Quantitative Precipitation Forecast
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FOUS30 KWBC 251401
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1001 AM EDT Wed Apr 25 2018

VALID 15Z Wed Apr 25 2018 - 12Z Thu Apr 26 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WSW BED 20 ESE PSM 35 NNE PVC 15 W MVY 10 NNE BID WST
15 NNE GON 15 WSW BED.


...15 UTC Update...

No change to previous.

Schichtel


...Eastern Massachusetts / Rhode Island / Far Eastern
Connecticut...

A trough composed of phasing upper level shortwaves (northern and
southern stream, respectively) will lift through the Northeast
today. A surface occlusion will remain just offshore, so that the
majority of precipitation will be rooted above the boundary layer.
The warm conveyor belt will promote relatively heavier totals,
likely 1 to 2 inch  24-hour amounts, from Connecticut to southern
Maine, but expect this to mainly be a stratiform event, and in
coordination with local offices we did not continue Marginal Risk
into Maine where rates are unlikely to reach flash flood guidance
values.

There is, however, a remote chance for some heavier convective
rain rates and associated flash flooding this afternoon in the
urban corridor from eastern Connecticut to southern and eastern
Massachusetts. The NAM forecasts a few hundred J/kg of MUCAPE here
during peak heating. There may be just enough time for this to
develop in the immediate wake of the early morning rainfall as
partial sun develops. If so, some shallow convectively-formed
showers/storms could yield briefly heavier rain rates, and wind
profiles may prove somewhat favorable for south to north training.
Given that FFG will likely come down after the morning rainfall,
this hypothetical afternoon convection could lead to issues with
surface runoff, especially in urbanized areas. The WRF-NMMB, which
was favored for QPF today, does actually depict this scenario, so
we included this area in a Marginal Risk.

Burke
$$




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