Ashburn, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

172
FXUS61 KLWX 211402
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
902 AM EST Thu Nov 21 2024

.SYNOPSIS...
Upper-level low pressure will drift over the area through
Saturday bringing below normal temperatures, gusty winds, and
accumulating mountain snow. High pressure will briefly return
Sunday before another area of low pressure and front impact the
area early next week. The weather pattern looks to remain active
heading towards the Thanksgiving holiday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Upper-level low pressure was pushing into PA from the OH Valley
as surface low pressure pushes toward Long Island as of mid
morning.

Snow showers will become more common across the Allegheny Front
today as the upper low sweeps towards the area from the
northwest. Further east, some cold rain showers will spill over
briefly in the afternoon and evening hours. Given the expected
temperature profile as the upper low moves overhead, could see
some graupel mix in east of the mountains with any showers
today. Daytime highs will only reach the upper 20s to low 30s
for the higher terrain, and 40s to low 50s further east as you
head toward the waters.

Snow showers along and west of the Allegheny Front will occur
in brief squalls coupled with drier patches throughout the day.
Overall totals for the day will be a few inches, then light
snow showers later tonight may add a couple more inches heading
into Friday when the steadier and heavier snow is expected to
mainly fall. Winter Storm Warnings remain in effect across the
Allegheny Front starting later today and heading into early
Saturday, as well as Winter Weather Advisories for a few zones
just off to the east. Overnight lows will be in the 20s west of
the Blue Ridge with 30s further east.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Winter Storm Warnings continue for the western slopes of the
Alleghenies through Saturday morning.

Upper level low pressure will sit just to the north of the area
Friday morning before drifting toward the New England coast late
Friday into Saturday. Multiple pieces of shortwave energy will
pivot around the upper level low Friday morning into Friday
afternoon and again Friday night into Saturday. Each piece of
shortwave energy will supply a reinforcing shot of wind, cold temperatures,
and enhanced upslope mountain snow.

The steadiest and heaviest upslope mountain snow shower activity
looks to occur Friday into Friday night. This is when the
strongest piece of shortwave energy pivots through as the
cutoff upper low progresses north and east toward New England.
00z/06z deterministic and ensemble guidance continues to hint at
snowfall rates of 1-2"/hr with persistent banding/squalls
working over the warning areas.

Highest snow totals (Accumulations from Thursday 11/21/24 through
11/23/24 Saturday) of 7-14 inches will be confined to elevations
above 2500 feet with lower totals down in the higher valley
locations along west of a line from Finzel, MD south toward Spruce
Knob, WV and Paddy Knob, VA. Higher ridge locations from Hoyes Crest
and into Canaan Valley could see localized totals up to 18".

Snow ratios will favor climatology with lower ratios in the 10:1 to
13:1 range during the daylight hours increasing to 16:1 to 18:1
during the early morning and overnight periods. This will lead to
periods of compaction although most of the snow Friday should be of
fluffier consistency given the colder airmass in place. H850 temps
will tank between -4 to -8 degrees C over the mountains Friday
morning with values of -2 to -4 further east.

Outside of the significant snow accumulation, blowing and drifting
will become problem. This is due largely in part to increasing winds
Friday afternoon into Saturday as the shortwave disturbance lifts
out of the region. Gusts will be close to Wind Advisory criteria (up
to 50 mph) along the higher ridges with 30 to 40 mph gusts down
below. This will yield wind chills in the teens and 20s on both
Friday and Saturday across the higher elevations.

Areas further east will likely remain dry outside of Friday morning
into Friday afternoon. The combination of FROUDE numbers less than 1
(blocked flow against the mountains) and downsloping will lead to
drier conditions. Even with that said, a few rain/snow showers may
squeak east Friday morning due to the intense nature of the
shortwave passing through. The highest potential for this would
be across the northern and western suburbs of Baltimore. Some minor
accumulations may be possible along Parr`s ridge in north-
central Maryland and in the Catoctins. A few snowflakes will mix in
even in Baltimore/Washington DC although temperatures will be too
warm for stickage. Any snow to the east of the mountains should
switch over to rain during the Friday afternoon as temperatures warm.

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.  By Saturday afternoon the
shortwave will pivot east and heights begin to rise. This will
result in pretty rapid drying out period across the mountains into
the afternoon/evening. Elsewhere, Saturday remains dry with
gusty northwesterly winds of around 25 to 35 mph, with gusts up to
40 mph, mainly on the ridges and over the open waters.

High temperatures will range from below freezing over the mountains
to mid to upper 40s and low 50s further east Friday. Lows Friday
night into Saturday morning will fall into the 30s and 40s. By
Saturday, temperatures warm back above freezing in the mountains
with upper 40s and low to mid 50s further east toward the metro
areas.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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 mid to upper 50s east of Alleghenies with low 60s for highs
Monday afternoon. Mountain locations will struggle to get out of the
40s on both days with the added snowpack on the ground. Lows Sunday
night will fall into the 30s with 40s expected Monday night into
early Tuesday morning.

Meanwhile, low pressure over the central U.S will track north and
east into the Great Lakes late Monday into Tuesday. This will send
another front into our region for the middle of next week. As it
stands now, the front looks to stall somewhere in the vicinity of
our region looks to cross the region Tuesday before stalling to the
south and east (across the Tennessee River Valley and Carolinas)
midweek. This will lead to increased precipitation chances during
this time. An active weather pattern looks to continue into the
upcoming Thanksgiving holiday ahead. 00z/06z deterministic guidance
shows another low pressure system cutting up through the Mid-South
by the middle part of next week. Current 8-14 day hazards from the
Climate Prediction Center highlight a slight risk for heavy snow
in our far western mountains with above normal precipitation
chances and below normal temperatures for the remainder of the
region heading into the upcoming holiday. We`ll continue to
monitor this threat over the coming days.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
Prevailing VFR conditions are expected at most terminals through
Saturday. Some brief periods of MVFR are possible, especially Friday
into Friday night as a potent piece of upper-level energy pivots
through. A few mixed rain/snow/graupel showers may be possible
this afternoon, but the vast majority of the day should remain
dry outside the terminals west of KMRB. Friday brings a slightly
higher chance of precipitation amongst the terminals north of
KCHO. A few showers with perhaps a few wet snowflakes or even a
little graupel are possible at KBWI, KMRB, KHGR, KOKV, and KFDK
Friday morning. Any frozen precipitation will quickly change to
rain Friday afternoon before dissipating Friday evening. Any
significant snow accumulations will remain west of KCBE.

Wind will be the biggest impact to aviation today through Saturday.
Expect sustained speeds of 10-20 kts during the day and nighttime
hours with gusts 20 to 30 kts each afternoon/evening. Highest winds
look to occur late Friday into early Saturday.

VFR conditions are expected Sunday and Monday with decreasing winds
as high pressure builds over the region. Winds turn more westerly on
Sunday and will be around 10 to 20 kts. Sub-VFR conditions remain
possible Tuesday into the middle of next week as a series of fronts
impact the region.

&&

.MARINE...
High end SCAs are likely to continue through Saturday night
with frequent gusts of 20 to 30 kts expected across all waters.
Gale-force gusts are possible over the open waters of the
Chesapeake Bay and lower tidal Potomac River late Friday into
early Saturday as winds surge behind a departing shortwave
trough. Winds taper off into Sunday, but SCAs seem likely to
continue, albeit closer to the low end.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until 1 AM EST Friday for MDZ008.
     Winter Storm Warning until midnight EST Friday night for
     MDZ001.
     Winter Weather Advisory until 10 PM EST this evening for
     MDZ501.
VA...Winter Storm Warning until 6 AM EST Saturday for VAZ503.
WV...Winter Weather Advisory until 10 PM EST this evening for
     WVZ503.
     Winter Storm Warning until 6 AM EST Saturday for WVZ501-505.
MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ530>543.

&&

$$

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