Mesoscale Precipitation Discussion 1063
NWS Weather Prediction Center College Park MD
336 PM EST Fri Dec 21 2018

Areas affected...New England

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

Valid 212033Z - 220230Z

Summary...Widespread moderate to heavy rain will continue to
affect portions of New England into the evening hours, with the
potential for areas of flooding. Additional rainfall amounts of
0.5 inches are likely by 10 PM, with localized totals up to 1.5
inches possible.

Discussion...Additional rain is likely across New England this
evening as significant northward moisture flux continues. RAP
forecast precipitable water values at 00Z would break monthly
records at all of the sounding locations in eastern New England,
including Chatham (CHH), Gray (GYX) and Caribou (CAR). For
context, the PW values observed in the deep plume of moisture are
would even be above average and approaching the 90th percentile in
parts of the summer months. The focus for rain should continue to
shift further east in New England between 21Z and 00Z, as RAP
analysis and CIRA blended TPW analysis have noted a corresponding
eastward shift in the PW axis over the past several hours.
Marginal instability (MUCAPE around 100-400 j/kg) in the coastal
areas may support some banding of the heavier rainfall, and could
support some localized areas where rain rates exceed 0.5 in/hr.
This may lead to flooding in urban areas of southern New England,
but significant rain rates are not expected to be very widespread
given the limited instability. Further north, in New Hampshire and
Maine, significant snow cover still exists in elevations mainly
above 1000 feet, and melting due to warmth and rain may contribute
to runoff beyond the broader rainfall. This could lead to flooding
despite a lack of significant rain rates, and especially in
upslope areas of the interior mountain ranges. These locations
should have the greatest remaining snow depth, and are also likely
to receive some of the heavier rain totals (via orographic
enhancement) over the next six hours.

Lamers

ATTN...WFO...BOX...CAR...GYX...OKX...

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

LAT...LON   46256853 46006759 45006678 44406735 43836907
            43437005 42807040 42297039 42066973 41537002
            41327083 41227172 41927218 42927234 43947204
            44687118 45467011