Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 150120

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
920 PM EDT Wed Mar 14 2018

Low pressure will linger over the Canadian Maritimes for the
next couple days. A weak cold front will cross the region on
Thursday. Another weak system will pass through the region
Saturday. High pressure will return Sunday. A stronger storm
system may threaten the region by the middle of next week.


Upper level low is located over New England this evening, while
surface low is north of New Brunswick. Winds have subsided a bit
with sunset, although many areas will keep a breeze most of the
night. Aloft, winds are increasing as a low level jet develops
ahead of the next shortwave trough axis (KIAD 00Z sounding
shows 40 kt at 5700 ft). The winds of this low level jet will
be realized on some of the higher ridge tops, and based on the
latest guidance, started the Wind Advisory at 9 PM. Note strong
winds will not be experienced in most valleys overnight, with
some of the deeper sheltered valleys possibly falling below 10
mph. There`s still plenty of mid level cloud cover to rotate
through the area, so am not expecting large scale breaks until
late tonight. Low temperatures in the mid to upper 20s appear on
track, although some locations might stay a bit warmer due to
the wind/cloud combination.

Weak warm advection ahead of a weak cold front will allow temps
to warm a bit on Thursday to highs in the 40s to possibly even
mid 50s in the Virginia foothills/piedmont. As the system
passes, clouds increase and a few showers or flurries may occur,
most likely across Maryland, with drier air in place further
south and west, except near the Allegheny Front. There, upslope
flow will get underway again in the morning and continue
through Thursday, with a few more inches of snow likely. Most
guidance would suggest additional snow totals remain below
Advisory criteria, but HREFv2 keeps it in the realm of
possibility. The strongest winds in the lowlands will likely
occur during the afternoon as the trough axis passes, with gusts
of 25-35 mph likely. Latest guidance would end the threat of
Advisory-level gusts on the ridges by early afternoon, but will
not adjust end time of headline at this juncture since trough
axis will be passing.


Low pressure will linger nearby on Friday, but with no further
upper level disturbances or weak reinforcing cold fronts
approaching, the chance of snow showers especially in the
mountains will diminish. Temperatures will be a few degrees
colder Thursday night and Friday, but big changes in
temperatures are not expected. With the low still nearby, it
will remain quite gusty, with winds still gusting above 30 mph
in the afternoon. Highs will be mostly in the 40s.

The next system approaches from the west Friday night. Most
guidance is still very slow with it, holding off precip until
Saturday, but a few models now bring precip into the region
before dawn. Given radiational cooling expected as winds relax
Friday night, this could present a wintry mix potential. For now
have held POPs at slight chance, but this will need further
review. Lows will again be below freezing Friday night.


High pressure will move in from the northwest heading into the
weekend. But a weak trof passing to our southwest could bring
some light rain or snow showers (or ZR if early enough in the
morning) to the southwest half of our forecast area Saturday.
The better chance of precipitation for all comes with a large
area of low pressure that moves towards the region from the
Plains and Midwest. Current guidance has the low passing
directly over our region late Mon and early Tuesday. Of course
this late in the winter, with spring starting Tuesday, timing
and track will be everything determining precip type. Time will


VFR thru Friday night all terminals, although cigs as low as
FL050 will occur at times through Thursday. Gusty northwest
winds will occur during the daylight hours Thursday and Friday,
with winds gusting up to 30 knots, but they will relax somewhat
at night. There can be a stray flurry or sprinkle at times,
most likely during the afternoon hours today and Thursday, but
they should not present any restrictions.

VFR conditions should be the rule until the large low can reach
us early next week.


Stabilization with sunset has reduced winds below 30 knots this
evening. There may be a slight uptick as low level jet continues
to increase, but am having increased confidence that the Gale
Warning will be able to be downgraded within the next hour. Am a
little concerned mid/upper Potomac may not drop below SCA late
tonight as forecast, so will take a look at that too.

There will be renewed gusts to just shy of gale again on
Thursday. Gusts again drop back a bit Thursday night but likely
return Friday.

No marine headlines or hazards are expected this weekend. Winds
will be on the increase early in the workweek around the large
area of low pressure expected to cross the region.


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 Thursday, 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 today. There will be an
enhanced threat for the spread of wildfires, especially across
central Virginia where winds will be strongest and relative
humidity will be lowest (near 30 percent). Have issued SPS for
this potential.

For Friday...more gusty winds are expected. Somewhat chillier
conditions may limit the RH drop a bit, but fuel moistures will
be quite low.


VA...Wind Advisory until 8 PM EDT Thursday for VAZ025-026-503-504-
WV...Wind Advisory until 8 PM EDT Thursday for WVZ505-506.
MARINE...Small Craft Advisory from midnight tonight to 6 AM EDT Friday
     for ANZ530>534-537>541-543.
     Gale Warning until midnight EDT tonight for ANZ530>543.
     Small Craft Advisory from midnight tonight to midnight EDT
     Thursday night for ANZ542.
     Small Craft Advisory from midnight tonight to 3 AM EDT
     Thursday for ANZ535-536.
     Small Craft Advisory from noon Thursday to midnight EDT
     Thursday night for ANZ535-536.


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