Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 120236
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
936 PM EST Sun Feb 11 2018

.SYNOPSIS...
A cold front will cross the area tonight and will gradually
move south of the area by late Monday. High pressure will cross
north of the area Tuesday. A warm front will cross the region
during midweek, followed by a cold front late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
The Flood Watch encompassing much of the region was cancelled
earlier this afternoon as the swath of heavy rainfall moved
east of the CWA. As of 8pm, there remains Flood Warnings in
effect for portions of Anne Arundel, Calvert, Prince Georges,
and Charles Counties in Maryland for this evening as flooding
is still occurring for small streams and creeks. Light rain
showers are moving northeastward across southern Maryland this
evening, as well western Maryland, bringing only additional
light accumulations to these areas.

With a stationary boundary residing just to the northwest of
the metro areas this evening, we are seeing a decent temperature
gradient over the area. Locations to the south and east of this
boundary are holding in the low to middle 60s, while those to
the north of the boundary are in the low to middle 40s. The
primary cold front currently entering WV and western PA will
press through our area overnight. Some additional rain showers
will be possible as this front moves through after midnight, but
with only minor accumulations expected. Winds will turn northwesterly
and gusty toward daybreak Monday as the front crosses the region.
Temperatures overnight will hold in the upper 40s to near 50
for locations south and east of D.C., to the upper 30s to middle
40s north and west.

&&

.SHORT TERM /MONDAY MORNING THROUGH TUESDAY NIGHT/...
The frontal zone will slowly limp east of the forecast area
Monday. Guidance suggests there may be another impulse riding
northeast along the frontal boundary, which will delay clearing.
Thus have stalled chance PoPs through the midday hours in
Monday. But, by Monday night, high pressure building east from
the Great Lakes will providing drying/clearing. No significant
weather expected through Tuesday due to the influence of high
pressure.

Cold advection will be the main temperature trend, so highs will
be near normal Monday, but we will be below normal by Tuesday.
Have a subfreezing low Tuesday morning. If skies do clear and
winds decouple, then lows could be lower than forecast.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Wed and Thu... Surface high pressure over the Southeast U.S. early
on Wednesday will continue to slide offshore and to the south. Upper
level 592 high covers the Gulf of Mexico and will keep our region in
zonal flow aloft. Mild air will stream in on Wednesday with highs a
good 10 degF warmer than on Tuesday. And Thursday looks to be the
warmest day of the week with temps even warmer with 60s common and
approaching 70F as far north as DC. There could be a chance for
light precipitation Wed night into Thurs morning as a weak warm
front passes across the region.

Fri...A cold front will cross the region early Friday bringing an
end to our mild weather. Impressive 190+ kt upper level nearly zonal
250 hPa jet over the Great Lakes/St. Lawrence valley on Friday. Some
differences in timing on the passage of the front...with the 12Z
GFS/GEFS guidance being much quicker than the latest 12Z ECMWF
deterministic model. Model QPF this far out is uncertain but most
likely the front will pass through with a decent band of rain. PWAT
values ahead of the front on Friday are nearly 2 standard deviations
above normal for this time of year (1.25 inches).

Sat...the front will be well south of the region by 12Z Saturday as
cold high pressure returns. Temperatures will sharply revert back to
seasonal values with dry weather expected.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
A stationary boundary has sectioned off MRB from our other
terminals this evening, and as a result, MVFR VIS is being
observed there due to fog. All other terminals are VFR this
evening as they remain in the warm sector and shower activity
has moved off to the east. A cold front will move across the
terminals later this evening and overnight from west to east,
helping scour out the MVFR conditions at MRB and turn winds
northwesterly by morning. A few showers could spark as the front
moves over the terminals, but do not expect significant or
prolonged flight reductions as a result.

VFR conditions will prevail the next several days with northwest
winds increasing early Monday, with 20-25 kt gusts possible.

A weak disturbance passing through on late Wednesday could bring
briefly MVFR cigs in light rain...but overall expecting mainly
VFR.

&&

.MARINE...
Southerly flow being observed this evening across our waters.
Some 15 to 20 kt gusts being observed over the lower tidal
potomac and open Chesapeake. SCA remains in effect overnight as
a cold front is slated to move across the region overnight.
There will be a bit of a lull as the front approaches, but gusts
will pick up as northwest flow takes hold Monday morning and
continuing through midday. High pressure will be building, which
will permit the gradient to relax.

With high pressure to the south of the waters...southerly
channeling on Wednesday could result in marginal SCA-level
gusts on the Ches Bay, but most locations will remain below SCA
wind criteria. Southwest to westerly flow on Thu will be below
SCA levels.

&&

.HYDROLOGY...
The Flood Watch that encompassed much of the region was
cancelled earlier this afternoon. Flood Warnings remain in
effect overnight for portions of Charles and Prince Georges
counties in Maryland. The threat of heavy rainfall has ended,
outside of a few spotty showers overnight with a frontal
passage, bringing only minor accumulations of less than a tenth
of an inch for the remainder of the night. The Western Branch
of the Patuxent River is in flood stage, as the gauge at Upper
Marlboro indicates the river has crested and starting to recede,
with that latest level at 13.2 feet just after 9pm this
evening. Conditions are expected to be improving over Charles
county as well, however reports of several road closures remain.
The available gauge at Mattawoman Creek is still in action
stage but water levels there too have crested and are receding.


&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until noon EST Monday for ANZ530>532-535-
     536-538>540.
     Small Craft Advisory until 6 PM EST Monday for ANZ533-534-537-
     541>543.

&&

$$
SYNOPSIS...HTS
NEAR TERM...BKF/HTS
SHORT TERM...HTS
LONG TERM...SMZ
AVIATION...BKF/HTS/SMZ
MARINE...BKF/HTS/SMZ
HYDROLOGY...BKF



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