488
FXUS61 KLWX 180205
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
905 PM EST Sun Nov 17 2024

.SYNOPSIS...
High pressure will drift south of the area through tonight while a
weak surface trough crosses from west to east. A dry cold front will
drop in from the north Monday night, then return northward as a warm
front Tuesday into Wednesday as strong low pressure moves from the
Plains to the Great Lakes. A second area of low pressure will likely
develop near the Mid-Atlantic Wednesday night into Thursday, then
track toward New England through the end of the week dragging a
series of cold fronts through the region.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
EVENING UPDATE...
Forecast remains on track for tonight with high clouds remaining
overhead and lows in the upper 30s to 40s.

PREVIOUS DISCUSSION FOLLOWS...
Ridging aloft will move offshore through tonight while an
upper-level low heads for the Saint Lawrence River Valley. At
the surface, high pressure will move off the coast as a trough
approaches from the west.

Temperatures will run about 3 to 6 degrees above normal through
tonight as thin high clouds increase. The clouds will be thin
enough to not hinder radiational cooling in sheltered valley
locations overnight.

Light southwest winds will become light and variable overnight.
Northwest winds will return by daybreak Monday as the weak
surface trough crosses the region. Other than perhaps an
isolated sprinkle or shower along and west of the Allegheny
Front in western Maryland, a dry passage of the trough is
expected.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
The aforementioned upper-level low will move across New England,
then merge with another upper-level low over the Canadian
Maritimes Monday into Monday night. The conglomerate cyclone
will then stall offshore of Nova Scotia and Newfoundland through
Tuesday due to a building anomalous ridge extending from Hudson
Bay to the Davis Strait. Locally, shortwave ridging will pivot
across the eastern CONUS. This will place the Mid-Atlantic in a
mild but dry pattern for the first part of the workweek.

A weak surface trough will depart offshore through midday
Monday. This boundary is denoted by little more than a wind
shift. The downsloping component to the NW wind and lack of
cold air advection is expected to send temperatures well into
the 60s to around 70 Monday afternoon east of the mountains,
with 50s for the higher elevations.

A dry cold front spiraling around the low to the northeast will
drop in from the north Monday night. A lack of forcing (given
ridging aloft) and moisture will result in its dry passage.

After stalling to the south briefly Tuesday, the front will
return northward as a warm front heading into midweek in
response to strong low pressure spiraling from the Plains toward
the Great Lakes. Above normal temperatures will persist during
this time locally, though daytime highs Tuesday will be a bit
cooler than Monday. Rain shower chances will gradually increase
from west to east Tuesday into Tuesday night as the warm front
lifts north and the parent upper trough driving the low into the
Great Lakes slowly approaches the Mid-Atlantic.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
The hemispheric pattern across the mid-latitudes will be very
amplified during the period. On Wednesday, key features include
closed lows east of Nova Scotia, across the Upper Midwest, and
another nearing the British Columbia coast. In particular, the
system across the middle of the country will usher in quite a
pattern change to the northeastern U.S. An upper low, comprised of
mid-level height anomalies around 2 standard deviations below
average, is forecast to track from the Upper Midwest toward the Ohio
Valley on Wednesday into Thursday. As embedded shortwave energy
translates eastward, a surface cyclone develops across the Ohio
Valley by Wednesday evening. Relative to previous day`s runs, the
trends have been weaker in terms of surface pressures. Eventually,
a triple point low forms over the local area Wednesday night
before pushing toward Long Island on Thursday. The overall
system tends to congeal and consolidate over New England by the
end of the workweek. A broad upper low persists over the
northeastern U.S. through Saturday before advancing into
southeastern Canada by the weekend`s end. Multi-cycle ensemble
trends have been to slightly speed up the system. However, with
this feature currently just south of the Gulf of Alaska, details
will likely change in the next day or so.

Regarding sensible weather impacts, this deep upper low is primed to
bring a plethora of hazards to the Mid-Atlantic region. While models
have trended a bit weaker with the lead surface low across the
Ohio Valley/Lower Great Lakes, a band of gusty showers is still
expected sometime Wednesday evening/night. There is quite a bit
of wind in the cloud-bearing layer, but with rather paltry
instability given the late timing of this activity. The action
quickly exits to the east ahead of daybreak on Thursday. The
focus then shifts to the Allegheny Front where the first
significant snows of the season are becoming likely. Model
guidance continues to favor a prolonged period of snow showers,
some becoming moderate to heavy at times. Much will depend on
the strength/direction of the lower tropospheric wind fields,
quality of moisture, and position of embedded shortwaves.
Overall, mountain travel may become very difficult given the
expectation of snow covered roads and areas of blowing snow.
With that in mind, wind gusts of 30 to 40 mph are possible as
gradients tighten over the area. The threat for snow showers
likely persists into Saturday given the prolonged cyclonic flow
aloft. Expect improving conditions to finish out the weekend.

Daily temperatures fall rather quickly with this powerful upper
trough. After mid-week highs in the mid 60s to low 70s, pronounced
cold advection and gusty winds take shape Thursday into Friday. On
Friday, most can expect high temperatures in the mid 40s to low 50s,
with 30s in the mountains. Winds are expected to gust around 25 to
35 mph, with higher gusts in the mountain locales. Overnight
temperatures each night largely remain seasonable in nature. While
much of the precipitation ends on Sunday, it remains cool but with
increasing sunshine.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
High pressure will drift to the south tonight. Light southwest
flow of 3-5 kts is expected ahead of a weak surface trough
approaching from the west through the evening. Light and
variable winds are likely overnight before becoming NW by
daybreak Monday. A few gusts of 15-20 kts are possible Monday,
except at KCHO where the gradient will be much weaker. A dry
cold front will drop in from the north Monday night turning
winds to the north, east, then south through Tuesday. VFR
conditions are forecast through Tuesday, then lower CIGs are
possible Tuesday night as the aforementioned dry cold front
returns north as a warm front. A few showers are possible
heading into Tuesday night as the warm front lifts through.

While Wednesday starts off with VFR conditions, a strong frontal
system approaching from the west may bring a band of gusty showers
to the area Wednesday evening into the night. This may lead to some
restrictions as this occurs. For Thursday and Friday, a persistent
upper low will support some shower activity, particularly during the
afternoon hours. Sub-VFR conditions are possible at times in this
regime. This also comes with gusty westerly winds on the order of 25
to 30 knots, perhaps higher depending on how strong the parent
system becomes.

&&

.MARINE...
Light southwest winds are expected through most of the night,
then northwest returns heading into Monday in the wake of a
weak surface trough. A few gusts of 15-20 kts are possible
around daybreak Monday as the surface trough crosses, then again
Monday midday/afternoon over the northern waters where the
gradient will be a bit stronger and vertical mixing will be a
bit deeper. Have held off on any SCAs due to the marginal/brief
nature of the expected winds. Flow will become north to east
Monday night in the wake of a dry cold front dropping in from
the north, then turn southerly through Tuesday night as the
boundary returns north as a warm front. A few showers could
approach the waters Tuesday night.

After starting off with sub-advisory levels winds on Wednesday,
expect a marked ramp up as a strong frontal system approaches the
waters from the west. Small Craft Advisories will be needed for
Wednesday evening through the night given gusty southerly
winds. This also may be accompanied by a threat of low-topped
convection which could tap into the stronger winds higher in the
storm clouds. As such, a few Special Marine Warnings may be
needed late Wednesday. A gusty westerly flow environment ensues
into Thursday and Friday which will necessitate Small Craft
Advisories. Given the strength of the system, gales are possible
as well. Will continue to monitor the situation.

&&

.TIDES/COASTAL FLOODING...
Light winds will allow some excess water to return northward up
the Chesapeake Bay and the tidal Potomac River through tonight.
Near minor flooding may result along vulnerable shoreline such
as Annapolis and Washington DC SW Waterfront for the evening
high tide (higher astronomically). Winds will briefly be
offshore Monday, before turning east then south through Tuesday
night. Anomalies will likely remain elevated with the threat of
at or near minor flooding lingering during the evening tides.

A large and deep area of low pressure will approach the region
Wednesday into Thursday. There is uncertainty in the exact track
and strength of the low, but given its anomalous depth and
potential track near the Mid-Atlantic, the threat of at least
minor tidal flooding could feasibly develop.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...DHOF
NEAR TERM...DHOF/CAS
SHORT TERM...DHOF
LONG TERM...BRO
AVIATION...BRO/DHOF
MARINE...BRO/DHOF
TIDES/COASTAL FLOODING...DHOF