Area Forecast Discussion
Issued by NWS Sterling, VA

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481
FXUS61 KLWX 202007
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
307 PM EST Fri Jan 20 2017

.SYNOPSIS...
A front will remain stalled south of the area through Saturday.
Low pressure will impact the area Sunday through Monday before
moving away Tuesday. A cold front will pass through the area
Wednesday into Wednesday night and an upper-level trough may build
overhead late next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Warm front remains to the south at this hour though some breaks
have appeared in the clouds west of the Blue Ridge. These are
struggling to make it east of the mountains, however, so still
think eastern areas will stay pretty cloudy tonight and at least
through Saturday morning. Last showers are currently pushing
northeast into the metro, then otherwise it should be dry except
for patchy drizzle, through Saturday, as a weak ridge builds aloft
and some drying also occurs aloft. Given the high low level
moisture now present, any breaks in the clouds will allow fog to
form, so have kept patchy fog in the forecast. Lows tonight should
stay mild, generally in the 40s, with 50s likely on Saturday
especially if we can get some breaks in the clouds.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Guidance continues to show a significant coastal storm system
Sunday and Monday, though they continue to shift on the details.
Today`s guidance has shifted west a bit, and somewhat weaker.
Overall however, still expect rain to overspread the area Sunday
with the first wave of low pressure, then another surge of rain
late Sunday night or early Monday with the main center. This
second, stronger low looks weaker than yesterday but still will
bring some breezy conditions. A wind advisory is still not out of
the question on Monday, but the odds look lower than yesterday
given the weaker low and its shift westward. Generally, between
the two waves of low pressure, looks like most of the region
should end up with around an inch of rain, with potential for up
to two inches. Given recent dry weather, this probably isn`t a big
flood threat, especially given the long period over which the rain
is expected to fall. Also given the shift westward on the
guidance, the small threat of snow that some models showed
yesterday is looking less likely today.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Surface low pressure over or near our area will continue to push
northeast away from our region Monday night into early Tuesday.
Precipitation associated to it should be tapering off, mainly east
of the Blue Ridge during this time... while higher elevations
could experience different p-types Monday night.

Dry conditions expected on Tuesday into Wednesday -some showers
possible at higher elevations per some GEFS members- before another
cold front moves through the region Wednesday night into early
Thursday, with limited precipitation. Upper trough to our west will
slowly move east, bringing precipitation west of the Allegheny Front
Thursday into Friday. Some precipitation could reach east of the
Blue Ridge Thursday night into Friday, but still highly uncertain if
it will, and what p-type.

High temperatures will be in the 40s and 50s Tuesday and Wednesday,
decreasing into the 30s and 40s on Thursday and Friday. Low
temperatures will be in the 30s and 40s, with Thursday night being
the coldest.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Very tricky aviation forecast. Guidance has grossly overdone
moisture today, so cigs and vis have generally verified
significantly less restrictive than expected. That having been
said, there are still some IFR cigs out there and these may
continue to affect terminals tonight into Saturday. There is
potential that the clearing west of the Blue Ridge may expand
eastward this evening, but this may open the window for fog. Winds
should remain light through Saturday night. Cig/vis should improve
Saturday afternoon, but rain moving in late Saturday night will
cause restrictions to return for Sunday and Monday. Winds will
also likely start getting gusty by Sunday night and Monday,
generally from a northeast direction.

Low pressure system will move away Monday night into early
Tuesday and precipitation will be tapering off during this time.
Breezy conditions expected, with wind gusts reaching 20 kts...
decreasing into Tuesday night. Dry conditions expected Tuesday
into Wednesday. Some showers possible Wednesday night. So, sub-VFR
conditions possible Monday night into Tuesday, becoming VFR
sometime Tuesday and remain into Wednesday.

&&

.MARINE...
Sub-SCA conditions through Saturday night with southerly winds
tonight, gradually turning southeasterly on Saturday. Winds
increase markedly for Sunday and Sunday night out of the
east/northeast with Small Craft Advisory conditions likely Sunday,
with Gales possible Sunday night.

Low pressure system will move away Monday night into early
Tuesday and precipitation will be tapering off during this time.
Breezy conditions expected, with wind gusts reaching 20 kts...
decreasing into Tuesday night. Dry conditions expected Tuesday
into Wednesday. Some showers possible Wednesday night. Small craft
advisory expected for Monday night into Tuesday night as winds
diminish below the threshold.

&&

.TIDES/COASTAL FLOODING...
Onshore flow will strengthen later Sunday through Monday as a
coastal storm moves northward into the area. Tidal flooding is
possible during this time. The flow will turn offshore later
Monday night and Tuesday as the storm moves away.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...IMR
AVIATION...IMR/RCM
MARINE...IMR/RCM
TIDES/COASTAL FLOODING...RCM



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