Tornado Watch 642

Issued

Sep 18, 2012, 10:54 AM EDT (14:54 UTC)

Expired

Sep 18, 2012, 7:53 PM EDT

In force

9 hr

Issued by

the Storm Prediction Center

Largest hail expected

0.5 in

Strongest gust expected

60 kt

The Norfolk radar (KAKQ), 95 km from the middle of the area, began a volume at 14:55 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.

Two or more tornadoes

60%

One or more EF2 to EF5 tornadoes

20%

Ten or more severe wind reports

80%

One or more gusts of 65 knots or more

30%

Ten or more severe hail reports

5%

One or more hailstones of 2 inches or more

5%

Six or more combined severe hail and wind reports

95%

• Mesoscale Discussion 1957Sep 18, 8:49 AM EDT
• Mesoscale Discussion 1960Sep 18, 11:19 AM EDT
• Mesoscale Discussion 1964Sep 18, 1:27 PM EDT
• Mesoscale Discussion 1965Sep 18, 1:56 PM EDT
• Mesoscale Discussion 1968Sep 18, 3:52 PM EDT
• Mesoscale Discussion 1973Sep 18, 6:15 PM EDT

423 
WWUS20 KWNS 181455
SEL2  
SPC WW 181455
DCZ000-MDZ000-NCZ000-VAZ000-WVZ000-CWZ000-182300-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 642
NWS STORM PREDICTION CENTER NORMAN OK
1055 AM EDT TUE SEP 18 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF 

       DISTRICT OF COLUMBIA
       MARYLAND
       NORTHERN NORTH CAROLINA
       CENTRAL AND EASTERN VIRGINIA
       EASTERN WEST VIRGINIA PANHANDLE
       COASTAL WATERS

EFFECTIVE THIS TUESDAY MORNING AND EVENING FROM 1055 AM UNTIL 700
PM EDT.

TORNADOES...HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 90 STATUTE
MILES EAST AND WEST OF A LINE FROM 35 MILES EAST SOUTHEAST OF
SOUTH HILL VIRGINIA TO 40 MILES NORTH NORTHEAST OF BALTIMORE
MARYLAND.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

OTHER WATCH INFORMATION...CONTINUE...WW 641...

DISCUSSION...A GRADUAL INCREASE IN STORM COVERAGE AND INTENSITY IS
EXPECTED TODAY AS LARGE-SCALE FORCING FOR ASCENT INCREASES ACROSS A
VERY MOIST AND MARGINALLY UNSTABLE WARM SECTOR.  CURRENT VAD AND
MODEL FORECAST DATA INDICATE A CONTINUED STRENGTHENING OF THE
DEEP-LAYER WIND FIELD THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE
WITH THE ENVIRONMENT BECOMING SUPPORTIVE OF EMBEDDED BOW/LEWP AND
SUPERCELL STRUCTURES CAPABLE OF TORNADOES AND DAMAGING WINDS.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 23040.


...MEAD

Tornado Watches in Virginia, 2012Tornado Watches in Maryland, 2012Tornado Watches in West Virginia, 2012Every tornado watch in 2012

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.