Ashburn, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

191
FXUS61 KLWX 180902
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
402 AM EST Sat Jan 18 2025

.SYNOPSIS...

A weak area of low pressure forming along an Arctic front will
pass through the area this evening. A second stronger area of
low pressure will pass south of the area Sunday afternoon.
Arctic high pressure will then build over the area Monday into
Tuesday with one or more waves of low pressure developing to the
south.

&&

.NEAR TERM /THROUGH TONIGHT/...

A weak wave of low pressure forming along an Arctic front will
bring some very light precip to the area today. Area remains in
the "warm" sector, relatively speaking, with temperatures
largely above freezing and steady southerly winds. Therefore,
precip today will be in the form of rain except for a rain/snow
mix at higher elevations. Precip will exit the area during the
afternoon east, but change to snow in mountains as Arctic
advances east.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...

Model guidance appear to have delayed somewhat the advance of
the Arctic air across the local area Sunday compared to recent
days with the Canadian model being the slowest model. Anyhow, a
second stronger area of low pressure will pass across southern
VA Sunday afternoon with the ECMWF indicating the low pressure
center passing across northern NC, GFS across southern VA, and
Canadian model across central VA. This will bring moderate
precip across the area Sunday, before exiting Sunday evening.
Limitations for a big snow storm are fast movement of this
system (i.e relatively short duration of precip 6-12 hours), and
lack of a closed upper air system. However, it looks like there
could be a 6-hr period, mainly 18Z Sun-00Z Mon where precip
rates could be quite heavy. Winter Storm Watches were upgraded
to Warnings where cold air will be locked in place, but expect
additional Advisories to be issued later today or tonight
further south where temps are more marginal/questionable.

Precip will exit early Sunday evening with very cold air
filtering in on brisk NW winds. Extreme Cold Watches remain in
effect and may need to be extended south and east.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...

Cold air continues to envelope the region Tuesday with a broad upper
trough encompassing most of the CONUS and high pressure building in
at the surface. High temperatures are expected to top out in the
teens to mid-20s outside of the mountains, with single digits in the
mountains. Low temperatures will range from near -10 in the
mountains to near +10 in far southern Maryland. While winds are
expected to lighten as high pressure builds in, it won`t take much
to bring apparent temperatures to near or just below zero Tuesday
night for much of the area. Apparent temperatures in along the
Alleghenies could even approach/exceed the -20 mark with continuing
NW gustiness. Similar conditions are expected Wednesday (though with
less cloud cover). An Extreme Cold Watch is in effect through
Thursday morning for the Alleghenies given the high confidence in
dangerous wind chills this far out. Further watches/advisories may
be added to the east later as we grow closer.

While the cold is the main story, there is also the potential for
snow Tuesday night into Wednesday morning, but there remains
uncertainty regarding the track of a progressive low just to our
south. As of now, the most likely areas to receive some snow are
upslope locations along the Alleghenies and possibly far southern
Maryland, with a large spread between these two areas. Given the
progressive nature of this low and how dry the air mass is,
accumulations are expected to be light at this time. Another shot of
quick snow is possible late in the week as an embedded shortwave
swings through, with similar uncertainties and a larger spread.
However, later in the extended would appear a more favorable pattern
with more available moisture. Temperatures are expected to warm into
the 30s (mountains 20s) by late week.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...

MVFR cigs today with spotty light rain. Then, snow on Sunday
with IFR conditions. Brisk NNW winds developing Sunday night
into Monday.

VFR conditions are expected Tuesday and Wednesday as high pressure
builds into the region. Cloudy skies Tuesday will gradually clear by
late Tuesday night/Wednesday morning. NW winds could gust to around
15 knots both days. Temperature wise, expect highs in the 20s both
days (or a bit cooler for MRB) and lows in the single digits. Wind
chills could approach or fall below zero both nights.

&&

.MARINE...

SCA conditions expected late Sunday into Tue morning. Freezing
Spray conditions also possible Monday into Tue morning.

SCA conditions could continue into Tuesday morning. NW winds are
then expected to diminish during the day Tuesday, but could approach
SCA criteria again Tuesday night/Wednesday morning over our southern
waters as low pressure passes to our south. With continued below
freezing conditions, freezing spray remains a concern.


&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory from 1 PM to 6 PM EST Sunday for MDZ008.
     Winter Storm Warning from 3 AM Sunday to 9 AM EST Monday for
     MDZ001.
     Extreme Cold Watch from late Sunday night through Thursday
     morning for MDZ001-501.
     Winter Storm Warning from 7 AM to 7 PM EST Sunday for
     MDZ003>006-502-507.
     Winter Storm Watch from late tonight through Sunday afternoon
     for MDZ501.
     Winter Storm Watch from Sunday morning through Sunday evening
     for MDZ503-505.
VA...Extreme Cold Watch from late Sunday night through Thursday
     morning for VAZ503.
     Winter Storm Warning from 7 AM to 7 PM EST Sunday for VAZ027-
     028-030-031-505-507.
     Winter Storm Watch from late tonight through Sunday afternoon
     for VAZ026-029-040-501-503.
     Winter Storm Watch from Sunday morning through Sunday evening
     for VAZ506-526.
WV...Winter Storm Warning from 3 AM Sunday to 9 AM EST Monday for
     WVZ501-505.
     Extreme Cold Watch from late Sunday night through Thursday
     morning for WVZ501-503-505.
     Winter Storm Warning from 7 AM to 7 PM EST Sunday for
     WVZ050>053-055.
     Winter Storm Watch from late tonight through Sunday afternoon
     for WVZ502>504-506.
MARINE...Small Craft Advisory from 1 PM to 6 PM EST Sunday for
     ANZ530>543.

&&

$$

SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...CAS
AVIATION...LFR/CAS
MARINE...LFR/CAS