Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 172005
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
305 PM EST Sat Feb 17 2018

.SYNOPSIS...
Low pressure will track northeastward along a stalled frontal
boundary well to our south through tonight. High pressure will
build in from the west on Sunday, migrating offshore by Monday.
Low pressure will move northeastward toward the Great Lakes
Monday, lifting a warm front northward through our region. A
cold front is poised to approach the region during the middle
portion of the work week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Precipitation has moved in across the area this afternoon,
starting as a snow/sleet mix along and north of the I-66
corridor, while some light rain started the festivities a little
further to the south. We are seeing a light mix of rain and snow
at DCA and BWI as temperatures hover near 40 degrees, but as
the column cools, do expect a transition to a snow/sleet mix.
Mainly snow is expected across the northern third of our CWA,
but some sleet mixing cannot be ruled out. One change to our
winter weather headlines was to include the remainder of
Baltimore county and the City of Baltimore in the Advisory, as
we could see 1 to 2 inches in those areas.

Precipitation will increase in intensity throughout this
afternoon and into this evening as favorable lift moves closer
to our region. The added lift is owing to the approach of a
potent shortwave and the proximity of the right entrance region
of the upper level jet moving overhead. By this evening, low
pressure off the MD/VA coast will also be developing in the
baroclinic zone residing along the coast. This low pressure
area will quickly move northeastward away from our region,
dragging with it much of the heavy precipitation off to our east
as well. The snow/sleet will have a hard time sticking to
pavement with the preceding warmth we`ve experienced, but if
precipitation comes down hard enough, these surfaces could
quickly cool and obtain a bit of slushiness, especially if
untreated. Do expect precipitation to come to an end for the
entire area by midnight, but likely a couple hours sooner
especially the further southwest you venture in our CWA.

Overall, storm total accumulations along the northern tier of
the CWA are expected to be between 2 to 5 inches, with 1 to 3
inches along and west of the Blue Ridge. The immediate D.C.
metro will likely see mostly a wintry mix, perhaps even some
rain this evening, which will keep totals at an inch or less,
mostly on grassy and elevated surfaces. Once again the highest
amounts will be found along and west of the Alleghenies, where
western Grant/Mineral are expected to receive upwards of 5 to 7
inches. Please visit our winter weather page at
weather.gov/lwx/winter for a myriad of snowfall projections for
this event.

Do have some concerns for icy spots overnight and early Sunday
morning as temperatures will fall to near freezing in the metro
areas, and below freezing to the north and west. If travelling
overnight and into early Sunday morning, use caution, especially
on untreated roadways and surfaces.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
High pressure quickly moves in behind the exiting low pressure
area to the northeast, resulting in a dry and clear conditions.
After a cold and perhaps icy start to the morning, temperatures
will rebound nicely, topping out in the mid 40s to lower 50s
region wide. High pressure shifts offshore Sunday night, keeping
a light return flow over the region and temperatures above
normal. Low pressure will move northeastward toward the Great
Lakes region on Monday, which will help lift a warm front
through our area. With warm air advection ongoing, could see
some shower activity on Monday, not a complete washout, but
definitely an increase in cloudiness. Highs Sunday/Monday will
be above average, ranging in the low to mid 50s. Lows Sunday
night will likely remain above freezing, and Monday night will
remain in the upper 40s to near 50 degrees.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
High pressure will be offshore on Tuesday with
return flow well settled over our region and an upper level ridge
centered over the SE CONUS. Dry and above normal temperatures are
expected Tuesday, with highs reaching the 70s for most of our CWA.

A similar scenario is expected on Wednesday before a slow moving
cold front approaches from the west. Guidance disagrees on the
timing of the front, but there seems to be a consensus between some
deterministic and ensembles that it will most likely move through
later Wednesday or early Thursday. The front will stall nearby
Thursday and into Friday which could keep the unsettled weather
through the end of the week, with cooler -but still above normal-
temperatures over our area. The front will lift as a warm front on
Saturday, continuing the chances of rain over our area.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
IFR and possibly LIFR CIGS/VIS at times this afternoon and into
tonight as wintry precipitation moves across the area from the
southwest. Periods of heavy snow/sleet are possible as
precipitation intensity maximizes late this afternoon and early
evening. The system quickly exits the terminals by 04z,
resulting in a return to VFR conditions, which will prevail
through Sunday night. Light winds at 10 knots or less are
expected.

A warm front will lift north of the area on Monday, bringing a
threat for shower activity and the potential for episodes of
sub VFR conditions.

VFR conditions expected Tuesday and part of the day
Wednesday before sub-VFR periods possible late on Wednesday and into
Thursday when unsettled weather could affect our area.

&&

.MARINE...
With low pressure crossing the region through tonight, expect a
weak gradient which will keep winds below criteria threshold. Winds
will remain below advisory criteria through Monday as high
pressure traverses our region and moves offshore, delivering
light southerly winds over the waters.

Winds are expected to remain below SCA criteria on Tuesday,
even though they will be breezy. Similar conditions expected on
Wednesday, therefore no small craft advisory expected these
days. Winds will decrease on Thursday and remain below criteria.

&&

.CLIMATE...
A period of exceptional warm weather is expected Tuesday and
Wednesday. Temperatures will be approaching if not exceeding record
values. Below is a listing of record warm highs and record warm lows
for this period.

Record warm daily maximum temperatures
SITE   TUE 2/20   WED 2/21
DCA    76 (1930)  75 (1953)
BWI    76 (1930)  74 (1930)
IAD    70 (1971)  70 (1997)

Record warm daily minimum temperatures
SITE   TUE 2/20   WED 2/21
DCA    59 (1939)  51 (1954)
BWI    57 (1939)  49 (1981)
IAD    46 (1981)  45 (1981)

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Winter Weather Advisory until midnight EST tonight for
     MDZ003>006-011-501>503-505-507-508.
VA...Winter Weather Advisory until midnight EST tonight for
     VAZ025>031-040-501-503>505-507-508.
WV...Winter Weather Advisory until midnight EST tonight for
     WVZ050>053-055-502-504>506.
     Winter Storm Warning until 2 AM EST Sunday for WVZ501-503.
MARINE...None.

&&

$$
SYNOPSIS...BKF
NEAR TERM...BKF
SHORT TERM...BKF
LONG TERM...IMR
AVIATION...IMR/BKF
MARINE...IMR/BKF
CLIMATE...RCM



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