Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 151854

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
254 PM EDT Sun Oct 15 2017

A cold front will push into the Mid Atlantic tonight followed
by a return to high pressure early in the week and hold through
the end of the week.

Low clouds have been frustratingly slow to clear in the
Baltimore-Washington corridor today. Evidently, the inversion
has been strong enough to trap low-level moisture, with the
mixing winds merely overriding the top of the saturated layer.
We still have broken clouds from GAI-DCA northeast as of 230 pm.
Am hopeful that these clouds will erode in the 4-5pm window if
not before.

The band of incoming precipitation has been thin, and is not
close to the forecast area...emerging off Lake Erie at this
time. Guidance has been backing off PoPs through the rest of
today, and have been following suit. While low-level convergence
and 850 mb thermal forcing good, these features outrun the upper
level support. As a result, mesoscale guidance all depict a
rapid weakening as soon as the line hits the Appalachians.
Regardless, the best chance will come in the night time hours...
Blue Ridge/Catoctins west at or before midnight, east of there
overnight. Am keeping this as chance PoPs for most places, but
there could be local enhancement as this line approaches
southern Maryland early Monday morning.


The front will be clearing the area Monday morning. Based on
current extent and speed, there could be some lingering showers
east of I-95 early. Otherwise, the day will be marked by clearing
skies and increasing winds due to a surge of cold advection.
Gusts to 20-25 mph seem likely. Temperatures may not be purely
diurnal, but advection and compression may balance out during
the afternoon.

High pressure will be building over the area Monday night
through Tuesday night. If winds decouple quick enough early
Tuesday morning, frost would be possible as radiational cooling
conditions should be otherwise nearly ideal. Have added it to
the HWO. Tuesday night into Wednesday morning would also have
that potential.


Dry weather conditions are expected in the long term period as
surface high pressure is centered near or over our area between
Wednesday and Sunday. At the upper levels, ridge will be
amplifying and building over our region Thursday night and
remain into Sunday. High temperatures will above normal, and
will be gradually increasing from the 60s and low 70s on
Wednesday to upper 70s/near 80 on Sunday.


Low clouds have been frustratingly slow to clear in the
Baltimore-Washington corridor today. MVFR conditions linger
across DCA/BWI/MTN; these should erode 19-21 UTC. As soon as
clouds do break up, gusty winds will commence...up to 20 kt.

A cold front will cross the terminals tonight. Precipitation
should be scattered and brief. Restrictions unlikely. The wind
shift will be the most notable item, within a few hours of
midnight. A period of VFR clouds (cigs 040-050) will also

Northwest winds will gust to 20-25 kt on Monday. Winds will
diminish Monday afternoon-evening. Otherwise VFR through


Persistent low clouds have been hindering good mixing, but 20 kt
winds have been present and have been punching through on
brief/random occasions. Clouds beginning to break apart. Small
Craft threshold gusts should become more common.

Likely will have a lull this evening as a cold front approaches
the area. But, after frontal passage, which will be pre-dawn, a
surge of northwest winds will have good momentum transfer
potential. Will keep a Small Craft Advisory for all waters
through Monday, and then end in a staggered fashion during
Monday night.

Winds will be lighter for the rest of the week as high pressure
crests overhead.


MARINE...Small Craft Advisory until 2 AM EDT Tuesday for ANZ531>533-
     Small Craft Advisory until 6 PM EDT Monday for ANZ530-535-536-
     Small Craft Advisory until 6 AM EDT Tuesday for ANZ534-537-543.


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