Office: LWX
FXUS61 KLWX 220057
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
857 PM EDT Sun Oct 21 2018
.SYNOPSIS...
High pressure will traverse the area through Monday night
before departing into the western Atlantic. A cold front
approaching from the Great Lakes will cross the region Tuesday,
followed by high pressure will persist through the second half
of the week. Low pressure may approach the area from the
southeastern U.S. or Tennessee Valley by next weekend.
&&
.NEAR TERM /THROUGH MONDAY/...
Winds will continue to subside overnight as high pressure
builds into the area. Clouds also continue to erode. As the
high crests overhead overnight, we will have excellent
radiational cooling conditions. Guidance picking up on this,
with forecast lows cooler than previous cycle. Have made some
more adjustments to the Frost/Freeze headlines...adding the
west/northwest outer suburbs of DC/Balt to the freeze warning.
Was tempted to expand eastward into Carroll/northern Balt/NW
Harford but given the better gradient there, held off for now.
The rest remains the same. Forecast lows in the 30s areawide,
except where the growing season has already ended...where we
have some patches of forecast lows in the 20s.
&&
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
High pressure will slide offshore Monday afternoon-evening, so
after a cold start, expect a moderating trend. Pretty good
consistency in high temperatures in the 50s, with perhaps some
increase in mid-upper level cloud cover. Warm advection (850
temps up to 7-9 degC lucking just south of DC) will have a
bigger influence on overnight lows, which will stay in the 40s.
A cold front will drop though Tuesday with little fanfare, as
atmosphere too dry for much more than a shallow layer of clouds
and an uptick of wind again in the wake of the front. However,
winds at 925-850 mb only support gusts near 20 kt, and that
assumes full mixing. Mostly clear and cool conditions continue
into Tuesday night.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Breezy northwest winds will continue ushering in a reinforcing
shot of cool air Wednesday into Wednesday evening as high
pressure builds toward the Mid-Atlantic from the Great Lakes.
This high will gradually move over the area through Friday night
or Saturday morning. The coldest 850 hPa temps look to pivot
across the area early Thursday morning, generally between -1 and
-5 C, before gradually rebounding to around 0 C by Saturday
morning. This would result in temperatures running several
degrees below normal (highs in the 50s, lows in the 30s to
around 40).
By Saturday, all guidance is in very good agreement with a
broad and sturdy ridge becoming anchored around 120 W (western
CONUS). They disagree rather substantially, however, on how
quickly the midweek upper trough departs the Canadian maritimes,
and thus the extent and placement of blocking downstream over
southeastern Canada and the northwestern Atlantic. The potential
exists for low pressure development near or along the East
Coast during this time, and ultimately this would bring our next
appreciable chance of precipitation, but it is far too early to
speculate much beyond that.
&&
.AVIATION /01Z MONDAY THROUGH FRIDAY/...
VFR conditions expected for the next few days as high pressure
passes overhead and a dry cold front crosses the terminals.
The bigger operational impact comes from the wind, and that
impact is diminishing. Believe winds will be light and variable
by midnight. Flow will be from the south Monday-Monday night.
Winds will turn west again on Tuesday as a cold front crosses
the terminals. However, moisture is shallow. While there should
be a period of ceilings late Tuesday, those cigs should still
be VFR.
Mainly VFR Wed-Thu in NW flow.
&&
.MARINE...
Have tweaked small craft advisory timing but otherwise, forecast
for tonight remains generally on track, with winds gradually
diminishing through the night.
High pressure keeps winds light Monday. In the wake of the
departing high, guidance attempting to mix some 20 kt gusts due
to southerly channeling in the main channel of the Bay. A Small
Craft advisory has been issued for Monday night.
Better mixing/opportunity for Small Craft Advisory conditions
comes late Tuesday in the wake of a passing cold front. Gusty
NW winds of 20 to 30 knots are likely through Wednesday behind
this front.
&&
.TIDES/COASTAL FLOODING...
Tides were running about 1 to 3 feet below Mean Lower Low Water
(MLLW) on Sunday due to strong northwest winds. Now that winds
are diminishing this evening, water levels should begin to
gradually recover to near astronomical norms by Tuesday. One
caveat is that anomalies are still +0.8 near Norfolk, so this
water will slosh back up the Bay when winds go light late
tonight into Monday. While this is not expected to cause any
flooding issues, anomalies could oscillate to near or a little
above astro norms quicker than currently forecast.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Frost Advisory from midnight tonight to 10 AM EDT Monday for
DCZ001.
MD...Freeze Warning from midnight tonight to 10 AM EDT Monday for
MDZ003-004-503.
Frost Advisory from midnight tonight to 10 AM EDT Monday for
MDZ005-006-011-013-014-016>018-504>508.
VA...Freeze Warning from midnight tonight to 10 AM EDT Monday for
VAZ025-036>040-050>052-055-056-501-502-505>508.
Frost Advisory from midnight tonight to 10 AM EDT Monday for
VAZ053-054-057.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ532>534-537-
540-541-543.
Small Craft Advisory from 6 PM Monday to 6 AM EDT Tuesday for
ANZ531>534-537-539>543.
Small Craft Advisory until midnight EDT tonight for ANZ530-531-
535-536-538-539-542.
&&
$$
SYNOPSIS...DHOF
NEAR TERM...HTS
SHORT TERM...HTS
LONG TERM...DHOF
AVIATION...HTS/DHOF
MARINE...HTS/DHOF
TIDES/COASTAL FLOODING...DHOF/RCM
