Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 281413
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1012 AM EDT FRI AUG 28 2015

...VALID 15Z FRI AUG 28 2015 - 12Z SAT AUG 29 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSE MLI 25 WNW GBG 15 SSW FFL CNC 15 ESE AMW 20 NNW MIW
20 ESE CCY 30 S LSE 20 NW DLL 10 E RYV RAC 10 WNW PWK 30 SSW SQI
20 SSE MLI.


...MID MS VALLEY/UPPER GREAT LAKES...

THE MCS THAT AFFECTED NE/IA DURING THE EARLY MORNING HOURS HAS
WEAKENED AS THE INSTABILITY HAS BECOME ELEVATED OVER THE WARM
FRONT EXTENDING TO ITS WEST. THE PRECIPITATION HAS BECOME
PREDOMINATELY STRATIFORM IN NATURE...WITH THE INSTABILITY BECOMING
THE LIMITING FACTOR FOR ADDITIONAL EXCESSIVE RAINFALL THIS
MORNING. MODERATE TO HEAVY RAINFALL REMAINS POSSIBLE THROUGH
IA/SOUTHERN WI.

HIGH RESOLUTION MODELS SUGGEST THAT ANOTHER SURGE OF MOISTURE (IN
THE FORM OF PRECIPITABLE WATER VALUES NEAR 1.75 INCHES) IS
TRANSPORTED NORTHEAST ON THE NOSE OF A 30 TO 40 KNOT LOW LEVEL
SOUTHWEST JET INTO EASTERN IA/NORTHWEST IL/SOUTHERN WI AFTER
28/21Z. THE LATEST NAM SIMULATED SATELLITE IMAGERY SUGGESTS THAT
ANOTHER CONVECTIVE COMPLEX/POSSIBLE MCS FORMS ON THE NOSE OF THE
LOW LEVEL JET OVER EASTERN IA/SOUTHERN WI BETWEEN 29/00Z AND
29/06Z...AND SOME OF THE HIGH RESOLUTION GUIDANCE SUGGESTS THE
POTENTIAL FOR EXCESSIVE RAINFALL IN THESE AREAS.

THERE IS A MULTI MODEL SIGNAL THAT INSTABILITY COULD END UP BEING
THE LIMITING FACTOR FOR DEEPER CONVECTION TO DEVELOP INTO A LARGER
CONVECTIVE COMPLEX OR MCS. IN ADDITION...THERE REMAINS MODEL
DIFFERENCES IN THE PLACEMENT OF THE QPF AXIS WITH THE CONVECTIVE
COMPLEX. WPC CONTINUES TO FAVOR MODEL SOLUTIONS FURTHER SOUTH
VERSUS FURTHER NORTH...FOLLOWING THE BETTER MOISTURE AND
INSTABILITY GRADIENT. FAVORING THE SOUTHERN POSITION HAS BEEN THE
BIAS THIS WARM SEASON...AND THIS BIAS HAS BEEN MAINTAINED FOR THIS
FORECAST. THE MORE SOUTHERN HIGH RESOLUTION MODELS (SUCH AS THE
00Z NSSL WRF/06Z REGIONAL GEM) INDICATE THE POSSIBILITY OF LOCAL 2
OR 3 INCH RAINFALL AMOUNTS. THREE HOUR FLASH FLOOD GUIDANCE VALUES
ARE AS LOW AS 1.50 INCHES OVER PORTIONS OF EASTERN IA...SO THE
FLASH FLOOD THREAT CONTINUES.

THE EXCESSIVE RAINFALL AREA WAS SHIFTED TO THE EAST...COVERING
MUCH OF EASTERN WI/NORTHWEST IL AND SOUTHERN WI. HOWEVER...IF THE
INSTABILITY DOES NOT IMPROVE THIS AFTERNOON...THE EXCESSIVE AREA
MAY NEED TO BE REDUCED THIS AFTERNOON

HAYES/ORAVEC
$$




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