Severe Thunderstorm Warning 64, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1012 AM EDT THU JUN 16 2016

.SYNOPSIS...
Low pressure in the Great Lakes this morning will slide southeast
across West Virginia and Virginia later today and tonight. It will
exit southeastward into the Atlantic Ocean on Friday. High
pressure from southern Canada will then build across the area
through the weekend. A cold front will slide southeast into the
area Tuesday night into Wednesday.

&&

.NEAR TERM /THROUGH FRIDAY/...
Closed low now located over eastern Michigan will push
southeastward and towards the region this afternoon and evening.
Stalled surface boundary also noticeable bisecting the region from
about central MD and through DC. South of the warm front...air
temperatures will likely warm quite a bit today with upper 80s and
low 90s expected. On the cooler side of the boundary, northeast
flow will keep areas in the upper 70s. Clearing line from this
early morning's convection now pushing through northern Virginia
which will allow for instability to develop later this morning and
into the afternoon hours. Also currently monitoring convective
line moving into western Pennsylvania as its ultimate evolution
will play a role in how our afternoon/evening thunderstorm threat
evolves.

May see thunderstorms initiate off any outflow boundaries that
ongoing MCS puts down, but also expecting some initiation back
across Ohio where surface convergence/wind shift is noticeable
this morning. SPC has maintained an Enhanced Risk of severe
thunderstorms across the region from DC south and west with slight
risk northeast of there. Agree with this assessment as areas on
warm side of boundary will certainly see greater instability with
upwards of 1000 J/KG MLCAPE expected to develop there. This
combined with 0-6KM wind shear of 40 knots or so and strong closed
low supports damaging wind threat across this region. Large hail
also a possibility, and even a possible tornado as directional
shear exists along the low level boundary.

Besides the severe threat...we also have potential heavy rain.
Flash flood watch in effect this evening and tonight. Portions of
Maryland have seen 0.5-1.0" of rain this morning already.
Expecting additional heavy rain amounts with convection this
afternoon, but greater threat exists when closed low tracks south
the DC region overnight and strong low level jet develops,
ushering in moisture rich air with precipitable water values
possibly in excess of 2". Greatest threat of localized flash
flooding currently though to exist in far northern VA, across DC,
and into central Maryland.

The system will slide southeast of us through the day Friday with
rain diminishing and some clearing likely later on. Highs will be
notably cooler across the board with the Canadian air mass pushing
in.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
Northerly flow aloft and high pressure from Canada building in
will result in a quiet period of weather to start the weekend.
Skies will be mostly clear and temperatures generally a few
degrees below normal...all-in-all, pretty nice for mid June.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
High pressure likely centered overhead Sunday morning with the
low pressure sequestered offshore south or southeast of the Mid-
Atlantic. High pressure remains over the area until that low
pressure curls back toward the coast, or a cold front reaches the
area late Tuesday. As of now the 00Z GFS/ECMWF operational runs
and GFS ensembles keep the low off the Mid-Atlantic coast through
at least Monday. Slightly below normal temperatures and dry
conditions under the high.

The best chances in the long term for precipitation is ahead of a
cold front that crosses Tuesday night. The parent low pressure
looks to be in the Gulf of St. Lawrence by Tuesday night.
Therefore, forcing looks weak from an organized thunderstorm
perspective, but strong enough to push through the area and into
the carolinas. Near or just above normal temperatures Tuesday
ahead of the cold front.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Reduced ceilings and visibilities in morning low clouds and mist
will give way to improving conditions briefly this afternoon.
Showers and thunderstorms then expected later this afternoon and
into tonight with periods of MVFR/IFR expected. Some of the
thunderstorms may also contain damaging winds and large hail.
Rain persists overnight with sub-VFR conditions likely persisting. Conditions
gradually improve Friday with VFR Friday night thru Monday under
high pressure.

&&

.MARINE...
System passing through tonight will bring northeasterly winds to
SCA levels tonight into Friday night...diminishing by Saturday as
the system departs. Rain and possibly gusty thunderstorms may also
result in SMW's this afternoon and evening.

Light winds and sunny skies under high pressure Sunday and Monday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flash Flood Watch from 5 PM EDT this afternoon through late
     tonight for DCZ001.
MD...Flash Flood Watch from 5 PM EDT this afternoon through late
     tonight for MDZ003>006-011-013-014-501>506.
VA...Flash Flood Watch from 5 PM EDT this afternoon through late
     tonight for VAZ026>031-039-040-051>054-501-502-505>507.
WV...Flash Flood Watch from 5 PM EDT this afternoon through late
     tonight for WVZ050>053-055-501>504.
MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT
     Saturday for ANZ532>534-537-540-541-543.
     Small Craft Advisory from 6 AM to 6 PM EDT Friday for ANZ530-
     535-536-538.
     Small Craft Advisory from 6 AM Friday to 6 AM EDT Saturday for
     ANZ542.
     Small Craft Advisory from 6 PM this evening to 6 PM EDT Friday
     for ANZ531-539.

&&

SYNOPSIS...RCM
NEAR TERM...MM/RCM
SHORT TERM...RCM
LONG TERM...BAJ
AVIATION...BAJ/MM/RCM
MARINE...BAJ/MM/RCM

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