275
FXUS61 KLWX 221431
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
931 AM EST Fri Nov 22 2024

.SYNOPSIS...
Chilly temperatures, accumulating mountain snow, and windy
conditions look to continue through tonight as low pressure meanders
across the northern Mid-Atlantic region. The upper-level low
will kick off the New England coast and toward the Canadian
Maritimes Saturday allowing high pressure to briefly return for
the latter half of the weekend. Another front pushes through the
region Monday with high pressure Tuesday into Wednesday. A more
potent front and low pressure system look to arrive for the
Thanksgiving holiday period.

&&

.NEAR TERM /THROUGH TONIGHT/...
A Blizzard Warning has been issued for western Grant and western
Pendleton Counties due to the expectation of persistent visibility
below 1/4 mile, frequent wind gusts over 35 mph, and heavy
falling and blowing snow. Travel will be very difficult to
impossible in these areas. Near blizzard conditions are possible
over Garrett County MD and northwestern Highland County VA.

Otherwise, Winter Storm Warnings remain in effect across the
Allegheny Front, with Winter Weather Advisories for western
Mineral/extreme western Allegany counties through tonight.
Accumulating upslope snow will lead to continued travel
disruptions, especially along the I-68 and US-219 corridors.

Upper-level low pressure will meander around the northern Mid-
Atlantic today before slowly kicking toward the New England
coast late tonight into early Saturday morning. A strong piece
of shortwave energy will pivot around the low later this morning
and into the afternoon hours delivering a reinforcing shot of
cold air (H850 temps running -2-6 degrees C), gusty winds, and
an enhanced period of upslope mountain snow.

The steadiest and heaviest upslope mountain snow shower activity
looks to occur later this morning through the early evening hours.
This is when the strongest piece of shortwave energy pivots through
as the cutoff upper low progresses north and east toward New
England. Latest deterministic and ensemble guidance continues to
advertise snowfall rates of 1-2"/hr with persistent banding/squalls
working over the warning/advisory areas. Snowfall accumulations so
far as of 3AM this morning range between 1 to 4 inches across the
western slopes of the Allegheny Mountains. An additional 6 to 12
inches of snow is forecast today through Saturday morning with
locally heavier amounts above 3000 feet. Storm total snow when it`s
all said and done, will range between 12-18 inches for locations
above 2500 feet with 2 to 6 inches at elevations above 1500 feet
(i.e Frostburg/Cumberland, MD south toward Keyser/Franklin, WV).

Outside of the significant snow accumulations, blowing and drifting
will be a problem. Brief whiteout conditions are expected at times
over the warning and advisory locations as winds increase this
afternoon into Saturday morning with the shortwave pivoting through.
Gusts up to 50 mph are likely over the higher ridges with 30 to 40
mph gusts in the high valley floors below. This will yield wind
chills in the teens and 20s across the mountains today into
Saturday. Locations above 3500 feet will likely see wind chills in
the single digits.

Areas east of the Alleghenies, will also pick up their first
snowflakes of the season. A band of rain/snow showers look to push
south by mid-morning into late afternoon. The highest confidence for
snow appears to be along and north of I-66/US-50 with temperatures
hovering between 32 and 37 degrees. Locations such as the Catoctins
and Parr`s Ridge in north-central MD could see as much as 1 to 3
inches of snow today as the deformation axis wraps around the low
pivoting nearby. Most other locations across central Maryland into
northeast Maryland near the PA/MD line will receive a coating to as
much as 2 inches. Highest confidence for accumulations on grassy
surfaces will be from a line that extends from northwest
Cecil/Harford counties back west toward northern
Baltimore/Carroll/Frederick counties. Wind gusts of 25 to 35 mph are
expected later this afternoon into tonight. Wind Advisories are in
effect for the crest of the Blue Ridge and downslope areas of the
Potomac Highlands for gusts up to 50 mph at times.

High temperatures will range from below freezing over the mountains
to mid to upper 40s and low 50s further east. Lows tonight into
Saturday morning will fall into the 30s and 40s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Snow shower activity will begin to decrease Saturday morning into
Saturday midday as the shortwave trough kicks east and the upper
level low exits off coastal New England. A period of freezing rain
or drizzle is possible early to mid Saturday morning along the
higher elevations of the Allegheny Front as deeper moisture vacates
halting ice crystal formation. A few one hundredths of ice
accumulation are expected with up to a tenth of an inch toward Big
Savage Mountain and Spruce Knob. By Saturday afternoon, the
shortwave will pivot east allowing heights to rise. Meanwhile,
surface high pressure will slide in from the Tennessee River Valley
and central Appalachians allowing conditions to slowly improve.

With incoming high pressure to the south and a departing
shortwave/upper level low pressure system to the northeast expect
windy conditions to continue. Sustained northwesterly winds of
around 20 to 30 mph are expected, with gusts up to 40 mph, mainly on
the ridges and over the open waters.

Temperatures warm back above freezing in the mountains Saturday with
upper 40s and low to mid 50s further east toward the metro areas.
Lows Saturday night will fall back into the mid to upper 30s outside
the mountains. High pressure briefly returns to the area Sunday
before pushing off the southeast U.S coast Monday. Dry
conditions are expected as a result along with moderating
temperatures. Highs Sunday will push into the low to mid 50s
with 40s over the mountains. Lows Sunday night will fall into
30s.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
On Monday, weak ridging briefly builds in aloft as one upper trough
exits to the east and another approaches from the west. Mostly dry
conditions are expected as a result, but as the second trough moves
in, some upslope precip (in the form of rain, likely too warm for
snow) will be possible, with the greatest chances for the
Alleghenies Monday night into Tuesday morning. Subsidence behind the
upper trough and surface high pressure will likely yield dry
conditions Tuesday into Wednesday.

The latter half of the week then demands attention, as guidance
consistently suggests a low developing over the central Plains and
tracking east to the Mid-Atlantic, and potentially along the coast as
a Nor`easter. The timing and strength of this low is still highly
uncertain this far out, but another round of snow is possible for
the Alleghenies, and possibly east of the mountains as well.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
Prevailing VFR conditions are expected at most terminals
through Sunday. Some brief periods of MVFR are possible,
especially later this morning into the late evening as a potent
piece of upper-level energy pivots through. Brief IFR is even
possible at KBWI/KMTN. A few showers with perhaps a few wet
snowflakes or even a little graupel are possible at KBWI, KMRB,
KHGR, KOKV, KIAD, and KFDK this morning into this afternoon
(16Z-21Z/10am-4pm). Any frozen precipitation will quickly
change to rain later this afternoon before dissipating tonight.
Significant snow accumulations will remain west of KCBE.

Wind will be the biggest impact to aviation today through Saturday.
Expect sustained speeds of 10 to 20 kts during the day and nighttime
hours with gusts 20 to 30 kts each afternoon/evening. Highest winds
look to occur this evening into early Saturday morning. West to
northwest winds will decrease slowly Sunday with gusts running 15 to
20 kts.

VFR conditions are expected Monday and Tuesday. Southerly winds
around 5-10 knots on Monday will gradually increase and then turn
WNW behind a mostly dry frontal passage on Tuesday. Gusty winds 10-
15 knots are possible Tuesday afternoon. Sub-VFR conditions remain
possible for middle of next week as another low pressure system
impacts the region.

&&

.MARINE...
High end SCAs are expected to continue through Saturday night with
frequent gusts of 20 to 30 kts expected across all waters. Gale
force gusts are likely over the open waters of the bay and lower
tidal Potomac late this afternoon into early Saturday morning as
winds surge behind a departing shortwave trough. Winds are slow to
taper Sunday with SCAs likely continue across most of the waters
with gusts up to 20 kts.

Winds over the waters become southerly on Monday, with the potential
for southerly channeling in the afternoon. Winds increase and turn
WSW Monday night as a dry cold front approaches, and could reach SCA
criteria. SCA conditions could continue into Tuesday with gusty WNW
winds behind the front.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Winter Storm Warning until 3 AM EST Saturday for MDZ001.
     Winter Weather Advisory until 6 PM EST this evening for MDZ501.
VA...Winter Storm Warning until 6 AM EST Saturday for VAZ503.
     Wind Advisory until 6 AM EST Saturday for VAZ503-504-507-508.
WV...Winter Weather Advisory until 6 PM EST this evening for WVZ503.
     Wind Advisory until 6 AM EST Saturday for WVZ506.
     Blizzard Warning until 6 AM EST Saturday for WVZ501-505.
MARINE...Small Craft Advisory until 7 PM EST Saturday for ANZ530-535-
     536-538.
     Small Craft Advisory until 4 PM EST this afternoon for
     ANZ531>534-537-539>543.
     Small Craft Advisory from 7 AM to 7 PM EST Saturday for
     ANZ531>534-537-539>543.
     Gale Warning from 4 PM this afternoon to 7 AM EST Saturday for
     ANZ531>534-537-539>543.

&&

$$

SYNOPSIS...DHOF/EST
NEAR TERM...DHOF/EST
SHORT TERM...DHOF/EST
LONG TERM...CAS
AVIATION...DHOF/CAS
MARINE...DHOF/CAS/EST