Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 240850
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
350 AM EST Sat Feb 24 2018

.SYNOPSIS...
A stationary boundary situated across our area will gradually lift
northward as a warm front through Sunday. A cold front will then
pass through from the west by Sunday evening, with high pressure
building in to the region through early next week.
&&

.NEAR TERM /THROUGH TONIGHT/...
Much of the area is covered in low clouds early this morning that
are trapped below a hefty inversion based just a couple thousand
feet off the ground, as sampled by the 00z KIAD sounding. Atop this
inversion is a nice wedge of warm air aloft, with temperatures in
the middle 50s at about 5kft. Back at the surface, temperatures
early this morning range from the lower 40s west of the Blue Ridge
to middle to upper 40s along and south of the D.C. metro area. Areas
of dense fog have been persistent, relegated mainly along and north
of the District, encompassing Baltimore and northeast MD. A Dense
Fog Advisory remains in effect until 8am this morning for these
areas.

Outside of light drizzle in the fog plagued areas, the KLWX radar is
mostly echo free. Do expect this to continue to be the case much of
the morning across the area, at least east of the Blue Ridge
mountains. We will start to see some showers encroach on our western
and northern zones mid to late morning hours as a wave of low
pressure moves northeastward over southern OH and WV. A stationary
boundary snaking down the Appalachians and across North Carolina
this morning will gain some momentum later today and gradually lift
northward as a warm front through our area into tonight. As a
result, highest rain chances will be this afternoon through the
overnight period. Heaviest rain will be found across western MD, the
Potomac Highlands, and the West Virginia Panhandle, where a half
inch to an inch of rain could fall by Sunday morning. East of these
areas, a tenth to a quarter of an inch can be expected, with lowest
amounts across southern MD. With much of the area residing on the
cool side of the frontal boundary today, temperatures stick in the
upper 40s over northern MD to the middle 50s surrounding the metro
areas. The locations favored to reside on the warm side of the
boundaries are the southern portions of the Northern Piedmont,
Central Foothills, and the Virginia Highlands, where highs will near
60 degrees and in to the middle 60s for the warm spots. Lows tonight
won`t budge much, with middle 40s to our north to middle 50s to the
south.
&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Come Sunday morning, a cold front will be moving eastward and
nearing the western portions of our CWA. The aforementioned warm
front will be lifting through and north of our area by Sunday
morning, allowing much warmer temperatures to prevail. High
temperatures will near 70 degrees for much of the area, with the
cooler middle to upper 60s over the northern third of the CWA.
Scattered shower activity Sunday morning will increase by midday as
the front nears from the west. With the warmer temperatures and
dewpoints creeping in to the lower 60s, along with frontogentical
forcing, a slight chance of thunderstorms is possible as the front
crosses the region by Sunday evening. Behind the front, clearing and
drying conditions will win out Sunday night, with temperatures still
above normal for late February, ranging from near 40 degrees to the
north/west to around 50 degrees along our southern border.

High pressure will build in from the west as we kick off the work
week. The frontal boundary will linger along the Carolina coast on
Monday, with the ECMWF indicating at least some rain chances for our
southern zones. As such, will keep chance POPs for these areas on
Monday, but the majority of our CWA will remain dry. Weak CAA behind
the front on Monday will not prevent temperatures from reaching the
upper 50s on Monday, with lows Monday night cooler in to the 30s
area wide as CAA is a bit stronger and 850 temperatures reside at or
just below 0C. This is in response to a low/mid level trough
swinging through the region Monday evening.
&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
The middle of the week will be quiet as high pressure will be
overhead. Tuesday will be the sunnier day; moisture will advance
Wednesday due to return flow/warm advection as the center of the
high will move into the western Atlantic. It remains to be seen if
there will be any showers. GFS pointing that way more than ECMWF.
Will back off PoPs for the period.

Have greater confidence that the end of the week will end on the wet
side, in spite of guidance timing/organizational differences. (ECMWF
placing more emphasis on distinct southern stream shortwave/energy
vs triple point from a well-defined northern stream system.)  Either
solution provides strong evidence of measurable precipitation, and
neither scenario suggests there will be type issues until the back
side (Friday night), when the qpf will be exiting.
&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
Widespread LIFR conditions at all area terminals this morning as low
clouds and areas of dense fog envelop the region. Winds remain calm
to light, favoring a southerly trajectory when registered by surface
observations. LIFR VIS/CIGs will continue through mid morning, with
some improvement to VIS, at least in terms of fog coverage, but low
clouds and drizzle will persist. Rain chances increase this
afternoon and evening as a wave of low pressure passes to the
northwest of the terminals. Highest rain chances will be at MRB, but
continued LIFR conditions expected through tonight.

A cold front will move through the terminals Sunday afternoon, with
plentiful rain chances and IFR/LIFR VIS/CIGs continuing ahead of it.
Southwesterly breezes at around 10 knots, gusting to near 20 knots
during the day on Sunday, will shift out of the northwest Sunday
night and fall to less than 10 knots in the wake of the frontal
passage. Conditions should improve to MVFR/VFR Sunday night, and
back to VFR through Monday night as high pressure moves in from the
west. Exception to this on Monday would be CHO, where some residual
shower activity is possible as the aforementioned boundary lingers
well to our south. This could result in periods of sub VFR
conditions there.

VFR conditions expected at this time due to high pressure.
&&

.MARINE...
No advisories expected through tonight for our waters as winds will
remain light as a stationary boundary to our south starts to lift
northward as warm front. As a cold front approaches from the west on
Sunday, winds will pick up and become gusty out of the south
southwest Sunday morning, with SCA conditions looking likely through
much of the day on Sunday until the front passes through our waters.
The frontal passage may bring with it a gusty line of showers, with
a slight chance of thunderstorms as well. High pressure will then
build in to the region behind the front through Monday night,
delivering lighter winds across our waters, and sub SCA
conditions.

Winds will remain below Small Craft Advisory thresholds due to high
pressure. Southerly flow will increase late Wed in the wake of the
high.
&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Dense Fog Advisory until 8 AM EST this morning for DCZ001.
MD...Dense Fog Advisory until 8 AM EST this morning for MDZ003>006-
     011-013-014-503>508.
VA...Dense Fog Advisory until 8 AM EST this morning for VAZ053-054-
     505-506.
WV...Dense Fog Advisory until 8 AM EST this morning for WVZ052-053.
MARINE...None.

&&

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


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