Mesoscale Discussion 508

Issued

Apr 13, 2012, 10:53 AM PDT (17:53 UTC)

Expired

Apr 13, 2012, 1:00 PM PDT

In force

2 hr

Issued by

the Storm Prediction Center

Counties Alameda County, CA, Contra Costa County, CA, Merced County, CA, Napa County, CA, Sacramento County, CA, San Joaquin County, CA, Santa Clara County, CA, Solano County, CA, Stanislaus County, CA, Yolo County, CA

The San Francisco radar (KMUX), 70 km from the middle of the area, began a volume at 17:55 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

882 
ACUS11 KWNS 131753
SWOMCD
SPC MCD 131753 
CAZ000-132000-

MESOSCALE DISCUSSION 0508
NWS STORM PREDICTION CENTER NORMAN OK
1253 PM CDT FRI APR 13 2012

AREAS AFFECTED...PARTS OF THE CNTRL CA VALLEY AND THE COASTAL RANGES
OF W-CNTRL CA

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 131753Z - 132000Z

A FEW STORMS COULD CONTAIN SMALL HAIL AND GUSTY WINDS THIS AFTERNOON
ACROSS PARTS OF THE CNTRL CA VALLEY AND THE COASTAL RANGES OF
W-CNTRL CA. WHILE AN ISOLATED MARGINALLY SVR STORM CANNOT BE RULED
OUT...THE THREAT IS TOO ISOLATED/MARGINAL FOR THE ISSUANCE OF A WW.

WATER VAPOR LOOP DEPICTS AN ELONGATED MID-LEVEL CYCLONE EXTENDING
FROM THE W-CNTRL CA COAST NNWWD TO AROUND 300 MILES OFF THE W-CNTRL
WA COAST. COLD MID-LEVEL TEMPERATURES ACCOMPANYING THE CYCLONE /-28C
AT 500 MB PER 12Z OAKLAND SOUNDING/ ARE SUPPORTING STEEP MID-LEVEL
LAPSE RATES OVER THE AREA -- I.E. 7.5 TO 8.5 C/KM WITHIN THE
700-500-MB LAYER. CLOUDS AND SHOWERS ACCOMPANYING A BAND OF FRONTAL
ASCENT WILL CONTINUE MOVING EWD/SWD ACROSS PARTS OF THE AREA THIS
AFTERNOON...FOLLOWED BY POCKETS OF CLEARING AND SFC DIABATIC HEATING
BENEATH THE COLD AIR ALOFT. VIS SATELLITE LOOP ALREADY INDICATES
SEVERAL AREAS OF CLEARING NEAR AND EAST OF THE SAN FRANCISCO
AREA...WITH THE AREA OF INSOLATION AND STEEPENING LOW-LEVEL LAPSE
RATES FORECAST TO CONTINUE EXPANDING EWD/SWD AS THE FRONTAL ASCENT
BECOMES INCREASINGLY REMOVED FROM THE AREA.

SUFFICIENT BUOYANCY AND LOW-LEVEL MOISTURE WILL BE PRESENT FOR
ISOLATED TO SCATTERED THUNDERSTORMS TO DEVELOP AFTER 19Z OWING TO
OROGRAPHIC EFFECTS...AS WELL AS CONVERGENCE ALONG A POST-FRONTAL
WIND-SHIFT AXIS. WHILE HANFORD VWP DATA CURRENTLY DEPICT SOME
DIRECTIONAL SHEAR IN THE LOWER LEVELS OWING TO THE VERTICALLY
VEERING WIND PROFILE... LOW-LEVEL AND DEEP-LAYER SHEAR ARE FORECAST
TO BECOME INCREASINGLY UNFAVORABLE FOR ORGANIZED STORM STRUCTURES AS
THE SFC WINDS VEER AND MID-LEVEL FLOW WEAKENS. AS SUCH...A PRIMARILY
PULSE CONVECTIVE MODE IS ANTICIPATED...WITH SMALL HAIL AND GUSTY
WINDS BEING THE PRIMARY CONCERNS WITH THE STRONGEST STORMS. AN
ISOLATED INSTANCE OF MARGINALLY SVR HAIL CANNOT BE RULED OUT GIVEN
THE MAGNITUDE OF THE MID-LEVEL LAPSE RATES...BUT THE ABSENCE OF
GREATER BUOYANCY / STRONGER VERTICAL SHEAR WILL MITIGATE A MORE
ROBUST THREAT FOR SVR STORMS.

..COHEN.. 04/13/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...HNX...STO...MTR...

LAT...LON   37442213 37872247 38202265 38532268 38942244 39092212
            38952135 38472079 37732042 37272015 36812004 36381999
            36232027 36322054 36532091 36942146 37442213

Mesoscale Discussions in California, 2012Every mesoscale discussion in 2012

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.