Mesoscale Discussion 0025
NWS Storm Prediction Center Norman OK
0218 AM CST Sat Jan 07 2017
Areas affected...Western/central NC...southern VA
Concerning...Winter mixed precipitation
Valid 070818Z - 071315Z
SUMMARY...A mix of winter precipitation is expected across portions
of western/central NC and southern VA over the next several hours.
Snowfall rates from one to two inches per hour and freezing rain
rates in excess of 0.02 inch per hour are possible across portions
of the region.
DISCUSSION...Recent regional radar imagery and surface observations
indicate a complex mix of precipitation types, as well as heavy
snowfall, across portions of western and central NC and southern VA.
Across the higher terrain of western NC and far southwestern VA,
persistent large-scale forcing for ascent associated with the
approaching shortwave trough coupled with modest upslope flow
resulting from north/northeasterly flow below 850 mb will support
continued heavy snowfall for the next few hours, while gradually
tapering off from west to east. Snowfall rates around 1 inch per
hour are possible.
Farther south and east (from south-central NC northeastward in far
northeastern NC and far southeastern VA), a transition zone from
snow to a mix of snow, sleet, and freezing rain, and then rain will
continue to drift slowly northward. As the upper system matures,
strengthening low-level winds will increase warm-air advection into
the region, with the resulting increase in ascent supporting the
possibility of moderate freezing rain rates (above 0.02 - 0.03 inch
an hour). These moderate rates are confirmed by observations at RWI
and RDU, which have recently reported 0.06 and 0.02 inches of ice
accretion, respectively, in the last hour.
From north-central NC northeastward to southern portions of the
Delmarva peninsula, snowfall rates are expected to gradually
increase as the low-level winds increase in response to the maturing
upper system. Subsequent increase in warm-air advection will support
strong mesoscale forcing for ascent, with rates near 2 inches per
hour possible in the 9Z to 12Z timeframe, particularly across
southeastern VA and the southern Delmarva peninsula.
LAT...LON 36298179 37158067 37667901 37967744 37757572 36887552
35977647 35347919 34928093 34968242 36298179