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fxus61 klwx 170050 
afdlwx

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
850 PM EDT Tue Jul 16 2019

Synopsis...
an upper level disturbance will cross the area this evening. The
remnants of Barry will then affect the region late Wednesday
into Thursday. High pressure will return for Friday and into the
weekend.

&&

Near term /until 6 am Wednesday morning/...
isolated showers and thunderstorms have occurred this afternoon
into this evening, but a mid-level cloud deck is the likely
reason why convection has not been more widespread. Having that
been said, cape values are still high this evening, and there is
a Bay breeze/outflow boundary moving toward the Metro areas.
Therefore, isolated showers and thunderstorms are possible
across these areas this evening. Elsewhere, mainly dry
conditions are expected but an isolated shower cannot be
completely ruled out.

For the overnight, dry conditions are most likely along with
more warm and humid conditions. Min temps will be in the 70s for
most areas. Patchy fog is possible toward morning, mainly in
sheltered valleys and river valleys of the Potomac Highlands.

&&

Short term /6 am Wednesday morning through Thursday night/...
the area will remain in a hot pattern through midweek as light
southwest flow will support 850 mb temperatures around 20c.
Looks like most guidance has low-level temps progged to be about
1-2 c higher Wednesday afternoon compared to Tuesday. Therefore,
Max temps should be around 2-4 f higher compared to today. Given
this trend, and keeping the dewpoints in the lower 70s for most
areas (mid to upper 70s near the waters), this should be enough
for heat indices to be right around 105 degrees for locations
near and east of Interstate 95. Therefore, a heat advisory has
been issued for those areas. Elsewhere, heat indices will be
close to 100 degrees during peak heating in the valleys and for
locations near the Blue Ridge mountains including the far
northern and western suburbs of Washington and Baltimore.

A trough axis will be crossing the area in the late
afternoon/evening hours. The added forcing on an inherently
unstable air mass will result in scattered to numerous
thunderstorms, any of which could be severe. Additionally,
precipitable water in excess of 2 inches suggests these storms
will be capable of heavy rainfall as well.

The trough will be overhead through at least the first half of
Thursday, and should pull eastward by late in the day. Scattered
shower/thunderstorm development is expected again, and will
likely happen sooner in the day than either today or Wednesday.
Therefore, given more cloud cover and earlier chances for
precipitation, temperatures will likely be several degrees
"cooler" than Wednesday, although dew points may tick up a
degree or two. Highs Thursday will generally be from 87-92f,
with heat index values in the upper 90s to low 100s. Lows
Thursday night from 70-80f.

&&

Long term /Friday through Tuesday/...
high pressure will shift back over our region Friday and remain in
place through the weekend. Weak upper level ridging will be in place
to our north which will lead to warm and humid air being advected
into our region. This synoptic setup is indicative of a very hot
pattern which will lead to daytime temperatures hovering in the mid
to upper 90s and possibly the low 100s. The combination of high
temperatures and dewpoints will lead to an environment conducive for
heat indexes reaching above 105 and possibly over 110. This suggest
that heat advisory criteria will likely be reached Friday through
Sunday and possibly reach heat warning levels this weekend. High
temps and dew points will also create an environment favorable for
the formation of pop up thunderstorms and showers. Models have
average cape values between 1500 and 2000 j/kg with little to no
shear. This indicates an isolated pulse severe storm threat.

On Monday, a cold front will move through out region. The models
have a focused line of storms and rain moving through Monday into
early Tuesday. The hot and humid air ahead of this boundary will
make the environment favorable for development of thunderstorms and
possibly severe weather. We will need to continue to monitor the
models for the timing and strength of these storms but there remains
a lot of uncertainty at this time.

&&

Aviation /01z Wednesday through Sunday/...
VFR will generally prevail outside of showers and thunderstorms
over the next several days. Each day through Thursday carries a
thunderstorm chance, with local/brief flight restrictions and
gusty winds. Wednesday's threat is most likely between 18-00z
for the western terminals and 21-03z for the eastern terminals.

Hot and humid conditions are expected Friday and into the weekend.
Skies should remain mostly clear along light winds out of the south
to southwest. Isolated thunderstorms and showers will be possible
especially for the cho and mrb terminals. VFR conditions expected at
this time for both Friday and Saturday.

&&

Marine...
south winds less than 10 kt this evening. However, an isolated
thunderstorm may produce locally gusty winds through late this
evening.

A similar story will carry through Thursday, with daily
shower/thunderstorm chances, especially during the
afternoon/evening hours. Marine warnings possible both days as
well. In addition, the gradient wind may be a bit stronger late
tomorrow. Do not have the confidence to raise a Small Craft
Advisory at this time, but would not rule out eventually.

Hot and humid conditions along with light winds out of the south
expected Friday and Saturday. Small craft advisories may be needed
due to the southerly flow.

&&

Lwx watches/warnings/advisories...
District of Columbia...heat advisory from 11 am to 8 PM EDT Wednesday for dcz001.
Maryland...heat advisory from 11 am to 8 PM EDT Wednesday for mdz011-013-
014-016>018-504-506-508.
Virginia...heat advisory from 11 am to 8 PM EDT Wednesday for vaz052>057.
WV...none.
Marine...none.

&&

$$
Synopsis...bjl/hts
near term...bjl/hts

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