Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 272135
QPFERD

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

...VALID 21Z THU AUG 27 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
15 S ALO 30 NNE CDJ 15 E STJ 25 W AFK 15 NW BVN 40 NNW ONL
15 NNE MHE 20 SSE RWF 15 SE AEL 15 S ALO.


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

A PREDICTABLE HEAVY RAIN EVENT IS EXPECTED OVERNIGHT WITH A
PRONOUNCED MID LEVEL SHORTWAVE ENHANCING THE PLAINS LOW LEVEL JET
CYCLE...AND UPGLIDE NORTH OF A WARM FRONT FURTHER AIDING IN 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.

FARTHER SOUTH...WE REMOVED THE SLIGHT RISK FROM EASTERN KANSAS
BASED ON A LACK OF ADDITIONAL QPF. IT APPEARS THAT WARM ADVECTION
THAT SPAWNED AN EARLIER HEAVY RAIN EVENT THERE WILL HAVE
DISLODGED. THIS MAY BE FOLLOWED BY A ROUND OF THUNDERSTORMS MOVING
ACROSS KANSAS IN A MORE DEEPLY MIXED AND PROGRESSIVE ENVIRONMENT
TONIGHT...BUT ANY ADDITIONAL RAINFALL OVER THE SATURATED AREAS IS
FORECAST TO BE MINIMAL...OR AT LEAST NOT HEAVY ON A LARGE SCALE.

TERRY/BURKE
$$





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