Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 311915

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
315 PM EDT Tue Mar 31 2020

Low pressure will move offshore of South Carolina this evening,
then head out to sea Wednesday as it strengthens. High pressure
will slowly build in from the Midwest through the end of the
week. The high will gradually move offshore over the weekend. A
cold front may approach from the Ohio Valley by early next week.


Surface low pressure is over Georgia this afternoon with its
associated overrunning rain shield extending up through the
southern half of Virginia. While the previously mentioned
backdoor front is losing its definition, there`s still a notable
demarcation with lower clouds and a cluster of showers across
the Baltimore metro. While there could be some light rain along
this boundary as it gradually continues its southwestward
motion, the main area of rain will be moving up from the south.
However, drier air will eventually work in behind the backdoor
boundary, which will limit its northward progress. Thus
locations near and north of US 50 may not see much rain at all,
and even across far southern areas, amounts should be less than
a half inch. Rain associated with the low will pivot to the
southeast after midnight, while moist onshore flow may cause
some light precip to linger until dawn along and west of the
Blue Ridge. Temperatures along the highest ridges will be
marginally supportive of snow, although amounts are expected to
be below advisory levels. Low temperatures will settle into the
mid 30s to lower 40s for most.

Upper level troughing will remain overhead on Wednesday, which
will likely promote cloud cover to persist much of the day. A
few showers are possible in the afternoon as a vort max crosses,
mainly near and west of the Blue Ridge. With continued cold
advection and cloud cover, temperatures will be held in the 50s.


A secondary boundary will slip southward Wednesday night. It
should be dry, but winds may pick up a bit. So even though low
temperatures will be in the mid 30s to around 40, the
probability of any frost is low.

Gusty winds will continue into Thursday between the deep low
pressure off the coast and high pressure extending across the
Great Lakes. Skies should be clearer overall though, with high
temperatures in the mid 50s to the lower 60s. Lows will again be
in the mid 30s to lower 40s as winds being to diminish.


Split zonal flow will be the story for Friday and Saturday, with
little to no chance of precipitation either day. Meanwhile, surface
ridge axis will be settled over the Ohio Valley, slowly moving east
over the region later Saturday. Temperatures on both days will be
seasonable, with highs in the upper 50s to low 60s.

A very weak cold front may push through the region on Sunday, but
precipitation chances with this seem rather low at this point. If
anything, just some light showers. Temperatures will be warmer
though, as winds turn more southerly ahead of the approaching front,
and behind the departing surface ridge. Highs expected to be closer
to the mid 60s.

Not much of a temperature drop at all behind the aforementioned
front, as highs on Monday expected to be in the upper 60s to near
70. This is a result of surface high pressure moving offshore of the
northeastern U.S. and turning winds back out of the southeast once
again. Showers will again be possible Monday.


Low pressure will be passing to the south through tonight,
though its rain shield will only be grazing the area. A backdoor
boundary has led to some showers and IFR conditions at MTN,
though progress to BWI is uncertain as the showers lifted to the
north. Elsewhere, VFR is continuing, but MVFR is expected to
continue to overspread the area (from the south and northeast)
during the late afternoon and evening. A period of IFR is
possible this evening, but removed it from DCA/BWI/MTN, as drier
air is progged to advect in behind the backdoor boundary. Rain
shouldn`t lower vsby below 3SM except perhaps at CHO. The drier
air will bring rising ceilings late tonight into Wednesday
morning as any chance of precipitation ends.

Upper level energy will keep VFR stratocumulus across the area
Wednesday and perhaps a brief shower in the afternoon. Ceilings
will clear out Wednesday night. Northwest winds will be gusty
(up to 25 kt) on Thursday.

VFR conditions expected Friday and Saturday, as high pressure builds
in from the west.


SCA conditions likely to develop at least on part of the waters
by this evening and continue into Wednesday as a low pressure
passes to the south. Have expanded the advisory in both area and
time based on latest guidance, and it`s possible further
expansions are possible. After a lull late Wednesday, another
front combined with high pressure building in likely leads to
another period of SCA conditions late Wednesday night and
Thursday. SCA conditions may linger into Friday on portions of
the water as the strong offshore low only slowly moves away.

No marine hazards expected on Saturday into Sunday, as high
pressure will be building in from the west.


The tide forecast still has some uncertainty tonight into
Wednesday due to distant but deep low pressure expected to pass
south and east of the region. Generally onshore flow would
result in increasing water levels. But the exact direction and
strength of the winds, as well as the timing of a wind shift to
a more northerly to northwesterly offshore direction will
determine exactly how high water levels are able to get over the
next several tide cycles. Right now, it appears minor inundation
is most likely for the more sensitive sites during the Wednesday
morning/midday high tide cycle.


MARINE...Small Craft Advisory from 9 PM this evening to 3 PM EDT
     Wednesday for ANZ531>533-539>542.
     Small Craft Advisory from 6 PM this evening to 6 PM EDT
     Wednesday for ANZ534-537-543.


TIDES/COASTAL FLOODING...DHOF/ADS is the U.S. government's official web portal to all federal, state and local government web resources and services.