Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 160822

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
322 AM EST Thu Nov 16 2017

High pressure will build into the region today through Friday. A
strong cold front will approach the area Saturday, then cross
Saturday night. High pressure will build to the south of the
region late Sunday into the first half of next week.


Pre-frontal showers (in much weakened form) are exiting across
the eastern shore of Maryland as of early this morning. A zone
of mid-level moisture remains in its wake with overcast
conditions around 5000 feet being observed across much of the
area. A brief period of clearing is possible around daybreak,
but recent satellite trends seem to argue against that.

Whatever clearing occurs will transition to a scattered to
broken cumulus field by midday as the upper level trough axis
pivots across. Strong and gusty northwest winds are expected,
with gusts of 30 to 45 mph possible, especially over the
ridges. Hedged the high temperature forecast toward the upper
tercile of guidance since temperatures often overperform in a
downsloping regime. The colder airmass moving in should begin to
overwhelm downsloping effects east of the mountains after
midday, with high temperatures likely being observed by early
afternoon and then falling thereafter.

Upslope showers will likely continue through the day and into
the first part of tonight, mixing with and changing to snow by
mid-morning this morning with colder air rushing in.
Precipitation should be light as the moisture layer is
relatively shallow, so accumulations should remain under an
inch. The moisture may become shallow enough to support a period
of freezing drizzle this evening along the western slopes of the
Allegheny Front, but deeper mixing/gusty winds may preclude this
so it`s of low confidence at the moment.

A secondary pressure surge occurs tonight which should keep
winds elevated into Friday morning, especially over the ridges.


Friday should be mainly sunny and much cooler as cool high
pressure moves overhead. The benign weather will be short-lived,
however, as a strong upper trough digs into the Great Lakes.

Strong surface cyclogenesis is forecast to the northwest of the
CWA Friday night into Saturday. This will drag a strong cold
front into the region by Saturday evening. The slow trend has
continued in the guidance and as such have backed off on PoPs
during the day Saturday (though non-zero in strong warm
advection), then ramp up quickly Saturday evening. A strong
southwesterly low-level jet of 60+ knots at 3000-5000 feet)
would suggest a potential for 40-45 knot surface gusts over the
ridges, and in the valleys in any heavier showers ahead of the
front, though mixing becomes more difficult at lower elevations
in SW flow especially given the unfavorable time of day
(evening and overnight hours).

Precipitation should change to snow showers over the western
ridges of the Allegheny Front after midnight after the cold
front passes and winds turn northwest.


The area will be on the back side of a strong cold front Sunday
morning with gusty northwest winds and below normal temperatures.
With strong northwest flow, upslope snow showers will be in progress
across the higher elevations near and along the Allegheny Front, and
some accumulation is likely. High temperatures will range from the
30s near the Allegheny Front to around 50F in central VA and
southern MD.

Much quieter weather is then anticipated for Monday and Tuesday as
high pressure builds overhead. Temperatures will start below normal
Sunday night into Monday but moderate back towards climatological
normals by Tuesday.

The next chance of precipitation will come in the middle of next
week as a fast moving northern stream trough moves towards the


Mainly VFR through Friday night. Scattered-broken cumulus
expected between 4000 and 6000 feet today. Gusty NW winds of 20
kts with gusts to 30 knots are expected as well today, peaking
in the afternoon and only slowly diminishing this evening.
Winds should fall below 10 knots by about midday Friday.

Some flight restrictions are possible by later Saturday,
becoming more likely Saturday night as a strong cold front
approaches. SW winds will also begin to increase Saturday, with
low-level wind shear likely by Saturday afternoon and persisting
into Saturday night. Winds at 2000 feet may approach 50 knots
during this time.

Primarily VFR conditions are expected Sunday through Tuesday. Gusty
northwest winds will be the main aviation weather concern on Sunday.
Winds lessen Sunday night and Monday as high pressure builds towards
the region.


A Small Craft Advisory is in effect for most waters starting at
6 AM, then all waters after 10 AM through noon Friday as strong
and NW winds are anticipated behind a cold front. Gale force
gusts are possible late this afternoon and evening as well, but
these winds are above 2000 feet so confidence is too low for a
headline at the moment.

Gusts diminish Friday, then resume late Friday night into
Saturday as southwest winds increase ahead of an approaching
strong cold front. Gales are possible Saturday into Saturday
night as well.

SCA gusts likely and gale conditions possible behind strong cold
front on Sunday and into Sunday night. SCA conditions may continue
through Monday.


Minor tidal flooding was observed overnight as Strait`s Point
and Annapolis. Tidal anomalies should decrease enough on NW flow
today to preclude any further flooding, but waters levels likely
rise ahead of a cold front again Saturday.


MD...Coastal Flood Advisory until 6 AM EST early this morning for
MARINE...Small Craft Advisory until noon EST Friday for ANZ530>532-539-
     Small Craft Advisory from 10 AM this morning to noon EST
     Friday for ANZ535-536-538.
     Small Craft Advisory from 10 AM this morning to 6 PM EST
     Friday for ANZ542.
     Small Craft Advisory until 6 PM EST Friday for ANZ533-534-537-


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