Area Forecast Discussion
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FXUS61 KLWX 250751
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
351 AM EDT Tue Oct 25 2016
High pressure will remain over the region through midweek. A cold
front will cross the area Thursday afternoon and evening. High
pressure returns Friday and Friday night.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Surface high pressure ridge still resides across the western Great
Lakes and Midwest. In spite of the pressure gradient across the
Northeastern United States, the central Shenandoah Vally has managed
to partially decouple...most notably at SHD and 8W2 where temperatures
already in the mid 30s. For that reason, believe the Frost Advisory
for the Valley looks good. West of there, its more iffy, but colder
conditions likely in the deeper valleys. Therefore, Frost/Freeze
still has a chance at verifying.
In spite of building high pressure today, there will be enough of a
pressure gradient to support breezy conditions, particularly across
Maryland. Model soundings support gusts around 20 kt. Cyclonic
stratocumulus clouds evident on satellite at this time in the
Appalachians and across Pennsylvania. Believe that will continue
through the morning. The cloud layer may thin in the afternoon, but
there is still respectable saturation near the LCL. Forecast high
temperatures seem to be on track.
.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
The high pressure ridge sits overhead tonight. Dry air and calm
winds suggest near ideal radiational cooling conditions, and
forecast low temperature below guidance. However, there is a
complication, in the form of return warm air advection present
across central Virginia by midnight. Therefore, am not confident on
how much will be a freeze vs. a frost. Believe there is time to
sort that out, as well as the state of the growing season after this
morning. Therefore have opted to keep the Freeze Watch in place for
now instead of making the warning/advisory decision. Nonetheless,
it will be a cold night, and areas of frost will be common.
Warm advection may not effectively mix to the surface until the
ridge axis exits to the east. That won`t be until Wednesday night.
Therefore, Wednesday`s high temperatures will be comparable to
today, if not a pinch cooler. The Thursday morning low, on the other
hand, will be significantly warmer.
There is decent model agreement in tracking low pressure from
Iowa/Missouri on Wednesday to near Lake Erie on Thursday. That will
keep the bulk of the upglide/vorticity forcing north of the forecast
area. Have scaled back POPs (20-30%) until early Thursday morning
for only the Potomac Highlands and Martinsburg-Hagerstown area.
Still believe that likely POPs prudent across the north on Thursday,
chance POPs elsewhere. The passage of the attendant cold front
Thursday afternoon will be the primary forcing mechanism.
.LONG TERM /FRIDAY THROUGH MONDAY/...
Post-frontal conditions are expected Friday as high pressure
moves into the region. Dry and cool conditions are expected with
temperatures reaching the U50s/L60s in most places. High pressure
moves overhead Friday night through Saturday before a warm front
advances northward from the Ohio Valley. Isolated to scattered
showers are possible Saturday however most activity should stay
north of Maryland. Low pressure will move across the northern
Great Lakes Saturday night into Sunday and an associated cold
front will likely slowly move southward from north to south Sunday
and rain showers are possible into Monday.
.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
VFR conditions anticipated for the valid TAF period under building
high pressure. Northwest winds will still gust to 15-20 kt upon
diurnal mixing today, but winds will become light tonight upon
VFR conditions Wednesday under high pressure. Flight restrictions
possible Thursday due to low clouds/showers as a cold front crosses
area. Periods of MVFR seem most plausible at this time.
VFR likely Friday into Saturday.
Winds have partially decoupled overnight, but occasional Small Craft
Advisory conditions ongoing on most of the Bay and lower tidal
Potomac. Upon sunrise believe that mixing will improve. Atmosphere
will still support 20 kt gusts. As such, SCA continues on all waters
today. Have extended SCA into tonight for the Bay and lower Potomac
based on guidance continuing a mixed atmosphere over the waters.
Winds will be much lighter by Wednesday morning as the ridge axis
will be overhead by that time. Return flow will hold off until
Wednesday night, and that will be from the east/southeast. Southerly
gradient returns during the day on Thursday, perhaps up to 15-20 kt
Small craft conditions, in northwest flow, may continue into
MD...Freeze Watch from late tonight through Wednesday morning for
VA...Freeze Watch from late tonight through Wednesday morning for
Freeze Warning until 9 AM EDT this morning for VAZ503-504.
Frost Advisory until 9 AM EDT this morning for VAZ025>027-029.
WV...Freeze Watch from late tonight through Wednesday morning for
Freeze Warning until 9 AM EDT this morning for WVZ505-506.
Frost Advisory until 9 AM EDT this morning for WVZ055-501-502.
MARINE...Small Craft Advisory until 3 AM EDT Wednesday for ANZ531>534-
Small Craft Advisory from 9 AM this morning to 6 PM EDT this
evening for ANZ530-535-536-538.