Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 160021
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
820 PM EDT SUN OCT 15 2017

...VALID 01Z MON OCT 16 2017 - 12Z MON OCT 16 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


...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.


...OUTLOOK FOR 01Z MONDAY TO 12Z MONDAY...

THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS
THAN 5 PERCENT.


CHENARD

$$





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