Feb 7, 2015 1:06 PM by Kris Kuyper
Our Friday storm was a big one! A weaker one is on the way Saturday evening, and another strong one is coming Sunday. Both of these new ones will work into a now somewhat unstable atmosphere, and there's a threat of Valley thunderstorms. With abundant morning sunshine Saturday, that's further acting to destabilize the atmosphere so a few scattered thunderstorms are possible Saturday afternoon in the Valley.
Sunday's storm is stronger, but the abundant cloud cover Sunday will attempt to hinder thunderstorm development. Still, the storm is a strong one, so a few strong afternoon thunderstorms are possible. I still believe Monday to be our best day for thunderstorms, with an unstable atmosphere and probably a good amount of morning sunshine working to destabilize the atmosphere.
The Storm Prediction Center has noticed this as well, and has issued a couple of statements about it. Here are their thoughts about Saturday:
WATER VAPOR LOOPS SHOW A COMPACT SHORTWAVE TROUGH OFF THE COAST OF NORTHERN CA. LIFT AHEAD OF THIS FEATURE WILL BEGIN TO AFFECT NORTHERN AND CENTRAL CA BY EARLY AFTERNOON...CONTINUING THROUGH MUCH OF THE EVENING HOURS. INCREASING SHOWERS WILL AFFECT THE NORTHERN AND CENTRAL CA VALLEY THIS AFTERNOON...WITH FORECAST SOUNDINGS
SHOWING SUFFICIENT LOW/MID LEVEL CAPE AND EFFECTIVE VERTICAL SHEAR FOR SOME RISK OF HAIL OR ROTATING STRUCTURES. HOWEVER...SHALLOW CAPE LAYER MAY LIMIT THE EXTENT OF LIGHTNING. NEVERTHELESS...HAVE OPTED TO INCLUDE THE REGION IN A GENERAL THUNDERSTORM OUTLOOK FOR THIS UPDATE.
And here are their thoughts about Sunday, especially about severe thunderstorms:
HAVE EXPANDED MARGINAL-RISK PROBABILITIES FARTHER W ACROSS THE REGION AND CONSIDERED AN UPGRADE THIS OUTLOOK FOR PARTS OF THE CNTRL VALLEY. ALTHOUGH TOTAL SEVERE PROBABILITIES DO NOT APPEAR AOA 15 PERCENT...INDIVIDUAL HAZARD PROBABILITIES AOA 5 PERCENT FOR TORNADOES APPEAR PLAUSIBLE.
MID-LEVEL DCVA WITH THE ERN PACIFIC TROUGH WILL YIELD STRONGLY-FORCED ASCENT OVERSPREADING THE COAST AND CNTRL VALLEY SUN AFTERNOON AND EARLY EVENING...FAVORABLY TIMED WITH THE DIURNAL HEATING CYCLE. WIDESPREAD CLOUDINESS APPEARS MOST LIKELY WITH NRN EXTENT...HINDERING SURFACE-BASED DESTABILIZATION DESPITE COOLING ALOFT/STEEPENING OF MID-LEVEL LAPSE RATES. WITH WRF/NMMB-BASED
GUIDANCE SUGGESTIVE OF MIDDLE 60S TO AROUND 70 DEG F SURFACE TEMPERATURES FARTHER S IN THE VALLEY...A NARROW CORRIDOR OF MLCAPE APPROACHING 500 J/KG MAY DEVELOP. STRENGTHENING LOW/DEEP-LAYER SHEAR WILL YIELD HODOGRAPHS QUITE FAVORABLE FOR UPDRAFT ROTATION BEFORE LOW-LEVEL FLOW BECOMES VEERED FROM WEST-TO-EAST DURING LATE AFTERNOON/EVENING.
OVERALL SETUP SHOULD SUPPORT POTENTIAL FOR SEVERAL WEAKLY ROTATING SHOWERS/STORMS. A FEW OF THESE MAY BECOME SUFFICIENTLY STRONG...WITH A RISK FOR A COUPLE TORNADOES...ALONG WITH LOCALLY DAMAGING WINDS AND PERHAPS MARGINALLY-SEVERE HAIL.
The Sunday setup sounds more significant, but with the clouds/rain impacting us in the north end of the Valley, I think the bigger threat may be towards Sacramento or Stockton for severe thunderstorms. Still, we'll be watching this very carefully.