Office: LWX
FXUS61 KLWX 042017
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
317 PM EST Thu Dec 4 2025
.SYNOPSIS...
A reinforcing cold front will pass through the area this evening.
Light wintry precipitation chances return late tonight through
Friday as low pressure passes to the south. High pressure
briefly returns this weekend before a pair of clipper-like
systems impact the area early to mid next week.
&&
.KEY MESSAGES...
- Light but potentially high impact snow event becoming
increasingly likely during the Friday morning commute.
- Uncertainty remains in the northern extent of snow, but
trends have been quicker and further north overall.
&&
.NEAR TERM /THROUGH FRIDAY/...
A reinforcing cold front will deliver another shot of Arctic air
(likely the coldest thus far this season) late tonight into Friday.
This sets the stage for a light but potentially high impact snow
event that will likely affect the Friday morning commute.
Confidence remains low in the northern extent of snow, but 12Z
guidance has come into much better agreement on a quicker and
further north trend. Ensemble members are more tightly clustered
with the northern edge of the snow, but there is still some room
for error. Certainty in accumulating snow is highest in the I-64
corridor, lower toward US-50/I-66, and even lower up toward I-70.
It is possible areas near/north of I-66/US-50 see little to no
snow depending on how tight the northern edge is.
With the quicker and further north trend in guidance (and in
upstream obs in TN/KY), opted to expand the Winter Weather Advisory
northward into the Baltimore MD and Washington DC metro areas. This
is supported by the latest rapid refresh guidance and extrapolation
from upstream radar/satellite trends. Although amounts are expected
to be light overall, especially further north, very cold
temperatures in the 20s when the snow begins (and the time of
day) will result in any snow sticking to all untreated surfaces.
Even a light coating of snow results in very slippery and icy
surfaces, especially elevated ones like bridges and overpasses.
Despite the distant surface low passing over the Carolinas, mid to
upper jet forcing is abundant with saturation as low as 850 mb.
This is thanks for a 150+ knot upper jet. The lift overlaps the
DGZ for a time, and these setups can in some cases "overperform"
expectations due to the fluffy nature of the snow enhanced by
the upper jet. This is probably why, in addition to the northward
shift upstream, guidance has shifted north today.
Snow looks to move into west-central VA around or just after
midnight, then expands steadily northeastward through the night
reaching the metro areas between 3-5AM. There will likely be a
tight gradient in the northern extent of the snow as the best
forcing is further south and dry air will have to be fought off
further north. Amounts overall are expected to be light, ranging
from a coating near I-70, to an inch or two south of I-66/US-50.
The highest totals in a relative sense will be along the I-64
corridor and the higher elevations of west-central Virginia
where as much as 4 or even 5 inches are possible.
Steadier snow may end rather quickly mid to late morning from
west to east. But, lingering flurries and perhaps freezing
drizzle may develop, evident in forecast soundings that show
drying aloft with weak low-level lift and saturation as well as
surface temperatures hovering near freezing. The end time for
the advisory was therefore left at 4PM, though if freezing
drizzle does not materialize it may be able to be cancelled
early. The freezing drizzle potential may linger Friday evening.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
Light to calm winds and lingering low-level moisture/cold air
could result in lingering drizzle or fog Friday evening and night.
With cold temperatures, slick spots may develop even in the absence
of additional precipitation as any melted snow refreezes.
High pressure will then nudge into the region to start the
weekend. This will result in mainly dry weather and seasonably
cool temperatures.
An approaching shortwave in the northern stream could bring a
return of flurries or a few snow showers to the Alleghenies
Saturday night.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Not too much of a change in the overall pattern with broad longwave
troughing across the eastern CONUS and ridging back toward the west.
The northern jet stream will remain quite active with several
perturbations set to work near or through the forecast area during
the early and middle part of next week.
The first set of disturbances to watch will occur during the Sunday
into Monday timeframe. An upper-level trough axis will shift
east out of the Ohio/Tennessee River Valleys with a shortwave
passing to the north across the Great Lakes, and another
shortwave passing to the south across the southern Appalachians
region. Meanwhile, high pressure will remain wedged south along
the eastern Appalachians. This will keep most of Sunday dry and
cloudy with highs in the upper 30s and lower 40s (low 30s
mountains).
A cold front looks to drop through the area Sunday afternoon and
evening, but may be fairly weak and moisture-starved as the
main energy sources remain on either side of the region. Light
wintry precipitation will work into the mountains Sunday
afternoon with perhaps a few spotty showers further east Sunday
evening into Monday as the trough axis swings overhead. Any
precipitation will quickly wrap up east of the mountains Sunday
night into Monday morning as the front works east and high
pressure builds in from the Ohio River Valley. Stout Canadian
cold air advection will filter into the area on north to
northwest flow Monday marking one of the coldest days by far
this late Fall/early Winter season. Highs Monday will struggle
to get out of the low 30s in most locations (20s mountains).
Lows Monday night are forecast to fall into the mid to upper
teens with low 20s along the Chesapeake Bay and in the
immediate Baltimore/DC city centers.
A pair of clipper-like systems will traverse the area Tuesday
through Thursday. Both of these systems look to swing across the
Great Lakes driving a series of fronts through the region. Each
storm system could deliver a period of light snow to the
mountains with perhaps a rain/snow mix further east. Of course
this will be dependent upon moisture availability and the
overall track of the low as it drops south/east. Highest
confidence for precipitation at this time appears to be over
northwestern portions of the forecast area including the
Allegheny/Potomac Highlands.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR conditions are expected through this evening as winds diminish.
Snow will move in quickly toward KCHO between 06Z-08Z, expanding
NE toward the metro TAF sites by 08Z-11Z. Conditions steadily
deteriorate to IFR or LIFR at KCHO, with IFR likely at IAD/DCA
and perhaps up into BWI/MTN/MRB, but confidence is lower there.
Winds will be light and generally out of the NE to SE through
Friday, then calm Friday night. Freezing drizzle is possible
once steadier snow departs between 14Z-18Z Friday, perhaps
lingering well into Friday evening. Fog may develop Friday
night. Therefore, improvements may be slow.
VFR will return Saturday with light W/SW flow. VFR conditions
likely persist Sunday into much of next week. Some temporary
sub-VFR reductions are possible late Sunday into Monday and
Tuesday through Thursday, especially over the mountains as
multiple clipper systems pass through. Winds will remain light
out of the north and northwest Sunday into Monday with speeds
less than 10 knots. Speeds increase with gusts up to 20 knots
in the wake of a front Monday afternoon.
&&
.MARINE...
Winds will diminish through this evening, becoming northeast
overnight then southeast Friday. A period of light snow is
likely with the highest confidence further south late tonight
through Friday morning. Some patchy drizzle or fog is then
possible through Friday night. Winds will be light and variable
Friday night, then west to southwest Saturday less than 10 kts.
A wave crosses aloft Saturday night, and that could bring
briefly higher gusts to portions of the waters.
Sub-SCA level north to northwesterly winds are expected through
Sunday. SCA level winds look to return to the waters Monday
through Thursday as a series of fronts pass through.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Winter Weather Advisory from 4 AM to 4 PM EST Friday for
DCZ001.
MD...Winter Weather Advisory from 4 AM to 4 PM EST Friday for
MDZ011-013-014-016>018-503>506.
VA...Winter Weather Advisory from 4 AM to 4 PM EST Friday for
VAZ053>055-057-501-502-505-506-526-527.
Winter Weather Advisory from 1 AM to 4 PM EST Friday for
VAZ025>027-029-030-036>040-050-051-056-503-504-507-508.
WV...Winter Weather Advisory from 1 AM to 4 PM EST Friday for
WVZ055-505-506.
MARINE...Small Craft Advisory until midnight EST tonight for ANZ530>532-
538>542.
Small Craft Advisory until 2 AM EST Friday for ANZ533-534-537-
543.
Small Craft Advisory until 9 PM EST this evening for ANZ535-
536.
&&
$$
SYNOPSIS...DHOF/EST
NEAR TERM...DHOF
SHORT TERM...DHOF
LONG TERM...KLW/EST
AVIATION...KLW/DHOF/EST
MARINE...KLW/DHOF/EST
