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WPC Met Watch

Mesoscale Precipitation Discussion: #0587 (2019)
(Issued at 1235 AM EDT Fri Jul 12 2019 )

MPD Selection

Graphic for MPD #0587

Mesoscale Precipitation Discussion 0587
NWS Weather Prediction Center College Park MD
1235 AM EDT Fri Jul 12 2019

Areas affected...Southern New England

Concerning...Heavy rainfall...Flash flooding likely

Valid 120435Z - 121030Z

SUMMARY...Showers and thunderstorms are expected to develop and
expand in coverage over the next few hours across southern New
England. Given the anomalous pool of moisture over the region, and
intense rainfall rates, some pockets of flash flooding will be

DISCUSSION...The latest GOES-16 IR/WV imagery is showing an axis
of improving large scale ascent over the region as upper level
divergence increases in response to the arrival of an upstream
shortwave trough and associated jet streak. Cloud tops have been
tending to cool across southern New England, and the latest radar
imagery is beginning to show some expansion of shower activity
across CT, RI and western MA. GLM from GOES-16 is not showing any
lightning activity as of yet over these areas, but the column over
the region is becoming very moist with upstream 00Z RAOB data out
of KOKX showing a deeply moist adiabatic sounding with a PWAT of
2.12 inches, a wet-bulb freezing level over 14000 feet, and nearly
800 j/kg of CAPE. All of this is reflective of a deep warm and
tropical-moist sounding.

Over the next couple of hours, larger scale ascent should increase
across southern New England as stronger shortwave energy arrives
and interacts with a retreating warm front across the region. In
fact, the latest 00Z hires guidance favors development of a weak
area of low pressure near the western tip of Long Island by 06Z.
This will help to facilitate stronger low-level convergence across
Long Island and adjacent areas to the northeast across southern
New England.

The result should be the development of shower and thunderstorm
activity that will be capable of producing very heavy rainfall
rates given the deeply warm/moist column that is advancing over
the region. Warm rain processes within a column of strengthening
low and mid-level omega fields should promote enhanced rainfall
efficiency with rates that may locally exceed 2 inches/hr.

The 00Z HREF suite of guidance favors locally as much as 2 to 4
inches of rain going through 09Z, with the last couple runs of the
HRRR even wetter with as much as 3 to 6 inches of rain. A
consensus of the guidance supports the heaviest swath aligning
across central CT up, the northern part of RI, and across
south-central/southeast MA (although not including the Cape).

Given the observational soundings and latest satellite/radar
trends, expect locally very heavy rains over the next several
hours to arrive which will include the suburbs and bigger
metropolitan areas along and adjacent a line from Hartford, CT to
Boston, MA. Some areas of flash flooding will be likely overnight
given the expected rainfall rates and storm totals.




LAT...LON   43177083 42747058 42387049 41977076 41527130
            41387160 41247228 41217281 41277342 41757327

Last Updated: 1239 AM EDT Fri Jul 12 2019

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Page last modified: Saturday, 01-Jan-2022 07:08:48 GMT