Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 200752

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
352 AM EDT Mon Mar 20 2017

High pressure will cross the region today. Low pressure will
cross the region tonight. A cold front will cross the area
Tuesday night. High pressure will return Wednesday through
Thursday night. A warm front will cross the region Friday. Low
pressure may affect the area Sunday.


High pressure resides over the upper Ohio Valley this morning.
Stratocumulus deck has been shrinking overnight and should
continue to do so through sunrise, leaving a mostly sunny start
to the day. HRRR/RAP have been trying to move a decaying remnant
of showers currently in Michigan toward the area by mid-
morning, but think this is a slim chance given the high pressure
and dry low level air.

The trend has been for the remainder of the day to be dry as
the center of the high slips toward the southeastern states,
although showers may approach the Highlands late. Clouds will
increase some during the afternoon as well. High temperatures
will be near normal, ranging from 50 in NE MD to the lower 60s
in central VA.


Convective complex in Illinois is expected to hold together in
some fashion across the Ohio Valley and move into the
Appalachians this evening. By this point, precipitation will be
driven by a shortwave trough and low level jet, with nearly zero
instability remaining. SREF MUCAPE and hi-res lightning threat
suggest if there was a stray rumble, it would be in the far
southwest CWA. This cluster of showers will move across the area
overnight. Have bumped POPs up, but have held off on 100s for
now due to some timing and placement differences amongst
guidance. Less than a quarter inch of rain is expected. Low
clouds/fog may develop as the rain exits, as the surface low
reflection passes south of the area and mixing will be poor.

Tuesday will be mostly cloudy as a broad baroclinic zone
settles southward. However, it should be dry and mild with
temperatures pushing above normal, from the upper 50s north to
near 70 south. GFS/NAM/ECMWF have taken a decided shift south
with the area of low pressure Tuesday night, keeping most of the
area dry. However, GEFS still shows a large spread of QPF, and
have thus only stepped POPs down 10-20% from previous forecast
at this time. With this southward shift, there is less of a
chance colder air arriving from the north will overlap moisture.

Reinforcing cold front will be pushing through the area around
daybreak Wednesday, resulting in gradually clearing skies.
However, cold advection will result in breezy conditions and
temperatures dipping back below normal. Highs will be in the
40s, up to the lower 50s in central VA. While high pressure will
be building in Wednesday night, it won`t be directly overhead,
so there will be some variance in decoupling. However, colder
spots are likely to dip into the teens with 20s elsewhere.


Guidance is in relatively good agreement regarding the
progression of systems through the long term. Canadian high
pressure will cross the region on Thursday, with unseasonably
cool temperatures remaining in place. Skies should be fairly
sunny with relatively light winds. A warm front will then
approach from the southwest on Friday as high pressure heads
east off the coast. There may be some overrunning rain with the
front, mainly in western MD and WV, as it crosses the area, but
right now most of the region appears to stay dry. As the front
pushes through, winds will become southerly to southwesterly and
should increase with some gusts up to 20-25 mph possible.
Temperatures will depend on the progression of the front, with
above normal temps possible wherever the front passes before
evening - most likely southern parts of the CWA. Saturday now
looks drier than it did yesterday, as the ridge aloft holds on
longer than previously projected. This should allow temps to
spike into the 70s across much of the region for the first time
since March 9th. A closed low then approaches from the west at
the same time as a cold front drops down from the north on
Sunday, with cooler and wetter weather possible to end the


VFR conditions today with high pressure and light northwesterly
winds. Disturbance will cross the area tonight with a 3-6 hour
window for showers. The showers will be fairly light, but it
does appear that as they exit, low clouds and possibly fog will
develop and last through mid morning. IFR will be possible, but
will keep at MVFR in TAFs now until certainty is higher.

The remainder of Tuesday should be VFR, although mid-level
clouds likely persist. Trend has been for low pressure to be
farther south Tuesday night, reducing precipitation chances.
Cold front pushes south early Wednesday morning, with gusty NW
winds to 25 kt possible through the rest of the day.

VFR conditions will dominate Thursday and Friday, though a few
showers and reduced cigs are possible Friday as a warm front
crosses the area. Winds will become southerly and may gust 15-20
knots behind the warm front.


Winds are diminishing, so will likely be able to cancel the
remaining portions of the SCA early. Winds will remain light
today as high pressure builds. A disturbance will bring showers
tonight, but no wind issues are expected. NW winds are expected
Tuesday as a front pushes south of the area, but am forecasting
sub-SCA at this time. Stronger winds will come with a
reinforcing cold front late Tuesday night and the last through
at least Wednesday evening. Northerly gusts of 20-30 kt will be
possible during this time.

Winds should be sub-SCA on Thursday as high pressure crosses the
area. A warm front will lift north across the area on Friday,
with 20 knot gusts possible as winds become southerly. A small
craft advisory may be necessary.


MARINE...Small Craft Advisory until 6 AM EDT early this morning for


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