Graphic for MPD #0819

Mesoscale Precipitation Discussion 0819
NWS Weather Prediction Center College Park MD
227 PM EDT Mon Sep 10 2018

Areas affected...Southern Appalachians into the Carolinas Piedmont

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

Valid 101826Z - 102326Z

Summary...Thunderstorms will continue to increase ahead of a cold
front along the spine of the Appalachians this afternoon. Training
of these storms will produce periods of heavy rainfall, with 1-3"
of rainfall expected. Flash flooding is possible.

Discussion...A cold front analyzed approaching the Blue Ridge is
extending from a triple point in SE Ohio. Ahead of this front, a
stationary boundary on the leading edge of a wedge of high
pressure is dropping through NC into the upstate of SC. Between
these two features, a clear pocket on GOES-16 visible imagery is
evidence of an increasingly unstable airmass with MLCape between
500-1500 J/kg advecting northward. This instability is fueling
convective development along the higher terrain of the Blue Ridge,
as well as ahead of the surface front. PWATs across the area are
analyzed by the latest RAP to be 1.6 to 2.0 inches, and will
continue to increase through the aftn.

A weak vorticity impulse moving overhead the threat area on deep
unidirectional SW flow will combine with subtle 250mb diffluence
to aid in producing large scale ascent. 700mb winds are strong,
25-30 kts on latest local VWP from KMRX and KJKL, and forecast
0-6km mean wind of 15-20 kts suggests storms will lift rapidly NE.
However, unidirectional flow parallel to the surface boundary and
corfidi vectors aligned closely with the 0-6km mean wind suggests
training of storms is likely. Additionally, 850mb flow from the SE
will transport higher mean RH from the Atlantic and across SC atop
the wedge front. Collision of cells from the SE with activity
along the terrain and/or the cold front will also favor higher
rainfall, especially over eastern slopes.

As PWATs surge and instability climbs, rainfall rates of 1-2" per
hour will be possible, although any one location will likely not
experience a full hour duration of heavy rainfall. Where storms
train or merge, especially across the sensitive higher terrain,
2-3" of rainfall will be enough to produce flash flooding.

Weiss

ATTN...WFO...FFC...GSP...JKL...MRX...RLX...RNK...

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...

LAT...LON   38178098 38118043 37878034 37248058 36788080
            36448094 36038121 35428164 34998210 34868262
            34578327 34678362 34658413 34738482 35128488
            35718418 36168383 36638334 37048289 37508230
            37788184 38118133


Last Updated: 227 PM EDT Mon Sep 10 2018