Alert archive / Virginia / Tornado Watches in 2017

Tornado Watch 509

October 23, 201724 counties in North Carolina; 44 counties in Virginia

The Storm Prediction Center issued this tornado watch at Oct 23, 2017, 5:40 PM EDT for 24 counties in North Carolina; 44 counties in Virginia. It was in force for 8 hr.

The area

The outline as issued.

The facts

Issued
Oct 23, 2017, 5:40 PM EDT (21:40 UTC)
Expired
Oct 24, 2017, 1:42 AM EDT
In force
8 hr
Issued by
the Storm Prediction Center
Largest hail expected
1 in
Strongest gust expected
60 kt
All 68 counties

Alamance County, NC, Chatham County, NC, Cumberland County, NC, Durham County, NC, Edgecombe County, NC, Franklin County, NC, Granville County, NC, Halifax County, NC, Harnett County, NC, Hoke County, NC, Johnston County, NC, Lee County, NC, Moore County, NC, Nash County, NC, Northampton County, NC, Orange County, NC, Person County, NC, Sampson County, NC, Scotland County, NC, Vance County, NC, Wake County, NC, Warren County, NC, Wayne County, NC, Wilson County, NC, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Augusta County, VA, Bedford County, VA, Botetourt County, VA, Brunswick County, VA, Buckingham County, VA, Campbell County, VA, Carroll County, VA, Charlotte County, VA, City of Buena Vista, VA, City of Danville, VA, City of Emporia, VA, City of Galax, VA, City of Lexington, VA, City of Lynchburg, VA, City of Martinsville, VA, City of Radford, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, City of Waynesboro, VA, Craig County, VA, Cumberland County, VA, Floyd County, VA, Franklin County, VA, Giles County, VA, Grayson County, VA, Greensville County, VA, Halifax County, VA, Henry County, VA, Lunenburg County, VA, Mecklenburg County, VA, Montgomery County, VA, Nelson County, VA, Nottoway County, VA, Patrick County, VA, Pittsylvania County, VA, Prince Edward County, VA, Pulaski County, VA, Roanoke County, VA, Rockbridge County, VA, Wythe County, VA

The radar

The Roanoke radar (KFCX), 83 km from the middle of the area, began a volume at 21:41 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
40%
One or more EF2 to EF5 tornadoes
20%
Ten or more severe wind reports
40%
One or more gusts of 65 knots or more
10%
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
80%

Warnings issued inside it

10 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

IssuedProductOfficeCountiesLasted
Oct 23, 5:47 PM EDTSevere Thunderstorm WarningRNKCarroll, Patrick58 min
Oct 23, 5:53 PM EDTFlash Flood WarningRNKCarroll, Floyd, Patrick6 hr
Oct 23, 5:55 PM EDTTornado WarningRNKCarroll, Grayson, City of Galax35 min
Oct 23, 6:16 PM EDTSevere Thunderstorm WarningRNKBland, Carroll, Floyd, Giles, Montgomery, Pulaski and 2 more59 min
Oct 23, 6:42 PM EDTSevere Thunderstorm WarningRNKCraig, Giles, Montgomery, Pulaski63 min
Oct 23, 6:46 PM EDTSevere Thunderstorm WarningRNKFloyd, Franklin, Henry, Patrick, Pittsylvania, City of Martinsville59 min
Oct 23, 6:58 PM EDTFlash Flood WarningRNKAlleghany, Craig, Floyd, Giles, Montgomery, City of Covington6 hr
Oct 23, 7:16 PM EDTTornado WarningRNKFranklin, Henry, Pittsylvania, City of Danville, City of Martinsville29 min
Oct 23, 7:28 PM EDTSevere Thunderstorm WarningRNKAlleghany, Bath, Botetourt, Craig, Roanoke, Rockbridge and 3 more62 min
Oct 23, 7:40 PM EDTSevere Thunderstorm WarningRNKAmherst, Bedford, Botetourt, Campbell, Franklin, Roanoke and 5 more65 min

Discussions around it

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

The nearest sounding before it

Roanoke, VA (KRNK), launched 12:00Z, 9.7 hours before the alert went out and 27 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, Roanoke, VA at 12:00Z on 2017-10-23Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Roanoke, VA at 12:00Z on 2017-10-23The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -65 square meters per square second.19395878Sfc1 km3 km6 km9 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
2764 m above ground
0-6 km bulk shear
54 kt
0-1 km storm-relative helicity
-65 m²/s²
0-3 km storm-relative helicity
-202 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

035 
WWUS20 KWNS 232137
SEL9  
SPC WW 232137
NCZ000-VAZ000-240600-

URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 509
NWS Storm Prediction Center Norman OK
540 PM EDT Mon Oct 23 2017

The NWS Storm Prediction Center has issued a

* Tornado Watch for portions of 
  Central North Carolina
  Southern Virginia

* Effective this Monday afternoon and Tuesday morning from 540 PM
  until 200 AM EDT.

* Primary threats include...
  A couple tornadoes possible
  Scattered damaging wind gusts to 70 mph possible

SUMMARY...Bands of storms including some embedded supercells will
continue to steadily progress east/northeastward this evening with
damaging winds and a few tornadoes possible.

The tornado watch area is approximately along and 85 statute miles
north and south of a line from 25 miles west southwest of Roanoke VA
to 20 miles north northeast of Rocky Mount NC. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU9).

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.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 508...

AVIATION...Tornadoes and a few severe thunderstorms with hail
surface and aloft to 1 inch. Extreme turbulence and surface wind
gusts to 60 knots. A few cumulonimbi with maximum tops to 450. Mean
storm motion vector 21040.

...Guyer

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Oct 23, 1:07 PM EDTMesoscale DiscussionSPCAlexander, Anson, Burke, Cabarrus, Caldwell, Catawba and 15 more113 min
Oct 23, 2:00 PM EDTTornado WatchSPCAlexander, Alleghany, Anson, Ashe, Avery, Burke and 28 more8 hr
Oct 23, 4:33 PM EDTMesoscale DiscussionSPCAlexander, Alleghany, Anson, Ashe, Burke, Cabarrus and 22 more57 min
Oct 23, 6:59 PM EDTMesoscale DiscussionSPCAnson, Bladen, Cabarrus, Columbus, Davidson, Davie and 12 more91 min
Oct 23, 7:34 PM EDTMesoscale DiscussionSPCAlamance, Bladen, Caswell, Chatham, Cumberland, Durham and 19 more116 min
Oct 23, 4:58 PM EDTMesoscale DiscussionSPCAmherst, Appomattox, Bedford, Botetourt, Campbell, Carroll and 19 more92 min

Nearby

Tornado Watches in Virginia, 2017Tornado Watches in North Carolina, 2017Every tornado watch 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.