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Office: LWX

FXUS61 KLWX 231802

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
202 PM EDT Tue Oct 23 2018

A cold front will move southeast of the region this evening. High
pressure will build in from the Great Lakes, moving over or just
north of the Mid-Atlantic Thursday night before retreating to
northern New England. Low pressure developing over the northern Gulf
Coast will the move northeastward toward the area Friday into the
weekend, and may be followed by a clipper-like system Monday.


Gusty northwest winds are likely for a time through early this
evening immediately behind a dry cold frontal passage. Winds
could gust 25 to 30 mph before diminishing by late evening.
Other than perhaps an isolated sprinkle or to over northeastern
Maryland, no precipitation is expected with the given a lack of
low-level moisture.

Cold air advection will be offset by a steady light northwest wind
late tonight, causing low temperatures to be similar to last night
(upper 30s to lower 40s).


Northwest wind gusts will resume during the mid to late morning
hours, possibly persisting into the early afternoon as diurnal
mixing increases. Downsloping/compressional heating will likely
offset continued cold air advection aloft somewhat, resulting in
highs in the 50s to near 60 in the lowlands (around 40 at the higher
elevations). There's not a lot of deep moisture, but there may be
just enough in northwest flow off of Lake Erie to result in a couple
sprinkles or flurries along the Allegheny Front during the morning.

Winds will gradually diminish later Wednesday into Wednesday night
as high pressure continues to build toward the region. Lows will be
a bit cooler, likely dropping below 40 even in the urbanized areas,
with lower to middle 30s for much of the rest of the area. Light but
steady northwest flow (around 5 mph) may preclude widespread frost
concerns in areas east of I-95 where the growing season is still
active despite the cooler temperatures.

High pressure will move directly overhead Thursday into Thursday
night with a mainly sunny sky and cooler than normal temperatures
(highs in the lower to middle 50s, about 10 degrees below normal).
Mid and high level clouds will begin streaming in ahead of a large
approaching upper trough over the mid-section of the country
Thursday night, foregoing what would otherwise be a radiational
cooling scenario.


A piece of upper-level shortwave energy ejects out of the
southwest U.S. Friday and absorbs leftover mid-level vorticity
associated with what is now Hurricane Willa. This happens along
a baroclinic zone along the Gulf Coast, spawning an area of
non-tropical low pressure early Friday morning in the northern
Gulf of Mexico.

This low will track along the eastern seaboard Friday into
Saturday. Recent guidance has come into better agreement that
this storm will ride along the coast, rather than staying
farther offshore. The recent runs of the GFS, FV3, European,
Canadian, and even the NAM all paint the same picture, as do the
respective ensemble camps. Nearly all guidance shows a period
of steady soaking rainfall across much of the forecast area
late Friday into Saturday. With strong easterly flow at 850mb
depicted in nearly all of the recent guidance, there will be
plenty of moisture advection to support a soaking rainfall.
With temperatures in the 30s overnight and only reaching the
low 40s during the daytime hours in the higher elevations,
introducing at least the chance for some snow to mix in with
rain across the Allegheny Highlands.

The coastal low likely exits the region late Saturday into
Sunday, but precip chances linger due to upper troughing
pivoting overhead. A secondary/clipper-like low pressure
system, associated with another piece of shortwave energy moving
out of the northern Plains, will move towards the area sometime
on Monday. The specifics on timing and location of this system
are still unclear at this time, but nearly every piece of
guidance suggests some precip across the area from this system,
so keeping chance POPs through Monday across the region, with a
chance of rain or snow across the highest elevations again.


VFR expected through Thursday night. NW winds will increase to 10-15
kts with gusts around 20-25 kts behind a cold front this aft/early
eve. There are some winds of 35-40 kts at about 6-7 kft; I doubt we
mix this high but there could be a few brief isolated gusts around
30 kts around sunset right behind the cold front.

Winds over the terminals should decrease to just under 10 kts by
late evening with few if any gusts (though it can't be ruled out
with ~25 kts at a few thousand feet).

Gusts increase again between 11-14Z Wednesday (mid-20s kts likely)
as mixing increases. Gradient should gradually relax through the day
with gusts becoming a bit less frequent and less in magnitude by
late afternoon. Generally 10 kts or less Wed night-Thu night.

Coastal low pressure will approach the area from the south on
Friday, bringing increasing clouds through the day. Winds will
increase in intensity and shift from easterly on Friday to
northerly by Saturday afternoon. Periods of moderate rain are
likely late Friday into Saturday, so sub-VFR conditions are


Northwest wind gusts are expected to increase rather sharply behind
a dry cold front this evening. A few gusts to near gale force are
possible. Mixing should bring gusts to below SCA thresholds over
most of the sheltered waters after midnight, but winds continue
gusting 20-30 kts over the open waters. As mixing increases
Wednesday morning, gusts will resume over sheltered waters and may
increase slightly elsewhere (again a few gusts to near gale force
are possible over the open waters during this time).

Winds will gradually diminish late Wednesday through Thursday,
eventually falling solidly below SCA criteria over all waters by
late Thursday as high pressure building in from the Great Lakes
moves overhead.

Small Craft Advisories are likely from late Friday afternoon
through Saturday. A coastal low pressure system will be
approaching the region from the south, causing winds to
gradually increase through the day on Friday and into Saturday
out of the east. Gale conditions will also be possible during
this time.


Tidal anomalies will likely increase in onshore flow ahead of
coastal low pressure Friday into Saturday, and may result in
flooding issues during this time.


MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ531-532-
     Small Craft Advisory until midnight EDT tonight for ANZ530-535-
     Small Craft Advisory from 8 AM to 6 PM EDT Wednesday for
     Small Craft Advisory from 6 PM this evening to 6 AM EDT
     Thursday for ANZ533-534-537-541>543.
     Small Craft Advisory from 6 PM this evening to 6 PM EDT
     Wednesday for ANZ536.