Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 282312
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
711 PM EDT FRI AUG 28 2015

...VALID 21Z 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
15 NE MSN MWC 10 E RAC 10 SSE UGN 10 SSE RPJ 15 NNW GBG
15 SSW MPZ 20 S OTM CNC 30 WNW DSM 10 W EBS 10 ESE DEH 15 NE MSN.


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

CONVECTION HAD REDEVELOPED ON THE BACK SIDE OF THE MCS THAT ROLLED
THROUGH IA THIS MORNING...AND THE CONVECTION IS BACKBUILDING
ACROSS CENTRAL IA. PLEASE REFER TO MESOSCALE PRECIPITATION
DISCUSSION # 472 FOR MORE DETAILS.

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 IA/NORTHERN IL AND SOUTHERN WI.

HURLEY/HAYES/ORAVEC
$$




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