Quantitative Precipitation Forecast
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351
FOUS30 KWBC 280022
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
821 PM EDT WED JUL 27 2016

...VALID 01Z THU JUL 28 2016 - 12Z THU JUL 28 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 N GWO 40 S GLH 25 ESE ELD 10 ESE HOT 25 NE FSM 20 WNW UNO
15 WSW EHR 15 S LEX 20 SSW LOZ 10 W BNA 15 S MKL 40 N GWO.



LOWER-MID MISSISSIPPI VALLEY/WESTERN TENNESSEE VALLEY/LOWER OHIO
VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~

2100-0100 UTC UPDATE

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
TO CONTRACT THE SLIGHT RISK AREA OVER THE LOWER-MID MS VLY
NORTHEAST INTO THE WESTERN TN VALLEY AND LOWER OH VALLEY. THIS IS
BASED ON THE LATEST STLT/RADAR LOOPS LATE THIS AFTERNOON...WHICH
ON A WHOLE DEPICT A GRADUAL WEAKENING TREND WITH THE WIDESPREAD
CONVECTION ASSOCIATED WITH THE BROAD UPPER LEVEL SHEAR AXIS
(FORMER TUTT CELL OVER FL AND THE GULF COAST) ACROSS THE LOWER MS
VLY...AS WELL AS WITH THE NUMEROUS CELLS FARTHER N-NE CLOSER TO
THE QUASI-STATIONARY SURFACE BOUNDARY. BASED ON THESE
OBSERVATIONAL TRENDS ALONG WITH THE LATEST
HRRR/PARALLEL-HRRR/EXPERIMENTAL HRRR OUTPUT...FORECAST CONFIDENCE
WAS HIGH ENOUGH TO CONFINE THE "SLIGHT RISK" TO AN AREA WHERE THE
DEEP-LAYER INSTABILITY HAD YET TO BE WORKED OVER...ESPECIALLY
GIVEN THE WEAK MID LEVEL LAPSE RATES (5.5-6.0 C/KM) AND THUS
LIKELIHOOD OF CAPES FURTHER DIMINISHING TOWARD AND ESPECIALLY
FOLLOWING SUNSET. GIVEN THE WEAK STEERING FLOW AND OVERALL SLOW
STORM MOTIONS...CELL MERGERS AND SHORT-FUSED TRAINING IN AREAS
WHERE THE INSTABILITY HAS NOT YET BEEN EXHAUSTED (MIXED LAYER
CAPES STILL 1000-2000 J/KG) WITHIN THE CURRENT HIGH PW ENVIRONMENT
(2-2.25 INCHES) WILL MAINTAIN INTENSE RAINFALL RATES UNDERNEATH
THE STRONGEST CLUSTERS.

HURLEY

PREVIOUS DISCUSSION...

A MODERATELY STRONG CIRCULATION AT 850 HPA LIFTS UP THE
MISSISSIPPI RIVER TODAY TOWARDS THE LOWER OH VALLEY.  PRECIPITABLE
WATER VALUES ARE SIGNIFICANT, IN THE 2.25-2.5" RANGE.  LOW-LEVEL
INFLOW ACROSS PORTIONS OF LA AND MS IS EXPECTED TO BE IN THE 20-30
KT RANGE THROUGH THE PERIOD, WHICH IN THE PRESENCE OF CAPE VALUES
RISING TO AT OR ABOVE 2000 J/KG COULD CAUSE ISSUES.  THE DEEP
LAYERED FLOW SHOULD BE FAIRLY DEEPLY OUT OF THE SOUTHWEST NEAR AND
EAST OF THE MISSISSIPPI RIVER, WHICH BRINGS THE SPECTER OF CELL
TRAINING.  THE GUIDANCE HAS A STRONG SIGNAL FOR LOCAL 3-5" AMOUNTS
WHICH SHOULD CHALLENGE FLASH FLOOD GUIDANCE VALUES, PARTICULARLY
ACROSS SOUTHERN MS AND EASTERN LA WHERE HEAVY RAINS OVER THE PAST
COUPLE DAYS HAVE PARTIALLY SATURATED SOILS.  A SLIGHT RISK OF
EXCESSIVE RAINFALL HAS BEEN ADDED IN THIS REGION, WHICH SHOULD SEE
THE MOST ORGANIZED CONVECTION THROUGH MUCH OF THE WEDNESDAY INTO
THURSDAY MORNING PERIOD.


WISCONSIN/MINNESOTA
~~~~~~~~~~~~~~~~~~~

A FRONTAL BOUNDARY SHOULD LURE PRECIPITABLE WATER VALUES OVER 1.5"
INTO THE REGION, WITH LOW-LEVEL INFLOW OF ~ 20 KTS THROUGH 00Z.
MUCAPE VALUES REMAIN NEAR 2000 J/KG OVERNIGHT, AND COULD RISE TO
3000 J/KG DURING THE AFTERNOON HOURS.  THE MESOSCALE GUIDANCE
SHOWS LOCAL MAXIMA IN THE 3-5" RANGE BETWEEN SOUTHERN MN AND
CENTRAL WI, WHICH IS POSSIBLE WITHIN THIS ATMOSPHERIC REGIME.  A
SEE TEXT/MARGINAL RISK OF EXCESSIVE RAINFALL AREA SHOULD COVER THE
FLASH FLOOD RISK FOR WI AND SOUTHEAST MN, WHICH APPEARS TO BE
RELATIVELY ISOLATED.


PORTIONS OF SOUTHERN VA/NORTHEAST NC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

DEEP WESTERLY FLOW NEAR A FRONTAL BOUNDARY WITH POOLED
PRECIPITABLE WATER VALUES OF NEAR 2" ALONG WITH MODERATE
INSTABILITY (2000-3000 J/KG) AND MODEST LOW-LEVEL INFLOW (~20 KTS)
COULD ORGANIZE CONVECTION AGAIN DURING DAYTIME HEATING.  CELL
TRAINING AND MERGERS ARE CONSIDERED THE MAIN HEAVY RAIN THREAT.
LOCAL AMOUNTS OF 2-4" ARE ADVERTISED IN THE MESOSCALE GUIDANCE
HERE WHICH COULD LEAD TO LOCALIZED ISSUES ON WEDNESDAY.  A SEE
TEXT/MARGINAL RISK OF EXCESSIVE RAINFALL AREA HAS BEEN ADDED TO
THE REGION.

ROTH
$$





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