the bunch. The orientation of the deep longwave trough off the coast will begin to shift by the weekend, directing parcels of positive vorticity right at NorCal. One of these disturbances will be in a very favorable position to rapidly develop a surface low as it approaches the coast on Saturday, and given the extremely moist subtropical atmosphere already expected to be in place at that point some very heavy precipitation could result. The persistent atmospheric river will be directed over Central California at this time, and may even shift back northward temporarily as the developing synoptic-scale storm system offshore matures. This could mean that the heavy precipitation band actually passes over a single location three times–first on its slow southward trek, then again as it lifts north ahead of the main front, then one final time as the front finally makes progress inland. Rainfall totals where this occurs are going to be excessive, and right now the focus of this final system is squarely on the Bay Area. Significant flooding will probably result if this scenario pans out as currently depicted. It’s also worth noting that the 12Z operational run of the GFS brings very strong winds with this final system as well, possibly stronger than the Wednesday storm.

It’s worth noting that Southern California isn’t likely to see a great deal of precipitation or wind out of any of these systems. While a soaking rain may occur as far south as Los Angeles, in general the rain/no rain (or probably more accurately the heavy rain/light rain) line will be rather sharp, as is often the case with atmospheric river-related heavy precipitation events. In any case, the best chance for some interesting weather in Socal out of this storm series probably will come with the Sunday system, as that one will dig significantly farther south along the coast than either the Wednesday or Friday storms in Norcal.

Even further out, the prognosis is pretty fuzzy. The models do generally depict a drying trend by Monday as the deep trough loses amplitude and the jet shifts northward. However, there are some indications that this break may be short-lived, with significant precipitation potentially returning by midweek (at least to northern portions of the state). Let’s get through the next week first…

© 2012 WEATHER WEST

  • redlands

    what happened to the postings ???? 204pm 11-27-12

  • redlands

    ooops u made a new posting —- doesnt sound good for southern calif till sunday — hope the storms dig farther south — we need the rain — my station has 1.98 of rain — which isnt too bad for the end of November — however we need at least one inch – preferably more by the end of December

    • Dan the Weatherman

      Redlands, what month do you start keeping track of rainfall for your yearly rain total? Do you go from July 1 to June 30, or some other schedule? Just curious.

      • redlands

        Dan — My season ends June-30th and starts July-1 — Why do u ask

        • Dan the Weatherman

          I have noticed that you rain total is much higher than what I have received so far this season and was wondering how far back your total went. I have received barely over 1/3″ inch here in Orange since July 1. If I remember correctly, you had more significant summer rainfall from the monsoon than areas closer to the coast did.

          • redlands

            Dan — My rain stats for the 2012-13 rain season July got 0.35 of rain — 3rd wettest — Aug 0.90 2nd wettest — wettest being 2.62 in 1983. Sep 0.00 Oct 0.01 Nov 0.71 — total of 1.97 —-

  • Tom in San Diego

    We aren’t entirely immune from this first storm. SDNWS issued a coastal flooding and high surf warning fro the next three days, surf 6 to 8 ft occasional sets to 9, and 7 to 10 foot sets Friday and Saturday. 40 % chance scattered showers or put another way 60% chance of scattered clouds.

    • Dan the Weatherman

      A bit further north up here in Orange County, there is a 70% chance of rain tomorrow night into Thursday morning, tapering off to a chance by afternoon, and then there is another chance for Friday and Friday night as well. It is not forecast to be very heavy this far south as Norcal will receive the brunt of it, but at least there is a decent chance of at least some precipitation. The Sunday storm may be the most significant of the three for this area.

      • Nicholas

        NWS has at its highest point a 60% chance of rain for my area. Metrostar shows a lot of 0.01 and 0.02 for the area all adding up to 0.68 when all is said and done.

  • Dan the Weatherman

    I only have been hearing the term “atmospheric river” lately, and am wondering if it is the same thing as a “Pineapple Express”, or is a “Pineapple Express” a certain type of atmospheric river event?

    • http://weatherwest.com Daniel Swain

      You’re exactly right–“Pineapple Express” events are a subset of all atmospheric river events (ARs), which are defined generally as long and relatively narrow plumes of concentrated water vapor. ARs occur in mid-latitude regions all around the world, and have only recently been recognized for their importance in transporting water vapor meridionally. I think the term has come into more common usage over the past five years because more people have been formally studying these events.

      • Dan the Weatherman

        Daniel, thanks for the information as you have cleared it up for me!

  • Ken K.

    It is looking like a very small amount of rainfall for the southern part of San Diego county a few hundredths. Then a possible Moderate Santa Ana mid next week. fire Season is not over for us in the south land. Unfortunately looking to stay dry here in the south land. like Tom said 60% of some clouds.
    You folks up north stay safe and enjoy the rain and wind.

    • Dan the Weatherman

      I just wish we would get a good soaking to douse the fire season for good this year. We have really dodged a bullet so far this fall in not having many brush fires, as the ones we have had have been really small. This has been the case simply because there has only been one significant Santa Ana so far and not because we have been wetter than normal.

  • sc100

    For those of you in Norcal, this is the website where you can keep track of the river levels in Northern California: http://water.weather.gov/ahps2/index.php?wfo=sto

    They also give forecasted levels and quite a few are already being raised to monitor or flood stage. The forecasts this far out are usually pretty conservative (basically baseline) so those rivers that are in the heaviest parts of the storm will likely see levels rise far above the current forecasted levels.

    Also, for those of you in the Sacramento area, here’s where you can keep track of the current creek and small stream levels: http://www.sacflood.org/sensdata/strmgrp.htm
    These have flooded hundreds of buildings in the past when they’ve flooded so we definitely need to keep an eye on them.

  • sc100

    I just listened to the NWS Sacramento forecast discussion video and they said they believe MOST creeks and streams will flood by the weekend. http://www.youtube.com/watch?v=tq0rfW5oWaA

    Also, the mudslides could make the news pretty big this time. Looks like we’ll see plenty of highways and roads taken out.

  • alan

    San Gabriel and San Bernardino mnts look to get the most rainfall down here as they collect all the moisture bumping up against the mountain crests. I think 2″-3″ is easy for my location by Sunday night. Today NWS has 50% rain tonight 90%, Thursday 80, and “rain likely” pops most all Friday through sunday.

    We’ll see what we can squeeze out, I’m a little surprised at all the “rain” or “rain likely” periods quite honestly…

  • David

    lighting is being reported in parts of the valley

    • David

      this AM

  • Nicholas

    Local media in So Cal is trying to get a hype up a whole lot of nothing for down here. They are are getting excited for a quarter of an inch of rain.

    • Tom in San Diego

      media mellow drama, oh the humanity!

  • sc100

    It’s been a good storm so far. Several areas approaching two inches in a short amount of time. My house is closing in on half an inch. Snow levels have been jumping around from 6,500 to 7,000 feet. Just a teaser for the main action to follow over the next several days. Interesting to watch the next storm start setting up on the satellite loop and see where it lines up exactly. The first areas that get it should get hammered. Very high rain rates, easily an inch per hour in many places. The North Bay could really get hit hard according the latest GFS. It’ll be interesting to see how much punch it loses at it moves south. Also, it looks like the west slope of the Sierra will see continuous rain from tomorrow night through Sunday night. That’s really going to rack up the rainfall totals up there.

    • http://weatherwest.com Daniel Swain

      The system was pretty unimpressive down on the Peninsula until the very end, at which point we got a burst of torrential rains and gusty winds. The local obs station actually clocked a full inch over a one hour period during frontal passage, so we ended up getting a considerable amount of rain here despite the brief duration. The real show is this weekend, though…

    • Dan the Weatherman

      sc100, are you in the Sacramento area or in the Sierras? I am just curious from a precipitation total standpoint when you report, since the totals in the mountains are usually much more than the valley floor.

  • mendodave

    Just over an inch (1.06) here in Mendocino, my station 7 miles away outside Little River recorded .71.

    Little River station on Wunderground is ICALITTL2 if you want to watch the precip.

    site is: http://mendodave.mcn.org/LWC.
    the wind data is not good, I have too many tall trees…

  • Dan the Weatherman

    The local news reported that it was raining in Ventura County as of around noon, but here in Orange it is still sunny right now with clouds approaching from the west.

  • redlands

    Yes — can people report there rainfall totals and locations —

  • http://www.norcalweather.net/ WxTracker15

    .70″ of rain from this front here in Rocklin. Average rainfall rate per hour was around .20″.

  • alan

    18z is going nuts on the central sierra for this weekend into monday – imagine snow totals above 10k yikes! Mammoth reporting anything yet – totals & expected totals?

  • Tom in San Diego

    CAVU down here this afternoon;
    Navy field Imperial Beach information Juliet: as of 1500:

    Temp. 64F
    Humidity72%
    Wind SpeedWSW 8 MPH
    Barometer30.15 in (1020.8 mb)
    Dewpoint53°F (12°C)
    Visibility10.00 mi

    Some mid level tropical looking strato-cumulous at 9 to 10K few miles to the west. Tops look to be 15 to 20 maybe. Radar looks pretty wimpy.
    70% chance of light rain tonight through tomorrow.

  • Shady Blues

    Front passed over here in L.A….was not even enough to wet the ground. what a joke!

    • David

      AHAHAH thats what you guys get for takeing 100s of cut off lows last winter so its pay back time

  • David

    this storm was nevere ment too for S CA any way olny N CA

  • sc100

    Dan – I live in the city of Sacramento, in the northern part. The hills and mountains east and northeast of here can get 4 to 5 times the precip Sacramento gets, which is about 20 inches a year. I think WxTracker15 said that his old house in the Butte County hills averaged 111 inches a year.

    • Dan the Weatherman

      Thanks. Now that I know approximately what region most people who post here are located and the fact that there is good diversity in the locations (mountains, inland areas, coastal areas, etc.), then it is easier to see how much impact a particular storm or series of storms is having on the state as a whole by the reports that I see here in addition to the standard NWS reporting stations.

  • sc100

    I saw someone from the state Flood Operations Center speak today on TV and he said they’re expecting this to be the biggest flood event in Norcal since 2005/2006. It seems like they think this could be just as bad and the Upper Sacramento River is already forecasted to hit three feet below the record level in 1997. I also saw an emergency manager from Sacramento County speak today and I think he was too dismissive of the flood threat from the creeks in the county. Looking back at newspapers I kept from past floods, most of the floods weren’t expected and occurred from storms that were much bigger than anticipated. Here’s an account from the 1997 New Years floods:

    Dec 31 – “Shasta Lake and Lake Oroville are expected to be able to handle the anticipated runoff without increased releases.”
    “At Lake Oroville, no increases are planned in the current 50,000 cfs releases.”

    Jan 2 – “Water was flowing into the reservoir at 300,000 cfs, a record for Lake Oroville, and was expected to be released at between 130,000 and 160,000 cfs.”
    “We are anticipating that the water will go over the emergency spillway, at which point we will have a major flood.”

    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    • Tom in San Diego

      SC, how are lakes Shasta and Oroville looking this year?

      I know Clear Lake over by Ukiah there naturally stays fairly full.

      • sc100

        They’re both about half full, should definitely be enough room for 20 to 25 inches of rain in the watersheds above. Those are the two biggest reservoirs in the state. They’ll be rising fast though so they’ll have to make some pretty big releases in order to keep the lakes low enough in case something like this happens again in the months to come. Rivers will be high here for a while.

        • Tom in San Diego

          Thanks.

  • http://www.norcalweather.net/ WxTracker15

    Classic atmospheric river setup (11/29/12 00z GFS 18z Sunday PW): http://www.norcalweather.net/Model%20Run%20Images/133.png

  • sc100

    Wow. 06z GFS continues the Pineapple into next week. That could be a game-changer. But like Daniel said, we have to get through Sunday first!

  • Tom in San Diego

    Boy they really backed off the progs down here! Last night they calling for slight chance everyday into next week, now it’s partly cloudy to Monday. at least.

  • sc100

    Storm #1 served as a teaser for Storm #2 and it looks like Storm #2 could serve as a teaser for Storm #3. It’s raining like crazy right now in Northwest CA. Here are some rainfall totals so far for Northwest CA through yesterday:

    Honeydew – 5.52
    Clear Creek – 3.52
    Coffee Ridge – 2.13

    Over the coming days I’m going to be listing daily and storm-total totals from spots throughout Norcal and Central Cal. I’m fully expecting to see some areas at 25 inches. Some of these areas can get some crazy amounts of rain.

  • mendodave

    Wunderground station here in Mendocino is KCAMENDO1, wind data is great here, we are right on the headlands. Average winds currently are 22mph, just had a gust to 36. No real rain from this one as of yet. (.004″)

    Baro: 29.83 and falling

    • Tom in San Diego

      LOL You’re in a windy corner up there as it is. I remember going out to Cape Mendocino light couple years ago and the winds were like 50 gusting to 65, and maintainer said that was just a little breezy!

  • Nicholas

    I still think the NWS is calling for to much rain in So Cal when all is said and done. 0.75-1.00 sounds like wish casting to me seeing all the model runs. This storm isn’t even worth me turning on GRL radar.

    Raintotals so far.
    Whittier, CA
    11/18-Trace
    11/19-0.13

  • mendodave

    Ok, rain has arrived in Mendocino, .29″/hr.
    baro stable at 29.83
    highest gust 43mph

  • sc100

    Basically all of Norcal is under flood watches and warnings at this point. The California Nevada River Forecast Center now has about a third of Norcal as likely to see significant river flooding. This includes some of the largest uncontrolled rivers as well as the Upper Sacramento River.

    http://www.cnrfc.noaa.gov/flood_outlook.php

    Portions of Northwest CA are closing in on 8 inch storm totals already.

  • http://weatherwest.com Daniel Swain

    Looks like Mendocino County and the Shasta Drainage could see some almost unbelievably high 5-day rainfall totals. It now appears that some locally serious flooding may be inevitable this weekend. One additional question is where the exact southern extent of the extremely heavy rain will be–it will probably encompass the northern Bay Area counties, but will the rest of the Bay Area see excessive precipitation? The 18z GFS will be interesting…

  • Nicholas

    shauntanner

    http://www.wunderground.com/blog/shauntanner/comment.html?entrynum=221#commenttop

    “Now, I know what you are thinking. When you look at those rainfall numbers, they don’t seem all that impressive. There is a lesson that can be learned from looking at these rainfall amounts. When a parade of storms like what the West Coast is experiencing sets up, the first of these storms often ends up being weaker than what the models had predicted. Arguably, this case could be made for the storm that moved through Northern California Wednesday. But, this shouldn’t be the lesson for the rest of the parade. Often, this first storm primes the atmosphere with moisture that the subsequent storms could utilize bring very heavy rain to the state. This appears to be the case for the next two storms”

    Sounds like the best precipitation is trending more and more north.

  • Nicholas

    Also just been getting this miserable drizzle all day over here in Whittier. Almost like what you would see in May or June. Just enough to be annoying and nothing els.

  • Ken K.

    Picked up .03 this morning at the Fire Station in Barona(Between Lakeside and Ramona) the models have back off the Sunday storm for So. Cal., now showing it pulling further north with very little if any rainfall.. Like Tom said, NWS has done the same. You folks to the north, enjoy that great weather you are recieving, we in the south will dream of the wind and heavy rain and maybe some lighting.

  • http://www.norcalweather.net/ WxTracker15

    029
    WGUS46 KSTO 292229
    FLWUSA
    BULLETIN – IMMEDIATE BROADCAST REQUESTED
    FLOOD WARNING
    NATIONAL WEATHER SERVICE SACRAMENTO CA
    229 PM PST THU NOV 29 2012

    …THE NATIONAL WEATHER SERVICE IN SACRAMENTO HAS ISSUED A FLOOD
    WARNING FOR THE FOLLOWING RIVERS IN CALIFORNIA…

    SACRAMENTO RIVER AT TEHAMA BRIDGE

    .PEAK RIVER STAGES WELL ABOVE FLOOD STAGE ARE EXPECTED AT MOST UPPER SACRAMENTO RIVER
    FORECAST POINTS BY SUNDAY WITH OVERFLOW EXPECTED AT ALL WEIRS BY LATER THIS WEEKEND.

    FORECASTS ARE BASED ON PRESENT AND FORECASTED METEOROLOGICAL AND
    HYDROLOGIC CONDITIONS AT TIME OF ISSUANCE.

    PRECAUTIONARY/PREPAREDNESS ACTIONS…

    UNLISTED FORECAST POINTS ARE EXPECTED TO REMAIN BELOW MONITOR STAGE.
    ALL THOSE AFFECTED BY RIVER CONDITIONS SHOULD REMAIN ALERT FOR RAPID
    CHANGES AND FOR POSSIBLE FORECAST REVISIONS.

    FOR MORE HYDROLOGIC INFORMATION AND STAGE DEFINITIONS REFER TO THE
    FOLLOWING WEB SITE (ALL LOWER CASE):
    http://WWW.WRH.NOAA.GOV/STO/HYDRO_DATA.PHP

    THE NEXT STATEMENT WILL BE ISSUED 900 PM THURSDAY NOVEMBER 29

  • http://www.norcalweather.net/ WxTracker15

    BULLETIN – EAS ACTIVATION REQUESTED
    FLOOD WARNING
    NATIONAL WEATHER SERVICE SACRAMENTO CA
    323 PM PST THU NOV 29 2012

    CAC007-011-021-033-035-057-063-089-091-101-103-113-115-302300-
    /O.NEW.KSTO.FA.W.0001.121129T2323Z-121130T2300Z/
    /00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
    YOLO CA-SIERRA CA-NEVADA CA-COLUSA CA-PLUMAS CA-SUTTER CA-LASSEN CA-
    LAKE CA-YUBA CA-SHASTA CA-GLENN CA-TEHAMA CA-BUTTE CA-
    323 PM PST THU NOV 29 2012

    THE NATIONAL WEATHER SERVICE IN SACRAMENTO HAS ISSUED A

    * FLOOD WARNING FOR URBAN AREAS AND SMALL STREAMS IN…
    COLUSA COUNTY…
    NEVADA COUNTY..
    SUTTER COUNTY…
    NORTHWESTERN YOLO COUNTY..
    YUBA COUNTY…
    BUTTE COUNTY…
    GLENN COUNTY…
    LAKE COUNTY…
    EXTREME WEST CENTRAL LASSEN COUNTY…
    WESTERN PLUMAS COUNTY…
    SHASTA COUNTY…
    WESTERN SIERRA COUNTY…
    TEHAMA COUNTY…

    * UNTIL 315 PM PST FRIDAY

    * AT 315 PM PST BANDS OF MODERATE TO HEAVY RAINFALL ARE DEVELOPING
    OVER MUCH OF NORTHERN CALIFORNIA AND WILL CONTINUE THROUGH THE NIGHT
    AND INTO FRIDAY. RAINFALL AMOUNTS OF 1 TO 2 INCHES WILL FALL OVER
    THE NEXT 3 HOURS ESPECIALLY AT HIGHER ELEVATIONS. TOTAL AMOUNTS FROM
    2 TO 3 INCHES OVER THE VALLEY AND 4 TO 8 INCHES OVER THE MOUNTAINS
    WILL OCCUR OVER THE NEXT 24 HOURS. THIS HEAVY RAINFALL WILL CAUSE
    SEVERAL SIGNIFICANT IMPACTS FOR THE WARNED AREA.

    * RAPID RISES AND SMALL STREAM FLOODING WILL OCCUR IN MANY AREA
    STREAMS. SOME CREEKS THAT ARE LIKELY TO HAVE SIGNIFICANT FLOODING
    INCLUDE COW CREEK…COTTONWOOD CREEK…BATTLE CREEK…CLEAR
    CREEK…DRY CREEK…BUTTE CREEK.

    * MOUNTAIN RIVER AND STREAM FLOODING ABOVE THE RESERVOIRS WILL
    OCCUR ALONG WITH WIDESPREAD MUD AND ROCK SLIDES.

    * DEBRIS FLOWS WILL OCCUR…ESPECIALLY NEAR RECENT BURN SCARS
    IN SHASTA…TEHAMA…COLUSA…AND PLUMAS COUNTIES.

    * WEIR OVERFLOW THROUGH BYPASSES WILL OCCUR AS THE SACRAMENTO RIVER
    SYSTEM IN THE VALLEY WILL RISE.

    A FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR HAS BEEN REPORTED.
    STREAM RISES WILL BE SLOW AND FLASH FLOODING IS NOT EXPECTED.
    HOWEVER…ALL INTERESTED PARTIES SHOULD TAKE NECESSARY PRECAUTIONS
    IMMEDIATELY.

    PRECAUTIONARY/PREPAREDNESS ACTIONS…

    MOST FLOOD RELATED DEATHS OCCUR IN AUTOMOBILES. DO NOT ATTEMPT TO
    CROSS WATER COVERED BRIDGES…DIPS…OR LOW WATER CROSSINGS. NEVER
    TRY TO CROSS A FLOWING STREAM…EVEN A SMALL ONE…ON FOOT. TO
    ESCAPE RISING WATER MOVE UP TO HIGHER GROUND.

    DO NOT UNDERESTIMATE THE POWER OF FLOOD WATERS. ONLY A FEW INCHES OF
    RAPIDLY FLOWING WATER CAN QUICKLY CARRY AWAY YOUR VEHICLE.

    &&

  • http://weatherwest.com Daniel Swain

    Remember…the best venue to post rapid-update storm news (including rain totals and flooding reports) is on the Weather West Facebook feed (https://www.facebook.com/pages/Weather-West/197150373743525). I would ask that people refrain from posting full-text NWS warnings/statements there unless something truly exceptional occurs. Full blog updates will continue here on the main site (and only here), but I think the Facebook interface is much better suited to posting photographs/multimedia information than the slightly clunky comment setup on this site. ;) I should have a new full update late tonight, after the 00Z models are in.

  • Dan the Weatherman

    Some light to moderate rain fell here in Orange overnight last night and early this morning, and was finally significant enough to cause puddling out in my patio. Today has been drizzly at times, but nothing really measurable. Hopefully more bands of showers pass through the area over the next few days as forecast and moistens up everything before a strong Santa Ana event occurs.