Flash Flood Guidance
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7
000
AWUS01 KWNH 180010
FFGMPD
CAZ000-180608-

MESOSCALE PRECIPITATION DISCUSSION 0056
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
709 PM EST FRI FEB 17 2017

AREAS AFFECTED...PORTIONS OF FAR SRN CA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 180008Z - 180608Z

SUMMARY...A THREAT FOR FLASH FLOODING WILL REMAIN FOR THE NEXT FEW
HOURS ACROSS PORTIONS OF THE HIGHER TERRAIN OF SRN CA ALONG WITH
URBAN FLOODING CONCERNS WITHIN METROPOLITAN AREAS FROM RIVERSIDE
TO SAN DIEGO.

DISCUSSION...AT 00Z...AN AXIS OF HEAVY RAINFALL WITH RAINFALL
RATES OF GENERALLY 0.5 TO 1.0 IN/HR WAS MOVING THROUGH PORTIONS OF
SRN CALIFORNIA JUST AHEAD OF AN OCCLUDED/COLD FRONT ANALYZED JUST
WEST Of SANTA CATALINA AND SAN CLEMENTE ISLANDS. WHILE THE BETTER
REGION OF UPPER DIFFLUENCE HAS BEEN STEADILY DROPPING SOUTH OF THE
REGION...THE LEFT EXIT REGION OF A POWERFUL 170+ KT UPPER LEVEL
JET CONTINUES TO PROVIDE ADDED DYNAMICAL LIFT OVER THE REGION WITH
THE GOES HD WIND PRODUCT  INDICATING NEAR 250 MB WINDS OF 80-90 KT
JUST OFFSHORE OF SRN CA.

WHILE INSTABILITY HAS BEEN LESS THAN ADVERTISED AHEAD OF THE
FRONTAL BOUNDARY WITH NOT MUCH IN THE WAY OF LIGHTNING...STRONG
DYNAMICS HAVE HELPED TO COMPENSATE. SLY 850 MB WINDS OF 50-60+ KT
VIA VAD WIND PLOTS...DIRECTLY ORTHOGONAL TO THE TRANSVERSE RANGES
ALONG WITH PWATS RANGING FROM 1.2 TO 1.3 INCHES HAVE HELPED TO
SUPPORT RAINFALL RATES OVER 1 IN/HR. AS THE FRONT CONTINUES TO
MOVE EAST...RAIN RATES OF 0.5 TO 1.0 IN/HR WILL FOLLOW IN A LINE
AHEAD OF THE FRONT FOR 1-2 HOURS...IMPACTING URBAN LOCATIONS FROM
THE SRN LOS ANGELES SUBURBS INTO SAN BERNARDINO/RIVERSIDE DOWN TO
SAN DIEGO. WEAK LOW LEVEL INSTABILITY WILL INCREASE AFTER THE
FRONT PASSES DUE TO COOLING LOW-MID LEVEL TEMPS SUPPORTING BRIEF
BUT INTENSE SHOWERS INTO COASTAL LOCATIONS.  AHEAD OF THE
FRONT...WHILE FLOW WILL BE MOSTLY PARALLEL TO THE PENINSULA
RANGES...A FEW SOUTH FACING SLOPES AS WELL BURN SCAR LOCATIONS AND
POOR DRAINAGE OF THE URBAN CORRIDOR WILL EXTEND THE FLASH FLOOD
THREAT THROUGH ABOUT 06Z. THE FLASH FLOOD THREAT IS EXPECTED TO
DIMINISH BEYOND 06Z WITH LOWERING PWATS AND WEAKENED DYNAMIC
SUPPORT INTO THE COLORADO RIVER BASIN AS THE FRONT MOVES THROUGH.

OTTO/SULLIVAN

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...LOX...SGX...

ATTN...RFC...CNRFC...

LAT...LON   34541841 34541746 34401689 33771650 33471633
            32951620 32511616 32331691 32761765 33821833
            34271871



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.