Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 280052
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
852 PM EDT THU AUG 27 2015

...VALID 01Z FRI AUG 28 2015 - 12Z FRI AUG 28 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S RWF 10 W AEL 30 SW CCY 15 SW TNU 25 SSW LWD 20 N STJ
20 SSE LNK 20 NNE AUH 15 SW BVN 15 NW BVN 15 ESE ONL 35 SE ICR
15 NE ICR 10 NNE 9V9 30 NE MHE 20 S RWF.


...MIDDLE MISSOURI VALLEY / CENTRAL PLAINS...

SEE MESOSCALE PRECIPITATION DISCUSSIONS FOR SMALLER SCALE TIMING
AND INTENSITY DETAILS. MPD NUMBER 470 WAS ISSUED TO BE IN EFFECT
THROUGH 0539Z.

A PREDICTABLE HEAVY RAIN EVENT IS EXPECTED OVERNIGHT...AND HAD
ALREADY BEGUN AS OF 01Z WITH SLOW MOVING HEAVY RAIN IN PARTS OF
NE/SD. A PRONOUNCED MID LEVEL SHORTWAVE WITH VORTICITY MAXIMA AT
ITS LEADING AND TRAILING EDGE...WILL ARRIVE IN RAPID
SUCCESSION...AND PHASE FAVORABLY WITH THE PLAINS LOW LEVEL JET
CYCLE. UPGLIDE NORTH OF A WARM FRONT WILL FURTHER AIDE IN
PRODUCING ASCENT OVER PARTS OF SD/NE/IA/MN. THE SHORTWAVE WAS NOT
PARTICULARLY STRONG...WITH 500 MB WINDS OF 25 KNOTS IN THE 12Z
UPPER AIR DATA...BUT ITS SHORT WAVELENGTH WILL HELP TO FOCUS AND
MAXIMIZE DEEP LAYER ASCENT...AND STEEP LAPSE RATES MAY ALLOW THE
EFFECTS OF LATENT HEAT RELEASE TO FEEDBACK ONTO THE SYNOPTIC
SCALE...AS THE MODELS INDICATE SOME STRENGTHENING OF THE WAVE BY
MORNING. HIGH RESOLUTION MODELS ARE INDICATIVE OF TWO SWATHS OF
HEAVY RAIN OCCURRING TONIGHT...ONE BASED CLOSER TO THE
SURFACE...AND ALONG THE NOSE OF THE 850 MB LOW LEVEL JET / EDGE OF
THE 10+ DEGREE 700 MB TEMPERATURES. THOUGH THERE IS ALWAYS SOME
UNCERTAINTY REGARDING PLACEMENT IN THESE SITUATIONS...THERE IS A
FAIRLY GOOD CONSENSUS THAT THIS AXIS WILL OCCUR IN NORTHEAST NE
AND ADJACENT PARTS OF SOUTHERN SD AND NORTHWEST IA. A SECOND
MAXIMUM OF DEEP CONVECTION IS FORECAST FARTHER NORTH...WHERE MID
LEVEL FRONTOGENESIS WILL BE MAXIMIZED OVER SOUTHERN MINNESOTA. THE
WPC QPF FORECAST RESEMBLES THE 12Z SSEO MEAN. MODEL CONSENSUS
POINTS TO AREAL AVERAGE RAINFALL AMOUNTS OF 1.5 TO 2.5 INCHES IN
THE NARROW CORRIDORS WHERE THE BETTER ORGANIZED CONVECTION OCCURS.
CELLS SHOULD BECOME INCREASINGLY EFFICIENT AS INITIALLY MARGINAL
PW VALUES INCREASE TO ABOVE 1.75 INCHES DURING THE MATURE PHASE OF
THE OVERNIGHT ACTIVITY. THIS COULD LEAD TO A PERIOD IN WHICH
RAINFALL EXCEEDS 2 INCHES PER HOUR LOCALLY...PUSHING EVENT TOTALS
AT LEAST TO NEAR 4 INCHES...WITH MOST OCCURRING IN 1 TO 6 HOURS AT
A GIVEN LOCATION...CARRYING AN ATTENDANT THREAT OF FLASH FLOODING.

TERRY/BURKE
$$




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