Reston, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

854
FXUS61 KLWX 220212
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
912 PM EST Sat Dec 21 2024

.SYNOPSIS...
Strong Canadian high pressure will build in through Monday,
with dry and very cold conditions. A weak low pressure system
will approach Monday night into Tuesday. High pressure will
build north of the area Wednesday.

&&

.NEAR TERM /UNTIL 7 AM SUNDAY MORNING/...
Longwave troughing currently extends from the Canadian
Maritimes down along the Eastern Seaboard. Northwesterly flow
within this configuration has continued to spawn lake-enhanced
snow showers off Lake Erie. Given high Froude numbers, a number
of these bands have been able to cross the terrain and spill
over the Alleghenies. While the appearance of such echoes are
not terribly impressive on radar, much of this activity is
likely focusing underneath the beam. Traffic cameras noted some
snow-covered roads across portions of Garrett County. A Winter
Weather Advisory continues until 10 PM, while likely being
allowed to expire given a downtick in activity into the night.
Otherwise, scattered flurries will persist farther east toward
the Shenandoah Valley and Blue Ridge Mountains.

High pressure will start building closer to the area tonight,
allowing winds to gradually diminish. However, the lingering
gradient won`t allow temperatures to completely crash, with lows
forecast in the mid teens to mid 20s. Wind chill values will be
in the teens for many areas, although northern Maryland could
dip into the single digits along with the higher elevations.
While the highest peaks could have values below 0, there doesn`t
appear to be a large enough area reaching -10 to warrant cold
advisories. Allegheny snow showers will taper to flurries
overnight. However, northwest flow will continue to allow clouds
to spill across the area.

&&

.SHORT TERM /7 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
Strong Canadian high continues its march across the Eastern
U.S. Sunday and Monday. Well below normal temperatures are
forecast Sunday as high struggle to reach freezing despite
increasing sun. A lingering wind of 5-10 mph will allow for wind
chill values to stay in the teens to mid 20s for much of the
day. Sunday night will be the coldest of the stretch. Kept the
forecast below NBM with widespread teens outside the urban
cores. Single digits aren`t out of the question in rural
valleys. Monday is not quite as cold, though still below normal
with highs in the 30s.

A clipper system will work through the Great Lakes Monday night
with trailing frontal zones pushing toward the local area.
Forcing and moisture appear to be limited, but there is some
model consensus for some light precipitation, especially in the
Alleghenies, but potentially anywhere across the northern half
of the area. Overnight temperatures should be below freezing for
most locations. Snow appears to be most favored if precipitation
were to occur, but slight warm advection aloft could result in
mixed precipitation types. Will continue to monitor.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Low pressure to the north on Tuesday may allow for some
weak moisture return across the northern portions of the local area.
A slight chance for a few rain-snow showers is possible early
Tuesday morning before probabilities diminish later in the day.
Highs will climb into the mid to upper 40s for the lower elevations
with 30s across the higher terrain. High pressure returns on
Christmas Day with not many precipitation chances other than the
Allegheny Front in the upslope areas.

Wednesday night will introduce additional chances for a few rain-
snow showers. Cannot rule out some freezing rain along the northern
zones for a few hours. High pressure will slowly move further north
and east and allow the next low pressure system to approach from the
west later in the week. PoPs increase heading into the remainder of
the workweek with mainly a cold rain expected east of the mountains.
Highs will continue to be in the 40s for most areas east of the
Alleghenies. Overnight lows will fluctuate early in the week in the
upper 20s to more 30s late in the work week.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
VFR conditions expected through Monday as a strong Canadian
high builds across the region (although broken ceilings may
continue into Sunday morning). Some flurries persist around the
Shenandoah Valley which supports vicinity showers at KMRB
through the evening. Winds will gradually diminish tonight into
Sunday.

Brief sub-VFR ceilings will be possible late Monday night into
Tuesday along with a low chance of wintry precipitation toward
some of the northern terminals like KMTN/KBWI/KMRB. Winds will
likely be less than 10 knots through Christmas Day as high
pressure briefly builds in across the region.

&&

.MARINE...
Hazardous marine conditions continue as a strong Canadian high
pressure builds across the region. As expected, wind gusts have
diminished after dark given the decrease in turbulent mixing.
However, winds do remain in SCA levels for portions of the
through Sunday afternoon. No changes to the advisory at this
time. Winds are forecast to fall below 10 knots Sunday night
into Monday as they eventually become southerly.

Sub-SCA winds are expected Tuesday and Wednesday as low
pressure moves north of the area and brings a few rain-snow
showers, especially for the northern waters.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until 10 AM EST Sunday for MDZ008.
     Winter Weather Advisory until 10 PM EST this evening for
     MDZ001.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 10 AM EST Sunday for ANZ530>532-536-
     538>540-542.
     Small Craft Advisory until 4 PM EST Sunday for ANZ533-534-537-
     541-543.
     Small Craft Advisory until 9 PM EST this evening for ANZ535.

&&

$$

SYNOPSIS...ADS
NEAR TERM...ADS/BRO
SHORT TERM...ADS
LONG TERM...ADM
AVIATION...ADS/BRO/ADM
MARINE...ADS/BRO/ADM