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fxus61 klwx 090907 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
407 am EST Mon Dec 9 2019

low pressure will develop over the central United States and lift
into the Great Lakes today. A warm front developing east of
this area of low pressure over the Carolinas is expected to lift
northward across the mid-Atlantic today. The aforementioned low
will drag its trailing cold front through the region Tuesday
into Wednesday. Strong Arctic high pressure will build from the
Great Lakes toward the mid-Atlantic Wednesday night through
Thursday night, then shift offshore of New England as low
pressure develops over and approaches from the southeastern
United States.


Near term /through tonight/...
rain showers/drizzle associated to a warm front/isentropic lift
are moving along southern and central Maryland. Upper level
trough will continue to push over the eastern Continental U.S. As front
approaches from the west today with southerly flow advecting
warm and moist air into our region. Rain showers/drizzle are
also observed over the Potomac Highlands.

Low pressure will develop over our area along the warm front
that is sitting to our east and will move NE and away form US
into the evening. Short term guidance and soundings supports
that rain showers/drizzle over south/central Maryland and the Potomac
Highlands will continue through early this morning before
widespread rain moves into our region mid Monday morning and
into the afternoon.

Rain showers are expected for most areas on Monday night as
forcing from the front moves away from US, with highest chance
over central Maryland and the Potomac Highlands.

Temperatures will be above normal today and tonight. High and
low temperatures will be in the 40s and 50s.


Short term /Tuesday through Wednesday night/...
surface cold front will move across our area on Tuesday and
showers will redevelop into Tuesday night. The front should be
east of our area by Tuesday evening but the upper jet dynamics
and a mid level energy ahead of a trough will allow for
anafrontal precipitation. Cold and dry air advection behind the
front will have an impact on the p-type on Tuesday night. A
changeover from rain to snow could occur Tuesday night, assuming
there is still enough moisture in the column.

If things come together, the most likely areas for snow
accumulations are over higher elevation. Highest amounts are
about 5 inches at the ridgetops, with up to 3 inches elsewhere
(see winter weather website). This of course will depend if cold
air moves in fast enough, so there is still some uncertainty
with this.

Precipitation will end on Wednesday as Arctic high pressure
builds in from the west on Wednesday into the night.


Long term /Thursday through Sunday/...
guidance is in relatively good agreement, better than last
night, regarding the end of week and weekend. High pressure
likely dominates on Thursday, with chilly temperatures but dry
conditions. By Friday, low pressure developing near the Gulf
Coast may start to spread precipitation into the region, but
this is more likely Friday night. With the chilly air mass in
place, some mixed precipitation, perhaps even freezing rain,
will be possible mainly west of the Blue Ridge. By Saturday, the
low lifts northward to our west, likely scouring out the cold
air and bringing temperatures back above normal across much of
the area, though rain showers will continue. As low pressure
then moves further away to the north and east by Sunday, drier
weather should return, but with little cold air behind the
system, temperatures look more likely to remain on the plus side
of normal.


Aviation /09z Monday through Friday/...
LIFR to IFR conditions are observed over BWI, mountain and dca.
Cloud decks and vsbys will continue to decrease through the day
today as rain widespread over the region. Periods of LIFR are
expected along with low level wind shear due to a strong low level jet. Gusts
near the surface can be up to 20 knots at times, especially
Monday afternoon into the night. Low level wind shear could linger through this
evening, sometime between 00 to 03z.

A lull in precipitation is expected Monday night but it will
generally remain sub-VFR through the night. Precipitation will
return again Tuesday as a cold front moves through with sub-VFR
conditions returning. Precipitation may linger through early
Wednesday, and a changeover to snow on Tuesday night is
possible, most likely for mrb. High pressure will build in late
on Wednesday allowing for VFR conditions.

VFR conditions expected Thursday. However, uncertainty exists
Friday as some guidance indicates a low pressure may try to lift
northward into the region, bringing potential for mixed


winds will remain below criteria through Monday afternoon.
Mixing is expected to increase this afternoon and winds will
reach criteria during this time and trough Monday night. Above
criteria wind gusts will continue on over parts of the waters on
Tuesday. Confidence is not high on exact location due to areas
that may actually experience a lull in the winds. Confidence is
higher on winds increasing behind the front Tuesday night into
Wednesday. A Small Craft Advisory is issued over most of the
waters through Monday night, also extended a section through
Tuesday afternoon. Small Craft Advisory will be needed for late Tuesday into
Wednesday for all waters.

Winds likely drop below Small Craft Advisory levels during the day Thursday as
high pressure builds in. Friday, some uncertainty exists as low
pressure may lift northward into the region, but most likely
winds stay sub-sca.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory from 6 PM this evening to 6 am EST
Tuesday for anz530>532-538>540-542.
Small Craft Advisory from 1 PM this afternoon to 1 PM EST
Tuesday for anz534-537-543.
Small Craft Advisory from 1 PM this afternoon to 6 am EST
Tuesday for anz533-541.


near term...imr

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