Severe Thunderstorm Warning 192, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
236 PM EDT Thu Aug 2 2018

.SYNOPSIS...
A cold front will approach the Mid-Atlantic from the Ohio Valley
today, then weaken over the area Friday. Meanwhile, high pressure
will remain over the western Atlantic through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
A line of showers and thunderstorms moving into the I-95
corridor as of 2pm. Meso-analysis indicating that effective
available shear around 40-45 kt, with around 1000-1500 J/kg
MLCAPE. In spite of rather meager lapse rates there has been
enough organization for rather interesting storm structures,
particularly for the cluster that has moved from metro
Charlottesville, headed toward the Washington DC metro area.
Following the faster CAM timing, believe that activity should
be approaching if not east of the Bay by 5 or 6pm.

There is considerable uncertainty as to what happens next. The
500 mb wind maximum will be sliding into/north of Pennsylvania,
which will reduce the shear profile. Even though the mountains
are less unstable, some CAMs suggest that a second round could
develop in the Appalachians. The HRRR leads this camp, but the
HRW-ARW/NMM both are on board.

Since the deep plume of moisture ahead of the longwave trough
will be closer to the forecast area tonight, and heights will be
lower as well, am hesitant to back off PoPs tonight. Will be
maintaining 40-50% chance overnight.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
The synoptic pattern will remain into Friday with the trough to our
west and the surface high pressure to our east. This will continue
to support southerly flow over our area streaming moist and warm
unstable air mass into our area. Showers and thunderstorms are
expected again on Friday with a higher concern of flooding due
to the possibility of training and slow moving thunderstorms.
Anomalously high PWAT values and strengthening 850-700 mb winds
likely will enhance the heavy rain threat. And, given enough
instability, there remains a localized damaging wind threat as
well.

Longwave trough weakens on Friday night and almost become zonal
by Saturday. More than sufficient moisture will still be
present, so scattered showers/thunderstorms still a concern. The
difference will be typical diurnal showers/thunderstorm vs
repeated torrential downpours from a stream of tropical moisture.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
On Sunday, a bit of weak ridging will build in at mid-levels. This
short wave ridging should limit the development of showers and
thunderstorms. For the first time in a long time, we may have a
mostly dry day.

We'll enter back into weak zonal flow aloft on Monday, but with no
mid-upper level features focusing ascent, conditions should stay
mostly dry. A trough will begin to approach from the Great Lakes
region on Tuesday. The main area of ascent associated with this
feature will still be located to our northwest, but it could spark a
few afternoon showers or thunderstorms across the area. Chances for
showers and thunderstorms will increase on Wednesday as the
aforementioned trough and it's associated cold front move closer by.
Temperatures will run a bit above normal through the long term
period, with high temperatures in the low 90s most days.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Conditions have risen to VFR across the area outside of
showers/thunderstorms. Cluster of note approaching DCA, which
likely will affect BWI/MTN as well. Brief aob IFR likely.

A bit uncertain what will transpire next in terms of rainfall,
but the risk of additional showers/storms exists. Am carrying a
vicinity remark through the evening to cover this threat.

Beyond this, believe that ceilings will be dropping. Have
confined these restrictions to MVFR for the TAFs, although the
threat of IFR does exist.

Similar conditions are expected on Friday. High pressure starts
building in on Friday night and conditions should be improving
into Saturday.

Conditions should stay primarily VFR on Sunday and Monday with
mostly dry conditions.

&&

.MARINE...
Small Craft Advisory remains in effect through this evening.
Wind gusts above threshold have been localized in south flow,
but the potential remains. This risk continues into Friday, but
confidence remains on the lower side at this point so will not
extend Advisory at this time.

Winds are expected to stay below the SCA threshold through the
duration of the long term period. Showers and thunderstorms may be
possible by late Tuesday and Wednesday.

&&

.HYDROLOGY...
The region will remain in a plume of 2+ inch PWAT air through the
end of the week. Storm motions may be somewhat quick today, but
training or repeated rounds of storms are possible given flow
parallel to a slowly approaching front. Upper flow slows a bit on
Friday while PWATs remain high, continuing the risk for repeated
heavy rain and potential flooding. This pattern should break down a
bit heading into the weekend.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flash Flood Watch through Friday morning for DCZ001.
MD...Flash Flood Watch through Friday morning for MDZ003>006-011-
     013-014-501>508.
VA...Flash Flood Watch through Friday morning for VAZ025>031-
     036>040-050>054-501>508.
WV...Flash Flood Watch through Friday morning for WVZ050>053-055-
     501>506.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.

&&

SYNOPSIS...
NEAR TERM...HTS
SHORT TERM...HTS
LONG TERM...KJP
AVIATION...HTS/KJP
MARINE...HTS/KJP
HYDROLOGY...

Hazardous Weather Outlook
National Weather Service Baltimore MD/Washington DC
511 AM EDT Thu Aug 2 2018

ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-030915-
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-
511 AM EDT Thu Aug 2 2018

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...Today and Tonight and Tonight

A Flash Flood Watch is in effect for the I-95 corridor north of
Fredericksburg. Isolated instances of flooding are also possible
outside the watch area near Fredericksburg to southern Maryland.

Thunderstorms may produce locally damaging wind gusts.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Showers and thunderstorms may result in locally damaging wind
gusts and flooding again on Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening.

MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053-
055-501>506-030915-
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-
511 AM EDT Thu Aug 2 2018

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...Today and Tonight and Tonight

A Flash Flood Watch is in effect today and tonight.

Thunderstorms may produce locally damaging wind gusts.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Showers and thunderstorms may result in locally damaging wind
gusts and flooding again on Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening.

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
557 PM EDT THU AUG 02 2018

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

0546 PM     FLOOD            1 SSE BOLLING AIR FORCE 38.83N  77.01W
08/02/2018                   DISTRICT OF COLUMB DC   911 CALL CENTER

            4000 BLOCK OF 1ST STREET CLOSED DUE TO FLOODING.

&&

EVENT NUMBER LWX1801392

JMG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
610 PM EDT THU AUG 02 2018

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

0553 PM     FLOOD            1 S KENILWORTH          38.89N  76.94W
08/02/2018                   DISTRICT OF COLUMB DC   911 CALL CENTER

            42ND FROM BENNING ROAD TO EAST CAPITAL STREET CLOSED
            DUE TO FLOODING.

&&

EVENT NUMBER LWX1801393

JMG