Alert archive / North Carolina / Tornado Watches in 2015

Tornado Watch 93

April 21, 201520 counties in North Carolina; 15 counties in Virginia

The Storm Prediction Center issued this tornado watch at Apr 21, 2015, 12:37 AM EDT for 20 counties in North Carolina; 15 counties in Virginia. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Apr 21, 2015, 12:37 AM EDT (04:37 UTC)
Expired: Apr 21, 2015, 5:00 AM EDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

All 35 counties

Bertie County, NC, Camden County, NC, Chowan County, NC, Currituck County, NC, Edgecombe County, NC, Franklin County, NC, Gates County, NC, Granville County, NC, Halifax County, NC, Hertford County, NC, Johnston County, NC, Martin County, NC, Nash County, NC, Northampton County, NC, Pasquotank County, NC, Perquimans County, NC, Vance County, NC, Wake County, NC, Warren County, NC, Wilson County, NC, Brunswick County, VA, City of Chesapeake, VA, City of Colonial Heights, VA, City of Emporia, VA, City of Franklin, VA, City of Norfolk, VA, City of Petersburg, VA, City of Portsmouth, VA, City of Suffolk, VA, City of Virginia Beach, VA, Greensville County, VA, Isle of Wight County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA

The radar

The Raleigh/Durham radar (KRAX), 100 km from the middle of the area, began a volume at 04:38 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 30%
One or more EF2 to EF5 tornadoes: 20%
Ten or more severe wind reports: 20%
One or more gusts of 65 knots or more: 5%
Ten or more severe hail reports: 20%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 50%

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Newport, NC (KMHX), launched 00:00Z, 4.6 hours before the alert went out and 176 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 11 J/kg
Mixed-layer CIN: -238 J/kg
Mixed-layer LCL: 1672 m above ground
0-6 km bulk shear: 43 kt
0-1 km storm-relative helicity: 232 m²/s²
0-3 km storm-relative helicity: 249 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.6

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

625 
WWUS20 KWNS 210434
SEL3  
SPC WW 210434
NCZ000-VAZ000-CWZ000-210900-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 93
NWS STORM PREDICTION CENTER NORMAN OK
1235 AM EDT TUE APR 21 2015

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* TORNADO WATCH FOR PORTIONS OF 
  NORTHEAST NORTH CAROLINA
  SOUTHEAST VIRGINIA
  COASTAL WATERS

* EFFECTIVE THIS TUESDAY MORNING FROM 1235 AM UNTIL 500 AM EDT.

* PRIMARY THREATS INCLUDE...
  A COUPLE TORNADOES POSSIBLE
  ISOLATED DAMAGING WIND GUSTS TO 70 MPH POSSIBLE
  ISOLATED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE

SUMMARY...BROKEN LINE OF THUNDERSTORMS NOW FORMING NEAR RALEIGH NC
EXPECTED TO EVOLVE INTO PERHAPS TWO OR THREE MORE INDIVIDUAL STORMS
THAT COULD BECOME CAPABLE OF A TORNADO OR TWO...IN ADDITION TO
LOCALLY DAMAGING WIND AND MARGINALLY SEVERE HAIL.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 65 STATUTE
MILES EAST AND WEST OF A LINE FROM 15 MILES SOUTHWEST OF ROCKY
MOUNT NORTH CAROLINA TO 15 MILES NORTHWEST OF NORFOLK VIRGINIA. 
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU3).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

&&

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 26040.


...CORFIDI

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 20, 11:37 PM EDT	Mesoscale Discussion	SPC	Chatham, Durham, Franklin, Granville, Halifax, Lee and 5 more	53 min
Apr 21, 2:33 AM EDT	Mesoscale Discussion	SPC	Bertie, Camden, Chowan, Edgecombe, Gates, Halifax and 4 more	87 min

Nearby

Tornado Watches in North Carolina, 2015 Tornado Watches in Virginia, 2015 Every tornado watch in 2015

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.