Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220750

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
350 AM EDT WED JUN 22 2016

High pressure will briefly build in from Canada today. A warm
front will lift north across the region tonight and the boundary
will drop south as a cold front later Thursday into Thursday
night. High pressure will return for Friday into the weekend.


Low pressure is located in northeastern New England this morning.
A frontal boundary is stretched from the New England coast
across southern PA. An upper level trough will swing across New
England this morning and northwest flow aloft will set up by this

Light winds across the region have led to a mild morning with
patchy fog in some low-lying areas. The frontal boundary will
move slowly southward across the region today. Sunny conditions
expected today as the Mid-Atlantic is between two upper level
features. Temps will reach the mid to upper 80s today.

Attention turns to the potential for severe weather and flooding
late tonight into Thursday across the Mid-Atlantic region. A
shortwave trough is expected to barrel across the Mid-West and
Ohio Valley today and tonight initiating convection across this
region. Surface low pressure will deepen in response to the
convection and due to the northwest flow aloft convection will
come towards the Mid- Atlantic. Conditions will be favorable for
thunderstorms overnight as a surge of high pwat air are collocated
with a 40-50kt LLJ reaching the Potomac Highlands after midnight
tonight. There is uncertainty with the timing of thunderstorms
moving into the region however there is a model consensus that
showers and thunderstorms will move through the region overnight
into Thursday morning. Thunderstorms have the potential for strong
winds. In addition to upper level support for these thunderstorms
the frontal boundary will be across the region and may lead to
redevelopment of showers and thunderstorms resulting in multiple
rounds of rain. Low flash flood guidance is across much of the
region due to the rain on Tuesday and a flash flood watch is in
effect for the Potomac Highlands. A extention in space and time is
possible for the flash flood watch as flash flood guidance is
lower further east and across the metros however due to the
uncertainity of size and timing of thunderstorm complext will hold
off and let future shifts re- evaluate.

Low pressure will move along the frontal boundary Thursday and
showers and thunderstorms are expected again. There is some
question as to the severity of thunderstorms since morning
convection may stabilize the environment however the Mid-Atlantic
region will be in the warm sector of a highly sheared environment
so attention is needed for Thursday. Thunderstorms have the
potential to be strong to severe Thursday afternoon.


The frontal boundary will sag southward Thursday night and into
Friday. Dry northerly flow will move into the region but it will
be slow. Showers and a few thunderstorms are possible mainly in
Central VA and the VA highlands Friday afternoon. Max temps will
be cooler with temps in the U70s/L80s and low humidity.


High pressure will build into the region Friday night through
Sunday...bringing drier and cooler conditions to the area. An
isolated shower cannot be ruled out near the Blue Ridge Mountains
and Potomac Highlands...but even across these areas much of the
time will be dry.

High pressure will move offshore Monday and a return flow will
allow for more humid conditions. A few showers and thunderstorms
are possible during this time. A cold front may impact the area
Tuesday into Wednesday.


VFR conditions expected today and into tonight. Mid-high
level clouds will increase from the west late this afternoon and
spread across the region overnight. SHRA are expected late tonight
into Thursday morning with the potential for TSRA after 6z tonight
into Thursday morning. TSRA will bring gusty winds as wind flow
aloft increases and LLWS may also be a concern Thursday morning.
Winds at 2k feet may be close to 40kts 12z Thurs coupled with TSRA
may make for a high impact aviation period across all terminals. Sub-
vfr conditions expected late tonight through Thursday as SHRA/TSRA
redevelop into Thursday afternoon. Gusty winds are possible in
activity Thursday afternoon.

High pressure will bring VFR conditions most of the time Friday
night through the weekend. High pressure will move offshore Monday
and a few showers and thunderstorms are possible.


Westerly winds persist on the waters this morning. Gusty
winds around 20kts are expected on the lower tidal potomac and
lower bay this morning. Winds will become SW today and gusty
winds around 20kts are expected on all the waters. Winds will
likely diminish in the late afternoon and SCA conditions will end
during this time. Winds should stay below SCA tonight however
winds will likely increase Thursday morning. Showers are also
expected across the waters Thursday morning and will continue into
the afternoon. Thunderstorms are possible and gusty winds will
likely bring SMW conditions.

High pressure will bring an easterly flow to the area Friday night
through the weekend. Winds should remain below sca criteria. The
high will move off the coast Monday and a cold front may impact
the waters during the middle portion of next week. More showers
and thunderstorms are possible during this time.


MD...Flash Flood Watch from late tonight through Thursday afternoon
     for MDZ003-501-502.
VA...Flash Flood Watch from late tonight through Thursday afternoon
     for VAZ027-028-030-031-503-504.
WV...Flash Flood Watch from late tonight through Thursday afternoon
     for WVZ050>053-055-501>506.
MARINE...Small Craft Advisory from 7 AM this morning to 6 PM EDT this
     evening for ANZ530>532-535-536-538>540.
     Small Craft Advisory until 6 PM EDT this evening for ANZ533-


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