Area Forecast Discussion
Issued by NWS Sterling, VA

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482
FXUS61 KLWX 300110
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
910 PM EDT Wed Mar 29 2017

.SYNOPSIS...
High pressure will pass north of the area tonight before moving
off the coast Thursday. Low pressure will pass through the area
Friday. High pressure will gradually return Saturday and Sunday
before another low pressure possibly impacts the area Monday
and Tuesday next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
High pressure is centered over eastern Ontario and western
Quebec this evening. Surface winds are taking a northeasterly
component, and the earlier cu field around Staunton and
Charlottesville is expanding into broken altostratus. Elsewhere,
only a little cirrus is found, which will be the case until the
lower cloud decks expand later tonight as the flow becomes
easterly. In addition, the easterly flow may result in some
spotty light rain or drizzle, mainly in the southern Shenandoah
Valley and adjacent highlands. Lows tonight will be cooler than
the last few nights, with readings in the 30s and 40s. Am not
planning any major adjustments to temperatures, though
variations in cloud cover and decoupling could modulate them up
or down, respectively, in some spots.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
CAD will more or less remain in place in the low levels
Thursday with the high pressure sliding eastward to our north.
At the same time, low pressure system will be ejecting out of
the plains with warm/moist air advection. In addition, the
upslope flow will result in lower clouds and perhaps some light
rain or drizzle in the mountains. Highs will be cooler than
today due to the lack of sun and onshore flow, with 50s
widespread and the cooler spots in the 40s.

Warm and moist air advection continues Thursday night and with
that we`ll see increasing chances for rain. Lows mainly in the
40s. Model guidance in good agreement that the low pressure
system will track east-northeastward from near St. Louis
Thursday evening to Ohio by Friday afternoon, before
redeveloping near the DelMarVa late Friday and Friday night.
Thus, most widespread coverage of moderate rain expected late
Thursday night and Friday morning, although chances of rain will
remain high into the afternoon. Half an inch of rain is likely
for most of the area, with over an inch wherever the most
favorable forcing aligns. We`ll also have to monitor how far
north the warm sector can make it Friday afternoon. Latest
guidance indicates it may approach portions of central VA and
southern MD, so have maintained a slight chance of tstorms there
Friday afternoon. Highs on Friday uncertain, with locations
that get south of the warm front possibly heading towards 70,
while northern locales near the Mason-Dixon line may struggle to
reach 50. Showers will begin to slowly wind down Friday night
as the low pulls away and winds turn northwesterly.

Low pressure slides northeast of the region Saturday, but
lingering instability and weak vort max could produce a few
stray showers still. Highs will be in the 50s to lower 60s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
High pressure will settle into the region Sunday through early
Monday. Dry and seasonable temperatures expected throughout the
period.

The next storm system will move into the region midday Monday
through Tuesday, bringing the chance for rain showers to the
region once again.

Brief high pressure will build into the region Wednesday before
the next storm system approaches Wednesday night.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
VFR will continue through at least the first half of Thursday
all terminals. Winds have become northeasterly this evening,
becoming east-southeasterly on Thursday. This will help usher
in additional clouds, although ceilings still expected to remain
VFR. Highest chances for some MVFR ceilings will be at CHO and
MRB, but the probability of this occurring is low until after
00Z Friday.

Greater chances for sub-VFR conditions will occur Thursday night
through Friday night with widespread rainfall. IFR conditions
likely.

A northwest flow will allow for cigs/vsbys to improve Saturday
behind departing low pressure...but a few showers cannot be
ruled out.

Vfr conditions evolving Saturday night. Winds northwest 5 knots
Saturday night. Vfr conditions expected Sunday into Sunday
night. Winds becoming light and variable Sunday and Sunday
night.

&&

.MARINE...
Winds have taken a NNE direction this evening, locally 10 to 15
knots. A surge of northeasterly winds is expected later
tonight, although magnitudes are a bit uncertain. Guidance
suggests the best window for SCA conditions will be between 11
pm and 3 am. So if gusts are not realized by this time, the SCA
for the more open waters of the Bay and lower Potomac may be
cancelled early.

Sub-SCA winds then expected Thursday, with next potential for
increasing winds on Thursday night/Friday ahead of our next
system (especially Friday), with the strongest winds expected
across our southern waters.

Low pressure will move away from the waters Saturday and
northwest flow will develop. A Small Craft Advisory may be
needed for portions of the waters during this time.

No marine hazards expected Saturday night through Sunday
night. Winds northwest 5 to 10 knots Saturday night through
Sunday night.

&&

.TIDES/COASTAL FLOODING...
Low pressure will pass through the area Friday night. An
onshore flow will develop ahead of the low and this will cause
elevated water levels Friday into Friday night. Minor tidal
flooding near high tide is possible during this time.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ530>534-
     537-539>541-543.

&&

$$
SYNOPSIS...ADS/RCM
NEAR TERM...ADS/RCM
SHORT TERM...ADS/RCM
LONG TERM...KLW
AVIATION...ADS/RCM/KLW
MARINE...ADS/RCM/KLW
TIDES/COASTAL FLOODING...LWX



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