And the latest AFD from LWX.
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Low pressure will track through the Gulf Coast States Saturday
into Saturday evening before transferring its energy to a
coastal low off the North and South Carolina Coast by Sunday
morning. The low will move off the Mid-Atlantic Coast Sunday and
high pressure will return for Sunday night. The closed upper-
level low associated with this system will get sheared apart as
it runs into a strong confluence zone, with shortwave energy and
jet maxes passing through Saturday into Sunday.
For Saturday...High pressure will remain over New England while
the surface ridge axis extends down through the Mid-Atlantic.
The low and mid-level flow will back to the southwest, causing
relatively warmer and more moist air to overrun the surface cold
air in plac. At the same time, shortwave energy well ahead of
the upper-level low will pass through the area. The overrunning
and shortwave energy should be enough to cause snow to break out
over much of the area, first across the Potomac Highlands and
Shenanodah Valley Saturday morning and across the rest of the
area Saturday afternoon. Temperatures will remain below freezing
or drop below freezing after precipitation begins, so
accumulating snow is likely.
The same pattern will persist for Saturday night with low
pressure transferring its energy to a coastal low as it passes
by to the south. Overrunning and shortwave energy will continue
to bring snow across the area with accumulation likely. The coastal low will will move out to sea Sunday and high pressure will wedge down from the north. This will cause snow to gradually end from north to south. Details are still a little uncertain at this time. Latest 00z guidance shows that the best chance for additional snow accumulation will be south of Interstate 66 and US 50. High pressure will continue to wedge into the area Sunday night. Most areas across the northern and central CWA should turn out
dry, but a little light snow or flurries cannot be ruled out
across central Virginia into southern Maryland where leftover
moisture will be tough to scour out.
As for accumulations, it does appear that snowfall rates will be
on the light to perhaps occasionally moderate side. This is
because the primary forcing mechanism appears to be overrunning.
Strong frontogentical forcing appears that it will remain to our
south, closer to the low. Therefore, latest thinking for most
likely snow amounts are around 2-4 inches near the Washington
and Baltimore Metropolitan areas into northern and central
Maryland as well as northern Virginia. Farther south and west, 4
to 8 inches are most likely at this time. The reason for the
higher amounts is that moisture will be a bit deeper closer to
the low and farther from the drier air associated with the high.
A Winter Storm Watch is in effect for these areas (Potomac
Highlands into central Virginia and extreme southern Maryland).
Most likely forecast do have amounts below temporal criteria for
a warning, (5" in 12 hours and 7" in 24 hours), but still
several inches of snow are likely at this point. Also, there is
still some uncertainty with the low track Sunday morning. Some
outlying guidance suggest that heavier snow is still possible
across these areas. Therefore, a Watch has been issued.