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AWUS01 KWNH 200352
FFGMPD
NYZ000-PAZ000-OHZ000-200800-

Mesoscale Precipitation Discussion 0637
NWS Weather Prediction Center College Park MD
1151 PM EDT Fri Jul 19 2019

Areas affected...Extreme NE Ohio, NW Pennsylvania

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

Valid 200350Z - 200800Z

Summary...A slowly weakening line of thunderstorms will continue
to produce heavy rain along residual outflow boundaries. Rainfall
rates of 1-2"/hr will gradually wane, but regneration along the
outflow will lead to at times nearly stationary storm movement.
This heavy rain on top of areas with very low FFG could lead to
flash flooding.

Discussion...A cluster of thunderstorms was evident on KCLE
WSR-88D across far NW Pennsylvania. These storms were generally
sinking E/SE in the 10-15 kts 850-300mb cloud layer mean wind, but
were pushing an outflow to the west. This outflow was becoming
more orthogonal to intense low-level moisture transport noted by
westerly 850mb winds of 20-30 kts advecting PWATs of 1.7-1.9
inches into the discussion area.

Although convection is expected to gradually wane with slow loss
of instability, MUCape was still analyzed at 2000-3000 J/kg on the
03Z RAP, and this moist/unstable air will continue to be advected
eastward towards the thunderstorm cluster. With moist isentropic
lift occurring as the LLJ is driven atop the outflow boundary,
regeneration/backbuilding of thunderstorms is likely, and is
evident on the most recent few scans of the local reflectivity.
The sustained inflow from the west should persist convective
redevelopment in the favorable thermodynamic environment, and rain
rates are likely to exceed 1"/hr at times. This could lead to
flash flooding, especially across parts of western PA where 1-hr
FFG is less than 0.75 inches. While the flash flood threat is not
expected to be widespread, localized rainfall of 1.5-2.5" on top
of saturated soils could quickly become runoff and lead to flash
flooding. The threat is expected to wane significantly after 08Z
with loss of instability, and this is reflected on the last few
runs of the HRRR.

Weiss

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...BUF...CLE...CTP...PBZ...

ATTN...RFC...MARFC...OHRFC...

LAT...LON   42238003 42007926 41727872 41487836 41077841
            40857858 40617893 40497923 40457952 40497983
            40528011 40668037 40898065 41368101 41608102
            41918086 42068052


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