Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 211617
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1217 PM EDT Mon Sep 21 2020

.SYNOPSIS...
High pressure will gradually build over and then south of the
area through the week while Teddy departs through the Canadian
Maritimes. A cold front will approach this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Northeasterly breezes continue between high pressure centered
over the Northeast and Teddy well offshore. These winds will
begin to lessen into this evening especially west of I-95 as
surface ridging builds in and the gradient relaxes. The light
winds coupled with a clear sky and dry airmass will setup
another radiational cooling setup tonight. Frost is expected for
many areas near/west of the Blue Ridge Mountains with patchy
freezing temperatures likely. The coverage of sub-freezing
temperatures looks somewhat small at the moment, so will
probably hold off on any Freeze Warnings for the time being
(this will be re-evaluated early this evening).

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As Teddy moves northward towards the Canadian Maritimes Tuesday
and Wednesday, high pressure will shift southward, becoming
centered over the Carolinas by Wednesday. This will allow winds
to turn westerly, resulting in warm advection across the region.
Highs will rise into the low 70s on Tuesday and to near 80
Wednesday, with lows staying in the 40s Tuesday night and closer
to 50 Wednesday night. Otherwise, dry weather will continue,
though clouds may increase a bit especially Wednesday as a weak
upper trough passes.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
High pressure will build offshore over the western Atlantic
Thursday and it will remain around there through Friday. A
southerly flow will allow for warmer conditions during this
time. There will be some more moisture that moves into the area
with the southerly flow, and shortwave energy may pass through
the area later Thursday and Friday that`s associated with the
southern Branch of the jet. A couple showers cannot be ruled out
late Thursday and Friday, but it appears that the deepest
moisture will remain to our south and forcing will be limited.
Therefore, will keep with the dry forecast for most areas, with
the one exception across central Virginia (closer to the deeper
moisture).

An upper-level trough is expected to deepen over the Great
Lakes and central CONUS Saturday through Sunday and the cold
front associated with this system will approach our area during
this time. A southerly flow ahead of the boundary will allow for
warm and more humid conditions as moisture continues to stream
into the area from the Atlantic and Gulf of Mexico. The cold
front along with the increased moisture will increase the chance
for precipitation. Timing is uncertain this far out, but the
best chance for precipitation appears that it would be Sunday or
Sunday night, when the cold front is closer to the area.

&&

.AVIATION /18Z MONDAY THROUGH FRIDAY/...
VFR expected thru Wed night. Patchy fog possible early Tue AM
near KMRB/KCHO but very low chc of it causing restrictions at
the terminals. NE flow gusting to 15 kt thru 18-20Z becomes
light tonight then W around 10 kt Tue-Wed.

High pressure will build offshore Thursday and Friday, and a
light southerly flow is expected along with VFR conditions for
most of the time. Patchy fog may briefly reduce vsbys during
the early morning hours both days.

&&

.MARINE...
Northeasterly winds will persist through tonight with gusts to
around 20 kt mainly south/east of Drum Point/Cobb Point around
high pressure to the north and Teddy well offshore. As the high
center weakens and shifts south, winds will become westerly
Tuesday into Wednesday. Gusts to around 20 kt may persist
through Tuesday night into Wednesday morning over the lower
tidal Potomac and middle bay.

High pressure will build offshore Thursday and Friday, and a
southerly flow is expected. However, the gradient should be
light enough for winds to remain below SCA criteria most of the
time.

&&

.TIDES/COASTAL FLOODING...
Onshore flow will maintain elevated water levels through
tonight. Minor flooding is likely for sensitive areas with the
high tide cycle later this afternoon into tonight.

The flow will turn more westerly for Tuesday and may cause
anomalies to decrease. However, there will be water piled up
near the mouth of the Bay, and some of that water may still make
it into our area since the flow will be relatively light.
Therefore, minor flooding is still possible. Confidence is low
at this time.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for
     ANZ530>533-535-536-538>542.
     Small Craft Advisory until 6 PM EDT Tuesday for ANZ534-537-543.

&&

$$
SYNOPSIS...DHOF
NEAR TERM...DHOF
SHORT TERM...RCM
LONG TERM...BJL
AVIATION...BJL/DHOF
MARINE...BJL/DHOF
TIDES/COASTAL FLOODING...BJL/RCM/DHOF



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