Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 180805
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 AM EDT SAT MAR 18 2017

...VALID 12Z SAT MAR 18 2017 - 12Z SUN MAR 19 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SE CWNM 15 ENE CWJR 50 E SZT 30 NE MLP 10 NNE MLP 40 WNW MSO
40 SW MSO 35 E P69 10 E P69 30 ENE LWS 25 NE PUW COE 15 WSW SZT
40 SSE CXWF 15 ESE CXWF 20 SE CWNM.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 NNW MYL 40 NE MYL 30 N SNT 25 SSE SNT 45 SSW SNT 25 NNE BOI
20 SW MYL 30 NNW MYL.


...CENTRAL-NORTHERN IDAHO AND NORTHWEST MONTANA...

A DEEP LAYER...FULL LATITUDE TROUGH WILL CONTINUE TO MIGRATE
INLAND EARLY TODAY...THEN SHEAR CONSIDERABLY DURING THE LATTER
HALF OF THE PERIOD (00-12Z SUN) AS IT IMPINGES ON THE
HIGHLY-AMPLIFIED DOWNSTREAM RIDGE. AS THE TROUGH EVOLVES TOWARD A
FLATTER...MORE NORTHERN-STREAM DOMINANT SYSTEM...THE EMPHASIS FOR
DEEPER LIFTING (ENHANCED BY RIGHT ENTRANCE REGION UPPER JET
FORCING/FRONTOGENESIS) AND MOISTURE TRANSPORT WILL BE CONFINED TO
THE NORTHERN STREAM...AFFECTING THE NORTHERN INTERMOUNTAIN WEST
AND NORTHERN ROCKIES. THIS PORTION OF THE TROUGH WILL BRING STRONG
SOUTHWESTERLY PRE-FRONTAL FLOW AND MODESTLY ANOMALOUS MOISTURE
FLUX...AS PRECIPITABLE WATER VALUES RISE TO NEAR 0.75 INCHES
ACROSS THE NORTHERN INTERMOUNTAIN WEST INTO THE NORTHERN ROCKIES.
OVER THESE AREAS...CONTINUE TO EXPECT OROGRAPHICALLY-ENHANCED
MOD-HEAVY PCPN...THE BULK OF WHICH OCCURRING UNDERNEATH THE BROAD
WARM CONVEYOR BELT (WCB) AS THE DEEP-LAYER FGEN INCREASES AND
PRE-FRONTAL MOISTURE ANOMALIES REMAIN HIGH (+3-3.5 STANDARD
DEVIATIONS PER THE SREF/GEFS). WPC UTILIZED A COMPOSITE OF 00Z
GUIDANCE WITH THE QPF...AGAIN LED BY THE HIGH-RES MEANS GIVEN THE
BETTER SENSITIVITY OVER THE TERRAIN. AREAL-AVERAGE TOTALS OF 1-2"
OF LIQUID EQUIVALENT PCPN ARE ANTICIPATED OVER THE HIGHER TERRAIN
IN CENTRAL-NORTHERN ID INTO NORTHWEST MT...THE BULK OF WHICH IS
EXPECTED TO FALL IN A 12-18 HOUR PERIOD. GIVEN THE RELATIVELY LOW
FFG ACROSS CENTRAL-NORTHERN ID (AS LOW AS 0.75" IN 3 HOURS AND 1"
IN 6 HOURS)...THESE TOTALS COULD LEAD TO LOCALIZED SHORT-TERM
RUNOFF ISSUES. AS A RESULT...THE MARGINAL RISK FOR EXCESSIVE
RAINFALL INHERITED FROM THE DAY 2 OUTLOOK WILL CONTINUE WITH THE
LATEST DAY 1 ERO.

HURLEY

$$





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