Very active weather in California this week

Filed in Uncategorized by on March 29, 2010 32 Comments

March, despite being a rather quiescent month weather-wise in the state of California, will end on a very active note. A major pattern change is already beginning to impact far northern California this evening, with light rain beginning to spread south from the North Coast. Mostly light rain will continue to spread as far south as about the Bay Area by tomorrow afternoon. By Tuesday, though, a major cold frontal boundary will push south across the northern half of the state, bringing increased rainfall and much colder temperatures (along with some windy conditions). Temperatures aloft will drop rapidly behind this main frontal boundary, below 0 C at 850 over all of NorCal by late Tuesday afternoon. As a result, lapse rates will begin to increase and isolated thunderstorms will be possible from around San Francisco northward on Tuesday and Tuesday night. The main event, though, will wait for Wednesday/Thursday.

Water vapor imagery depicting active Pacific storm track (NOAA)

On Wednesday, strong cold air advection will continue over the northern two thirds of the state and begin across the southern third, and 850 mb temperature will further drop to as low as -4 C near Sacramento and -5 C near Eureka. 500 mb temps will drop to around -34 C or even a bit lower. These are very cold temperatures for late March/early April in Calif0rnia and in conjunction with solar surface heating during the day on Wednesday will lead to extremely steep lapse rates. Thunderstorms are almost certain on Wednesday in some part of NorCal, though the aerial coverage of deep convection is hard to pinpoint this far out. If the main impulse remains offshore until late in the day or overnight, convection will be more of the “popcorn” variety with scattered to numerous showers and isolated to scattered thunderstorms with lots of small hail.

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NAM depiction of main "impulse" moving ashore in NorCal on Wednesday night (NCEP)

When the aforementioned impulse does move ashore, however, convection will likely become much more widespread in coverage and potentially more organized. Recent model runs indicate that this impulse may not traverse the region at peak heating, which would tend to mitigate the severe weather potential. Even so, however, hail and heavy rain would be expected in virtually all stronger cells, and some severe storms are certainly not out of the question. NorCal will also be in the jet exit region at this time, with a strong cyclonically curved jet just to our south, so the severe potential is not negligible. Southern California will begin to see increasing lapse rates and convective chances by late Wednesday, as well, but especially on Thursday. Thursday may be another convectively active day in NorCal, depending on how quickly the trough axis moves to the east. Southern California stands a decent chance of some thunderstorm activity in this time frame, as well.

Low snow levels will also be a concern with this system, as well. Unseasonably cold air aloft will bring snow levels and/or wet bulb zero levels to 2000 feet or lower throughout NorCal. I would not be surprised to hear of some snow reports from Redding or the far northern Sacramento Valley between 1000-1500 feet overnight on Wednesday. In fact, it’s possible that snow levels could even drop as low as 1500-2000 feet in Southern California, so snowfall is possible in some of the higher inland valleys. The Sierra foothills and the higher Bay Area peaks could see rather significant early April snowfall accumulations, as well. Accumulations of small hail in intense showers or thunderstorms are likely in isolated locations throughout the state, irrespective of elevation.

It does not appear that the active pattern will end on Friday (though there may be a break on that day). Model progs are currently indicating the potential for another cold/cutoff low in the 7-10 day time frame. All in all, a pretty active spring pattern is shaping up for the entire state, with some highly beneficial late-season snowfall in the mountains.

UPDATE: 3/29

Convective chances for Wednesday still on track. Below is a rather impressive visible satellite loop depicting the vast field of cold air cellular cloudiness (cumulus) over the Pacific headed for CA…

Visible satellite imagery showing extensive cold air convective cloudiness over Pacific (NRL)

© 2010 WEATHER WEST

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  • nicholas

    12z was a disappointing run. Keeping all the covective activity south of LA County (surprise).

    12z was a fairly odd pattern I don’t recall ever seeing. Anyone even seen something like this? Look at days 15-16

    http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/images/gfs_slp_336s.gif

  • Ken K.

    Looks like a closed low to me, course this time of year and so far out, most likely will change, pretty warm and dry again today, I was down in La Jolla, I did not see any marine layer, just some high clouds. Time will tell.

  • nicholas

    Well the 18z showed hardly any rain for LA County. Looks like all the action might go south of the area.

  • Tom in San Diego

    Wow, look at that stuff filtering through the Aleutians! I guess Ive never noticed any thing like that.

  • nicholas

    ^_^ Be a good storm.

  • alan

    nothing’s looking too promising :( bah-humbug

  • Ken K.

    Looks like this one is going into Baja also, seems to be the case this season, might pick up some showers, clouding up, but good stuff will be Baja’s bonus.

  • alan

    so how’d everyone fair with this storm? Looks like San Diego’s getting it right now,but falling apart as it heads inland. Less than 1″ of snow in san bernardino mountains, but very cold, 23 degrees @ 6300′. so much for 7 to 12″ :(

  • Tom in San Diego

    Got about an hour or so steady downfall, .32 inches at Navy Field in Imperial Beach, Brown Field had a little less.

  • Tom in San Diego

    Calling for residual showers today, but you know how that goes.

  • redlands

    another flop storm — nothing in redlands, ca very disappointing — 4th march in a row with bone dry conditions — looks like april will be bone dry

    • Dan the Weatherman

      It was certainly another disappointing March here in Orange as well, the 4th in a row as you well said above. It is too early to tell whether April will be bone dry, but I certainly hope not.

  • nicholas

    I saw a few lightning strikes down by Chula Vista early in the morning. It was raining good in that area. Whittier only got a few drops :(

    • Tom in San Diego

      Thats news to me! I live pretty close to Chula, and if they got lightning, it must have been the thunderless kind.

  • Dan the Weatherman

    It was a flop storm here in Orange with a measly .03″ falling here. I was certainly expecting more than that, but it looked like the storm passed by offshore (outside slider) once again which seems to be a trend in recent years for some reason I don’t know. Sounds like the San Diego area got the brunt of this one.

  • Ken K.

    It was not much here in the San Digo Foothills, about .10 engough to get the ground wet, the south bay I think picked up the best near the border. Sounds like Tom was the bonus winner down this way, looked like the mountians did receive a dusting of snow. It is looking like for So. Cal. Summer is a coming, with not much more rain for us. Course soon as I say this, it will prove me wrong. I wish. Grass is turning brown and before long we will be chasing grass fires.

  • alan

    Well NWS is showing 40% for Monday, northern areas (orange/LA/IE) might even fair better on that one then this last round. And then 60% for April 11th.

  • nicholas

    12z brought back the April 11th storm. :)

  • Dan the Weatherman

    I hope it doesn’t rain during the day on April 11, because I am going to an outdoor event that afternoon. It can rain all it wants before and after, though, as I still want to see late season rain and the fact we need it.

    • Dan the Weatherman

      I hope that this coming Sunday night-Monday morning’s storm brings more rain to Orange than this last system did.

  • nicholas

    The 0z went back to a much more active pattern.

  • David

    ok Daniel time too come out of hideing and say some in we are looking at the best storm of the year

    where in the heck are you i have not seen you make a post in DAYS in fac i have not seen you make a post from the time you started this blog and yes its been that long

    ITS TIME TOO COME OUT AND SAY SOME IN ABOUT ARE STORM TOODAY Daniel WHERE ARE YOU

    • http://weatherwest.com/current_weather Daniel Swain

      I’ll have a new post later today. This is not, though, the storm of the year by any means.

      • David

        hello Daniel if temper are right here snow levels on the NW coast could be down too sea level where Crescent_City

        http://www.wunderground.com/US/CA/Crescent_City.html?MR=1

        • http://weatherwest.com/current_weather Daniel Swain

          Snow has begun to fall on the North Coast this afternoon. This means snow levels are at sea level. Eureka airport is currently reporting light to moderate snow rates with plummeting temperatures. This is fairly surprising, and may affect expected conditions tonight elsewhere in NorCal. Again, I will update later…

  • nicholas

    Also happy Easter everyone.

  • Tom in San Diego

    Just had a moderate earth quake , in fact its still rolling a bit, in San Diego, at 1545.

    • Tom in San Diego

      Lived here 0over v30 years, and have had several, but this was the strongest Ive felt.

  • nicholas

    Man never thought that earthquake was going to stop. It was the rolling motion here in Whittier. I hope everything is okay down there Tom.

  • Ken K.

    Strongest quake I have felt since a kid here. 6.9 south of Calexico, Julian had a 3.9 just after and looks like a 4.1 in the Bay area, the ole fault line is a moving.
    A lot of after shocks in the desert around 4.0. had some things fall in the closets, and long one for sure.

    • Tom in San Diego

      Felt like a train going over rough track. Like there should a been a slow order for that stretch!

  • nicholas

    Its like a swarm growing :(