Forecast Discussion
396
FXUS61 KLWX 210223
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
923 PM EST Wed Nov 20 2024
.SYNOPSIS...
A strong cold front will move through the area overnight. An
upper level low will circulate overhead through Saturday. An
area of low pressure will track to our northwest through the
Great Lakes early next week. High pressure will build back in
for the middle of the week.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A strong cold front is currently aligned from north to south
from central Maryland to eastern Virginia. Ahead of it and along
it is a broad area of heavy showers and embedded thunderstorms.
As this area of convection passes across Northeast Maryland,
southern Maryland, and the Chesapeake Bay over the next hour or
two, it will bring most areas a quick one-half to one inch of
rain. Occasional lightning strikes, and wind gusts of 45 to 55
mph are also noted to accompany this band of convection.
Winds behind the front and this convection will remain gusty out
of the west-northwest to northwest along with lingering showers
or drizzle. At higher elevations of western Maryland and eastern
West Virginia, rain showers are beginning to mix with and/or
change over to all snow and should continue into much of the
night. Wind Advisories are in effect across the northern half of
the region with Winter Storm Warning and Winter Weather
Advisories in the western mountains and over the Blue Ridge.
A Special Weather Statement also remains in effect for a little
while before expiring later this evening.
Conditions will dry out during the second half of the overnight
east of the mountains, but strong cold advection will continue.
Low temperatures will be in the upper 30s to near 40 for most,
with low to mid 30s in the mountains.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
Previous discussion...
Conditions should start to dry out tomorrow, but the boundary
layer will destabilize by the late morning to early afternoon
hours as the core of the upper low approaches from the west.
Snow showers will form within upslope flow to the west of the
Alleghenies during the late morning hours, with additional
showers forming to the east of the mountains during the
afternoon hours. Coverage of showers should remain fairly low to
the east of the mountains, with the bulk of the day remaining
dry. Temperatures will climb up into the 40s to near 50 by
afternoon, but temperatures will decrease rapidly with height as
the upper low moves overhead, so these showers would likely
occur as a mix of rain and graupel to the east of the mountains.
The snow shower activity along and west of the Allegheny Front
will be intermittent, but squally in nature, with multiple short
duration heavy bursts of snow and then dry periods (and even
some sun possible) in between. The snow in the mountains will be
rather light and fluffy tomorrow, as instability extends up
into the dendritic snow growth zone. A few inches will be
possible by tomorrow evening. There will be a bit of a lull in
the activity tomorrow night once daytime heating and resultant
boundary layer instability is lost. Light snow may continue on
and off through the night, and a couple of additional inches may
be possible by Friday morning.
Another disturbance embedded within the much larger upper level
low will rotate in from the north on Friday. The steadiest and
likely heaviest snow in the mountains will occur late Friday
morning through Friday evening as low-level warm advection
overlaps upslope flow intersecting the terrain. Snowfall rates
may approach an inch per hour at times Friday afternoon. The
snow on Friday will be a wetter snow as the column starts to
warm.
Some snow may also occur to the east of the mountains Friday
morning, with the first snowflakes of the year possible in the
DC and Baltimore metro areas. Temperatures will likely be too
warm for accumulations along the I-95 corridor, but some minor
accumulations may be possible along Parr`s ridge in north-
central Maryland and in the Catoctins. Any snow to the east of
the mountains should switch over to rain during the afternoon as
temperatures warm.
Precipitation will continue in the mountains through Friday
night. As temperatures continue to warm, some of the lower
elevations in the mountains may switch over to rain before
ending, but the highest elevations (above 2500 feet) should
stay all snow through the night. By the time all is said and
done, 6-12 inches is expected along and west of the Allegheny
Front, with isolated totals of 12-18 inches possible along the
highest ridgetops. Winter Storm Warnings are in effect for
Garrett, western Grant, western Pendleton and western Highland
counties starting at 10 AM tomorrow. Those Warnings continue
through Friday night. A Winter Weather Advisory is also in
effect for western Mineral county from 10 AM tomorrow through 10
PM tomorrow night.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Snow showers will begin to taper off after daybreak on Saturday and
transition to more of a rain/snow mix, and perhaps even over to
freezing drizzle at the highest elevations. Not expecting much
additional snow accumulation beyond early Saturday morning, but
could see at least a few hundredths of an inch of ice accretion on
the ridges. By Saturday afternoon the shortwave will pivot east and
heights begin to rise. This will result in pretty rapid drying out
into the afternoon/evening. Elsewhere, Saturday remains dry with
gusty northwesterly winds of around 25 to 35 mph, with gusts up to
40 mph, mainly on the ridges and over the open waters.
Sunday into Monday look to remain mostly dry as high pressure
returns to the region. Sunday will see highs around the mid 50s,
then increasing to around the low 60s on Monday.
Meanwhile, low pressure over the central U.S will track north and
east into the Great Lakes late Monday into Tuesday. This will send
another front into our region for the middle of next week. As it
stands now, the front looks to stall somewhere in the vicinity of
our region Tuesday into Wednesday. This will lead to increased
precipitation chances during this time. Active weather continues
through the extended could potentially continue into Thanksgiving
and towards next weekend.
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
A strong cold front approaching the I-95 corridor will move east
overnight and across the Chesapeake Bay. Winds have or will
shift to a west-northwest to northwest direction and gust over
40 knots. Heavy rain and embedded thunder will lower ceilings to
LIFR or IFR but visibility should be MVFR to VFR. Showers may
linger for a few hours behind the front before conditions dry
out during the second half of the night. Low level wind shear
will also be possible immediately in the wake of the front this
evening.
Previous discussion...
Prevailing VFR conditions are expected tomorrow. A few mixed
rain/snow/graupel showers may be possible tomorrow afternoon,
but the vast majority of the time should remain dry. Winds will
remain out of the west. Mixed rain and snow may potentially
impact some of the terminals Friday morning. Any precipitation
would change over to plain rain by Friday afternoon.
Gusty WNW winds around 20 to 30 kts will be the main threat to the
terminals on Saturday at the terminals. Otherwise, VFR conditions
are expected as we transition into a period of high pressure that
will then continue into Sunday. Winds turn more westerly on Sunday
and will be around 10 to 20 kts.
&&
.MARINE...
A cold front will cross the Potomac River and Chesapeake Bay
later this evening and overnight. Winds will rapidly shift from
southeast to west-northwest or northwest and gust over 40 knots
in many places. Gale force winds will be imminent in many waters
with a few possible Storm force gusts over the widest waters.
Special Marine Warnings are currently in effect for most of the
northern and central Chesapeake Bay waters and Potomac Basin.
Some thunder may be possible in association with the squall
line. Winds gradually decrease late tonight into tomorrow
morning, but Small Craft Advisory conditions will continue
through Thursday and Friday. Gusts may near low- end Gale levels
Friday afternoon into Friday night.
In the wake of a strong cold front, high-end SCAs will continue
through much of the day Saturday. Gale conditions may even briefly
be possible early Saturday.
Winds taper off into Sunday, but SCAs seem likely to continue,
albeit closer to the low end.
&&
.TIDES/COASTAL FLOODING...
Minor coastal flooding is possible at the more sensitive tidal
sites like DC SW Waterfront with the tide cycle this evening.
Water levels will decrease tonight through the upcoming weekend
as winds turn westerly.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Wind Advisory until 1 AM EST Thursday for DCZ001.
MD...Gale Warning until 6 AM EST Thursday for MDZ008.
Wind Advisory until 1 AM EST Thursday for MDZ001-004>006-008-
011-013-014-016>018-501-503>508.
Winter Storm Warning from 10 AM Thursday to midnight EST
Friday night for MDZ001.
Wind Advisory until 11 PM EST this evening for MDZ003-502.
Winter Weather Advisory from 10 AM to 10 PM EST Thursday for
MDZ501.
VA...Wind Advisory until 1 AM EST Thursday for VAZ040-053-054-501-
503-505>508-526-527.
Wind Advisory until 11 PM EST this evening for VAZ027>031.
Winter Storm Warning from 10 AM Thursday to 6 AM EST Saturday
for VAZ503.
WV...Wind Advisory until 1 AM EST Thursday for WVZ501-503-505.
Wind Advisory until 11 PM EST this evening for WVZ050>053-055-
502-504.
Winter Weather Advisory from 10 AM to 10 PM EST Thursday for
WVZ503.
Winter Storm Warning from 10 AM Thursday to 6 AM EST Saturday
for WVZ501-505.
MARINE...Gale Warning until 6 AM EST Thursday for ANZ530>543.
Wind Advisory until 1 AM EST Thursday for ANZ530.
&&
$$
SYNOPSIS...KJP
NEAR TERM...KLW/KJP
SHORT TERM...KJP
LONG TERM...CJL
AVIATION...KLW/CJL
MARINE...KLW/CJL/99
TIDES/COASTAL FLOODING...KLW
