Mesoscale Precipitation Discussion 1059
NWS Weather Prediction Center College Park MD
507 PM EST Thu Dec 20 2018

Areas affected...Enter areas affected

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

Valid 202205Z - 210405Z

Summary...A period of heavy rainfall with rainfall rates peaking
near 0.5 in/hr is expected to produce 1-2 inches of rain, with
locally higher totals, across portions of the central Appalachians
by 04Z. Given wet antecedent conditions, flooding appears likely
with possible flash flooding.

Discussion...2130Z radar and water vapor satellite imagery showed
a low level vorticity center in north-central SC, tracking toward
the north. An area of heavy rain existed ahead and west of this
feature with observed rainfall rates between 0.4 and 0.7 in/hr
between Columbia and Greenville, SC through 21Z. Precipitable
water values ranged from about 1 inch near the foothills of the
Appalachians to 1.7 inches along the Southeast Coast, but a lack
of higher instability across inland locations has prevented
rainfall rates from being higher toward the west. However, 850 mb
flow of 50-60 kt was measured ahead of the vorticity max from KCAE
VAD wind data with the past few runs of the RAP taking the axis of
highest 850 mb moisture flux steadily northward across central NC
and VA.

While some decrease in rainfall intensity is expected to the
northwest of the low level vorticity max as the circulation moves
into a lower precipitable water environment, the nose of a low
level jet containing forecast 60-70 kt with an orientation nearly
orthogonal to the Blue Ridge Mountains and portions of the
Appalachian chain should allow for an increase in rain rates into
the early overnight. Rainfall rates of 0.25 to 0.5 in/hr at times
are expected to impact the upslope favored terrain across western
NC into VA allowing for 6 hour rainfall totals of 1-2 inches with
locally higher amounts possible. While flooding is expected given
wet antecedent conditions, using 3-hr flash flood guidance values
of 1 inch in 3 hours as a guide across portions of western VA
north of a Roanoke to Lynchburg line, localized flash flooding
will also be possible.

Otto

ATTN...WFO...AKQ...GSP...LWX...MRX...RAH...RNK...

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

LAT...LON   38957843 38807798 38047806 36997906 36417950
            35928030 35758113 35838160 36018186 36268182
            36938089 37987991 38737902