Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 271420
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1020 AM EDT THU APR 27 2017

...VALID 15Z THU APR 27 2017 - 12Z FRI APR 28 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 N ABY 35 WNW OZR MXF ATL 10 NE GRD 20 SW CAE 10 NE DBN
25 N ABY.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSE JST 25 SSE EKN 20 ENE BLF 6V3 40 WNW I16 30 NE PKB
15 ESE FKL 20 W DSV PEO 20 W UNV 20 SSE JST.


1500 UTC UPDATE

NO CHANGES MADE TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL
OUTLOOK

ORAVEC

...SOUTHEAST STATES AL/GA/SC...

STEERING FLOW WILL BECOME MORE UNIDIRECTIONAL AT THE BASE OF THE
TROUGH LIFTING THROUGH THE EASTERN STATES THIS MORNING. THIS MAY
ALLOW FOR SOME SW TO NE TRAINING OF CONVECTION AS SIGNALED BY A
FEW HI-RES MODELS IN THEIR HOURLY TO THREE-HOURLY QPFS. MOISTURE
AND INSTABILITY PARAMETERS ARE NOT OVERWHELMING...BUT ARE
RESPECTABLE...AND COULD SUPPORT HOURLY RAIN RATES APPROACHING TWO
INCHES. IN MOST CASES THIS WOULD NOT REACH THE VERY HIGH FLASH
FLOOD GUIDANCE VALUES ACROSS THIS REGION...BUT COULD LEAD TO RAPID
RUNOFF IN POORLY DRAINED OR PARTICULARLY SUSCEPTIBLE AREAS. A
SMALL MARGINAL RISK AREA WAS INTRODUCED WHERE WPC QPF INDICATES
AREAL AVERAGE PRECIPITATION GREATER THAN A HALF INCH AND WHERE
SOME HI-RES RUNS PRODUCE SPOTTY 2 TO 3 INCH AMOUNTS.


...CENTRAL/NORTHERN APPALACHIANS...

A TROUGH WILL SWING UP THROUGH THE NORTHEAST U.S...PUSHING A COLD
FRONT INTO THE APPALACHIANS. AN ASSOCIATED MOISTURE PLUME IS
FORECAST TO COME ACROSS THE HIGH TERRAIN OF WEST VIRGINIA AND INTO
THE MOUNTAINOUS TERRAIN IN WESTERN PENNSYLVANIA DURING PEAK
HEATING. THIS TIMING SHOULD YIELD A BOOST TO CAPE VALUES AND
COVERAGE OF CONVECTIVE RAINFALL IN AREAS OF RELATIVELY LOW FLASH
FLOOD GUIDANCE. CELL MOTIONS SHOULD BE FAIRLY PROGRESSIVE...BUT
LOCALLY BACKED INFLOW...ESPECIALLY IN PA/NY...MAY SLOW DOWN CELL
MOTIONS AND PROMOTE BRIEF BOUTS OF TRAINING. HEAVY SHORT TERM RAIN
RATES ARE CAUSE FOR SOME CONCERN GIVEN THE PARTICULARLY
SUSCEPTIBLE TERRAIN IN THIS REGION...BUT GIVEN THE HI-RES MODEL
QPF SIGNAL IS NOT ESPECIALLY HEAVY WE WILL INTRODUCE ONLY A
MARGINAL RISK AREA.

BURKE
$$




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