Area Forecast Discussion
Issued by NWS Sterling, VA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
000
FXUS61 KLWX 231900
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
200 PM EST Fri Feb 23 2018

.SYNOPSIS...
A warm front will gradually push north across the region
tonight through Sunday morning. A cold front will then cross the
region Sunday night. High pressure will return early next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Latest surface analysis places low pressure near Lake Superior,
hig pressure near Nova Scotia, and another high pressure betwen
the Carolinas and Bermuda. A warm front extends between the two
high pressures, westward across North Carolina, then northward
along the Appalachians to the vicinity of Pittsburgh. There it
turns west and meets the cold front extending southward from the
low in the Great Lakes. The cold front then continues southwest
toward Memphis and finally approaches Houston.

Tonight through Saturday, the low pressure will head eastward to
our north. Southerly flow will encourage the warm front to push
northward as well, but the odds it reaches very far into our CWA
are not high. The more pessimistic but often more realistic (in
these situations, at least) NAM shows the warm front reaching
portions of the West Virginia eastern Panhandle and the
Shenandoah Valley, but struggling to reach any portion of the
CWA east of the Blue Ridge. There may be an attempt at a little
clearing this evening as this all tries to occur, but otherwise,
clouds and drizzle with patchy mist/fog will likely continue.
With the main forcing staying to our north, significant rainfall
is not expected across our region, but a few showers could skim
the region, particularly western Maryland. Temperatures will be
fairly steady, perhaps even rising a bit, but large changes are
not expected in most of the region.

On Saturday, the front may actually sink back south a bit as the
passage of the low to our north causes the flow to shift a bit
more northerly. Thus, the morning should be more of the
same...damp and dreary, but not a washout. Later in the morning
and in the afternoon, low pressure developing to the west over
the Plains will bring increased warm advection aloft and FGEN
across western zones, spreading eastward late in the day. This
will increase the risk of steadier rain. Given ample moisture
available, some locally heavy rain could occur in the western
portions of the forecast area, but confidence is low regarding
any flooding risk, so have not issued any flood watches yet.
Highs on Saturday will be a bit warmer than today as the warm
front once again attempts to lift north, with 50s and 60s
becoming more common. However, if the front ends up further
south than currently expected, it could stay cooler.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
Warm front makes more progress northward on Saturday night and
Sunday as low pressure wave pushes northeastward to our
northwest. This should allow temperatures to warm more
significantly after the rain Saturday night, with 70s looking
more likely on Sunday. An interval of relatively pleasant
weather may occur late morning into early afternoon, with more
sunshine, but then the cold front will approach from the
northwest. Still some uncertainty on any severe threat, but
certainly with the available moisture and warmth, some
instability will be present, so allowed slight chance of
thunder into the forecast Sunday afternoon. The front will slide
southeast across the region Sunday night, so a drying, cooling
trend will develop. However, the front will slow down overnight
as yet another wave of low pressure develops to our southwest,
so rain chances will not completely end in southern parts of the
region.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
With exception to a couple of lingering rain showers near
Southern Maryland and parts of the central Chesapeake Bay Monday
morning, conditions will dry out as a ridge of high pressure
builds in from the west. The high will persist through Tuesday
night before moving offshore early Wednesday.

Interaction between the high pressure and a developing low
pressure system over the central Great Plains will provide a
southerly return flow into our region. Expect milder and more
moist air to return Wednesday and Wednesday night. There could
be a couple of rain showers develop over the Appalachians and in
parts of the Central Shenandoah Valley later in the day
Wednesday.

A developing warm front over southwest Virginia and western
North Carolina will work its way north across our region
Wednesday night. Ahead of and along this warm front, additional
rain showers will develop and spread northeastward across our
region Wednesday night. Even more warmer and moist air is
expected to follow the warm front northward Wednesday night into
Thursday.

Showers, some moderate at times, should persist into Thursday
morning as the warm front moves to the Mason-Dixon region just
ahead of an approaching cold front that should pass through our
area Thursday night. Some drier and cooler air will work in
behind the passing cold front; however, models are trying to
push a cut-off low pressure system over the Great Lakes region
eastward. This cut-off low, it`s upper level energy support, and
a little daytime heating could spawn additional rain showers
later Thursday night and during the day Friday. Northwesterly
winds could become quite gusty as well in the wake of the
passing surface cold front and ahead of the cut- off low
pressure system.

Overall, temperatures throughout next week will be mild with
highs approaching 60 degrees or higher in any warm sector.
Friday may be the exception and could be cooler, but for now we
will keep temperatures near normal.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Changeable conditions expected through the next 48-60 hours as a
warm front remains stalled to our south much of the time,
resulting periods of low clouds, fog, mist and drizzle. Guidance
suggests a break in the low clouds could develop late this
afternoon and this evening, but given the cold air damning wedge
over the region, this does not seem likely, so have kept all the
TAFs at least MVFR through the TAF period. If conditions do
relax, it won`t be for long, as we will likely see fog or low
clouds redevelop quickly overnight. The warm front will probably
stay south of all the terminals, save perhaps CHO, during the
day Saturday, resulting in more of the same. Steadier rain may
overspread the region, especially the northern terminals, by
Saturday night. Conditions look more likely to improve from DC
on south and west on Sunday as a warm front lifts northward, but
BWI/MTN may have trouble breaking out of the low clouds and fog
as the front may struggle to pass that area. Cold front then
finally drops southeast across the region, bringing showers and
perhaps a thunderstorm Sunday afternoon, but likely resulting
conditions finally going back to VFR with drier air filtering
south Sunday night.

VFR conditions expected Monday through Tuesday night. Winds
northwest 5 knots or less Monday and Monday night. Winds
becoming southwest around 5 knots Tuesday and Tuesday night.

&&

.MARINE...
With weak gradient and a front to the south, expect winds to
stay below Small Craft Advisory strength through Saturday
evening across all waters. Late Saturday night, warm front
approaching from the south may finally lift north of the middle
Bay, allowing the strong southerly flow to reach the surface and
bring gusts up to SCA levels, but for now am waiting to issue a
headline. SCA looks likely across at least the southern waters
we cover, perhaps reaching up to the northern bay as well, as
the warm front lifts north and gusty south winds develop in the
warm sector. As with the recent round on Tuesday and Wednesday,
this will be primarily near-shore gusts, with weaker winds over
the open waters due to the chilly water temperatures limiting
mixing. Cold front will push southeast across the waters Sunday
night, but at this time SCA does not appear likely with this
frontal passage.

No marine hazards expected Monday through Tuesday night. Winds
northwest 5 to 10 knots Monday and Monday night. Winds becoming
southwest 5 to 10 knots Tuesday and Tuesday night.

&&

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

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...KLW
AVIATION...RCM/KLW
MARINE...RCM/KLW



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.