Quantitative Precipitation Forecast
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FOUS30 KWBC 150056
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
855 PM EDT SAT OCT 14 2017

...VALID 01Z SUN OCT 15 2017 - 12Z SUN OCT 15 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE EWK 15 N MCI 10 E AWG FEP 15 NE MKE 15 NW P58 20 N CWAJ
10 NNW FWA 25 S IJX 30 SSW TBN 25 NNW CHK 20 ESE EWK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 WSW PPF 15 SSE UKL 25 S CDJ 10 SSW MPZ 15 SW MLI 10 E SQI
20 NNW DPA 25 WSW BIV 15 E GRR RNP 15 W ARB 10 SSE IKK
15 SSW IKK 10 NW IJX 35 NE COU 45 NW SGF 10 WSW PPF.


...CHANGES TO THE EXCESSIVE RAINFALL OUTLOOK DEFINITION AND
THRESHOLD PROBABILITIES...

NOTE TO USERS...ON FRIDAY OCTOBER 14TH WPC IMPLEMENTED CHANGES TO
THE EXCESSIVE RAINFALL OUTLOOK. THE DEFINITION OF THIS PRODUCT
CHANGES FROM A POINT PROBABILITY TO A NEIGHBORHOOD PROBABILITY. BY
CAPTURING MORE AREA AROUND A POINT...THE PROBABILITIES ASSOCIATED
WITH EACH RESPECTIVE CATEGORY WILL NECESSARILY INCREASE. SEE THE
GRAPHIC LEGEND FOR THE NEW PROBABILITIES. THE PRODUCT WILL LOOK
AND BEHAVE THE SAME AS IT ALWAYS HAS...BUT STUDIES SHOW THAT THE
RISK CONTOURS WPC DRAWS ARE BETTER CALIBRATED TO THE NEW
DEFINITION AND HIGHER ASSOCIATED PROBABILITIES. THESE CHANGES
BETTER ALIGN THE EXCESSIVE RAINFALL OUTLOOK WITH OTHER OUTLOOKS
FROM NATIONAL CENTERS...AND THE PRODUCT IS NOW DEFINED AS THE
PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE WITHIN 40
KM OR 25 MILES...OF A POINT.


...LOWER MISSOURI VALLEY TO THE LOWER GREAT LAKES...

AS OF 01Z A BROKEN LINE OF THUNDERSTORMS STRETCHES FROM NORTHERN
IL SOUTHWEST INTO EASTERN KS. WITH THE MID/UPPER LEVEL FORCING
EJECTING QUICKLY EASTWARD...AND THE DEEPENING SURFACE LOW
ACCELERATING OFF TO THE NORTHEAST...WOULD EXPECT CONVECTION TO
TAKE ON AN INCREASINGLY PROGRESSIVE NATURE THIS EVENING INTO THE
OVERNIGHT. STILL HAVE A NARROW CORRIDOR WHERE SOME FLASH FLOOD
ISSUES COULD DEVELOP. THE AREA AT HIGHEST RISK IS FROM NORTHERN IL
INTO SOUTHWEST MI. THIS AREA HAS SEEN 2-4" OF RAIN OVER THE LAST
24 HOURS HELPING SATURATE SOILS...WITH AN ADDITIONAL 1-3" EXPECTED
OVER THE NEXT SEVERAL HOURS. FURTHER SOUTH ACROSS EASTERN KS INTO
MO...HIGH PWATS AND INTENSE CONVECTIVE CORES SHOULD CONTINUE TO
SUPPORT RAINFALL TOTALS APPROACHING 1.5" IN AN HOUR...WHICH MAY
CAUSE SOME LOCALIZED FLASH FLOOD ISSUES. ALTHOUGH WOULD NOT EXPECT
ANYTHING SIGNIFICANT HERE GIVEN THE DRIER ANTECEDENT CONDITIONS
AND PROGRESSIVE NATURE OF STORMS. RAINFALL RATES AND THE FLASH
FLOOD THREAT SHOULD DROP OFF PRETTY QUICKLY AFTER 06Z AS
CONVECTION MOVES INTO A MORE STABLE AIRMASS AND CONTINUES TO PICK
UP FORWARD SPEED.

CHENARD



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