Morning AFD from LWX... they thought of upgrading to warnings around DC metro
This system will continue to carve out an upper-level trough
upstream today, and that jetmax and the upper-level trough axis
will pass through the region tonight. This will cause surface low
pressure to strengthen on the boundary to our south. The jetmax
will track far enough to the south to put is in a favorable
region of upper-level divergence, and the upper-level trough
axis will actually turn toward a negative tilt as it passes
through our area. This will case the coastal low to strengthen.
While this system will not phase until it is well to our
northeast, it does appear that the negative tilt will have
enough of a reflection in the lower levels and at the surface to
produce an area of low-level frontogenetical forcing.
Temperatures will remain plenty cold enough due to the high
settling overhead today. Therefore, a band of moderate to
perhaps even heavy snow is expected tonight. The one thing
preventing higher snowfall amounts will be that this is fast
moving.
Snow is expected to overspread the Allegheny and Potomac
Highlands later this afternoon, and then across the rest of the
area from southwest to northeast this evening. This system will
quickly move off to the east late tonight with snow dissipating
from west to east. A Winter Storm Warning is in effect for the
Blue Ridge Mountains, and portions of the Potomac Highlands and
a Winter Weather Advisory is in effect for all other locations.
The band of snow combined with higher SLR`s is why the warning
was issued for those areas. Snowfall totals around 4 to 8
inches are most likely. Across the rest of the area, snowfall
totals around 2 to 4 inches are most likely. However, there are
signs that a localized band of heavier snow is possible. There
is still some uncertainty as to exactly where this will setup
and exactly how strong it will be. The more negative tilt to the
trough, the stronger the low-level frontogenetical forcing will
be. The 00z GFS is most bullish with this. As of now, the most
likely area for it to setup would be somewhere near central
Maryland (southern suburbs of Baltimore) to around Washington DC
and the nearby suburbs. Confidence was not high enough to
upgrade to a warning due to the uncertainty previously
mentioned, but localized amounts around 5 to 6 inches are
possible.
Either way, with cold temperatures in place and accumulating
snow, conditions will deteriorate once precipitation begins.
Even though it is a short duration event, snowfall rates around
1 inch per hour (due to the banding snow) are likely, and this
will cause snow covered and slippery roads to develop quickly
for most areas. Snow may mix with a little sleet/rain at the
beginning across our extreme southern zones in central VA and
southern MD, but if there is a mix it will change to snow.
