Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 180800
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EDT Sat Mar 18 2017
.SYNOPSIS...Low pressure and associated cold front will move
through the area late this afternoon. High pressure builds over
the area early next week. Another cold front will cross the area
.NEAR TERM /THROUGH TONIGHT/...Warm air advection precip will be
ending in the next couple of hours if not by 12Z. Some drizzle
and/or areas of fog are possible over the higher elevs. Main wx
maker this afternoon and tonight will be an upper low over the
upper midwest that will be digging southeast next 24 hrs. Upper
level divergence and strong height falls (150 meters/24 hrs)
will help trigger convective showers later today into early
Sunday. An inverted sfc trof also sets up across the area
tonight increasing sfc convergence with showers expected through
the night into early Sun. Raised PoPs significantly for today
into early Sun given strong lift Thermal profiles indicate
p-type mainly liquid east of the Blue Ridge through the evening
with colder air filtering and rain changing or mixing with snow
by 12Z Sun. Have generally 1-2 inches of snow accumulation for
the Potomac highlands which is short of an advzy.
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...Precip endind by
midday Sun with high pressure building in from the west. Turning
cooler under decent CAA. High pres shifts south Mon afternoon
with sct rain showers expected with next frontal passage. Cdfnt
clears the area by 12Z Tue.
.LONG TERM /TUESDAY THROUGH FRIDAY/...Computer model guidance is in
good agreement about the extended portion of the forecast.
Aloft, troughing will persist through the middle of the week,
giving way to a ridge by Friday. At the surface, a cold front
will be settling south of the area Tuesday morning. A wave of
low pressure will ride along the front Tuesday night, while a
secondary front pushes south into the area by Wednesday morning.
Canadian high pressure will then settle southeast, crossing the
area Thursday and continuing offshore Friday.
In terms of precipitation, the only notable chance comes with the
Tuesday night low pressure. While there is some spread in QPF
fields, the consensus at the moment has the best opportunity for the
southern quarter of the forecast area. Deterministic runs suggest
profiles will be warm enough for rain, but a few GEFS members crash
in enough cold air with the secondary front for a changeover to snow
before ending. At the moment, it doesn`t appear to be an impactful
system regardless of p-type.
The coldest period of the week will be Wednesday into Thursday
behind the second cold front, with highs in the 40s to lower 50s and
lows below freezing. The rest of the period will be fairly close to
.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...IFR cigs this
morning as warm front lifts through, then MVFR today and
tonight with ra/sn showers. Gusty N or NNW winds on Sunday.
A period of sub-VFR conditions is possible in rain and low clouds,
mainly at CHO, Tuesday into Tuesday night as low pressure moves
south of the area. Otherwise VFR prevails through Wednesday. NW
winds could gust to 20 kt both Tuesday and Wednesday.
.MARINE...Winds will diminish later this morning and remain
below SCA through early this evening. Winds strengthen tonight
with solid SCA conditions expected. Winds will begin to
gradually diminish Sun night but remain at aoa SCA into Monday.
After a cold front pushes south, NW flow will dominate Tuesday into
Wednesday, although it could become NE-N for a period as low
pressure passes to the south Tuesday night. SCA conditions will be
possible both days.
MARINE...Small Craft Advisory from 11 PM this evening to 6 PM EDT
Sunday for ANZ530>543.