Alert archive / Alabama / Severe Thunderstorm Watches in 2018

Severe Thunderstorm Watch 421

November 1, 20189 counties in Alabama; 7 counties in Florida

The Storm Prediction Center issued this severe thunderstorm watch at Nov 1, 2018, 9:40 AM CDT for 9 counties in Alabama; 7 counties in Florida. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Nov 1, 2018, 9:40 AM CDT (14:40 UTC)
Expired: Nov 1, 2018, 2:00 PM CDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 0.5 in
Strongest gust expected: 50 kt

Counties Barbour County, AL, Bullock County, AL, Coffee County, AL, Dale County, AL, Geneva County, AL, Henry County, AL, Houston County, AL, Pike County, AL, Russell County, AL, Bay County, FL, Calhoun County, FL, Gulf County, FL, Holmes County, FL, Jackson County, FL, Walton County, FL, Washington County, FL

The radar

The Ft Rucker radar (KEOX), 28 km from the middle of the area, began a volume at 14:40 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: 10%
Ten or more severe wind reports: 30%
One or more gusts of 65 knots or more: 5%
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: 40%

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
Nov 1, 10:24 AM CDT	Severe Thunderstorm Warning	TAE	Coffee	51 min
Nov 1, 11:04 AM CDT	Tornado Warning	TAE	Dale	26 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

Tallahassee Rgnl, FL (KTLH), launched 12:00Z, 2.7 hours before the alert went out and 170 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: 21 J/kg
Mixed-layer CIN: -16 J/kg
Mixed-layer LCL: 739 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: 241 m²/s²
0-3 km storm-relative helicity: 221 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

394 
WWUS20 KWNS 011437
SEL1  
SPC WW 011437
ALZ000-FLZ000-011900-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 421
NWS Storm Prediction Center Norman OK
940 AM CDT Thu Nov 1 2018

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Southeast Alabama
  Central Florida Panhandle

* Effective this Thursday morning and afternoon from 940 AM until
  200 PM CDT.

* Primary threats include...
  Isolated damaging wind gusts to 60 mph possible
  A tornado or two possible

SUMMARY...Line of strong storms will push east across the rest of
southeast Alabama and the central Florida Panhandle through about
midday. Isolated damaging wind gusts and a brief tornado are the
primary hazards.

The severe thunderstorm watch area is approximately along and 75
statute miles north and south of a line from 45 miles west southwest
of Dothan AL to 25 miles east southeast of Dothan AL. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU1).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 420...

AVIATION...A few severe thunderstorms with hail surface and aloft to
0.5 inches. Extreme turbulence and surface wind gusts to 50 knots. A
few cumulonimbi with maximum tops to 450. Mean storm motion vector
25030.

...Grams

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Nov 1, 4:30 AM CDT	Mesoscale Discussion	SPC	Autauga, Baldwin, Bibb, Butler, Chilton, Choctaw and 23 more	2 hr
Nov 1, 5:27 AM CDT	Tornado Watch	SPC	Autauga, Baldwin, Bibb, Butler, Chilton, Choctaw and 32 more	7 hr
Nov 1, 7:50 AM CDT	Mesoscale Discussion	SPC	Autauga, Baldwin, Bibb, Butler, Chilton, Clarke and 22 more	115 min
Nov 1, 8:43 AM CDT	Mesoscale Discussion	SPC	Coffee, Dale, Geneva, Henry, Houston	2 hr
Nov 1, 12:03 PM CDT	Mesoscale Discussion	SPC	Chambers, Cherokee, Cleburne, DeKalb, Henry, Houston and 3 more	117 min

Nearby

Severe Thunderstorm Watches in Alabama, 2018 Severe Thunderstorm Watches in Florida, 2018 Every severe thunderstorm watch in 2018

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.