Alert archive / Mississippi / Mesoscale Discussions in 2012

Mesoscale Discussion 1949

September 17, 20125 counties in Alabama; Plaquemines Parish, Saint Bernard Parish, Louisiana; 15 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Sep 17, 2012, 12:58 PM CDT for 5 counties in Alabama; Plaquemines Parish, Saint Bernard Parish, Louisiana; 15 counties in Mississippi. It was in force for 92 min.

The area

The outline as issued.

The facts

Issued: Sep 17, 2012, 12:58 PM CDT (17:58 UTC)
Expired: Sep 17, 2012, 2:30 PM CDT
In force: 92 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 22 counties

Baldwin County, AL, Choctaw County, AL, Clarke County, AL, Mobile County, AL, Washington County, AL, Plaquemines Parish, LA, Saint Bernard Parish, LA, Clarke County, MS, Covington County, MS, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Jasper County, MS, Jones County, MS, Lamar County, MS, Pearl River County, MS, Perry County, MS, Stone County, MS, Wayne County, MS

The radar

The Mobile radar (KMOB), 52 km from the middle of the area, began a volume at 18:00 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 12:00Z, 6.0 hours before the alert went out and 104 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: 1889 J/kg
Mixed-layer CIN: -3 J/kg
Mixed-layer LCL: 560 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: 105 m²/s²
0-3 km storm-relative helicity: 121 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

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

395 
ACUS11 KWNS 171759
SWOMCD
SPC MCD 171758
ALZ000-FLZ000-MSZ000-LAZ000-171930-

MESOSCALE DISCUSSION 1949
NWS STORM PREDICTION CENTER NORMAN OK
1258 PM CDT MON SEP 17 2012

AREAS AFFECTED...FAR SE LA...SRN MS AND SW AL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 171758Z - 171930Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...A SEVERE THREAT IS EXPECTED TO DEVELOP ACROSS THE REGION
THIS AFTERNOON. ROTATING CELLS COULD POSE A THREAT FOR TORNADOES. WW
ISSUANCE MAY BE REQUIRED.

DISCUSSION...SEVERAL BANDS OF STORMS ARE CURRENTLY ONGOING FROM FAR
SE LA EXTENDING NEWD INTO THE VICINITY OF MOBILE AL. THIS ACTIVITY
IS LOCATED JUST AHEAD OF A SHORTWAVE TROUGH AND WELL-DEFINED
VORTICITY MAXIMA EVIDENT ON WATERY VAPOR IMAGERY NEAR THE MS RIVER
DELTA. FORCING ASSOCIATED WITH THE VORT MAX AND SFC HEATING WILL
HELP THE STORM ORGANIZATION THIS AFTERNOON. IN ADDITION...THE
WSR-88D VWPS AT MOBILE AND NEW ORLEANS SHOW INCREASING LOW-LEVEL
SHEAR WITH TIME WITH 0-1 KM SHEAR AROUND 25 KT AND 0-6 KM SHEAR OF
30 TO 40 KT. THIS AMOUNT OF SHEAR SHOULD BE SUPPORTIVE OF ROTATING
CELLS AND AN ISOLATED TORNADO THREAT IS EXPECTED TO DEVELOP THIS
AFTERNOON. WIND DAMAGE POTENTIAL COULD ALSO DEVELOP ESPECIALLY IF
INSTABILITY CAN INCREASE AHEAD OF THE ACTIVITY IN SRN MS AND SRN AL.

..BROYLES/MEAD.. 09/17/2012

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

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

LAT...LON   32088816 32098903 31688956 30828967 29908975 29238979
            29038908 29528852 30358755 31348725 32088816

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 17, 3:53 PM CDT	Mesoscale Discussion	SPC	Blount, Calhoun, Cherokee, Clay, Cleburne, Cullman and 13 more	97 min
Sep 17, 5:14 PM CDT	Mesoscale Discussion	SPC	Barbour, Dale, Henry, Houston	2 hr

Nearby

Mesoscale Discussions in Mississippi, 2012 Mesoscale Discussions in Alabama, 2012 Mesoscale Discussions in Louisiana, 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.