Alert archive / Virginia / Severe Thunderstorm Warnings in 2017

Severe Thunderstorm Warning 196, NWS Baltimore/Washington

August 3, 2017Loudoun County, Virginia; Frederick County, Maryland

NWS Baltimore/Washington issued this severe thunderstorm warning at Aug 3, 2017, 8:11 PM EDT for Loudoun County, Virginia; Frederick County, Maryland. It was in force for 26 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued
Aug 3, 2017, 8:11 PM EDT (00:11 UTC)
Expired
Aug 3, 2017, 8:37 PM EDT
In force
26 min
Issued by
NWS Baltimore/Washington
Area
Storm-based polygon
Hail
1.0 in
Wind
60.0 mph

Counties Frederick County, MD, Loudoun County, VA

The radar

The Sterling radar (KLWX), 34 km from the middle of the area, began a volume at 00:13 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 00:00Z, 0.2 hours before the alert went out and 38 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Washington/Dulle, VA at 00:00Z on 2017-08-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 759 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Washington/Dulle, VA at 00:00Z on 2017-08-04The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 79 square meters per square second.1939Sfc1 km3 km6 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
759 J/kg
Mixed-layer CIN
-52 J/kg
Mixed-layer LCL
1379 m above ground
0-6 km bulk shear
20 kt
0-1 km storm-relative helicity
79 m²/s²
0-3 km storm-relative helicity
118 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Baltimore/Washington wrote its last area forecast discussion before this severe thunderstorm warning went out at Aug 3, 3:09 PM EDT, 5 hours 2 minutes earlier.

Area forecast discussion, Aug 3, 3:09 PM EDT, 5 hours 2 minutes before
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
309 PM EDT Thu Aug 3 2017

.SYNOPSIS...
High pressure will remain offshore through Friday. A cold front
will move across the area from the west Friday night into
Saturday morning. High pressure will return Sunday. A stationary
front looks to set up near the area Monday into Tuesday.

&&

.NEAR TERM /THROUGH FRIDAY/...
MLCAPE 1000 to 2000 j/kg with activity popped from the ridges.
Bulk shear below 20 knots again today, so slow moving activity
will once again have isolated severe and flash flood potential
into the early evening.

Decent amount of cloud cover tonight should limit fog
development to preferred valleys only. Dewpoints upper 60s west
to low 70s east make for min temps around there.

Cold front approaches Friday, but associated clouds generally
hold off until the evening in prefrontal activity. That should
set up more terrain circulations for convective initiation in
the afternoon with more more activity than today given an
increase in bulk shear to around 20 knots.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
Cold front crosses the area from the west Friday night into
Saturday morning. Bumped up PoPs associated with this feature
to at least likely. Activity should wane on normal nocturnal
trends, but would not be surprised if slight risk shifted
farther east from the Allegheny Highlands with aforementioned
insolation ahead of the front.

High pressure then builds through Saturday night with welcome
tranquil, drier, and cooler conditions.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
An area of high pressure will bring dry and breezy conditions to
most of the region Sunday. There could be a late afternoon or
evening shower or thunderstorm in parts of the Potomac Highlands.
Temperatures will be below normal.

As the high pressure moves off the coast Sunday night, a return flow
will fuel a couple of showers and thunderstorms across the region
Monday. A few disturbances and associated frontal boundary will ride
eastward.

A front is expected to stall across the region Tuesday through
Thursday. Thus, unsettled conditions will linger with a chance of
showers and thunderstorms each period.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Scattered thunderstorms into this evening will bring locally
IFR conds during the heaviest activity.

Vfr conditions expected outside of morning fog in typical
valleys Sunday and Sunday night under high pressure.

Mvfr to ifr conditions Monday and Monday night with showers and
thunderstorms increasing over the region as a stationary front
sets up. Winds light and variable Sunday and Sunday night. Winds
becoming south to southwest at 5 to 10 knots Monday and Monday
night.

&&

.MARINE...
High pressure offshore through Friday. SEly channeling
increases through the rest of the afternoon with 20 knot gusts
for southern MD Bay waters where an SCA is in effect into
tonight. Isolated thunderstorms near over over the Bay through
this evening.

A cold front crosses the Bay from the west late Friday night
into Saturday morning.

No marine hazards expected Sunday through Monday night. Winds light
and variable Sunday and Sunday night. Winds becoming south around 10
knots Monday and Monday night.

&&

.TIDES/COASTAL FLOODING...
Elevated water levels will persist for the next couple of days
with minor coastal flooding likely at sensitive sites like Annapolis
and Straits Point near the preferred high tide each day through
the weekend.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ532>534-537-
     541-543.

&&

SYNOPSIS...BAJ
NEAR TERM...BAJ
SHORT TERM...BAJ
LONG TERM...KLW
AVIATION...BAJ/KLW
MARINE...BAJ/KLW
TIDES/COASTAL FLOODING...BAJ
Hazardous weather outlook, Aug 3, 4:07 PM EDT, 4 hours 4 minutes before
Hazardous Weather Outlook
National Weather Service Baltimore MD/Washington DC
407 PM EDT Thu Aug 3 2017

ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-042015-
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-
407 PM EDT Thu Aug 3 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...Tonight

Isolated severe thunderstorms with large hail and damaging winds
are possible this evening.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Widespread showers and thunderstorms are expected Monday and
Monday evening along and ahead of a slow moving cold front.
Locally heavy rain with isolated incidents of flash flooding is
possible especially over the I-95 urban corridor in Baltimore and
northeast Maryland.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053-
055-501>506-042015-
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-
407 PM EDT Thu Aug 3 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...Tonight

Isolated severe thunderstorms with large hail and damaging winds
are possible this evening.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Isolated severe thunderstorms with damaging wind gusts and hail
are possible over western Maryland and portions of eastern West
Virginia Friday afternoon and evening.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

In the hours before

Local storm report, Aug 3, 6:14 PM EDT, 1 hour 57 minutes before
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
614 PM EDT THU AUG 03 2017

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

0538 PM     TSTM WND DMG     2 NE TIMONIUM           39.45N  76.59W
08/03/2017                   BALTIMORE          MD   EMERGENCY MNGR

            MULTIPLE TREES... BRANCHES AND WIRES DOWN ALONG MD 146
            DULANEY VALLEY ROAD BETWEEN OLD BOSLEY ROAD AND TIMONIUM
            ROAD

&&

EVENT NUMBER LWX1702648

RCM
Local storm report, Aug 3, 6:16 PM EDT, 1 hour 55 minutes before
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
616 PM EDT THU AUG 03 2017

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

0545 PM     TSTM WND DMG     WESTMINSTER             39.58N  77.01W
08/03/2017                   CARROLL            MD   911 CALL CENTER

            DOWNED TREE NEAR FLAG MARSH ROAD AND GRIMVILLE RD

&&

EVENT NUMBER LWX1702649

IMR
Local storm report, Aug 3, 6:19 PM EDT, 1 hour 52 minutes before
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
619 PM EDT THU AUG 03 2017

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

0619 PM     HAIL             1 E ANNANDALE           38.83N  77.20W
08/03/2017  M0.88 INCH       FAIRFAX            VA   TRAINED SPOTTER

&&

EVENT NUMBER LWX1702650

RCM
Local storm report, Aug 3, 6:24 PM EDT, 1 hour 47 minutes before
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    <section class="card" role="status" aria-live="polite">
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The office that day

Everything else NWS Baltimore/Washington issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Aug 4, 1:02 AM EDTSmall Craft AdvisoryLWX25 hr
Aug 4, 1:02 AM EDTSmall Craft AdvisoryLWX47 hr
Aug 4, 7:17 PM EDTSevere Thunderstorm WarningLWXRockingham28 min
Aug 4, 7:44 PM EDTSevere Thunderstorm WarningLWXRockingham, Shenandoah46 min
Aug 3, 10:23 PM EDTCoastal Flood AdvisoryLWXAnne Arundel, Saint Mary's9 hr
Aug 4, 2:22 PM EDTCoastal Flood AdvisoryLWXAnne Arundel, Baltimore, Calvert, Saint Mary's, City of Baltimore17 hr
Aug 4, 5:03 PM EDTSevere Thunderstorm WarningLWXAllegany27 min
Aug 4, 5:29 PM EDTSevere Thunderstorm WarningLWXAllegany, Washington31 min
Aug 4, 5:49 PM EDTSevere Thunderstorm WarningLWXAllegany, Washington27 min
Aug 4, 6:07 PM EDTSevere Thunderstorm WarningLWXPendleton23 min

Nearby

Severe Thunderstorm Warnings in Virginia, 2017Severe Thunderstorm Warnings in Maryland, 2017Every severe thunderstorm warning in 2017

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.