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fxus61 klwx 091445 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
945 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/...
a steady rain has developed over much of the area, just about to
the I-95 corridor as of 9:30am. This rain will continue to
overspread the rest of the mid-Atlantic through midday (except
perhaps a touch less widespread/steady over southern Maryland,
further from upper forcing).

As a lead shortwave impulse in the 700-500 hpa layer pushes
northeast by nightfall, the steadier rain will come to an end.
The warm front currently positioned to our south should
subsequently move northward, with rain becoming more spotty and
showery in nature through tonight.


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 /15z Monday through Friday/...
fog near dca/BWI/mtn lifting as of 15z, but will soon be
followed by vsby reductions in rain (this will affect all
terminals today, steadiest north of cho). Cigs look IFR/LIFR
much of today as well with strong low level moist advection just
above a surface temperature inversion. Low level wind shear is likely until
00-03z this evening as low level jet strengthens to 40+ kts at 2 kft.
Surface winds out of the south may gust to 20 kts this evening.

A lull in precipitation is expected tonight, but it may remain
sub-VFR through much of the night (though conditions may lift
after midnight as the warm front lifts north, am skeptical as to
just how quickly/if conditions return to vfr). Precipitation
will return again Tuesday, most likely after 15z as a cold
front moves through with sub-VFR conditions highly likely during
this time. Precipitation may linger through early Wednesday,
and a changeover to snow on Tuesday night is expected, with any
appreciable accums most likely for the mrb terminal.

High pressure will build in Wednesday, allowing for VFR
conditions to return by around or shortly after midday. Northwest winds
will increase and become gusty.

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


Small Craft Advisory this afternoon for mid Chesapeake Bay/lower tidal Potomac,
expanding northward tonight into tomorrow as low level stability
decreases and winds mix down a little more readily. After a
potential lull Tuesday, confidence is high on winds increasing
out of the northwest behind the front Tuesday night into

Winds likely drop below Small Craft Advisory levels by Thursday as high pressure
builds in. Friday, some uncertainty exists as low pressure may
lift northward into the region.


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.



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