Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 270759

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EDT Tue Jun 27 2017


A weak level trough will move track north of the region today.
High pressure builds over the area Wednesday before moving
offshore Thursday. Warm conditions expected towards the end of
the week and through the weekend.



As of 3am, an upper trough rounds the Great Lakes (with the axis
from MI to St. Louis) per water vapor imagery. A 1021mb surface high
is centered over the central Great Plains. This surface high will
continue to drift east in the wake of the upper trough axis to the
central Mid-Atlantic through tonight. The high center will move off
the mouth of the Chesapeake Bay Wednesday. West flow and cold air
advection under the upper trough will keep temperatures below normal
through Wednesday night.

A weak cold front which switched the wind direction from SW to NW is
still moving SE across St. Marys county and will clear the MD
portion of the Chesapeake Bay by 5am. A line of showers and
thunderstorms developed over the northern Chesapeake Bay as the
trough crossed those warm waters earlier tonight. A similar
phenomenon is possible this evening as another cold front (this one
under the upper trough axis) pushes east through the area.

The northern Potomac Highlands will see light to locally moderate
showers move east across the area through 7am. These should
generally dissipate as they encounter downsloping east of the
Allegheny Front. However, this activity is riding potential
vorticity advection ahead of the upper trough axis and the early
diurnal heating this time of year should enable redevelopment east
of the Blue Ridge per high resolution guidance.

Maintained low chance PoPs east of the Blue Ridge for this afternoon
when a second round of precip is likely given the approach of the
upper trough axis and peak heating.

Max temps raised to low 80s today as 11C 850mb temps mix down in
westerly flow.



The surface high pressure center crosses the LWX CWA Wednesday
morning. Return southerly flow develops Wednesday afternoon with a
gradual return to summerlike conditions. Pressure gradient looks
light enough for good radiational cooling Wednesday night.

Max temps around 90F on Thursday with dewpoints rising into the 60s.



High pressure will have moved well offshore by Friday. This
will allow warmth/humidity to stream into the Mid Atlantic.
Upper level ridge will not bring the east coast especially high
heights so expect to see highs around end-of-June climo norms
of near 90.

Low pressure is expected to spin over Ontario/Quebec this
weekend. This will allow a weak cold front/trough to be in the
vicinity of the Mid Atlantic which could provide a focus for
shower/thunderstorm activity, although by no means should the
weekend be a washout.

Looking out to the 4th of July - there are differences between
the Euro and GFS. One thing seems certain is that the possibility
of it being an extremely hot day does not look to be in the
cards. Euro shows east coast "in between short waves" while GFS
has a short wave approaching the Appalachians Tuesay night. We
have a chance of showers/thunderstorms in the forecast but we`ll
continue to monitor in the coming days.



VFR prevails through the week as high pressure slowly builds from
the west. Passing shower/isolated thunderstorm both this morning and
later this afternoon across the DC metros ahead of a cold front.

High pressure overhead Wednesday with return southerly flow into the

Majority of Friday/Saturday should be VFR. There will be
potential for showers/thunderstorms - especially Saturday, which
could drop conditions briefly below VFR.



Weak cold front will continue moving SE through southern MD Bay
waters through sunrise with Wly/NWly flow through tonight as surface
high pressure slowly builds.

Return southerly flow begins Wednesday night as the high shifts to

Winds expected to be below SCA values Friday/Saturday.
Showers/isolated thunderstoms will be possible on the waters


MARINE...Small Craft Advisory until 4 AM EDT early this morning for


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