Quantitative Precipitation Forecast
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FOUS30 KWBC 240658
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT SUN AUG 24 2014

...VALID 06Z SUN AUG 24 2014 - 12Z MON AUG 25 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SW CWAQ 10 E JDN 60 NNE BIL 25 ESE 3HT 30 ESE GFA 20 S HVR
50 SSE CWEH 30 NE CWVN 25 SW CWAQ.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
60 E LWT 15 SSW LWT 25 NNW LWT 70 NW JDN 25 W GGW 20 SSW GGW
30 WNW JDN 60 E LWT.



...EASTERN FOOTHILLS OF THE NORTHERN ROCKIES INTO THE NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY...

A SIGNIFICANT RAINFALL EVENT WAS UNDERWAY FROM THE THE EASTERN
FOOTHILLS OF THE NORTHERN ROCKIES EASTWARD INTO THE NORTHERN
PLAINS IN PROXIMITY TO AN ANAMOLOUS UPPER LOW OVER MT AND IN THE
WARM/MOIST CONVEYOR BELT OVER THE EASTERN DAKOTAS.

THE MID/UPPER LEVEL FLOW WAS HIGHLY DIFLUENT AND DIVERGENT AS AN
ANOMALOUSLY STRONG UPPER/MIDDLE LOW SPUN OVER MT.  THE SYSTEM HAS
HAD A WELL DEFINED WARM CONVEYOR BELT FEEDING PLENTY OF MOISTURE
INTO THE TROWL/DEFORMATION ZONE ON THE NORTHWEST SIDE OF THE LOW.
HOWEVER THE CONVEYOR BELT WITH THE MOISTURE HAS BECOME
INCREASINGLY DIRECTED INTO THE EASTERN DAKOTAS AND UP INTO CANADA
LEAVING THE UPPER LOW DETACHED FROM ITS SOURCE OF DEEP MOISTURE.
TENDED TO FOLLOW THE ECMWF AND GFS/NAM WHICH ALL DEPICTED VARYING
DEGREES OF THIS DRY SLOT.  MAINTAINED AN INCH PER 6 HOURS IN THE
24/06 TO 24/12Z TIME FRAME ACROSS MT NEAR THE VORT CENTER AND THEN
GRADUALLY DIMINISHED THE MAX PCPN AMOUNT DURING THE DAY AS THE
SYSTEM OPENS AND LIFTS NORTH OF THE BORDER. FLASH FLOOD GUIDANCE
VALUES WERE QUITE LOW OVER MT IN AND NEAR THE POSITION OF THE
UPPER LOW...ON THE ORDER OF A TENTH OF AN INCH PER 3 HOURS.

OVER THE EASTERN DAKOTAS AND WESTERN MN...CONVECTION WITH A
HISTORY OF HEAVY TO EXCESSIVE RAINFALL WILL BE MOVING EASTWARD
THROUGH THE EARLY MORNING HOURS.  SATELLITE IMAGERY THROUGH
24/0515Z SHOWED CLOUD TOP TEMPS OVER ERN SD FINALLY BEGINNING TO
WARM.  THIS AT LEAST SUGGESTED AN EVENTUAL DECRASE IN THE RAINFALL
RATES AND AMOUNTS. SUSPECT MOST MODELS WERE TOO QUICK TO END
CONVECTION GIVEN THE LOW LEVEL JET STILL DRAWING IN AIR WITH PW
VALUES AT OR ABOVE 1.75 INCHES AND H85 MOISTURE TRANSPORT STILL
DIRECTED INTO WRN MN AHEAD OF THE LINE.  CONSEQUENTLY THE WPC
MANUAL GRAPHICS WENT ABOVE GUIDANCE EARLY IN THE PERIOD. DESPITE
THE APPROACH OF THE INTENSE RAINFALL FROM THE WEST...A SLIGHT RISK
WAS KEPT IN THE AREA SINCE THE FLASH FLOOD GUIDANCE VALUES WERE
CONSIDERABLY HIGHER THAN IN PARTS OF THE ERN DAKOTAS. WITH THE
EVENTUAL DOWNTURN IN RAFL INTENSITY AS SHOWN BY THE WARMING CLOUD
TOPS...MAINTAINED A SLIGHT RISK AND REFRAINED FROM ANYTHING
HIGHER.

BANN
$$




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