Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 200834
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT MON MAR 20 2017

...VALID 12Z MON MAR 20 2017 - 12Z TUE MAR 21 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 WSW OTH 30 SSW OTH 30 ENE CEC 35 ENE ACV 20 WSW MHS
30 ESE SIY 45 ENE RDD 40 E RDD 30 N BLU 15 SE BLU 10 ENE BAB
10 E OVE 10 NNE OVE 15 NNE RDD 25 WSW RDD 20 W RBL 40 NE UKI
30 NNE STS 70 WSW STS.


DEEP-LAYER WAA/MOISTURE WITHIN THE INITIAL WARM CONVEYOR BELT
(WCB) EARLY IN THE PERIOD WILL SEGUE TO ANOTHER (MORE MERIDIONAL)
WCB ACROSS THE WESTERN CONUS DURING DAY 1. THIS AS THE UPPER FLOW
BECOMES INCREASINGLY DIFFLUENT AHEAD OF AN AMPLIFYING (REINFORCED)
UPPER TROUGH OFF THE COAST...AS THE UPPER LEVEL JET STREAK ROUNDS
THE TROUGH BASE AND APPROACHES SOUTHERN CA BY THE END OF THE
PERIOD (12Z TUE). THE PERSISTENT BROAD-SCALE QS VECTOR CONVERGENCE
AND ATTENDANT DEEP-LAYER WWA FORCING/MOIST ISENTROPIC ASCENT WILL
GENERATE ADDITIONAL MODERATE-HEAVY PCPN ACROSS NORTHERN CA AND FAR
SOUTHWEST OR...WITH THE HEAVIEST AMOUNTS ONCE AGAIN TIED TO THE
TERRAIN. THIS INCLUDES THE COASTAL RANGES...SHASTA/SISKIYOUS...AND
NORTHERN SIERRA...AREAS THAT WILL BENEFIT THE MOST AT THE LEADING
EDGE OF THE SUBTROPICAL MOISTURE PLUME (PWS AOA 1.0").
AREAL-AVERAGE QPF TOTALS ARE EXPECTED TO RANGE BETWEEN 1-2+" OVER
THE OROGRAPHICALLY-FAVORED RANGES...WITH THE ASSORTMENT OF
HIGH-RES GUIDANCE SUPPORTIVE OF LOCALLY HIGHER AMOUNTS (3-4
INCHES) ACROSS THE AFOREMENTIONED NORTHERN CA-SOUTHWEST OR RANGES.

AS FAR AS THE 00Z GUIDANCE GOES...THERE IS HIGH FORECAST
CONFIDENCE IN A NON-GFS GENERAL MODEL COMPROMISE...WITH EMPHASIS
ON THE HIGH-RES MEANS (INCLUDING THE HREF... IN-HOUSE BIAS
CORRECTED HIGH-RES ENSEMBLE...AND PARALLEL NBM) GIVEN THE BETTER
SENSITIVITY OVER THE HIGHER TERRAIN. THE GFS WAS A NOTICEABLY WET
OUTLIER OVER FAR NORTHWEST CA AND SOUTHWEST OR...DEPICTING A
POCKET OF AREAL-AVERAGE TOTALS OVER 2 INCHES.

THE UPSHOT...A MARGINAL RISK FOR EXCESSIVE RAINFALL CONTINUES IN
EFFECT FROM 12Z MON - 12Z TUE ACROSS NORTHERN CA AND FAR SOUTHWEST
OREGON...INCLUDING THE COASTAL...SHASTA/SISKIYOUS...AND NORTHERN
SIERRA RANGES THEREIN. LOCALIZED TOTALS OF 3-4"...THE BULK OF
WHICH EXPECTED TO FALL WITHIN 12-18 HOURS MON AFTERNOON AND
OVERNIGHT...WILL POTENTIALLY LEAD TO LOCALIZED SHORT-TERM RUNOFF
ISSUES...PARTICULARLY IN AREAS OF MORE RAPID SNOWMELT.

HURLEY
$$




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