Flash Flood Guidance
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000
AWUS01 KWNH 240624
FFGMPD
CAZ000-ORZ000-241800-

MESOSCALE PRECIPITATION DISCUSSION 0080
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
223 AM EDT FRI MAR 24 2017

AREAS AFFECTED...NORTHERN CA...EXTREME SOUTHWEST OR

CONCERNING...HEAVY RAINFALL

VALID 240622Z - 241800Z

SUMMARY...HEAVY RAINS WILL ARRIVE ACROSS THE NORTHERN CA AND
EXTREME SOUTHWEST OR THROUGH THE LATE NIGHT HOURS AND CONTINUE
THROUGH FRIDAY MORNING.

DISCUSSION...GOES-W IR/WV IMAGERY SHOWS A WELL-DEFINED UPPER
TROUGH OFF THE WEST COAST GRADUALLY ADVANCING EASTWARD ALONG WITH
A WELL-DEFINED SURFACE FRONT AS SEEN IN THE LATEST AMSU 89GHZ
DATA. ALREADY AREAS OF LIGHT TO MODERATE RAIN ARE MOVING ASHORE
ACROSS NORTHERN CA AND SOUTHWEST OR...BUT THESE RAINFALL RATES ARE
EXPECTED TO INCREASE AS A STRENGTHENING SOUTH-SOUTHWEST LOW LEVEL
JET...REACHING OVER 50 KTS...ARRIVES AHEAD OF THE COLD FRONT
TOWARD 12Z.

OFFSHORE RAINFALL RATES PER A 0242Z AMSU PASS ARE NEAR A 0.25
INCH/HR...BUT THE LATEST CIRA-LPW DATA SHOWS A WELL-DEFINED PLUME
OF DEEPER MOISTURE...ESPECIALLY IN THE 850/500 MB LAYER WITH SOME
SUBTROPICAL ORIGIN ADVANCING NORTHEAST UP ALONG THE OFFSHORE
FRONTAL ZONE. THIS COUPLED WITH FAVORABLE RIGHT-ENTRANCE REGION
JET DYNAMICS RELATIVE TO A 130-140 KT 250 MB JET STREAK SHOULD
FOSTER SOME INCREASE IN OFFSHORE RAINFALL RATES OVERNIGHT WHICH
WILL THEN OVERSPREAD FAR SOUTHWEST OR AND NORTHERN CA THROUGH THE
MORNING HOURS.

THE LATEST HIRES MODEL CONSENSUS BETWEEN THE 00Z ARW/NMMB AND
NSSL-WRF SUGGEST 1 TO 2 INCHES OF RAIN BETWEEN 06Z AND 12Z...WITH
ANOTHER 1 TO 2 INCHES BETWEEN 12Z AND 18Z. THE HEAVIEST RAINS
SHOULD BE ACROSS THE IMMEDIATE COASTAL RANGES WHERE SOME ISOLATED
5 INCH AMOUNTS WILL BE POSSIBLE THROUGH 18Z. HOURLY RAINFALL RATES
ARE EXPECTED TO OCCASIONALLY REACH UP TO OVER A 0.50 INCH/HR AS
THE FRONT APPROACHES AND BEGINS CROSSING THE REGION BY MID TO LATE
MORNING. GIVEN THE RELATIVELY WET ANTECEDENT ASSOCIATED WITH HEAVY
RAIN OVER THE LAST COUPLE OF WEEKS...SOME RUNOFF PROBLEMS WILL BE
POSSIBLE.

ORRISON

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

ATTN...WFO...EKA...MFR...MTR...STO...

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

LAT...LON   42542357 42092284 40922251 39522244 38302200
            37932216 37862289 38632339 39052406 39612406
            40362449 40582449 41572456 42442425


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