Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 121856

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
256 PM EDT Mon Mar 12 2018

Low pressure off the Carolina coast will rapidly intensify as
it moves northeastward toward the Canadian Maritimes through
Tuesday night. Canadian high pressure will build southward into
the central U.S. and eventually the southeastern U.S. by
Thursday. A weak cold front will push through the region
Thursday with Canadian high pressure building overhead for the
first half of the weekend.


Energy transfer is ongoing from the inland low to the coastal
low, with rapid dryslotting occurring in the areas where snow
has been falling all day. The last of the snow is in the higher
elevations of the Central Blue Ridge; even there, additional
accumulations aren`t expected to be much before it tapers off.
The remaining advisory was allowed to expire at 2pm despite the
lingering snow showers.

Now we watch the axis of precipitation extending from east-
central Virginia northeastward into southern Maryland. Because
of the dry boundary layer, some wintry precip has been reported
with this even with temps in the 40s (obviously with no impact).
However, as areas are wetbulbing, they seem to be doing so in
the 33 to 36 degree range of temperatures, meaning that while it
may be snowing, it`s not accumulating much if at all in those
areas. Will be keeping a close eye on this through the evening.
I have a dusting in the total snow grid right along the Bay but
confidence is low.

Then we turn to a rather prolonged upslope snow event, given
persistent W/NW winds starting tonight. A few inches of snow may
occur at the highest elevations through Tuesday, with models
showing a ramp-up in the precip intensity by Tuesday afternoon
as additional upper energy pivots into the region. I did not get
a chance to give this the look it deserves due to ongoing
weather, so this will be further assessed on upcoming shifts.
Elsewhere, Tuesday will be breezy/blustery. Even though air
temps may reach the mid/upper 40s east of the Blue Ridge, wind
chills hold in the 30s all day.


The duration of the short term period, Tuesday night through
Wednesday night, will feature continued upslope snow. I can`t
rule out a shower escaping further east on Wednesday, but kept
chances in the 10-20 percent range east of the Highlands. It`s
possible that enough snow could fall Tuesday through Wednesday
to warrant advisories, but the most likely scenario right snow
seems prolonged light snow with moderate periods that could
tally several inches.

For most of us though, this period will simply be cooler than
normal for mid-March, and still a bit breezy.


On Thursday an upper level shortwave will allow for some snow
showers mainly west of the Allegheny Front, but cannot rule out
having them elsewhere in our CWA. Thursday into Friday a high
pressure system centered over the Gulf Coast states will be
shifting east allowing for return flow to settle over our region
with dry conditions. On Friday a boundary will be sliding south
of our area as a high pressure then builds from the north. The
high will be over us on Saturday and then offshore on Sunday
allowing for continued dry weather. A boundary may affect us on
Monday increasing the PoPs over our area.

High temperatures will be in the 40s and 50s Thursday into Saturday,
then in the 50s and 60s Sunday and Monday. Low temperatures will be
in the 20s and 30s Thursday and Friday night, increasing to the 30s
and 40s Saturday and Sunday night.


With the snow tapering off at CHO...VFR conditions are generally
expected through the valid TAF period. Can`t rule out MVFR cigs
in particular at MTN, and some RA/SN showers at BWI and MTN (and
maybe even at DCA). Otherwise, VFR is expected at the TAF sites
through Wednesday, aside from perhaps a passing shower mainly at
MRB, but with periods of gusty winds especially during the
daytime hours.

Expecting mainly VFR conditions Thursday but some passing snow
showers cannot be ruled out. These may bring periods of sub-VFR
conditions. Then, VFR conditions expected Friday and Saturday.


A Small Craft Advisory remains in effect for all waters through
the day on Tuesday, and has been extended for all but the upper
and middle tidal Potomac on Tuesday night. Low pressure will
develop and strengthen off the Carolina coast later today and
moving northeastward through tonight. A strong pressure gradient
will reside over the waters through Wednesday as low pressure
churns near New England and Canadian high pressure slides
southward in to the central and southeastern U.S. There is the
potential for a short period of gale force gusts Tuesday
afternoon/evening, but not lengthy enough to go with the warning
at this time.

Wind gusts stay above the small craft advisory criteria
Wednesday into Thursday, and perhaps even Friday. Winds should
decrease into Saturday and fall below SCA


MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ530>534-
     Small Craft Advisory until 8 PM EDT Tuesday for ANZ535-536.


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