Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 261853

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
153 PM EST Sat Nov 26 2016

High pressure will move across the region through Sunday, then
move offshore on Monday, ushering in southerly winds and warmer
temperatures. A storm system will begin to approach the region on
Tuesday, but the associated cold front will not move through until
Wednesday or Wednesday night.


Plenty of clouds out this afternoon as a shortwave finishes
rolling through the area. Forecast simulations show the existing
low cloud layer beginning to dry after sunset tonight, and we
should quickly clear in most areas. We will remain in a reasonably
tight pressure gradient between the high over the southern
Appalachians and the departing low in the Atlantic, so decoupling
of winds should be limited to mainly sheltered valleys, especially
in our southwestern counties. As a result, I leaned toward the
warm side of guidance, with lows near 40 in downtown DC/Baltimore
and in bayshore communities, but potentially mid 20s in Highland

Still could see an upslope rain or snow shower out west, and I
extended the ongoing PoPs through the entire night rather than
just the evening hours. Cannot rule out a sprinkle further east
but probability is way too small to include.

For Sunday, high pressure and dry air will result in just a few
clouds and an increasingly less breezy day. Temperatures will be
fairly similar to today, but with less wind it will feel a little
less chilly.


Sunday night will be the coldest of the upcoming stretch, with
high pressure allowing for fairly widespread decoupling of the
winds. Lows mainly in the 20s except in the usual warm spots (and
on ridgetops). Clouds increase Monday. There is a bit of model
disagreement on temperatures. The consensus shows southerly flow
by afternoon, but the GFS doesn`t have it at all, and therefore is
cooler. Will stick with the consensus for now.

The previous forecast seems to have a good handle on the precip
onset Monday night. Of note, it looks like a good chance
temperatures will warm at least for the second half of the night,
so no precip type issues like we sometimes have at onset.


A warm front will lift north across the region Tuesday morning,
followed by a cold front moving northwest to southeast Tuesday
evening. A persistent southerly flow will fuel rain showers
throughout the day Tuesday.

As the cold front slides across southern Maryland and east-
central Virginia Tuesday evening, there could be a brief break in
the rain shower activity into the overnight hours.

A second storm system is expected to develop along the tail-end
of the cold front over the interior Southeast U.S. Wednesday
morning. The storm should ride northeast along the front
Wednesday and Wednesday night, bringing more rain showers to
the region.

The storm system will continue to move northeastward toward
southern New England Thursday. High pressure will build in
behind the storm and its associated cold front Thursday and
Thursday night. Drier and colder air will filter into the

An upper level trough of low pressure is expected to sag southward
into the region from the Eastern Great Lakes Thursday night and
Friday. There may not be a lot of moisture available to fuel any
showers with the trough. Plus, a downsloping flow over the
Appalachian Mountains could encourage a dry day Friday.

High pressure will build in behind the trough of low pressure
Friday night and Saturday. Dry and chilly conditions expected.


Ceiling heights have lifted above the MVFR threshold solidly and
will remain so until the clouds break tonight. Ongoing wind gusts
up to 25 knots will decrease after sunset. Could be a few more
gusts to 20 knots tomorrow during the day. Otherwise, VFR through
the TAF period and even through Monday.

Conditions will quickly deteriorate to IFR or even LIFR as precip
onset occurs late Monday night or early Tuesday. Rain showers
expected through the day with gusty southerly winds. Low clouds
hang in for Tuesday night and a second round of showers Wednesday.
Could be yet a third round of showers and low ceilings either
Wednesday night or Thursday morning before drying and clearing


Seeing fairly widespread SCA gusts today, and high-res models say
these will continue, except in the upper Tidal Potomac, through
the night as the relatively warm water allows mixing down of
gusts. Winds should gradually subside on Sunday, but uncertainty
in how quickly they decrease prompts leaving up the SCA. It could
be dropped early, however. No marine concerns Sunday night through
Monday night.

Small craft advisories likely Tuesday with winds southerly 15 to
20 knots and higher gusts. Channeling may lead to gale force gusts
on Tuesday. Small craft advisory conditions are possible Tuesday
evening. Winds southerly 10 to 15 knots with higher gusts Tuesday
night. May be a second round of southerly channeling up the bay on


Water levels are dropping below normal. Model guidance was too
early in creating a blowout so we are correcting to the observed
anomaly. We could approach a foot below normal tides before winds
shift on Monday and the anomaly starts to rebuild. The southerly
channeling favors elevated water levels, but our model output is
not handling it very well this far out. Bottom line is that minor
coastal flooding is possible along the bay Tuesday/Wednesday but
uncertainty is high.


MARINE...Small Craft Advisory until 6 PM EST Sunday for ANZ530>534-
     Small Craft Advisory until 9 PM EST this evening for ANZ535.
     Small Craft Advisory from 6 AM to 6 PM EST Sunday for ANZ535.


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