Subj : MESO: Heavy rain/Flooding
To   : All
From : Mike Powell
Date : Mon Dec 11 2023 10:54:00

AWUS01 KWNH 111325
FFGMPD
MEZ000-111853-

Mesoscale Precipitation Discussion 1199
NWS Weather Prediction Center College Park MD
824 AM EST Mon Dec 11 2023

Areas affected...Eastern Maine

Concerning...Heavy rainfall...Flash flooding possible

Valid 111323Z - 111853Z

Summary...Widespread and steady moderate to locally heavy rainfall
today will pose a flooding risk across eastern Maine. Hourly
totals between 0.5-0.75" will be possible and an additional 1-3"
of rainfall is likely.

Discussion...A nearly stationary boundary is currently analyzed
across far eastern Massachusetts through coastal/eastern Maine
this morning while a couple waves of low pressure were lifting
north/northeast. Along and ahead of this feature, a very anomalous
plume of moisture has reached the region, characterized by
precipitable water values in excess of 1", locally 1.3" per recent
mesoanalysis. These values are between 3-4 standard deviations
above normal for this time of year in the region.

As the upper trough takes on a more neutral tilt today, this will
slow/stall the advancing front just enough to allow for a
prolonged moderate to heavy rain event to continue, primarily
across eastern Maine. The aforementioned waves of low pressure
will lift northward through the region, providing the necessary
low level convergence to enhance rain rates and totals. The latest
hi-res guidance is in fairly good agreement for a stripe of 1-3"
of additional rainfall across far eastern Maine with the 06Z HREF
neighborhood probabilities showing at least a moderate chance
(>40%) of seeing hourly totals greater than 0.5" for a few hours.
There is a slight chance (10-15%) of totals exceeding 3 inches.

Current flash flood guidance shows 3-hr and 6-hr values that would
be exceeded by the expected rainfall, and current NASA SPoRT soil
moisture percentiles are near to above normal, so this additional
rainfall may result in flooding, particularly for any urban or
poor drainage locations. 

Taylor

ATTN...WFO...CAR...GYX...

ATTN...RFC...NERFC...NWC...

LAT...LON   46106766 46026695 45506656 44676644 44086746 
            43486853 43706977 44436933 45446847 

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