Alert archive / Tennessee / Severe Thunderstorm Watches in 2012
Severe Thunderstorm Watch 671
The Storm Prediction Center issued this severe thunderstorm watch at Oct 17, 2012, 8:43 PM CDT for Colbert County, Franklin County, Lauderdale County, Alabama; 20 counties in Tennessee. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Oct 17, 2012, 8:43 PM CDT (01:43 UTC)
- Expired
- Oct 18, 2012, 12:36 AM CDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1 in
- Strongest gust expected
- 50 kt
All 23 counties
Colbert County, AL, Franklin County, AL, Lauderdale County, AL, Benton County, TN, Carroll County, TN, Cheatham County, TN, Chester County, TN, Decatur County, TN, Dickson County, TN, Hardin County, TN, Henderson County, TN, Henry County, TN, Hickman County, TN, Houston County, TN, Humphreys County, TN, Lawrence County, TN, Lewis County, TN, McNairy County, TN, Montgomery County, TN, Perry County, TN, Robertson County, TN, Stewart County, TN, Wayne County, TN
The radar
The Memphis radar (KNQA), 137 km from the middle of the area, began a volume at 01:46 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
- 20%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 5%
- Ten or more severe hail reports
- 10%
- One or more hailstones of 2 inches or more
- 5%
- Six or more combined severe hail and wind reports
- 50%
Warnings issued inside it
2 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Oct 17, 9:51 PM CDT | Severe Thunderstorm Warning | MEG | Chester, Hardeman, McNairy | 39 min |
| Oct 17, 10:26 PM CDT | Severe Thunderstorm Warning | MEG | Decatur, Hardin, McNairy | 64 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
Nashville Metro, TN (KBNA), launched 00:00Z, 1.7 hours before the alert went out and 173 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.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1963 m above ground
- 0-6 km bulk shear
- 37 kt
- 0-1 km storm-relative helicity
- 169 m²/s²
- 0-3 km storm-relative helicity
- 300 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
524
WWUS20 KWNS 180146
SEL1
SPC WW 180146
ALZ000-TNZ000-180800-
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 671
NWS STORM PREDICTION CENTER NORMAN OK
845 PM CDT WED OCT 17 2012
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
NORTHWEST ALABAMA
WEST AND WESTERN MIDDLE TENNESSEE
EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 845 PM
UNTIL 300 AM CDT.
HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 60
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60
STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES WEST
NORTHWEST OF FORT CAMPBELL KENTUCKY TO 40 MILES EAST OF OXFORD
MISSISSIPPI. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).
REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.
OTHER WATCH INFORMATION...CONTINUE...WW 667...WW 668...WW
669...WW 670...
DISCUSSION...SQLN CROSSING THE MS RIVER EXPECTED TO CONTINUE EWD
INTO LEE UNSTABLE LOW-LVL ENVIRONMENT OVER THE LWR TN VLY. STRENGTH
OF LARGE SCALE FORCING FOR ASCENT AND CURRENT WIND FIELD SUGGEST A
CONTINUED RISK FOR LOCALLY DMGG WIND EWD BEYOND WW 667 IN PARTS OF
WRN TN THROUGH LATE EVE.
AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 50 KNOTS.
A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM MOTION
VECTOR 25045.
...CORFIDISPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Oct 17, 11:10 PM CDT | Mesoscale Discussion | SPC | Bibb, Blount, Calhoun, Cherokee, Chilton, Coosa and 24 more | 95 min |
| Oct 18, 1:09 AM CDT | Mesoscale Discussion | SPC | Choctaw, Clarke, Mobile, Monroe, Washington | 96 min |
| Oct 18, 2:40 AM CDT | Mesoscale Discussion | SPC | Choctaw, Clarke, Conecuh, Escambia, Marengo, Monroe and 2 more | 65 min |
| Oct 17, 7:35 PM CDT | Mesoscale Discussion | SPC | Ballard, Carlisle, Fulton, Hickman | 85 min |
| Oct 17, 7:47 PM CDT | Severe Thunderstorm Watch | SPC | Caldwell, Calloway, Christian, Crittenden, Daviess, Henderson and 10 more | 75 min |
| Oct 17, 8:07 PM CDT | Mesoscale Discussion | SPC | Calloway | 53 min |
| Oct 18, 2:07 PM CDT | Mesoscale Discussion | SPC | Pike | 83 min |
| Oct 17, 7:01 PM CDT | Tornado Watch | SPC | Adams, Attala, Bolivar, Carroll, Choctaw, Claiborne and 35 more | 8 hr |
| Oct 17, 8:23 PM CDT | Tornado Watch | SPC | Alcorn, Benton, Calhoun, Chickasaw, Itawamba, Lafayette and 8 more | 5 hr |
| Oct 17, 9:28 PM CDT | Mesoscale Discussion | SPC | Alcorn, Attala, Benton, Bolivar, Calhoun, Carroll and 42 more | 92 min |
| Oct 17, 11:49 PM CDT | Mesoscale Discussion | SPC | Attala, Calhoun, Carroll, Chickasaw, Choctaw, Claiborne and 31 more | 86 min |
Nearby
Severe Thunderstorm Watches in Tennessee, 2012Severe Thunderstorm Watches in Alabama, 2012Every severe thunderstorm watch in 2012
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.