WPC Met Watch |
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Mesoscale Precipitation Discussion: #0064 (2017) |
(Issued at 308 AM EST MON FEB 27 2017
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MPD Selection |
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MESOSCALE PRECIPITATION DISCUSSION 0064
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
308 AM EST MON FEB 27 2017
AREAS AFFECTED...SOUTHWEST CALIFORNIA
CONCERNING...HEAVY RAINFALL
VALID 270808Z - 271800Z
SUMMARY...DEEP MOISTURE REACHING SW CA COAST WITH LGT TO MDT
SHOWERS STARTING AROUND 11-12Z TO RAMP UP WITH MAIN SURGE OF
MOISTURE/LIFT AFTER 16Z.
DISCUSSION...SYNOPTIC SETUP FROM GOES-W WV AND RECENT 89 GHZ AMSU
MOSAIC DENOTES A DEEP NORTHERN STREAM TROF DESCENDING THROUGH NW
CA ATTM...TIGHTENING THE GRADIENT ACROSS S CA AND ENHANCING THE
JET TO AROUND 100 KTS THAT WILL STEADILY INCREASE THROUGHOUT THE
MORNING TO 120KTS WITH FAVORABLE RIGHT ENTRANCE PLACED OVER AREA
OF CONCERN. WV ALSO DENOTES A SHEARED REMNANT SUB-TROPICAL LOW
NEAR 30N 135W. THE INFLUENCE OF THE NORTHERN STREAM WILL CONTINUE
TO PRESS IT SOUTH WHILE SHEARING IT...HELPING TO PUMP UP THE
SUBTROPICAL RIDGING AHEAD OF IT. IN THE LOWER LEVELS...BLENDED
TPW AND 89GHZ DENOTE A STATIONARY FRONT EXTENDING FROM JUST SOUTH
OF THE US/MEX BORDER TOWARD A WEAK INFLECTION NEAR 120W.
INCREASED FLOW AND UPPER LEVEL SUPPORT WILL HELP TO AMPLIFY THE
WAVE SLIGHTLY NEARING THE COAST TOWARD 12Z BRINGING MODEST SWLY
LOW LEVEL FLOW AND MOISTURE FLUX.
CURRENT IR SHOWS MILKY/FOGGY BANK OF THE LEADING PORTION OF
HIGHER/DEEP MOISTURE STREAM CROSSING SAN CLEMENTE ISLAND NEARING
THE SW SAN DIEGO COUNTY COAST INTO NW BAJA CALIFORNIA...THIS AREA
SEEMS TO BE A BIT FURTHER NORTH AND LIKELY HAS SLIGHTLY INCREASED
VALUES OF MOISTURE COMPARED TO THE CURRENT BLENDED TPW WHICH
DENOTES .5-.7" IN THE VICINITY. THIS IS FURTHER NORTH THAN OLDER
MODEL GUIDANCE SUGGESTED AS NEW 00Z AND RAPID REFRESH GUIDANCE
LATCHING ONTO THIS SLIGHT NORTHWARD SHIFT. TIMING SUGGESTS LGT TO
MODERATE SHOWERS ARE EXPECTED AROUND THE 10-11Z TIME FRAME WITH
THIS SFC WAVE/SWLY FLOW INCREASING TO 40-45 KTS. WITH TPWS UP TO
1.0" AND THIS FLOW...OROGRAPHIC ASCENT SHOULD SUPPORT .25"/HR
RATES WITH LOCALLY HIGHER AMOUNTS POSSIBLE WITH THIS SURGE FOCUSED
ON THE LAGUNA MTN RANGE FROM 14-16Z TIME PERIOD. THIS ALONE IS
NOT TOO CONCERNING BUT COULD SET THE STAGE AND LOWER FFG VALUES
FOR THE MAIN SURGE OF MOISTURE/RAINFALL.
AS THE SHORTWAVES INTERACT AND AMPLIFY THE JET...THE BEST
INTERSECTION OF THE COUPLING JET ASCENT REGIONS SHOULD ADVANCE ON
THE SW CA/N BAJA COAST TOWARD 15-16Z AIDING INCREASED ASCENT.
THIS MAY BE A BIT NORTH OF THE LOWER LEVEL MOISTURE AXIS AS THE
CURRENT TREND OF BLENDED TPW/LAYERED TPW PRODUCTS FROM POLAR
SATELLITES DO NOT SUPPORT THE NORTHWARD SHIFT OF THE MOISTURE AXIS
KEEPING THE INTERPOLATED AXIS SOUTH OF THE U.S. BORDER. THIS IS
THE GREATEST UNCERTAINTY ON WHETHER OR NOT THERE IS A SOLID THREAT
OF FLOODING/FLASH FLOODING INTO THE U.S. OR REMAIN SOUTH IN BAJA
CALIFORNIA. HI-RES GUIDANCE INCLUDING RECENT RUNS OF THE HRRR AND
00Z ARW SUGGEST
THE MOISTURE/ASCENT CHANNEL WILL BE FAR ENOUGH NORTH TO GENERATE
RATES IN EXCESS OF .4-.5"/HR STARTING AROUND 16-18Z. WHILE THIS
MAY PLAY OUT CONCERN IS REMOTE SENSED DATA TRENDS SUGGEST
OTHERWISE. STILL...A GLANCING BLOW WITH MORE MODEST RATES IN .25"
RANGE WITH THE SECOND LONGER DURATION SURGE ARE STILL CONCERNING
FOR LOCALIZED TOTALS OF 1-2" BY 18Z INCREASING THE THREAT FOR
FLOODING AFTER 18Z. WILL CONTINUE TO MONITOR AND UPDATE AS
NECESSARY AS NEW DATA BECOMES AVAILABLE/CONFIDENCE GROWS.
GALLINA
ATTN...WFO...SGX...
ATTN...RFC...CNRFC...
LAT...LON 33931662 33871645 33621636 33371636 33061630
32691618 32301602 31991579 31531585 31591655
32401710 32781731 33141732 33561718 33841695
Last Updated: 308 AM EST MON FEB 27 2017
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