Severe Thunderstorm Warning 309, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
311 PM EST Fri Dec 21 2018

.SYNOPSIS...Low pressure and its associated cold front will
cross the area late this evening. High pressure will return for
Saturday before an upper-level disturbance and a weak cold
front pass through Sunday. High pressure will build overhead
early next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

Showers will continue to increase in coverage into early evening especially
west of I-95 as deep low pressure and its associated cold front
cross the area . Isolated brief thunderstorms are also
possible. GLM data just picked up some lightning east of Dulles
Airport over Fairfax County. Main threat with these
showers/t-storms are expected to be gusty winds of 30-40 mph and
brief heavy rainfall. Showers will remain possible into the
early morning until upper trough axis crosses the area but we
should lose the thunderstorm threat by mid evening. Turning
colder and windy overnight due tightening pressure gradient and
strong pressure surge of up to 7mb/3hr. Snow will accumulate
over the higher elevs with a few inches likely. Winds could gust
up to about 45 mph at higher elevs and up to about 30-35 mph at
lower elevs.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...

Cooler and breezy/windy Saturday on NW winds behind deep low
pressure. Winds and snow should diminish by midday as subsidence
inversion strengthens and pressure gradient weakens.

Next low pressure system will cross the area Sunday afternoon
bringing the next chance of rain showers to the area and snow
showers to the mtns. Associated cdfnt crosses the area late Sun
evening with precip ending.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...

Overall, a very quiet stretch of weather is expected through the
long term period. By Monday morning, a shortwave will depart off the
Atlantic Coastline, and high pressure will move overhead in it's
wake for Monday and Tuesday. A weak shortwave embedded in
northwesterly flow aloft will pass to our north Tuesday Night. Some
very light precipitation can't be entirely ruled out as this feature
passes by , but the vast majority of both deterministic and ensemble
guidance keep us dry.

By Wednesday, a high amplitude trough will drop across portions of
the Desert Southwest. In response, a large-scale ridge will build
downstream across the eastern two-thirds of the CONUS. The presence
of this ridge, coupled with high pressure at the surface will lead
to dry conditions on both Wednesday and Thursday. Temperatures will
run near to slightly below normal, with highs in the low-mid
40s.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...

Showers and isolated thunderstorms through about 03Z, then gusty
NW winds up to 25-30kt behind frontal passage. Winds diminish
Saturday afternoon.

VFR conditions are expected at the terminals on Monday through
Thursday.

&&

.MARINE...

Gale Warning issued for the waters valid 06Z-16Z. Isolated
thunderstorms possible which may require SMWs.

SCA level winds will be possible in the wake of a departing cold
front on Monday. High pressure will build in for the middle of the
week, leading to light winds on the waters.

&&

.HYDROLOGY...

Threat of flooding now too localized to maintain a Flood Watch.
Please refer to River Flood Warnings for ongoing flooding along
the Potomac River.

&&

.TIDES/COASTAL FLOODING...

Coastal Flood Warnings were extended for Washington DC and St.
Marys as water continues to pile up on southerly winds. Water
levels begin to drop Saturday morning.

&&

.CLIMATE...

Rainfall totals continue to creep upward, with Baltimore MD and
Washington DC setting the annual record already. Here are the
current rankings for wettest year on record (through December
20th):

Washington DC area (DCA)
1. 64.58 inches (2018)
2. 61.33 inches (1889)

Weather records for the Washington DC area have been kept at
what is now Ronald Reagan Washington National Airport (DCA)
since 1945. Precipitation records observed downtown extend the
period of record back to 1871.

Baltimore MD area (BWI)
1. 69.60 inches (2018)
2. 62.66 inches (2003)

Weather records for the Baltimore MD area have been kept at
what is now Baltimore-Washington International Thurgood Marshall
Airport (BWI) since 1950. Precipitation records observed
downtown extend the period of record back to 1871.

Dulles VA area (IAD)
1. 65.67 inches (2003)
2. 64.72 inches (2018)
3. 59.05 inches (1972)

Weather records have been kept at what is now Washington Dulles
International Airport (IAD) since 1960.

NOTE: All climate data are considered preliminary until
reviewed by the National Centers for Environmental Information
(NCEI).

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Warning until 10 AM EST Saturday for DCZ001.
MD...Coastal Flood Warning until 7 PM EST this evening for MDZ014.
     Coastal Flood Advisory from 7 PM to 11 PM EST this evening for
     MDZ014.
     Coastal Flood Advisory until 4 AM EST Saturday for MDZ016-018.
     Coastal Flood Warning until 3 AM EST Saturday for MDZ017.
     Coastal Flood Advisory from 6 PM this evening to midnight EST
     tonight for MDZ508.
     Coastal Flood Advisory until 11 PM EST this evening for MDZ011.
VA...Wind Advisory from 7 PM this evening to noon EST Saturday for
     VAZ025-026-504-507-508.
     Coastal Flood Advisory until 4 AM EST Saturday for VAZ057.
     Winter Weather Advisory from 7 PM this evening to 10 AM EST
     Saturday for VAZ503.
     Coastal Flood Advisory until 10 PM EST this evening for VAZ054.
WV...Wind Advisory from 7 PM this evening to noon EST Saturday for
     WVZ506.
     Winter Weather Advisory from 7 PM this evening to 10 AM EST
     Saturday for WVZ501-505.
MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ530>543.
     Gale Warning from 1 AM to 11 AM EST Saturday for ANZ530>543.

&&

SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...KJP
AVIATION...LFR/KJP
MARINE...LFR/KJP
HYDROLOGY...LWX
TIDES/COASTAL FLOODING...
CLIMATE...LWX

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