Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 121358

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
958 AM EDT Thu Apr 12 2018

A warm front will cross the region today. High pressure will
build across the western Atlantic through Saturday. A large area
of low pressure is then expected to develop over the Mid-
Mississippi River Valley Sunday and move northeastward into the
eastern Great Lakes, dragging a powerful cold front across the
Mid-Atlantic Sunday night and early Monday.


A band of echoes on radar are moving east across Maryland and
northern Virginia this mid morning. The dry low levels of the
atmosphere are evaporating much of it before it reaches the
ground. But sprinkles are being reported and expecting a few
measurable reports of rain as this moves through...mainly along
the northern tier of Maryland.

A noticeable change in weather conditions will occur today as a warm
front crosses the region today, clearing the clouds and ushering
in warm and dry southwest flow. After frontal passage,
southwest flow will increase, skies will begin to clear, and
temperatures are expected to rise. High temperatures should peak
in the 70s area-wide by late this afternoon under mostly sunny
skies. Southwest winds will increase markedly as well with gusts
to around 35 mph developing by late in the day. Thus fire
weather is the main weather concern of the day, see fire weather
discussion for additional details.


Relatively mild conditions with a southwest breeze are expected
tonight. Lows tonight drop into the upper 40s to mid 50s. On Friday,
mostly sunny skies and dry conditions continue. Temperatures should
soar into the upper 70s and low 80s, with a dry southwest breeze.
Conditions will not be quite as windy as today, with gusts on the
order of 25-30 mph. Lows Friday night will be even milder than
tonight, generally in the 50s to locally near 60F.

Low pressure will then begin to move eastward during the day
Saturday, although our region will remain in warm southerly flow.
Moisture will begin to return with dew points rising back into the
50s. This will allow for some additional cloud cover, and perhaps
even an isolated shower or two across the higher terrain. This may
keep temperatures a couple of degrees cooler than Friday, but
nevertheless highs in the 70s to around 80F are expected again.

The low pressure area will continue its eastward trek Saturday
night. Flow will turn more southerly vs. southwesterly, and this
will continue to increase low level moisture. Dew points reach the
upper 50s and may approach 60F in some locations by Sunday morning.
In addition, there may be the presence of some lower clouds that
develop Saturday night into Sunday morning. Lows generally upper 50s
to low 60s.


On Sunday... a low pressure system centered over
the Ohio Valley will be moving northeast and into the southern Great
Lakes. At the same time a high pressure system will be centered over
the west Atlantic. Southerly flow ahead of this front will continue
to advect warm and moist air into our region allowing for surface
dew points to the upper 50s and low 60s with cloudy skies.

A front associated with the aforementioned low pressure system
is expected to moved across the region on Sunday night.
Precipitation associated to this front could start as early as
Sunday afternoon, but the highest QPF amounts are expected
Sunday night into Monday morning with the strongest forcing
moving across the area. Instability seems marginal and currently
it seems that any thunder is more likely west of the Blue
Ridge, but cannot be ruled out for the rest of the region. Gusty
winds are expected behind the front on Monday and into possibly

High pressure builds in from the southwest Monday night and will
remain in control into mid-weed before another front approaches the


VFR is expected through Saturday. Main aviation weather concern
today is developing gusty southwest winds this afternoon and evening
with gusts to around 30-33 knots expected. These winds lessen
overnight, but return 20-25 knots on Friday. There is potential for
some lower clouds Saturday night that may result in a period of sub-
VFR conditions.

VFR conditions expected on Sunday and gradually
becoming sub-VFR into Sunday night as a front approaches the area
bringing rain and maybe thunder over our area. VFR conditions return
later on Monday and remain into Tuesday.


SCA is in effect for all waters through today for developing gusty
south/southwest winds. Widespread gusts from 25 to 30 knots are
expected. There may be a brief window late this afternoon and
evening where Gale conditions are met, but confidence in occurrence
and duration is not high enough at this time for a Gale Warning
given potentially lower atmospheric mixing with warm air
temperatures and cooler waters. The strongest gusts today will be
along the shorelines and near-shore waters.

SCA continues tonight over the central Chesapeake Bay and lower
Tidal Potomac, and then returns across all waters on Friday. These
will likely need to be extended for portions of the waters through
Saturday/Saturday night.

Small craft advisory possible from Sunday and into
Tuesday as winds will be near or above the threshold. Later on
Tuesday winds should gradually decrease below criteria.


Red Flag conditions are expected today for portions of the region
with developing gusty southwest winds and drying conditions. High
temperatures reaching into the 70s and low dew points will lead to
relative humidity values falling to between 20 and 30 percent this
afternoon and evening for eastern West Virginia, portions of central
and western Maryland, the District of Columbia, and all of
central/northern Virginia. Across northeastern Maryland and near the
Chesapeake Bay, relative humidity values may stay a bit more
elevated, between 30 and 35 percent. Winds will also markedly
increase this afternoon with sustained winds from 20-25 mph and
gusts to around 35 mph. With 10-hour fuel moistures between 7 and 8
percent, will issue a Red Flag Warning for much of the region, with
a Special Weather Statement for northeastern MD and along the
Chesapeake Bay.


A strong upper trough and attendant surface front will barrel
through the area Sunday night. PWATs ahead of the front are
progged to be around 1.5 inches, near record highs for the month
of April. Unidirectional flow and the parent upper low cutting
off suggests training of heavy rain is possible, though the
flooding threat may be mitigated by fast rain/storm motions and
antecedent dry conditions.


DC...Red Flag Warning until 8 PM EDT this evening for DCZ001.
MD...Red Flag Warning until 8 PM EDT this evening for MDZ003-013-
VA...Red Flag Warning until 8 PM EDT this evening for VAZ025>031-
WV...Red Flag Warning until 8 PM EDT this evening for WVZ050>053-
MARINE...Small Craft Advisory until 6 PM EDT Friday for ANZ532>534-537-
     Small Craft Advisory until midnight EDT tonight for ANZ530-531-
     Small Craft Advisory from 9 AM to 6 PM EDT Friday for ANZ530-


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