Area Forecast Discussion
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FXUS61 KLWX 300859
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EST Wed Nov 30 2016
Low pressure over the upper Great Lakes will track into eastern
Canada tonight. An associated cold front night will push through
the Mid Atlantic late tonight. High pressure will return to the
region Friday and Saturday. Low pressure will track to the west of the
region Sunday night. High pressure returns Monday.
.NEAR TERM /TODAY/...
As of 3 am, persistent vertically stacked/occluded low with 997mb
surface low centered over the Twin Cities of MN. Longwave trough
axis is ejecting onto the southern Great Plains. Weak surface flow
and moisture from rain yesterday caused areas of dense radiation fog
to develop. Dense Fog Advisory is in effect until 7 am for most
of the CWA (Srn MD and Potomac Highlands are exception). Thick
clouds are spreading NE across the and have reached the Blue
Ridge. There are fewer 1/4SM reports west of the Blue Ridge now,
but will need to keep the advisory at least for now. NErn sections
of the CWA stand the best chance to have an extension to the fog
Showers and isolated thunderstorms area spreading north from SWrn VA.
RAP has some MUCAPE where current lightning is, but not in the SWrn
section of the LWX CWA, so only rain/showers will continue to be
forecast for the morning.
Instability is expected to develop SE of the main slug of rainfall
by midday with negative LI`s at 18Z according to the 00Z GFS. A
marginal risk is in effect across the area with the strong low level
jet potentially mixing down with the strongest activity. Furthermore,
discrete super cells are possible east of I-95 (most likely for
southern MD). Hence a 2 percent tornado risk. Expect locally heavy
rain with QPF generally half inch with locally one or more inches.
.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
The longwave trough axis currently over the southern Great Plains
will reach the mid-Atlantic by sunrise Thursday. An associated cold
front will cross the area tonight, clearing out rain.
Gusty west wind up to 30 mph both Thursday and Friday with little
upslope snow. Maxima mid to upper 50s in dry air advection Thursday
and five or so degrees less Friday after continued cold air
.LONG TERM /SATURDAY THROUGH TUESDAY/...
High pressure will reside over the east coast Saturday. With the
upper level flow in a zonal pattern temperatures will be right
around climo norms for the beginning of Dec - near 50. Radiational
cooling will allow temps to fall to around or slightly below the
freezing Saturday night.
Last night the models had some differences regarding the Sunday
forecast but these seem in better line today. An open short wave
is expected to track to our NW while high pressure moves into the
Atlantic. There`ll be a chance of rain during the afternoon in the
central Shenandoah Valley..with the moisture tracking north Sunday
night. We are presently forecasting mixed precipitation west of
I-95...but confidence is low with regard to the frozen precip.
The high moving away means that cold air will not be held to our
north which is essential..especially in a marginal situation like
this. Lows expected to be in the lower to mid 30s.
High pressure returns for Monday. Highs near 50. Monday night lows
in the lower 30s.
.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Areas of dense fog with LIFR cigs across the central Mid-Atlantic
early this morning will slowly lift/diminish as clouds and rain
spread northeast across the area through sunrise. However, IFR conds
expected to prevail into the afternoon as potentially gusty showers
cross the area continues. Isolated thunder risk this afternoon and
evening, particularly southeast of DC. South winds increase by midday
with gusts into the 20 kt range.
Cold front crosses the area after midnight tonight with a shift to
west winds. Gusts in 25 kt range Friday and Saturday with VFR conds.
VFR conditions Saturday into the at least the first part of
Sunday. Clouds are expected to increase Sunday night with a chance
Just like yesterday, south winds increase today as rain overspreads
the area through the morning. Gusty showers and isolated
thunderstorms may trigger special marine warnings, particularly in
A cold front crosses the area tonight with a shift to west winds
after midnight. West winds mix down through Thursday with gusts
around 25 knots across the waters. SCA through Thursday for now and
is likely again both Friday and Saturday.
SCA level wind gusts possible Saturday. No problems foreseen
Southerly flow continues on the water today ahead of a cold front
that will cross late tonight. Winds will generally be 15 knots
gusting 20 knots which would not cause much of a surge and the
forecast is for water levels to remain a few inches below minor
flood thresholds for the preferred high tide this afternoon and
evening. However, stronger winds may mix down as showers and isolated
thunderstorms cross this afternoon. A stronger surge could occur with
this activity, perhaps raising levels to minor coastal flood levels.
New moon is today.
DC...Dense Fog Advisory until 7 AM EST this morning for DCZ001.
MD...Dense Fog Advisory until 7 AM EST this morning for MDZ003>006-
VA...Dense Fog Advisory until 7 AM EST this morning for VAZ025>031-
WV...Dense Fog Advisory until 7 AM EST this morning for WVZ050>053-
MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ530>532-
Small Craft Advisory until 6 PM EST Thursday for ANZ533-534-