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fxus61 klwx 130930 aaa 

Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
430 am EST Wed Nov 13 2019

Arctic high pressure will remain overhead through tonight
before shifting offshore Thursday. A weak cold front will pass
through Thursday night and high pressure will return for Friday.
Coastal low pressure will intensify off the southeast coast
Saturday before moving northeast off the mid-Atlantic coast
Sunday. High pressure will build over New England during this
time. Another low may impact the area early next week.


Near term /through tonight/...
Arctic high pressure over the Ohio Valley early this morning
will build overhead today. A northwest flow will continue, but
winds will be much lighter compared to Tuesday. With the Arctic
high overhead, more bitterly cold conditions are expected for
this time of year, despite sunshine.

Max temps will range from the 20s in the mountains to the mid
and upper 30s for most other locations. There will be some high
clouds today, especially later this morning and afternoon well
ahead of an upper-level disturbance over the central Continental U.S..
however, the cloud deck should be thin allowing for partly to
mostly sunny skies.

The high will begin to shift eastward the mid-Atlantic coast
tonight. A return flow will develop, but the flow should be
light and latest thinking is that most areas will decouple. With
only very thin high clouds in place, this provides a good setup
for radiational cooling. Therefore, the latest forecast leans
toward the colder guidance for rural areas and valleys. Min
temps are forecast to range from the teens in many locations to
the upper 20s/near 30 in downtown Washington and Baltimore as
well as near the Bay/Potomac River.


Short term /Thursday through Friday night/...
high pressure will shift offshore for Thursday and a return flow
will strengthen a little. This will allow for milder conditions,
despite a cold start. There will be some high clouds around, but
again the deck should be thin enough for partly to mostly sunny

A very weak boundary will move through the area Thursday night
with little impact on the weather. However, northern and
southern stream energy will begin to phase in a split flow
over the Gulf Coast states Thursday night, leading to the
development of low pressure over the southeastern Continental U.S.. at the
same time, high pressure will be building toward our area from
the Ohio Valley. Latest guidance suggests that the high should
bring dry and chilly conditions to much of the area. However,
jet energy well ahead of the low will lead to more clouds and
perhaps even some rain across southeastern areas (va Piedmont
and southern Maryland most likely). Across these areas, temperatures
should be warm enough for the p-type to be rain. However, if the
precipitation develops farther northwest than currently
expected...there may be just enough shallow cold air for
freezing rain. As of now, this is not expected but it will have
to be monitored.

The jet energy should depart Friday while low pressure cuts off
from the jetstream over the southeastern Continental U.S.. at the same
time, high pressure will be building toward New England. The
ridge axis from this high should build south into our area,
bringing dry and seasonable conditions Friday and Friday night.


Long term /Saturday through Tuesday/...
somewhat active long term period on tap for the area with multiple
shortwaves passing overhead, inducing a few surface lows off the
East Coast.

Saturday looks mainly dry but windy and cold as a cutoff upper
low and attendant surface low move away from the Carolina
coast and into the western Atlantic. Gusty northerly winds are
likely (perhaps as high as 30 to 40 mph near/east of the Blue
Ridge where the pressure gradient is strongest). These winds
combined with high temperatures struggling to reach 40 degrees
will make it feel below freezing most of the day.

This low will lift slowly northeastward out at sea through Sunday,
likely staying far enough offshore to keep heavier precipitation
east of the Delmarva, though some spotty light precipitation is
possible as far west as the Metro areas (per prob >= 0.01" from 00z
ecens). Chances for precipitation increase early next week,
first as a lead shortwave pivots over the area late Sunday
night into Monday, then later Monday through Tuesday as an
amplifying northern stream trough digs southeastward, catching
whatever vorticity/shortwave energy is left near the
southeastern U.S. Models have been trending more amplified with
this trough, which makes sense giving the unseasonably strong
blocking surface high downstream over northern New England and
the Canadian Maritimes. This system will have to be monitored
for the potential of more significant precipitation, with at
least higher elevation snows possible in what currently appears
to be a marginal thermodynamic environment (in terms of winter
ptype). Overall, temperatures should be on a gradual warming
trend through early next week, but the question is how quick,
especially for the mountainous areas and perhaps near the PA

Any storm system that develops should be lifting northeastward away
from the region on Wednesday, and subsequently taper pops downward
during this time (though non-zero given timing uncertainties this
far in advance).


Aviation /10z Wednesday through Sunday/...
VFR conditions are expected through Friday night. Northwest
winds gusting around 15 knots through midday will diminish later
this afternoon. A southerly flow is expected Thursday with gusts
around 15 knots in the afternoon. Light north to northwest winds
are expected Friday.

Mainly VFR Sat with gusty north winds 25-30+ kts possible. North or NE
flow remains sun and still gusty (though perhaps not quite as
strong). Precip chances gradually increase by Sun night but may
ultimately remain dry through the weekend.


high pressure will build overhead through tonight, causing winds
to gradually diminish. An Small Craft Advisory remains in effect portions of the
waters through this morning. Winds should drop below Small Craft Advisory levels
this afternoon and tonight.

High pressure will move offshore Thursday and a southerly flow
will develop. Winds should remain below Small Craft Advisory criteria, but it
will be close for a period Thursday afternoon.

Low pressure will intensify near the southeast coast Friday
through Friday night. An Small Craft Advisory will likely be needed for portions
of the waters during this time. A Gale Warning may also be
needed for portions of the waters late Friday night.

Strong northerly flow near gale force is expected Saturday, only
gradually subsiding through Sunday as low pressure over the
western Atlantic fights its way northeastward toward strong
high pressure over northern New England and the Canadian


Tides/coastal flooding...
strong offshore flow has resulted in below normal tides, with
near blowout from near Baltimore Inner Harbor northward on the
Chesapeake Bay. Winds will become lighter today with tide
levels rising.


the Arctic airmass has moved into the region. Here are the
current record lows and record cold highs.

Site low 11/13 high 11/13 low 11/14
dca 22/1911 31/1911 19/1920
BWI 22/1911 32/1911 18/1986
iad 21/1963 38/1996 13/1986


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory until noon EST today for anz531>534-
Small Craft Advisory until 6 am EST early this morning for


near term...bjl
short term...bjl

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