Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 221355 AAA
Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
955 AM EDT Thu Sep 22 2016
Low Pressure remains off the Carolina coast while high pressure
is centered over New England. A backdoor cold front will move
through the area Saturday. High pressure returns to the region
Sunday through early next week.
.NEAR TERM /TODAY/...
Forecast on track...as we remain sandwiched between high pressure
centered over New England and low pressure off the coast of the
Carolinas. Satellite imagery depicts scattered high clouds from
the low continuing to impinge on extreme S MD and the Central
Foothills of VA. Elsewhere, it remains mostly sunny with a few
thin high-level clouds. Guidance continues to indicate these
trends will continue through the afternoon, with most places
remaining mostly sunny. While a few spotty showers were observed
across S MD earlier this morning, observations/guidance indicates
showers will remain south of our area for the remainder of the
Autumnal equinox is at 1021 AM EDT this morning...though it won`t
feel much like fall by afternoon with high temperatures 5-10 F
above normal and at least a hint of humidity, with dewpoints AOA
60F east of the Blue Ridge.
.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
Skies should remain mostly clear tonight through Friday night.
Fog development is possible during the overnight hours in the
central Shenandoah Valley/I-81 corridor and point west. An
approaching short wave/cold front should finally dislodge the weak
coastal low. Lows tonight 60-65 east of the mountains...55-60
west. Friday should be an even warmer day on warm air advection
ahead of the front. Friday night should see similar temperatures
to Thursday night.
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Dry stretch of weather likely to continue through the weekend and
into next week.
Cold front will be passing across the region Saturday morning with
winds turning to the north and some increased cloud cover. However,
will be a mainly dry frontal passage with really only chance of rain
being a spot shower across the higher terrain. Mixing will
increase behind front, so despite falling 850mb temperatures,
still expecting an above normal temperature day with highs in the
low 80s for most.
The remainder of the extended period will be dominated by developing
omega block with upper lows over the NW Atlantic and central US,
with large amplified upper level ridge over the eastern US. This
will continue to lead to a mainly dry forecast. However, position of
surface ridge will eventually determine how early next week`s
weather plays out. Current GFS/ECMWF depictions place surface ridge
just offshore, which would promote an onshore flow with increased
clouds, perhaps some nocturnal fog/drizzle, and cooler temperatures.
Given strength of ridge/block, expecting any approaching frontal
system to remain west of the region through Wednesday. Highs
generally 70s, lows 50s/60s.
.AVIATION /14Z THURSDAY THROUGH MONDAY/...
VFR conditions expected today. Fog could develop tonight at the
more favored locations - CHO and MRB especially. VFR expected
everywhere Friday and Friday night.
Mainly VFR expected Saturday and Sunday, however, developing onshore
flow may promote the development of Sub-VFR conditions by Monday.
A Marine Weather Statement was issued early this morning for isolated
wind gusts near SCA criteria across lower portions of the
Chesapeake Bay and lower Tidal Potomac. Statement is set to expire
at 10 AM, as guidance indicates gusts AOA SCA criteria will be
short-lived. Winds remain below SCA values this afternoon through
Small Craft Advisories will likely be needed Saturday and Saturday
night with increased northerly flow behind frontal passage. Winds
diminish for Sunday and Monday and Sub-SCA conditions likely.
No coastal flooding anticipated with this morning`s/afternoon`s high
tide cycle, however, our more sensitive sites may approach or exceed
minor flood stage with this evening`s/tonight`s high tide cycle.
Annapolis and DC/Alexandria most at risk.