Mesoscale Discussion 2174

Issued

Sep 13, 2011, 3:56 PM PDT (22:56 UTC)

Expired

Sep 13, 2011, 5:30 PM PDT

In force

94 min

Issued by

the Storm Prediction Center

Counties Imperial County, CA, Riverside County, CA

The Santa Ana Mts radar (KSOX), 52 km from the middle of the area, began a volume at 22:58 UTC, the scan nearest the moment this went out.

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

425 
ACUS11 KWNS 132257
SWOMCD
SPC MCD 132256
CAZ000-140030-

MESOSCALE DISCUSSION 2174
NWS STORM PREDICTION CENTER NORMAN OK
0556 PM CDT TUE SEP 13 2011

AREAS AFFECTED...PARTS OF SRN CA

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 132256Z - 140030Z

A FEW STORMS COULD CONTAIN SMALL HAIL AND GUSTY WINDS INTO THE
EVENING...MAINLY OVER THE MOUNTAINS. A WW IS NOT NEEDED.

OBSERVED SAN NICOLAS ISLAND 16Z SOUNDING SAMPLED THE POCKET OF
RELATIVELY COLD TEMPERATURES /H5 TEMPERATURE OF -12.7C/ IN
ASSOCIATION WITH A MID/UPPER-LEVEL LOW OFF THE SRN CA
COAST...CENTERED APPROXIMATELY 45 MILES S OF LONG BEACH PER RECENT
WATER VAPOR IMAGERY. WITH THESE FEATURES GRADUALLY TRANSLATING
TOWARD THE COAST...700-500-MB LAPSE RATES OF 7-7.5 C/KM ATOP SFC
TEMPERATURES IN THE 80S AND DEWPOINTS IN THE 50S ARE SUPPORTING
MLCAPE VALUES AROUND 1000 J/KG ACROSS THE COASTAL RANGE. AS
SUCH...VISIBLE SATELLITE AND REGIONAL RADAR IMAGERY DEPICT SCATTERED
CONVECTION INCREASING IN NUMBER/INTENSITY FROM THE SANTA BARBARA /
KERN / VENTURA COUNTY MOUNTAINS SEWD TOWARD THE LOS ANGELES /
RIVERSIDE / SAN DIEGO COUNTY MOUNTAINS. STORMS ARE EXPECTED TO
MOSTLY REMAIN ANCHORED TO HIGHER TERRAIN WHERE ASCENT /DUE TO
OROGRAPHIC EFFECTS/ WILL BE STRONGEST...AND AS LOS ANGELES VWP DATA
SUGGEST LOWER/MIDDLE TROPOSPHERIC FLOW AOB 10 KT. SMALL HAIL AND
GUSTY WINDS WILL BE THE PRIMARY THREATS WITH THIS ACTIVITY.
FURTHERMORE...THE INFLUX OF ABUNDANT MID-LEVEL MOISTURE FROM THE
GULF OF CALIFORNIA IS SUPPORTING PW VALUES IN EXCESS OF 1 INCH --
AROUND 150 PERCENT OF NORMAL PER AMSU/SSMI DATA. WITH GENERALLY SLOW
STORM MOTIONS...VERY HEAVY RAIN...WITH RAINFALL RATES OF 1-2
IN/HR...WILL BE POSSIBLE.

A FEW STORMS COULD MOVE OVER THE LOWER ELEVATIONS EAST OF THE
COASTAL RANGE...INCLUDING THE ANTELOPE VALLEY...SOUTHERN CA
DESERTS...AND COACHELLA/IMPERIAL VALLEYS DUE TO COLD-POOL-DRIVEN
PROPAGATION EFFECTS. IN THESE AREAS...WARMER/DEEPER BOUNDARY LAYERS
SHOULD SUPPORT MORE OF A GUSTY WIND THREAT. THUNDERSTORMS ARE NOT
EXPECTED TO AFFECT THE COASTAL PLAIN ATTM...WHERE FORMIDABLE CAPPING
OWING TO THE INLAND-ADVECTION OF THE MARINE LAYER IS DEPICTED IN
AREA RUC SOUNDINGS.

DESPITE THE THREAT FOR STRONG STORMS...THE CONVECTIVE VIGOR ACROSS
THE DISCUSSION AREA WILL BE LESSENED BY THE ABSENCE OF STRONGER
DEEP-LAYER SHEAR AND FORCING FOR ASCENT...WHICH ARE LOCATED WELL SE
OF THE DISCUSSION AREA. STORMS ARE EXPECTED TO WEAKEN AFTER 03Z IN
RESPONSE TO NOCTURNAL STABILIZATION.

..COHEN.. 09/13/2011

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

ATTN...WFO...PSR...VEF...SGX...HNX...LOX...

LAT...LON   32651546 32561594 32691648 33171678 33471708 33801749
            34221805 34401882 34651975 34901964 34991855 34861797
            34661724 34501645 34341575 33821524 32971513 32651546

Mesoscale Discussions in California, 2011Every mesoscale discussion in 2011

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.