Severe Thunderstorm Warning 129, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
237 PM EDT Thu Jul 6 2017

.SYNOPSIS...
A weak frontal boundary persists across the Mid-Atlantic through
tonight. Low pressure crosses the area tonight. A cold front
will cross through the region Friday night into Saturday
morning. High pressure builds into the Mid-Atlantic behind the
front this weekend and persists into Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Have expanded/lengthened the flash flood watch. Given the
history of the atmosphere over the past 24 hours, the fact that
the regional radar shows a line of heavy showers forming along
the Mason-Dixon line westward to central OH/western KY moving
east, and the WPC day 1 excessive rainfall graphic (they've done
very well in the past two days) feel this is the proper track.
Hopefully this won't come to fruition. Have heard that in
Fairfax Co several roads are closed due to high water. Our
radar operators will be on guard through the evening.

Previous...

High pressure has moved off the ME coast and in response the
boundary has dropped further in the western Atlantic and then
moving northwest across our forecast area. This has provided the
focus for very heavy rainfall this morning - NHK received 1.05"
in 23 minutes this morning. IAD 12Z sounding had a PWAT of
2.14", which is even higher than yesterday morning's 1.89. As a
result showers which formed were extremely efficient rain
producers.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...

Cold front approaches the area from the NW late Friday into
Saturday...with a possibility of thunderstorms reaching the far NW
portion of the forecast area by Friday evening.

Dewpoints in the 50s Saturday night should be most welcome.

Areas should remain dry into Sunday as high pressure building
into the area allows for drier air to filter into the region.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...

Models are in excellent agreement with strong high pressure building
over the area Sunday. Pleasantly warm temperatures and unseasonably
dry conditions are expected during this time.

The high will move offshore early next week resulting in increasing
temperatures and humidity Monday into Tuesday. Good model agreement
on this, though some guidance tries to have enough moisture return
to result in showers as early as Monday afternoon (given the
synoptic setup, believe this is a little quick, but during this time
of year pop up showers are typical during the heat of the day, so
cannot be ruled out).

A slow-moving cold front will drop into the area during the middle
of next week offering the next chance of more widespread showers
and (potentially heavy) thunderstorms. GFS guidance becomes notably
quicker (by about 6-12 hours) than the EC guidance by midweek,
introducing more uncertainty to the forecast at this time range.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Showers and thunderstorm chances continue through tonight...
with flight restrictions likely in the heaviest activity.
Improving conditions expected late Friday into the weekend as
drier air filters into the region.

VFR flight conditions expected Sunday into Monday.

&&

.MARINE...
Showers and thunderstorms with very heavy rainfall are
possible. A few storms across the Tidal Potomac and middle Bay
could contain gusty winds...with perhaps an isolated SMW. Winds
could increase to SCA Friday into Saturday as a cold front
crosses the area.

Light winds are expected Sunday into Monday as high pressure
moves overhead, though if the high moves offshore a little quicker,
gusts close to SCA levels are possible Monday.

&&

.TIDES/COASTAL FLOODING...

Coastal flood advisory in effect for St. Mary's through 4 am.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flash Flood Watch until 2 AM EDT Friday for DCZ001.
MD...Flash Flood Watch until 2 AM EDT Friday for MDZ003>006-011-013-
     014-016>018-501>508.
     Coastal Flood Advisory until 4 AM EDT Friday for MDZ017.
VA...Flash Flood Watch until 2 AM EDT Friday for VAZ027>031-038>040-
     050>057-501-502-505>507.
WV...Flash Flood Watch until 2 AM EDT Friday for WVZ050>053-055-
     501>504.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.

&&

PRODUCTS...WOODY!/DFH

Hazardous Weather Outlook
National Weather Service Baltimore MD/Washington DC
209 PM EDT Thu Jul 6 2017

ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-071815-
Chesapeake Bay north of Pooles Island MD-
Chesapeake Bay from Pooles Island to Sandy Point MD-
Chesapeake Bay from Sandy Point to North Beach MD-
Chesapeake Bay from North Beach to Drum Point MD-
Chesapeake Bay from Drum Point MD to Smith Point VA-
Tidal Potomac from Key Bridge to Indian Head MD-
Tidal Potomac from Indian Head to Cobb Island MD-
Tidal Potomac from Cobb Island MD to Smith Point VA-
Patapsco River including Baltimore Harbor-
Chester River to Queenstown MD-Eastern Bay-
Choptank River to Cambridge MD and the Little Choptank River-
Patuxent River to Broomes Island MD-
Tangier Sound and the inland waters surrounding Bloodsworth
Island-District of Columbia-Southern Baltimore-Prince Georges-
Anne Arundel-Charles-St. Marys-Calvert-Southeast Harford-
Prince William/Manassas/Manassas Park-Fairfax-
Arlington/Falls Church/Alexandria-Stafford-Spotsylvania-
King George-
209 PM EDT Thu Jul 6 2017

This Hazardous Weather Outlook is for the Maryland portion of the
Chesapeake Bay, Tidal Potomac River, and adjacent counties in
central Maryland and northern Virginia as well as the District of
Columbia.

.DAY ONE...This Afternoon and Tonight

A Flash Flood Watch is in effect for the area through 2 am. Slow
moving showers and thunderstorms capable of producing heavy rain
will be possible. These may lead to flash flooding.

Isolated thunderstorms capable of producing gusty winds over the
waters are possible this afternoon and evening across the Tidal
Potomac and Chesapeake Bay.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time. However, please
forward rainfall and high water reports to the National Weather
Service.

MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053-
055-501>506-071815-
Washington-Frederick MD-Carroll-Northern Baltimore-
Extreme Western Allegany-Central and Eastern Allegany-
Northwest Montgomery-Central and Southeast Montgomery-
Northwest Howard-Central and Southeast Howard-Northwest Harford-
Augusta-Rockingham-Shenandoah-Frederick VA-Page-Warren-Clarke-
Nelson-Albemarle-Greene-Madison-Rappahannock-Orange-Culpeper-
Northern Fauquier-Southern Fauquier-Western Highland-
Eastern Highland-Western Loudoun-Eastern Loudoun-
Northern Virginia Blue Ridge-Central Virginia Blue Ridge-
Hampshire-Morgan-Berkeley-Jefferson-Hardy-Western Grant-
Eastern Grant-Western Mineral-Eastern Mineral-Western Pendleton-
Eastern Pendleton-
209 PM EDT Thu Jul 6 2017

This Hazardous Weather Outlook is for eastern West Virginia,
northern and central Virginia, and central and western Maryland
with the exception of Garrett County.

.DAY ONE...This Afternoon and Tonight

A Flash Flood Watch is in effect for much of the area through 2 am.
Slow moving showers and thunderstorms capable of producing heavy
rain will be possible. These may lead to flash flooding.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time. However, please
forward rainfall and high water reports to the National Weather
Service.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
432 PM EDT THU JUL 06 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0815 PM     TORNADO          1 ENE RANSON            39.30N  77.85W
07/05/2017                   JEFFERSON          WV   NWS STORM SURVEY

            BRIEF EF-0 TORNADO. SIGN DAMAGED AT JEFFERSON CROSSING
            SHOPPING CENTER. BARNS DAMAGED AT HOLLYWOOD CASINO AT
            CHARLES TOWN RACES.

&&

EVENT NUMBER LWX1702283

DH

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