Tornado Warning 16, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
930 PM EDT Tue Sep 12 2023

.SYNOPSIS...
A boundary will remain nearby through this evening before moving
to the east as a cool front later tonight. A stronger cold front
and its associated upper-level trough will pass through the
area later Wednesday into Wednesday night. Canadian high
pressure will build overhead for late in the week into the
weekend.

&&

.NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/...
Upper trough across the western Great Lks is expected to
amplify across the northern Mid-Atlantic into the central
Applachians next 24 to 36 hrs hours. As it does so, height falls
will overspread the area tonight leading to large scale forcing
and widespread showers and perhaps a few thunderstorms. This is
already underway per KLWX radar trends and lightning data. Rainfall
amounts are expected to be around a quarter of an inch, except
in northeast MD where moisture convergence and instability will
be maximized and HREF probabilities indicate possibility of
intense rainfall rates and amounts up to 3 inches. In addition,
this area has seen the most rain in the past 5 days or so and
may be the most vulnerable to flooding. For this reason, a Flood
Watch has been issued for Cecil and Harford Counties from 03Z
till 15Z Wed. As far as severe weather is concerned, a low end
threat for a brief spin-up tornado cannot be ruled as low-level
flow continues to increase. The 01Z RAP objective analysis shows
a bullseye in the Supercell Composite field across northeastern
Maryland.

&&

.SHORT TERM /7 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
Sfc cold front will be crossing the area after 12Z Wed, but 925
and 850 mb dewpoint fronts will be lagging behind as well as
500 mb trof axis. So, expect the risk of showers to persist
through much of the day particularly east of the Blue Ridge
Mountains. However, with the best moisture and instabillity axis
shifting east of the Chesapeake Bay, expect any flooding or
severe wx to remain well east of the Chesapeake Bay.

Weak high pressure builds over the region for the second half of
the week leading to cooler and fair weather conditions.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
High pressure is expected to remain overhead Friday through Sunday,
yielding dry conditions with normal temperatures. By the
weekend temperatures may gradually warm to near or just above
normal with the high pressure and ample sunshine, though the
further into the extended, the more dependent conditions will be
on the track of Lee. As we continue to monitor Lee, stay up to
date with the latest information on the tropics at nhc.noaa.gov.
For now, dry conditions are expected to continue through the
weekend with a possible weak frontal passage Sunday into the
early part of the work week. Some precipitation is possible with
this fropa, but will depend on how dry the air mass is.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
Showers and possible thunderstorms are expected tonight mainly
through the overnight hours. The greatest chances have shifted
northward given current radar trends. This places the main
threat across the DC terminals initially, before shifting to
KBWI and KMTN within the next couple hours. Some brief cig
and/or vsby restrictions are possible. Scattered showers are
still possible Wed, but most showers should be done by 15Z. As
the upper trough passes overhead, a few showers may fire up
during the afternoon, especially I-66 southward.

VFR conditions are expected Friday and Saturday as high pressure
sits overhead. Thanks to the tight pressure gradient with Lee
offshore, winds both days will be 10-15kt out of the N/NW with gusts
15-20kts, though winds will likely be strongest Friday.

&&

.MARINE...
Widespread showers and isold/sct t-storms expected tonight
through 18Z Wed. A few SMWs may be required. Gradient winds
strengthen late Wed night and remain in SCA category into the
weekend.

SCAs are likely Friday and possible during the day Saturday as a
tight pressure gradient from Lee passing offshore creates gusty NW
winds over the waters. Winds gradually diminish by Saturday night.

&&

.HYDROLOGY...
A Flood Watch remains in effect across Harford and Cecil
Counties from 11 PM this evening until 11 AM Wednesday. This
area has seen the most rainfall within the past 5 days which
would increase the risk for future flash flooding. Toward the
D.C. and Baltimore metros, locally heavy rainfall could lead to
isolated flooding across the typical more vulnerable locations.
The latter threat essentially subsides through the overnight
hours.

&&

.TIDES/COASTAL FLOODING...
With tidal anomalies slightly elevated, a couple of the more
sensitive locations should push into Action stage during the
next high tide. However, water levels should quickly drop off
behind a strong cold front which pushes through midday
Wednesday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Flood Watch through Wednesday morning for MDZ008-507-508.
VA...None.
WV...None.
MARINE...None.

&&

SYNOPSIS...LFR
NEAR TERM...LFR/BRO
SHORT TERM...LFR
LONG TERM...CAS
AVIATION...LFR/BRO/CAS
MARINE...LFR/CAS
HYDROLOGY...
TIDES/COASTAL FLOODING...

Hazardous Weather Outlook
National Weather Service Baltimore MD/Washington DC
1001 PM EDT Tue Sep 12 2023

ANZ530>543-DCZ001-MDZ008-011-013-014-016>018-504-506-508-
VAZ053>057-527-140215-
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-Cecil-Southern Baltimore-
Prince Georges-Anne Arundel-Charles-St. Marys-Calvert-
Central and Southeast Montgomery-Central and Southeast Howard-
Southeast Harford-Fairfax-Arlington/Falls Church/Alexandria-
Stafford-Spotsylvania-King George-
Central and Southeast Prince William/Manassas/Manassas Park-
1001 PM EDT Tue Sep 12 2023

This Hazardous Weather Outlook is for the Maryland portion of the
Chesapeake Bay, Tidal Potomac River, and I-95 corridor through
central Maryland, northern Virginia, and District of Columbia.

.DAY ONE...Tonight

A Flood Watch is in effect for Cecil and Harford Counties from 11
PM tonight through 11 AM Wednesday.

A severe thunderstorm with damaging wind gusts along with isolated
instances of flooding is possible tonight.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

The Flood Watch continues for Cecil and Harford Counties until
11 AM Wednesday.

.SPOTTER INFORMATION STATEMENT...

Please send any severe or flood reports to the National Weather
Service in Sterling, Virginia.

MDZ003>006-503-505-507-VAZ025>031-036>040-050-051-501-502-505>508-
526-WVZ050>053-055-140215-
Washington-Frederick MD-Carroll-Northern Baltimore-
Northwest Montgomery-Northwest Howard-Northwest Harford-Augusta-
Rockingham-Shenandoah-Frederick VA-Page-Warren-Clarke-Nelson-
Albemarle-Greene-Madison-Rappahannock-Orange-Culpeper-
Northern Fauquier-Southern Fauquier-Western Loudoun-
Eastern Loudoun-Northern Virginia Blue Ridge-
Central Virginia Blue Ridge-Northwest Prince William-Hampshire-
Morgan-Berkeley-Jefferson-Hardy-
1001 PM EDT Tue Sep 12 2023

This Hazardous Weather Outlook is for portions of eastern West
Virginia, northern and central Virginia, and central and western
Maryland.

.DAY ONE...Tonight

A Flood Watch is in effect for Carroll and northern Baltimore
Counties from 11 PM tonight through 11 AM Wednesday.

A severe thunderstorm with damaging wind gusts along with isolated
instances of flooding is possible tonight, especially near and
east of the Blue Ridge and Catoctin Mountains.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

The Flood Watch continues for Carroll and northern Baltimore
Counties until 11 AM Wednesday.

.SPOTTER INFORMATION STATEMENT...

Please send any severe or flood reports to the National Weather
Service in Sterling, Virginia.

MDZ001-501-502-VAZ503-504-WVZ501>506-140215-
Garrett-Extreme Western Allegany-Central and Eastern Allegany-
Western Highland-Eastern Highland-Western Grant-Eastern Grant-
Western Mineral-Eastern Mineral-Western Pendleton-
Eastern Pendleton-
1001 PM EDT Tue Sep 12 2023

This Hazardous Weather Outlook is for the Allegheny Front
counties in western Maryland, eastern West Virginia, and Highland
County Virginia.

.DAY ONE...Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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