Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 140821
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
320 AM EST TUE FEB 14 2017

...VALID 12Z TUE FEB 14 2017 - 12Z WED FEB 15 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ESE BYY 45 WNW VCT AUS 15 WSW INJ 15 E SPS 15 SE OKM
40 NE RUE 25 SE SRC 20 ESE PBF 50 W TUP 20 NE 1M4 20 WSW 8A0 BHM
30 E JAN 10 SW ACP 10 ESE BYY.


...SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI AND TENNESSEE
VALLEYS...

THE CLOSED UPPER LOW INITIALLY OVER THE SOUTHERN HIGH PLAINS EARLY
TUE MORNING WILL BE PROGRESSING STEADILY EASTWARD ACROSS TX
TODAY...THEN SHEAR SOMEWHAT OVERNIGHT ACROSS THE LOWER MS VALLEY
AS IT BEGINS TO GET ABSORBED BY THE DIGGING NORTHERN STREAM
TROUGH. PRECIPITATION CONTINUES TO EXPAND SW-NE WITHIN THE
RELATIVELY COMPACT WARM CONVEYOR BELT (WCB) ACROSS CENTRAL TX
NORTHEAST INTO EASTERN OK WITHIN THE AREA OF INCREASINGLY
FAVORABLE UPPER DIFFLUENCE AND ALONG-STREAM UPPER DIVERGENCE
(DEEP-LAYER QS CONVERGENCE) AHEAD OF THE UPPER LOW.
MEANWHILE...THE NORTHERN PCPN SHIELD CONTINUES TO EVOLVE INTO A
MORE W-E ORIENTATION ACROSS NORTHEAST OK INTO NORTHWEST AR AND
SOUTHERN MO...INDICATIVE OF THE STRONG UPPER LEVEL CONFLUENCE AND
W-E JET AXIS TO THE NORTH AND INHERENT RIGHT ENTRANCE REGION
FORCING (UPPER DIVERGENCE...LOW-MID LEVEL FGEN) TO THE SOUTH
ACROSS THESE AREAS.

THE QPF CHALLENGE FOR DAY 1 WILL CONTINUE TO REVOLVE AROUND THE 2
DISTINCT AREAS OF FAVORABLE FORCING...WHICH WILL LIKELY RESULT IN
2 DISJOINTED AXES OF MAXIMUM RAINFALL...ONE NORTH ASSOCIATED ALONG
THE AFOREMENTIONED W-E DEEP-LAYER FGEN ZONE... AND ANOTHER ONE
FARTHER SOUTH CLOSER TO THE GULF COAST ASSOCIATED AHEAD OF THE
BEST DPVA AND ALONG THE AXIS OF MORE FAVORABLE DEEP-LAYER
INSTABILITY AND ANOMALOUS MOISTURE. A GENERAL BLEND OF THE
GUIDANCE WAS PREFERRED WITH THE NORTHERN AXIS GIVEN THE OVERALL
GOOD MODEL CONSENSUS WITHIN THE MORE STRATIFORM PCPN REGION (BOTH
WITH MASS FIELDS AS WELL AS QPF). IN ADDITION... BASED ON THE
LIMITED SPREAD WITH THE QPF (IN TERMS OF LATITUDINAL PLACEMENT AND
AMOUNTS) AND THUS INCREASED FORECAST CONFIDENCE...WPC BOOSTED
TOTALS SLIGHTLY ALONG THE ARKLATEX REGION N-NW INTO WEST-CENTRAL
AR AND SOUTHEAST OK. 24 HOUR AREAL-AVERAGE AMOUNTS BETWEEN 1-2+
INCHES ARE EXPECTED WITHIN THIS REGION.

FARTHER SOUTH ACROSS THE MIDDLE-UPPER TX COAST NORTHEAST INTO
NORTHERN LA AND MS...WPC CONTINUED TO ADVERTISE A SECONDARY SWATH
OF  1-2+ INCH AREAL-AVERAGE AMOUNTS...LEANING AGAIN TOWARD THE
HIGH-RES WRF-ARW GUIDANCE...SUPPORTED BY THE AFOREMENTIONED
DYNAMICAL FORCING ALONG WITH MODEST AVAILABLE INSTABILITY (MUCAPES
500-1000 J/KG)...MORE ANOMALOUS PW VALUES (1.25-1.5")...AND MORE
FAVORABLE 850-700 MB MOISTURE FLUX (BETWEEN 3-4 STANDARD
DEVIATIONS ABOVE NORMAL PER THE SREF AND GEFS) ALONG AND JUST
NORTH OF THE MIDDLE-UPPER TX COAST. DESPITE A MORE FAVORABLE
THERMODYNAMICAL PROFILE OVER THIS REGION...BECAUSE OF THE EXPECTED
SWIFT EASTWARD PROGRESSION OF THE STRONGER CONVECTION (GIVEN THE
STRONG DIRECTIONAL WIND SHEAR AND DOWNWIND/EASTWARD PROPAGATING
CORFIDI VECTORS ALONG WITH THE PROGRESSIVE HEIGHT FALLS/INCREASING
NEGATIVE PW ADVECTION WITH TIME)...WPC WILL MAINTAIN NO HIGHER
THAN A MARGINAL RISK IN THE NEW DAY 1 EXCESSIVE RAINFALL OUTLOOK
(ERO). THE LACK OF A SIGNAL WITHIN THE HIGH-RES CAM GUIDANCE FOR
LOCALIZED AMOUNTS SUBSTANTIALLY HIGHER THAN THE TOP RANGE OF THE
AREAL-AVERAGE QPF (I.E. 2-2.5" IN 24 HRS) SUPPORTS THIS
IDEA...ESPECIALLY GIVEN THE COMPARATIVELY HIGH 1/3/6 HOURLY FFG
VALUES.

HURLEY

$$





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