Quantitative Precipitation Forecast
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FOUS30 KWBC 271401
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1000 AM EDT WED JUL 27 2016

...VALID 15Z WED JUL 27 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
ARA 10 NNW ACP 25 NNW ELD 20 SSW LIT 25 N ARG 30 S FAM SAR FOA
10 SSW BAK 10 SSW HAO 20 ENE LUK 30 SE ILN 35 NW HTS 50 W HTS
20 NE LEX 20 SW FFT 25 SSW BWG 15 SSW BNA 25 ENE MSL 25 N NMM
10 S ASD 10 NE NBG 20 WNW 2GL ARA.


1500 UTC UPDATE

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
TO EXPAND THE SLIGHT RISK AREA NORTH-NORTHEASTWARD INTO THE LOWER
TO MID OH VALLEY.  THIS IS IN THE VICINITY OF THE WEAK STATIONARY
FRONTAL  BOUNDARY CURRENTLY STRETCHING FROM THE OH VALLEY INTO THE
MID ATLANTIC.  WITH PW VALUES 1.5-2 STANDARD DEVIATIONS ABOVE THE
MEAN IN THIS AXIS---HEAVY RAINFALL TOTALS POSSIBLE.  THE TIME
LAGGED HRRR ENSEMBLES SUPPORT THE NORTHEASTWARD EXTENSION OF THE
SLIGHT RISK AREA ACROSS THIS REGION WITH HIGH PROBABILITIES OF
1-2"+ PRECIP TOTALS...OVER THE LOWER OH VALLEY REGION INTO THIS
AFTERNOON AND FARTHER UPSTREAM OF THE OH RIVER AFTER 0000 UTC JUL
28.

ORAVEC

PREVIOUS DISCUSSION

LOWER MISSISSIPPI VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~
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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