Potomac, Maryland 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

945
FXUS61 KLWX 040159 AAA
AFDLWX

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
859 PM EST Tue Dec 3 2024

.SYNOPSIS...
Well below normal temperatures will continue through the end of
the week. A potent area of low pressure will drag a strong cold
front across the area Wednesday night into Thursday. This
brings mountain snow, strong gusty winds, and colder
temperatures to the area. High pressure returns Friday into the
weekend, which will bring a gradual warming trend back towards
normal temperatures.

&&

.NEAR TERM /THROUGH WEDNESDAY/...

Clear and cold overnight with diminishing winds. Low clouds over
the mountains will gradually dissipate overnight, but there will
be some increase in high clouds overnight.

Previous afd...

Winds will drop off markedly overnight as high pressure moves
overhead. With clear skies accompanying the light winds, still
setting up to be the coldest night of this stretch with
widespread lows in the teens to low 20s. Rural portions of the
VA Piedmont and sheltered valleys west of the Blue Ridge likely
drop into the low to mid teens tonight.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
The aforementioned upper-level ridge will be overhead on Wednesday
while high pressure pushes offshore. This will result in temps in
the low to mid 40s (30s in the mountains). Light south-southwest
winds in the morning increase through the day.

Looking upstream, a powerful upper-level trough digs south out of
central Canada late in the day into Wednesday evening. The surface
reflection of this upper-level system will push a very strong cold
front through the region Wednesday night into Thursday. The
increasing pressure gradient across the Mid-Atlantic becomes
noticeable by Wednesday evening as WAA allows stronger winds aloft
to begin mixing down to the surface.

South-southwest winds sustained at 15-20 mph and gusting 25-30
mph are expected Wednesday evening into Wednesday night.
Stronger winds are anticipated for the mountains, where gusts
of 40-50 mph are expected Wednesday night. Even stronger winds
arrive after the front passes, with Wind Advisories and High
Wind Watches/Warnings likely needed for parts of the area for
Thursday. One caveat is that the winds may not quite be aligned
with height, meaning there is about a 20 to 30 degree directional
change from the surface to about 5 km AGL. This could prevent
those strongest values from making it down. Peak gusts of 40-45
mph, with up to 55-60 mph along the highest ridges of the
Alleghenies and Blue Ridge/ Catoctin Mountains are most likely
through early Thursday evening.

Precipitation begins to move into the area late Wednesday evening,
ahead of a rapidly advancing cold front. It likely is snow in the
mountains and a mix of rain/snow to the east, at least at the onset.
The models indicate strong CAA in the 850-925 mb layer Wednesday
night, that should allow precipitation to quickly transition to all
snow for most of the areas along/west of the Blue Ridge after 12AM
to 3AM Thursday morning. To the east of the Blue Ridge, temperatures
are much more marginal, likely to be in the mid to upper 30s,
with near freezing temps between US-15 and the Blue Ridge. The
exact temperature will be critical for any potential impacts
from any light accumulating snowfall Thursday morning.

Also, given the gusty to windy downslope conditions that
quickly develop early Thursday morning, that will help keeps
temps from dropping too much. At the very least, rain/snow
showers probably make their way to the I-95 corridor. The
forecast maintains very light accumulations all the way to the
metro areas. Thinking that with such a powerful front and upper-
level forcing, there will be heavy snow showers/squalls
embedded within the upslope snow; east of the mountains, a line
of snow showers is possible. These could cause issues on roadways
due to reduced visibility, gusty winds, and some slick spots.

In the mountains, blizzard conditions are becoming likely for most
areas along and west of the Allegheny Front. Very cold air and
a deep moisture connection to the Great Lakes will set the stage
for a potent snow squall event along the Allegheny Front.
Forecast snow amounts between Wednesday night and Thursday
morning are between 4 and 6 inches with potentially higher
amounts up to around 9 inches along the western-facing slopes
above 2500 feet. In most of the Alleghenies, winds likely gust
well above 35-40 mph. With an air mass this cold, the
snow/liquid ratios are going to be very high, leading to a fine,
powdery snow. This paired with the aforementioned wind gusts
could lead to whiteout conditions at times. Treacherous travel
conditions are likely in the mountains Thursday morning. Even
after snow ends, the blowing snow will make travel difficult at
best through Thursday night.

Highs on Thursday afternoon outside of the mountains should be in
the 30s for most, with sunny conditions returning by early
afternoon. Strong winds continuing throughout the day advect in
colder air, meaning we are not really going to see "high
temperatures" during the afternoon given wind chills in the 20s
for most (single digits in the mountains).

As we move into Thursday night, colder air rushes into the
region resulting in lows in the 20s (teens in the mountains).
Winds remain quite strong even overnight, so wind chills are
going to be the coldest of the season thus far. For areas east
of the Blue Ridge, wind chills will drop into the teens. Further
west, wind chills drop into the single digits along and west of
the Blue Ridge, and even well into the negative single digits
along the ridges above 2500 feet. Cold Weather headlines are
possible in the mountains during this time. Given the
possibility of power outages from the strong winds, it is
important to make preparations now ahead of this event and be
prepared to find a way to stay warm.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
A broad trough of low pressure across the eastern half of the U.S.
will linger Friday and Saturday. A strong surface high will build
eastward across the region. This high will help to continue to
circulate cold air from the northwest into the region Friday and
Saturday. Dry conditions both days with exception to some snow
showers in the mountains early Friday. Temperatures both days will
be below average by about 15 degrees. Highs in the upper 30s to near
40 both days. Lows near 20 to lower 20s both nights.

The high will move to the East Coast as the trough of low pressure
flattens and shifts to the east as well. A southerly flow is
expected to develop Sunday and Monday to allow for our temperatures
to modify to near average to slightly above average both days. Some
rain could move into our western zones Sunday night and early
Monday, before spreading east across the rest of the region through
the day Monday. Highs Sunday upper 40s to lower 50s. Highs Monday
middle 50s.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions are expected through Wednesday. Winds then taper
off overnight as high pressure moves overhead and eventually
offshore. This will turn winds out of the S/SW heading into
Wednesday.

A strong area of low pressure approaches the area late Wednesday
into Thursday, causing winds to increase once again, with gusts
of 20-25 knots out of the S/SW likely Wednesday afternoon into
Wednesday night.

A significant wind surge comes along and behind a cold front
into Thursday morning. Winds will quickly shift out of the W/NW
between 09z and 13z Thursday with gusts to around 35 to 45
knots. Some snow is also possible on Thursday morning at all
terminals, especially at MRB, IAD, DCA, BWI, and MTN. CHO may be
a bit too far south to get any snow, but can`t completely rule
it out. There are even some indications that some streamers
could even drop some brief heavier snow in isolated spots.
Should one of these move over a terminal, it could certainly
result in issues with VSBY and runway conditions, albeit
briefly.

VFR conditions through the period. Winds northwest 10 to 15 knots
gusts up to 25 knots Friday, diminishing Friday night. Winds
becoming southwest 5 to 10 knots Saturday.

&&

.MARINE...
Have upgraded the Gale Watches to Gale Warnings for Wednesday
night into Thursday.

Gusty northwest winds are expected to continue across all the waters
through this evening before tapering off overnight as high
pressure approaches. Small Craft Advisories are in effect for
all the waters through the evening.

Winds drop below SCA conditions for a brief time period Wednesday
morning, then begin to increase substantially on Wednesday
afternoon as a strong area of low pressure approaches the
region. SCA conditions begin again Wednesday afternoon, with
south-southwest gusts of 20-25 knots likely, then increasing to
25-30 knots over most of the waters Wednesday night. Some gusts
to near gale force, around 35 knots, are likely over the open
waters of the Chesapeake Bay. Still think the best chance for
gale-force winds comes on Thursday as winds turn out of the NW
as cold air rushes in behind the aforementioned cold front. SCAs
will certainly be needed into Thursday night, but still not
sure if gale conditions continue that long. For that reason,
currently ending the Gale Warning at 7PM Thursday.

Small Craft Advisories likely Friday into Friday evening. No
marine hazards expected overnight Friday through Saturday night.
Winds northwest 15 to 20 knots gusts 25 to 30 knots Friday and
Friday evening. Winds becoming southwest around 10 knots gusts
15 knots Saturday and Saturday night.

&&

.TIDES/COASTAL FLOODING...
The main period of interest will be Wednesday evening into Thursday
as a powerful cold front pushes across the area. Expect a marked
increase in water levels ahead of this system. This places a few of
the more sensitive locations into Action around the time of high
tide. In the wake of this boundary, a blustery westerly wind will
quickly lower water levels. Further drops are possible on Friday as
winds turn more northwesterly. During this phase on Thursday and
Friday, there is some potential for blowout tides.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until 10 PM EST this evening for MDZ008.
     Small Craft Advisory from 11 AM Wednesday to 6 AM EST Thursday
     for MDZ008.
     Gale Warning from 6 AM to 7 PM EST Thursday for MDZ008.
     Winter Storm Watch from Wednesday evening through Thursday
     afternoon for MDZ001.
VA...None.
WV...Winter Storm Watch from Wednesday evening through Thursday
     afternoon for WVZ501-505.
MARINE...Small Craft Advisory until 10 PM EST this evening for
     ANZ530>532-538>540.
     Small Craft Advisory from 11 AM Wednesday to 6 AM EST Thursday
     for ANZ530-531-535-536-538-539-542.
     Gale Warning from 6 AM to 7 PM EST Thursday for ANZ530-531-535-
     536-538-539-542.
     Small Craft Advisory from 11 AM to 6 PM EST Wednesday for
     ANZ532>534-537-540-541-543.
     Gale Warning from 6 PM Wednesday to 7 PM EST Thursday for
     ANZ532>534-537-540-541-543.
     Small Craft Advisory until 3 AM EST Wednesday for ANZ533-534-
     537-541>543.

&&

$$

SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...DHOF/CJL/KRR
LONG TERM...KLW
AVIATION...LFR/KLW
MARINE...LFR/KLW
TIDES/COASTAL FLOODING...LWX