Alert archive / Alabama / Mesoscale Discussions in 2012

Mesoscale Discussion 2073

October 18, 20125 counties in Alabama; 4 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Oct 18, 2012, 1:09 AM CDT for 5 counties in Alabama; 4 counties in Mississippi. It was in force for 96 min.

The area

The outline as issued.

The facts

Issued: Oct 18, 2012, 1:09 AM CDT (06:09 UTC)
Expired: Oct 18, 2012, 2:45 AM CDT
In force: 96 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

Counties Choctaw County, AL, Clarke County, AL, Mobile County, AL, Monroe County, AL, Washington County, AL, George County, MS, Greene County, MS, Perry County, MS, Stone County, MS

The radar

The Mobile radar (KMOB), 46 km from the middle of the area, began a volume at 06:11 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.

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 6.2 hours before the alert went out and 155 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: 518 J/kg
Mixed-layer CIN: -6 J/kg
Mixed-layer LCL: 686 m above ground
0-6 km bulk shear: 34 kt
0-1 km storm-relative helicity: 145 m²/s²
0-3 km storm-relative helicity: 212 m²/s²
Significant tornado parameter: 0.3
Supercell composite: 2.0

Open this sounding in Storm Lab

The text

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

922 
ACUS11 KWNS 180609
SWOMCD
SPC MCD 180609 
ALZ000-FLZ000-MSZ000-180745-

MESOSCALE DISCUSSION 2073
NWS STORM PREDICTION CENTER NORMAN OK
0109 AM CDT THU OCT 18 2012

AREAS AFFECTED...EXTREME SERN MS INTO SWRN AL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 180609Z - 180745Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...POTENTIAL EXISTS FOR SEVERE AND POSSIBLE TORNADO THREAT TO
DEVELOP INTO SWRN AL INTO THE EARLY MORNING. CONVECTIVE TRENDS ARE
BEING MONITORED FOR A POSSIBLE TORNADO WATCH.

DISCUSSION...EARLY THIS MORNING A WARM FRONT EXTENDS FROM CNTRL
THROUGH SERN MS. A MT TROPICAL AIRMASS IS IN PLACE WEST OF THIS
BOUNDARY WHERE SFC DEWPOINTS ARE IN THE LOW 70S WITH 1500 J/KG
MLCAPE. THETA-E ADVECTION ALONG SRN EXTENSION OF WSWLY LLJ WILL
CONTRIBUTE TO EWD DESTABILIZATION INTO SWRN AL. STORMS WILL LIKELY
CONTINUE DEVELOPING SEWD NEXT FEW HOURS WITHIN BELT OF ASCENT ALONG
WARM CONVEYOR BELT...BUT TENDENCY WILL BE FOR THE DEEPER FORCING TO
GRADUALLY SHIFT NEWD AWAY FROM THE WARM SECTOR. A GRADUAL WEAKENING
AND VEERING OF LOW LEVEL WINDS AND CORRESPONDING DECREASE IN 0-2 KM
HODOGRAPHS SIZE WILL ALSO OCCUR AFTER 09Z AS LLJ GRADUALLY SHIFTS
NEWD THROUGH THE TN AND OH VALLEYS IN ASSOCIATION WITH MIGRATORY
UPPER JET EXIT REGION. IN THE MEANTIME AT LEAST A 4-5 HOUR WINDOW OF
FAVORABLE SHEAR/INSTABILITY PARAMETER SPACE FOR ISOLATED TORNADOES
MAY TRANSPIRE ACROSS A PORTION OF SWRN AL EARLY THIS MORNING.

..DIAL/MEAD.. 10/18/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...BMX...MOB...JAN...LIX...

LAT...LON   30638963 32088824 31758721 30888730 30458834 30638963

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Oct 17, 8:43 PM CDT	Severe Thunderstorm Watch	SPC	Colbert, Franklin, Lauderdale	4 hr
Oct 17, 11:10 PM CDT	Mesoscale Discussion	SPC	Bibb, Blount, Calhoun, Cherokee, Chilton, Coosa and 24 more	95 min
Oct 18, 2:40 AM CDT	Mesoscale Discussion	SPC	Choctaw, Clarke, Conecuh, Escambia, Marengo, Monroe and 2 more	65 min
Oct 17, 7:01 PM CDT	Tornado Watch	SPC	Adams, Attala, Bolivar, Carroll, Choctaw, Claiborne and 35 more	8 hr
Oct 17, 7:35 PM CDT	Mesoscale Discussion	SPC	Bolivar, Coahoma, DeSoto, Panola, Quitman, Tallahatchie and 2 more	85 min
Oct 17, 8:07 PM CDT	Mesoscale Discussion	SPC	Alcorn	53 min
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

Mesoscale Discussions in Alabama, 2012 Mesoscale Discussions in Mississippi, 2012 Every mesoscale discussion 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.