Quantitative Precipitation Forecast
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056
FOUS30 KWBC 160831
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Mon Apr 16 2018

VALID 12Z Mon Apr 16 2018 - 12Z Tue Apr 17 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 ESE BLM 10 ENE BLM BLM 15 WSW 12N 10 N MSV 30 SW ALB
10 E ALB 10 ESE DDH 15 WNW EEN 15 WNW CON 10 NE LCI 20 E BML
30 WNW WVL 10 ENE WVL 15 E BGR 35 NE BHB 40 WSW CWVU 30 SW CYQI.


...Mid Atlantic into the Northeast and Great Lakes...

As of 08z a line of heavy showers and embedded thunderstorms
stretches from southern PA into eastern NC...with this line
continuing to progress off to the northeast through the day
Monday. This remains a very dynamic system with the negatively
tilted mid/upper level trough supporting strong upper level
divergence. While mid/upper level forcing will persist through the
day, would appear the overall dynamics become a bit less
impressive with time...as the shortwave responsible for the
increasingly negative tilt to the trough weakens along with a
weakening upper jet. Also, anticipate CAPE will be harder and to
come by as this area of rain moves northeast, with it taking on an
increasingly stratiform nature with time. Some limited MUCAPE
should however allow for continued embedded heavier convective
cores within the rain shield.

In general, would anticipate these factors to result in decreasing
rain rates after 12z, although localized rates peaking in the
0.5"-0.75" in an hour range...and up to around 1.5" in any three
hour period...will remain possible. It does however appear likely
that as the system occludes we actually see a focused slightly
more persistent 850 mb moisture transport axis focus into portions
of southeast NY into adjacent MA/CT. This should result in a bit
longer duration of the moderate rainfall rates...resulting in
storm total amounts at least locally getting into the 2-3" range.
These 1-3" amounts should stretch from southeast NY across
southern New England and into eastern NH/ME...with the potential
for a few locally heavier amounts, especially where orographic
impacts may be maximized +in the strong southerly flow.

Will continue to carry a Marginal risk for these areas. Think
rainfall rates will generally not be high enough to exceed 1 or 3
hour FFG. However, rainfall of the magnitude forecast may still be
enough to cause some urban flooding concerns.

Chenard


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