Really good summary by LWX
A powerful storm system will impact the entire region Tuesday
into Tuesday night. A highly amplified mid/upper trough over the
Central Plains pushes eastward toward the MS Valley. A
tremendous amount of upper diffluence will cause a surface low
to develop and rapidly deepen as it tracks from the lee of the
Rockies, across the Central Plains and central Great Lakes. A
secondary wave of low pressure develops near the northern Gulf
Coast, and is scooped up by the larger low to the north. As the
entire complex pushes east, very strong WAA advection and an
associated strong cold front are likely to bring significant
impacts to our area. Temperatures ahead of this system shoot up
to the 50s to low 60s east of I-81, although temperatures will
likely follow a nondiurnal curve.
Wintry Mix: A residual cold air mass ahead of this system will
likely result in a wintry mix of snow and freezing rain for areas
west of US-15 Tuesday morning. Some snow accumulation and ice
accretion are possible, especially in the higher elevations
along and west of the Blue Ridge. However, it`s possible some of
the valleys stay cold enough for some accumulation as well. The
strong synoptic forcing is going to help produce a quick burst
of wintry precip, then strong WAA quickly transitions all p-
type to rain by, although it may take until the afternoon in the
typical cold pocket near the Allegheny Front around Cumberland.
It`s possible these areas see higher end advisory amounts of
ice and/or snow as a sizeable amount of QPF may fall before
temperatures rise above freezing.
Heavy Rain: A period of moderate to heavy rain is likely to
overspread the area Tuesday afternoon and evening, with the heaviest
rain along and east of the Blue Ridge. However, there will be
added response from any remaining snowpack in western areas. Widespread
rain amounts of 1.5-2.5 inches are currently forecast, though
given the strong moisture flux, deep moist airmass, and strong
diffluence, those totals could certainly end up higher. A
heavier band of elevated convection Tuesday evening will likely
result in the highest rain rates. This heavy rainfall could lead
to urban, small stream, and river flooding.
Strong Winds: There are several periods/areas of concern for
strong winds. The first is earlier Tuesday into the daytime
hours with strong southeast flow overtop of the residual cold
pool. This looks to mainly be a downsloping issue west of the
Eastern Continental Divide. However, some areas from western
Garrett southward down the divide may need Wind Advisories for
this period. Then toward evening, an exceptional low level jet
(60+ knots or 5 sigma at 925 mb) will expand north along the
coast. This is incredibly tricky as steady rainfall and warm air
over the cool marine waters will likely result in a notable
near-surface stable layer. Most model wind gust output is likely
well overdone, although MOS guidance sustained winds of 15-25 kt
could not be taking into account the anomalous nature of the
event. With that said, winds could very well approach Wind
Advisory levels for a time Tuesday evening before quickly
subsiding overnight. The Blue Ridge could also be near advisory
levels. This could lead to some sporadic wind damage,
particularly with trees in increasingly saturated soils. The
third period of stronger winds will come Wednesday (see long
term section below).
