Germantown, Maryland 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

190
FXUS61 KLWX 180237
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
937 PM EST Fri Jan 17 2025

.SYNOPSIS...
An arctic front will cross the area west to east Saturday. A low
pressure system will form along this boundary as the boundary
stalls just to our southeast Saturday night into Sunday. A
stronger low will develop over the Tennessee River Valley then
move northeast toward southern New England by Monday morning.
Arctic high pressure will follow for much of next week as one or
more waves of low pressure develop to the south.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
High pressure to our east and southeast will allow for a
southerly wind to develop along with increasing clouds
overnight. Temperatures should slowly rise around daybreak
Saturday. Lows will drop to the upper 20s to lower 30s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
An increase in a southerly flow Saturday will set the stage for
scattered to numerous rain showers. There could be a light snow
or a wintry mix to start the day Saturday in the morning before
transitioning over to mainly rain through the rest of the day.

Previous discussion...
An Arctic Front will reside in the vicinity of the Mid-Atlantic
Saturday night into Sunday as kind of the middle piece of this
leader-follower system. The leader system that impacted the area
Saturday will leave the trailing cold front behind, but also bring
the cold for the Sunday event. For the follower - the potential snow
event across the area Sunday - models historically have issues
with these set-ups. This case is no different with considerable
differences in model guidance just ~40 hours out from the onset
of precipitation.

Synoptically, an UL trough will move eastward into the Ohio
Valley Saturday night. A piece of energy will move ahead of this
feature being one of the parts of this storm. The region will
reside in the left exit region of a ~100 kt H5 jet. This is
favorable for upward motion, as indicated by several methods
including the long Q-vectors. Good agreement in FGEN bands
across the area as well. It should be noted the differences
between global models/ensembles. The CMCE/GEFS are notably more
bullish than the EPS. Regional models split differences among
themselves. Of note, the AI EURO has been consistent with
0.2-0.4" of QPF across the area for several days. This model
tends to overdo the broader field of QPF at further lead times,
but this signal is noteworthy based on latest verification
research.

Given the potential for 5" of snow (6" in the mountains), have
coordinated with neighboring offices and WPC in a Winter Storm Watch
for climo favored areas. Have concerns about mixing further
southeast towards the metros coupled with lower ratios. The current
snow forecast will likely change, so please monitor the latest
forecast for updates.

Upslope snow showers will persist through Sunday night across the
Alleghenies.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Low pressure will be exiting off the East Coast by early Monday
morning, with high pressure building in from the west. On
Monday, highs will range from the single digits out across the
Allegheny Front to 20s further east toward the metro areas.
Conditions should remain dry throughout the day with gusty winds
around 25 to 35 mph, especially during the afternoon hours. The
well amplified high pressure settled overhead will likely aid
in bringing well below normal temperatures across the area
(perhaps as low as 20 to 30 degrees below normal). This,
coupled with gusty northwest winds, will create bitterly cold
wind chills across the area. In particular, the Allegheny Front
zones are expected to get winds chills as low as negative 30
degrees late Sunday night through Thursday morning.

An Extreme Cold Watch is in effect across the Alleghenies for
the dangerously cold wind chills. Further east, additional cold
weather headlines may be needed considering wind chills below
zero are possible further east towards the I-95 corridor early
to mid next week. Dry conditions should prevail into Tuesday
before a coastal system may bring another chance of wintry
precipitation. There has been a northward shift of a few hundred
miles in the guidance with this system over the last couple of
days. There is still a lot of uncertainty with this particular
system. Another system may impact the area Thursday into Friday
that may bring additional wintry precipitation chances. Trends
in teleconnections (AO/NAO/MJO/EPO/PNA) broadly favor the
second half of next week for potential wintry precipitation as
the pattern begins to shift from very cold and dry to warmer and
potentially wetter.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Previous discussion...
Clouds will increase overnight into Saturday morning as a cold
front approaches from the west. Increasing southerly flow at a
few thousand feet AGL could result in marginal LLWS depending on
how well wind mixes late tonight through Saturday morning. Sub-
VFR CIGs and intermittent light showers are anticipated
generally 12Z Saturday through 00Z Sunday. Brief visibility
drops or light wintry mixed precipitation are also possible, but
plain rain is expected after ~18Z at all terminals. Any wintry
precipitation would likely be non- accumulating on runways, but
could still be falling out of the sky at times.

Winds will remain southerly through Saturday, then shift to
northwesterly Saturday night after the front crosses. Some guidance
hints at lingering low clouds/fog depending on where the front
stalls and the exact strength of low-level winds/dry air advection.
Uncertainty increases substantially heading into Sunday and Sunday
night as another wave of low pressure approaches from the Tennessee
River Valley. The exact track and strength of this low are still
very much in question given the latest suites of guidance, with
light precipitation (likely in the form of snow) and MVFR conditions
to steadier snow and L/IFR conditions, to a mix or even rain near I-
95 with intermittent MVFR/IFR conditions (and heavy snow NW) all
within the realm of possibility. The forecast will need to be
monitored closely to fine tune specific impacts from early Sunday
morning through Sunday evening.

VFR conditions are expected Monday into Tuesday with gusty northwest
winds 20 to 30 knots. Bitterly cold wind chills are expected Monday
and Tuesday, potentially getting below zero at many of the terminals.

&&

.MARINE...
SCA conditions are likely into Saturday morning before the
gradient weakens, and low- level stability strengthens with
warmer air moving over colder water. Scattered showers are
anticipated Saturday. Winds will turn northwest Saturday night
as a front crosses and slows. Uncertainty increases
substantially heading into Sunday as another wave of low
pressure moves toward the Mid-Atlantic from the Tennessee River
Valley. Depending on the exact track and strength of this low
(which are still very much in question), SCA conditions are
possible as early as Sunday morning; but, SCA conditions could
hold off until Sunday night when stronger cold advection/north
flow takes hold. A mix of precipitation is likely on Sunday,
with the exact type and intensity also depending on the eventual
evolution of the low.

SCA conditions are expected Monday into Tuesday morning. Freezing
spray is also becoming increasingly likely given the new snow and
already frozen parts of the waters as well as very cold temps and
gusty winds.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Winter Storm Watch from late Saturday night through Monday
     morning for MDZ001.
     Extreme Cold Watch from late Sunday night through Thursday
     morning for MDZ001-501.
     Winter Storm Watch from Sunday morning through Sunday evening
     for MDZ003>006-503-505-507.
     Winter Storm Watch from late Saturday night through Sunday
     afternoon for MDZ501-502.
VA...Extreme Cold Watch from late Sunday night through Thursday
     morning for VAZ503.
     Winter Storm Watch from Sunday morning through Sunday evening
     for VAZ505-506-526.
     Winter Storm Watch from late Saturday night through Sunday
     afternoon for VAZ026>031-040-501-503-507.
WV...Winter Storm Watch from late Saturday night through Monday
     morning for WVZ501-505.
     Extreme Cold Watch from late Sunday night through Thursday
     morning for WVZ501-503-505.
     Winter Storm Watch from late Saturday night through Sunday
     afternoon for WVZ050>053-055-502>504-506.
MARINE...Small Craft Advisory until 4 AM EST Saturday for ANZ531>534-
     540-541-543.

&&

$$

SYNOPSIS...DHOF
NEAR TERM...KLW/DHOF
SHORT TERM...CPB
LONG TERM...ADM
AVIATION...KLW/ADM
MARINE...KLW/ADM