Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 230135

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
935 PM EDT Thu Mar 22 2018

High pressure will build in from the west through Saturday. Low
pressure will move from the mid-Mississippi Valley Saturday to
the Carolinas Saturday night. High pressure will follow for the
beginning of next week.


High pressure over the Mississippi River Valley will build east
tonight and Friday. An upper level disturbance and jet energy
have supported ample high level clouds. Believe that the cirrus
will remain much of tonight, but impact will be limited. Upper
level moisture will be more sparse Friday; expect a sunnier day.

In terms of temperatures, should have slightly better nocturnal
cooling tonight vs early this past morning. Am maintaining sub-
freezing lows areawide...even DC/Baltimore City. Daytime highs
Friday should be comparable to today...perhaps a degree higher
due to sun and less snow cover.


Friday night the forecast area will still be under control of
high pressure. With clear skies and little wind, lows will
likely be a category or two cooler, though less snow cover could
push things the other direction.

Low pressure will be diving across the center of the CONUS
Saturday-Saturday night. Warm advection east of the low will
support upglide. Anticipate increasing clouds during the day.
The question has been and continues to be how much moisture will
spread into the forecast area, and what form that will take.
Output from 12Z and 18Z model cycle suggests the track may be a
pinch further south. Cannot say that there is high confidence
in the northern edge of the forecast shield. However,
incorporating the latest information does edge PoPs a pinch
further south. Forcing within the swath looks fairly robust, and
would expect accumulating precipitation in this zone...
especially in the afternoon and evening. Further, timing
generally supports a precipitation type of snow...potentially
significant. The row of counties from Highland to Nelson at the
greatest risk; however, still do not have adequate confidence
to raise a Watch for those counties at this time. The threat
seems to increase southwest though. Based on latest guidance
continuing to trend SW, did nudge forecast accums down a notch.
Later cycles may adjust where the stripe belongs.


A low pressure system and its associated boundary will be
situated to our south early on Sunday, bringing a chance of
precipitation to much of the CWA, though highest POP will be
south and very early. This system will shift easterly away from
our area through the day as high pressure settles into the area
from the north through Tuesday. Temperatures will be rising
gradually through the first half of next week as warm air
advects into our region ahead of an approaching front. A chance
of precipitation is possible Wednesday into Thursday as a slow
moving front approaches the region.


VFR flight conditions should prevail through Friday night, with
mixing supporting daily diurnal wind gusts 20-25 kt in the

Low pressure forecast to drop across southern
Virginia/Carolinas Saturday. The precipitation shield, likely
snow, could clip CHO in the afternoon and evening.

Sub-VFR conditions are possible, with best odds around CHO,
early on Sunday as a low pressure system moves south of our
area. VFR conditions expected behind this system later on Sunday
and into Tuesday as high pressure builds into our region.


Small Craft Advisory conditions prevail across the waters this
evening. Similar conditions will persist through Friday across
the open waters, but may temporarily cut off at night on the
Potomac and in the inlets.

Low pressure will pass south of the waters Saturday afternoon-
night. Poor mixing may preclude any marine hazards.

Winds will be close or above SCA criteria on Sunday and into
early Tuesday, therefore advisory is possible for some zones in
the long term. Winds will likely decrease below criteria on


MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ531>534-
     Small Craft Advisory until midnight EDT Friday night for
     Small Craft Advisory until midnight EDT tonight for ANZ530-535.
     Small Craft Advisory from 9 AM Friday to midnight EDT Friday
     night for ANZ530-535.


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