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fxus61 klwx 230752 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
252 am EST Tue Jan 23 2018

a cold front will cross the area today. High pressure will build
over the area during the second half of the week, then move
offshore this weekend as another cold front approaches.


Near term /through tonight/...
the mid-Atlantic is solidly in the warm sector of vertically
stacked low pressure located over the Great Lakes early on this
January morning. Dew points are surging through the 40s and
should make it into the 50s ahead of an approaching cold front.

A broken line of showers and embedded thunderstorms has been
moving eastward across West Virginia overnight. Hi-res guidance
has this line weakening as it crosses the mountains, with
embedded convective elements re-developing in a larger area of
showers that develops east of the mountains. Hints of this are
already coming together over central North Carolina.

Given the highly unusual warm and humid airmass, moderately
strong forcing for ascent and low level wind fields in excess of
50 knots, believe a broken line of heavy showers and
thunderstorms should re-invigorate as it crosses the Blue Ridge
mountains this morning. This line could be accompanied by
isolated surface gusts of over 50 mph with spotty wind damage
possible. Hrrr guidance has sped up the timing of this line
and have trended the forecast in this direction, clearing the
I-95 corridor by early afternoon.

Dry air racing in aloft should result in a mostly sunny sky by
mid to late afternoon for much of the County Warning Area. Winds will shift from
south to west and gust to around 30 mph. The cold airmass lags a
bit behind the front, so with some sun and downsloping flow,
temperatures are expected to once again rise well into the 60s.

As the upper trough lifts out to the northeast, upslope snow
showers are expected tonight. Flow is blocked, so I don't think
there will be much east of the ridges. But along the western
slopes of the Allegheny Front, there will likely be about 1 to 3
inches of snowfall through the night. Elsewhere, dry conditions
are expected with more seasonable temperatures (20s and 30s).


Short term /Wednesday through Thursday night/...
as the main upper low departs to the northeast Wednesday, a
secondary vort Max pivots in from the west and reaches the area
by nightfall. Believe this will result in a partly sunny day
with cumulus floating across ahead of the trough. Another light
round of upslope snow showers seems likely (an inch or less)
Wednesday evening as the trough axis moves across. 850 mb
temperatures of around -8 c and decent mixing should result in
high temperatures generally in the 40s (25-30 for the ridges).

A secondary pressure surge will probably keep winds up a bit in
the evening even in The Lowlands, but as high pressure builds
overhead toward daybreak Thursday, would expect winds to go
light in the valleys allowing for some radiational cooling. Have
leaned toward the lower end of guidance for lows in the valleys
for this reason.

Ridging at the surface and aloft moves overhead Thursday with
seasonable temperatures and some high clouds spilling over the
ridge expected. Light winds and a mainly clear sky with dew
points in the teens should allow temperatures to fall into the
20s Thursday night, possibly lower in a few spots.


Long term /Friday through Monday/...
high pressure will remain atop the forecast area Friday. That should
translate to nearly clear skies. Temperature-wise though, the
thermal trough will start to pull out, but doubt the warm advection
aloft will have a tangible effect at the ground so highs will still
be in the 40s to near 50. Lows Friday night will be a bit warmer
than Thursday night...near freezing.

No significant weather Saturday either, as the high moves east and
warm advection becomes stronger. The isentropic lift will lead to
increasing cloud cover and highs in the 50s. There is a small chance
that this lift could lead to some light rain, but those pops (30%)
will be confined to the mountains.

A better chance of precip will come Saturday night into Sunday
night...especially during the day a cold front drops
across the area. Most of this should be rain. The only question will
be whether precip can exit before cold air arrives. Usually it can,
but at this time frame there is limited skill in details.

Theres not a ton of cold advection behind this front. While
temperatures will be cooler once again, anticipating the result to
be near climo.


Aviation /08z Tuesday through Saturday/...
IFR conditions expected for most if not all terminals for a time
this morning mainly before 14-15z. An area of showers with an
embedded line of heavier downpours/possible thunder will move
from SW to NE during this time. This line may be accompanied by
brief gusty surface winds of greater than 35-40 kts. Otherwise,
expect low level wind shear of about 40-45 kts through 2 kft. Winds generally
south 10-15 kts gusts 20-25 kts outside of shra/tsra.

Low level wind shear decreases and conditions rapidly return to VFR by 15-18z.
Winds shift to west 10-20 kts g 25 kts until around midnight.

VFR Wed-Thu with northwest flow 10-15 kts, gusty at times especially
Wed aft/eve.

VFR conditions Fri-Sat under high pressure. Flight restrictions
could arrive Sat night in rain ahead of a cold front.


sporadic Small Craft Advisory gusts are gradually becoming more widespread as of
early this morning. Expect this trend to continue ahead of an
approaching cold front. A broken line of showers and
thunderstorms is expected to cross the waters late this morning,
and could be accompanied by stronger gusts in excess of 30 kts.
A few smws may be necessary. Held off on a Gale Warning due to
relatively cool water and poor mixing on warm S wind.

West winds expected behind cold frontal passage this afternoon, with Small Craft Advisory
gusts expected for all waters until around midnight. As diurnal
mixing decreases, wind gusts likely confine themselves to the
open waters during the late overnight, before making a Cameo
during the day Wednesday. Gusts likely persist into Wednesday
evening before becoming light late as high pressure moves in.

Light winds Friday will increase Saturday ahead of a cold front.
However, cool water should keep gusts below Small Craft Advisory


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory until midnight EST tonight for anz530>532-
Small Craft Advisory from 8 am to 7 PM EST Wednesday for
Small Craft Advisory until 7 PM EST Wednesday for anz533-534-



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