Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 150753

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
353 AM EDT Thu Mar 15 2018

Low pressure will linger over the Canadian Maritimes through
Saturday. A weak cold front will cross the region today and
surface high pressure will build toward the region Friday.
Another weak system will pass through the area Saturday before
high pressure returns for Sunday. A stronger storm system will
likely impact the area during the middle portion of next week.


Deep large scale trough remains in place across the eastern
United States today, with the next feature in a series of weak
systems moving through the cyclonic flow aloft approaching the
area this morning. The upper level energy will cross the region
this morning, with the surface reflection passing across during
the afternoon hours. Another period of upslope snow showers
along and near the Allegheny Front is expected today with this
feature, although accumulations will be light and below advisory
thresholds. Elsewhere, aside from a few flurries this morning,
some isolated- scattered showers will be possible, especially in
the afternoon from the DC metro region north/east. However by
that time, temperatures should have been able to rise back
through the 40s and 50s, to possibly even near 60F southwards
towards Charlottesville/Fredericksburg, so precip type will be
mainly rain. That being said, with dry low levels, some cooling
may result as precip falls, so some snow may still mix in,
mainly across northern MD.

Gusty winds will also once again be on the increase this
afternoon, with gusts peaking in the 25-35 mph range in the
valley locations. The higher elevations of the Blue Ridge and
Potomac Highlands will likely see gusts in the 40-50 mph range,
so the Wind Advisory remains in effect for those locations.


Northwest flow persists tonight, with upslope snow showers
continuing. Once again though, accumulations are expected to
remain  on the light side, with total snow from today and
tonight in the 1- 3" range. Dry conditions are expected
elsewhere, with temperatures falling back into the 20s to low
30s again.

Surface high pressure will gradually build into the region
during the day Friday, but gusty northwest winds are expected
yet again, with gusts peaking in the 25-35 mph range. Friday
should be a bit sunnier, although temperatures will only rise
into the 40s.

The surface high will move overhead Friday night, allowing for
winds to lessen and temperatures to drop into the 20s to near
30F. As a low pressure system begins to approach from the
central US overnight, warm air advection will begin late Friday
night, leading to the potential for some mixed precipitation
Saturday morning. Uncertainty still exists with respect to the
coverage and intensity of the precipitation as well as the
temperature profiles, however a light period of mixed precip is
possible before changing over to light rain Saturday afternoon
as temperatures warm into the 40s. Locations west of the Blue
Ridge as well as in central/northern MD have the highest risk of
seeing any mixed precip.

The system will then pass south and east and away from the area
Saturday night, leading to drying conditions as high pressure
builds back in.


High pressure will build overhead for Sunday and Sunday night,
bringing dry and seasonable conditions. Low pressure will likely
track through the central CONUS Monday and toward the
Appalachians Monday night before transferring its energy to a
coastal low that will track up the Mid-Atlantic Coast Tuesday
and toward New England Wednesday.

There are still a lot of uncertainties with this storm regarding
precipitation type. The synoptic pattern appears favorable for a
storm to have a favorable track for mixed precipitation or even
some snow. A confluence zone between upper-level low pressure
over the Canadian Maritimes and ridging over the north-central
CONUS should allow the primary low to transfer its energy to the
coastal low south of our latitude. This would keep us on the
cold side of the storm. However, it is the middle of March so
there is still a question as to how much cold air there will be
for snow/wintry precipitation. Latest deterministic guidance
shows rain mixing with or changing to a period of snow before
ending. Obviously details are highly uncertain this far out.
Will continue with rain or snow in the forecast. Factors that
will determine whether or not snow will have an impact would be
intensity and location of heavier bands of precipitation,
strength and exact location of the low, and topography. It`s too
early to tell for two of these factors (banding precipitation
and strength/exact location of the low).


VFR is expected through Friday night. Broken-overcast ceilings
will develop again today around 6000-7000 feet, but remain
VFR. A few light rain and snow showers are possible today, but
no significant reductions in visibilities are forecast.
Southwest winds will develop this morning before a frontal
passage, with winds turning west-northwest and gusting 25-30
knots by the afternoon behind the front. These winds will lessen
overnight, but are expected to return on Friday. A period of
light rain or mixed precipitation is possible Saturday and this
may bring some sub-VFR conditions.

High pressure will build over the terminals Sunday. Low pressure
will approach from the west later Monday and this may impact the
terminals with precipitation, especially Monday night.


Small Craft Advisory conditions are expected across the waters
today, tonight, and Friday. Southwest winds will increase briefly
this morning prior to frontal passage, but the strongest winds are
expected later this afternoon and evening as winds turn to the west-
northwest. Gusty winds will continue out of the northwest on Friday.
Winds will then likely finally drop to sub-SCA levels Friday night
and Saturday.

High pressure will build over the waters Sunday. Low pressure
will approach from the west Monday before transferring its
energy to a coastal low Monday night too our south. Small Craft
headlines may be needed Monday and Monday night.


Low pressure will remain over the Canadian Maritimes through
Friday. High pressure will approach from the north and west
during this time. A tight gradient between these systems will
bring gusty winds to the area, especially from the late morning
through the early evening hours each day. A downsloping west to
northwest flow will cause low relative humidity.

For today, lower fuel moistures are expected along with gusty
winds and low relative humidity. Temps will be in the 40s and
50s, a bit warmer compared to Wednesday. There will be an
enhanced threat for the spread of wildfires, especially across
northern and central Virginia, the eastern Panhandle of West
Virginia and portions of central and southern Maryland where
relative humidity will be lowest (20 to 30 percent).
Meteorological conditions (wind and rh) support Red Flag
Warnings, but fuel moistures are still above 8 percent. Will
continue with a Special Weather Statement instead of a Red Flag
Warning for now given the relatively higher fuel moistures.

For Friday...more gusty winds are expected. Somewhat chillier
conditions are expected as well with high temps in the 40s but
fuels should be noticeably drier. The relative humidity will
drop to between 15 and 25 percent across central Virginia and 25
to 35 percent across northern Virginia, eastern West Virginia
and Maryland. The strongest winds will be displaced from the
lowest RH values (strongest winds over Maryland, northern
Virginia and eastern West Virginia). An enhanced threat for the
spread of wildfires is possible Friday given the fact that fuels
will be dry and RH values will be low. Will have dayshift
coordinate to see if any Fire Weather Watch is necessary where
the winds will be stronger across the northern and central
portions of the CWA.


VA...Wind Advisory until 8 PM EDT this evening for VAZ025-026-503-
WV...Wind Advisory until 8 PM EDT this evening for WVZ505-506.
MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ530>534-
     Small Craft Advisory until midnight EDT tonight for ANZ542.
     Small Craft Advisory from noon today to midnight EDT tonight
     for ANZ535-536.


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