Quantitative Precipitation Forecast
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FOUS30 KWBC 011335
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
934 AM EDT WED APR 01 2015

...VALID 15Z WED APR 01 2015 - 12Z THU APR 02 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SW UKL 15 SE SLN 35 W HJH 10 NE OFK 25 SE SPW 25 NE AMW
25 WSW OTM 25 ESE CDJ 15 SSE LXT 15 SW UKL.


15Z UPDATE...

NO CHANGES AT THIS POINT TO THE PREVIOUS EXCESSIVE
OUTLOOK...PENDING ARRIVAL OF THE 12Z MODEL GUIDANCE.

ORRISON

PREV DISCUSSION...

...NE/IA/KS/MO...

A CONVECTIVE EVENT WILL RAPIDLY TAKE SHAPE WEDNESDAY AFTERNOON AS
LOWER 60S DEWPOINTS RACE NORTHWARD TO MEET AN IMPENDING SHARP
FRONTAL PASSAGE OVER EASTERN NE...NORTHWEST IA...SOUTHERN MN...AND
POINTS TO THE SOUTH AND EAST. DESPITE JUST MODEST BOUNDARY LAYER
MOISTURE AND INTEGRATED PW VALUES APPROACHING ONLY 1.2
INCHES...MODEL DEPICTED MU/ML CAPES OF 1500-3000 J/KG DUE TO STEEP
MID LEVEL LAPSE RATES...SUPPORT A BRIEF WINDOW OF HIGH RAINFALL
RATES AT ANY GIVEN LOCATION. TO THE NORTH...INCLUDING NORTHERN
IOWA INTO SOUTHERN WISCONSIN...FORWARD PROPAGATING CHARACTERISTICS
ARE ANTICIPATED AND COULD EVEN SHUT PRECIPITATION DOWN EARLY IF
MOISTURE RETURN TO THE NORTH IS SUFFICIENTLY INTERRUPTED AND A
DEEP MESO-HIGH FORMS FARTHER SOUTH. THE ACTIVITY AS A WHOLE SHOULD
QUICKLY GROW UPSCALE OWING TO THE AVAILABLE INSTABILITY AND STRONG
FORCING. WHEN THIS OCCURS...THE SOUTHERN FLANK OF THE CONVECTION
SEEMS THE MOST LIKELY LOCATION FOR SOME REPEAT
DEVELOPMENT/TRAINING AS OUTFLOWS POINT INTO THE MOISTURE/CAPE
GRADIENT. THE MODELS ARE LIKELY HANDLING THIS EVENT FAIRLY WELL
GIVEN THE WELL DEFINED FORCING MECHANISMS. GREATER PRECIPITATION
AMOUNTS ARE FORECAST FARTHER SOUTH...WHICH INCLUDES THE BORDERS OF
NEBRASKA/IOWA/KANSAS/MISSOURI...AND PERHAPS DROPPING INTO MORE OF
EASTERN KS/WESTERN MO WITH TIME. ONE TO THREE HOUR FLASH FLOOD
GUIDANCE VALUES IN THE 1 TO 2 INCH RANGE MAY JUST BE ACHIEVABLE IN
THIS REGION. A SLIGHT RISK OF EXCESSIVE RAINFALL WAS THEREFORE
CARRIED OVER FROM THE PREVIOUS DAY 2 FORECAST.


...AR/MS/TN...

THUNDERSTORMS WITH HEAVY RAIN LATE TUESDAY AND EARLY WEDNESDAY HAD
BEEN ROOTED AROUND 750 MB...JUST NORTH OF A REMNANT FRONTAL
BOUNDARY NOW BEING ANALYZED AS A SURFACE TROUGH. THE TROUGH
SEPARATES A MARITIME POLAR AIRMASS OFF THE GULF FROM CONTINENTAL
POLAR AIR...DRIER CONDITIONS...TO THE NORTH. A REINFORCING
BOUNDARY WAS DROPPING TOWARD THIS REGION...ANALYZED IN SOUTHERN TN
AND NORTHERN AR 06Z...AND WILL SETTLE JUST ABOUT INTO THE SAME
POSITION AS THE EXISTING SURFACE TROUGH DURING THE DAY. A LOW
AMPLITUDE MID LEVEL TROUGH ACCOMPANIED THE ARRIVAL OF THE
REINFORCING BOUNDARY. PER NAM/GFS/ECMWF FORECASTS THIS WAVE SHOULD
PROGRESS TOWARD GEORGIA... AND CONVECTION ACROSS AR/MS/TN WILL
WANE EARLY IN THE MORNING. THE REGION WILL REMAIN UNSTABLE...
HOWEVER...WITH ANOTHER HEATING CYCLE CONTRIBUTING TO MOST UNSTABLE
CAPE VALUES OVER 2000 J/KG OVER MUCH OF ARKANSAS...NORTHERN
MISSISSIPPI...AND SOUTHWEST TENNESSEE BY AFTERNOON. AT THE SAME
TIME...A SOUTHERN STREAM TROUGH AS WELL AS AN MCV FROM OVERNIGHT
CONVECTION IN OKLAHOMA...WILL APPROACH FROM THE WEST. THESE
FORCING MECHANISMS WILL AGAIN PROVIDING LIFT IN THE 850-750 MB
LAYER TO YIELD ANOTHER ROUND OF THUNDERSTORMS DURING THE AFTERNOON
AND EVENING. MEAN 0-6 KM WINDS WILL TURN MORE WESTERLY AND
ENCOURAGE MORE EASTWARD DEVELOPMENT WITH TIME...BUT WIND PROFILES
DO SUGGEST SOME OPPORTUNITY FOR SLOWER...RIGHT MOVING STORMS...AT
LEAST DURING THE EARLY STAGES OF DEVELOPMENT.

FLASH FLOOD GUIDANCE VALUES ARE HIGH GIVEN RECENT DRY WEATHER IN
THIS REGION. THE VERTICAL PROFILES OF MOISTURE AND TEMPERATURE
ALSO FAVOR A BETTER DEFINED SEVERE WEATHER RISK RATHER THAN
WIDESPREAD FLASH FLOODING. ANTECEDENT RAINFALL HAVING OCCURRED
LATE TUE AND EARLY WED PRODUCED ONLY SPOTTY 1 TO 2 INCH AMOUNTS
BASED ON WHAT GAUGE MEASUREMENTS WERE AVAILABLE. WITH ADDITIONAL
HEAVY RAINFALL ISOLATED FLASH FLOODING WILL BE POSSIBLE...BUT THE
ODDS AT A GIVEN LOCATION ARE ESTIMATED TO BE JUST SHY OF REQUIRING
A SLIGHT RISK.

BURKE
$$




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