Area Forecast Discussion
Issued by NWS Sterling, VA

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624
FXUS61 KLWX 231841
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
241 PM EDT Mon Oct 23 2017

.SYNOPSIS...A cold front will move across the area late tonight
and push east of the Chesapeake Bay Tuesday morning. High
pressure will gradually build across the region during the
second half of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...

Deepening sfc and upper level low pressure area over the OH
valley will force a narrow squall line across the area tonight
with the line of shallow convection entering Highland county
around 9PM and exiting the Chesapeake Bay by 6AM Tue. Despite
the lack of instability, the magnitude of the low-levels winds
is so strong (40kt at 500 meters) that the line should be able
to produce 40-50 mph gusts as it moves through. The strongest
part of the line should remain farther south across central VA
and may affect Albemarle and Nelson counties. Wouldn`t be
surprised if a severe t-storm watch is issued for that part of
VA later this evening.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...

Cdfnt will push east of the bay by 12Z with showers ending.
Still mild under westerly flow. Upper trough axis crosses the
area Wed (GFS) or Wed night (ECMWF) with temps staying in the
60s during the day and 40s at night. Any precip would be
confined to the upslope areas.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...

Troughing will remain entrenched over the eastern CONUS through the
period as ridging persists out west and over the North Atlantic.
This will lead to near normal temperatures late this week into the
weekend. A spoke of energy will rotate around an upper low stationed
just southwest of James Bay likely bringing another period of
unsettled weather at some point next weekend, but timing/placement
details remain fuzzy this far out.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...

Shallow line of convection will move across terminals tonight
first at KCHO between 01Z-03Z and then across the rest of the
terminals between 03Z-09Z. MVFR cigs and wind gusts to 45 kt can
be expected with this line of showers. No t-storms anticipated
due to shallow equilibrium levels.

Mainly VFR expected late in the week with light flow.

&&

.MARINE...Winds are expected to strengthen rapidly tonight in
response to strengthening low-level jet. Main channel of the bay
and lower Potomac should experience gale force winds easily
while the upper bay and upper Potomac the winds will depend more
on strength/intensity of convection. Think there could be a 3-hr
period where they also experience brief gales, so raised the
gale warning everywhere. Convective line moves east of the bay
by 15Z Tue at the latest with winds diminishing and showers
ending. SMWs may also be required later tonight.

Light flow with high pressure over the waters Thu-Fri.

&&

.TIDES/COASTAL FLOODING...Water levels are expected to rise
quickly this evening as srly flow strengthens. ESTOFS performing
much better than ETSS as it typically does in srly flow, but
magnitude of surge is almost always overestimated especially in
the upper parts of the bay. Don`t have enough confidence to
raise an advzy for Baltimore and Havre de Grace, but have enough
confidence that Annapolis will experience minor coastal flooding
for the next two high tide cycles, so raised the advzy for them.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory from 7 PM this evening to 1 PM EDT
     Tuesday for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for
     ANZ530>543.
     Small Craft Advisory from 8 AM to 6 PM EDT Tuesday for
     ANZ530>533-537>542.
     Gale Warning from 6 PM this evening to 8 AM EDT Tuesday for
     ANZ530>533-535>542.
     Gale Warning from 6 PM this evening to 3 PM EDT Tuesday for
     ANZ534-543.

&&

$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...DFH
AVIATION...LFR/DFH
MARINE...LFR/DFH
TIDES/COASTAL FLOODING...lfr



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