Quantitative Precipitation Forecast
Issued by NWS

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359
FOUS30 KWBC 192218
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
616 PM EDT MON SEP 19 2016

...VALID 2158Z MON SEP 19 2016 - 12Z TUE SEP 20 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 ESE SUT 10 SE ILM 15 SW ISO 20 SE RZZ 15 NNE FYJ 15 WSW WWD
30 SSE MJX.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
60 S MRH 30 SE NCA 20 S ASJ 20 WNW WAL 20 E WWD.


2200 UTC UPDATE...

CHANGES TO THE DAY 1 EXCESSIVE RAINFALL OUTLOOK WERE MADE TO PULL
THE BACK EDGE OF THE MARGINAL AND SLIGHT RISK AREAS FARTHER EAST
CLOSER TO THE MID ATLANTIC COAST. THIS WAS BASED ON THE LATEST
SHORT-RANGE MODEL GUIDANCE (INCLUDING HIGH-RES) ALONG WITH RECENT
TRENDS OF THE LATEST COMPOSITE RADAR IMAGERY... SATELLITE IR/WV
LOOPS...AND MESOANALYSIS (DECREASING MUCAPE OVER THE PAST FEW
HOURS).

HURLEY


PREVIOUS DISCUSSION BELOW...


A HEAVY TO EXCESSIVE RAINFALL THREAT DEVELOPING MONDAY ALONG AND
TO THE EAST OF A WEAKENING FRONTAL BOUNDARY STRETCHING FROM THE
MID ATLANTIC INTO NEW ENGLAND.  PW VALUES IN THE VICINITY OF THIS
BOUNDARY EXPECTED TO BE MUCH ABOVE AVERAGE..1.75-2.00"+...1.5 TO
2+ STANDARD DEVIATIONS ABOVE THE MEAN.  THIS ALONG WITH FAVORABLE
UPPER DIFFLUENCE FROM THE RIGHT ENTRANCE REGION OF A JET MOVING
ACROSS THE NORTHERN MID ATLANTIC AND UPPER DIFFLUENCE AHEAD OF A
CLOSING OFF UPPER LOW OVER THE SOUTHEAST WILL SUPPORT WIDESPREAD
HEAVY RAINFALL POTENTIAL.  THE SET UP IS SIMILAR TO A PREDECESSOR
RAINFALL EVENT TO THE NORTH OF A LAND FALLING TROPICAL SYSTEM.
TRAINING OR SLOW MOVING OF PRECIPITATION AREAS IN A SOUTHWEST TO
NORTHEASTERLY DIRECTION LIKELY EARLY MONDAY FROM IN THE VICINITY
OF RICHMOND---DC--BALTIMORE---PHL TO NEAR NYC AND ACROSS LONG
ISLAND--WITH THIS POTENTIAL TRAINING AXIS THEN SINKING EAST
SOUTHEASTWARD TOWARD THE COASTAL SECTIONS FROM NORTHEAST
NC---ACROSS NORFOLK--THE SOUTHERN DELMARVA AND COASTAL CENTRAL TO
SOUTHERN NJ MONDAY AFTERNOON/EVENING.  OVERALL--THERE IS A STRONG
SIGNAL IN THE LATEST GUIDANCE FOR THE HEAVY TO EXCESSIVE RAINFALL
THREAT---WITH DIFFERENCES PRIMARILY WITH THE DETAILS OF THE AXIS.
THE HI RES ARW AND NSSL WRF WERE USED PRIMARILY FOR THE QPF AXES
GIVEN HIGHER OVERALL CONFIDENCE WITH THESE MODELS.  AREAL AVERAGE
1-2" AMOUNTS DEPICTED---WITH POTENTIAL FOR ISOLATED TOTALS OF
3-5"+ IN AREAS OF TRAINING.  WHILE FFG VALUES ARE HIGH ACROSS
THESE AREAS GIVEN RECENT DRY WEATHER---THE POTENTIAL FOR
TRAINING---ESPECIALLY IN URBAN AREAS---WILL POSE A THREAT OF
EXCESSIVE RAINFALL AMOUNTS.


ORAVEC
$$





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