Alert archive / Mississippi / Mesoscale Discussions in 2017

Mesoscale Discussion 21

January 6, 201720 counties in Alabama; 10 parishes in Louisiana; 29 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Jan 6, 2017, 4:15 PM CST for 20 counties in Alabama; 10 parishes in Louisiana; 29 counties in Mississippi. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Jan 6, 2017, 4:15 PM CST (22:15 UTC)
Expired: Jan 6, 2017, 8:15 PM CST
In force: 4 hr
Issued by: the Storm Prediction Center

All 59 counties

Autauga County, AL, Bibb County, AL, Calhoun County, AL, Chilton County, AL, Choctaw County, AL, Clay County, AL, Cleburne County, AL, Coosa County, AL, Dallas County, AL, Greene County, AL, Hale County, AL, Jefferson County, AL, Marengo County, AL, Perry County, AL, Pickens County, AL, Shelby County, AL, St. Clair County, AL, Sumter County, AL, Talladega County, AL, Tuscaloosa County, AL, Avoyelles Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, Evangeline Parish, LA, Grant Parish, LA, LaSalle Parish, LA, Rapides Parish, LA, Tensas Parish, LA, Vernon Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Claiborne County, MS, Clarke County, MS, Copiah County, MS, Covington County, MS, Franklin County, MS, Hinds County, MS, Jasper County, MS, Jefferson County, MS, Jefferson Davis County, MS, Jones County, MS, Kemper County, MS, Lauderdale County, MS, Lawrence County, MS, Leake County, MS, Lincoln County, MS, Madison County, MS, Neshoba County, MS, Newton County, MS, Noxubee County, MS, Pike County, MS, Rankin County, MS, Scott County, MS, Simpson County, MS, Smith County, MS, Warren County, MS, Wilkinson County, MS, Winston County, MS

The radar

The Jackson/Brandon,MS radar (KDGX), 32 km from the middle of the area, began a volume at 22:15 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

Jackson, MS (KJAN), launched 12:00Z, 10.3 hours before the alert went out and 42 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 725 m above ground
0-6 km bulk shear: 73 kt
0-1 km storm-relative helicity: 133 m²/s²
0-3 km storm-relative helicity: 354 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

535 
ACUS11 KWNS 062216
SWOMCD
SPC MCD 062215 COR
ALZ000-MSZ000-LAZ000-070215-

Mesoscale Discussion 0021
NWS Storm Prediction Center Norman OK
0415 PM CST Fri Jan 06 2017

Areas affected...central LA...southern and central MS and central AL

Concerning...Winter mixed precipitation 

Valid 062215Z - 070215Z

CORRECTED FOR LOCATION SPECIFICATION

SUMMARY...Freezing rain and sleet will increase along a corridor
from central LA, across central MS, into central AL this
afternoon/evening.  Significant icing, with rates approaching .10
inch/hr in heavier convection, is expected.

DISCUSSION...Latest vis satellite imagery exhibits deepening
convection across the lower Sabine river valley extending into
southern portions of MS.  Lightning is increasing within the taller
updrafts, partly in response to increasing ascent ahead of
approaching short-wave trough.  An elongated corridor of
precipitation, with embedded thunderstorms, is expected to expand in
areal coverage/intensity over the next several hours from the lower
Mississippi Valley to the central Gulf states.

With boundary-layer temperatures expected to cool a few degrees
along this corridor it appears the risk for significant icing will
increase as the afternoon progresses into the evening hours.  As the
cold air deepens, sleet will become common along the nrn edge of
this expanding precip shield.  With time, mixed precipitation will
spread into northern GA later this evening.

..Darrow.. 01/06/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BMX...MOB...JAN...LIX...LCH...SHV...

LAT...LON   31239343 32499079 34008642 33738539 32538652 31448923
            30599225 31239343

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jan 6, 5:24 AM CST	Mesoscale Discussion	SPC	Caldwell, East Carroll, Franklin, Madison, Ouachita, Richland and 2 more	4 hr

Nearby

Mesoscale Discussions in Mississippi, 2017 Mesoscale Discussions in Alabama, 2017 Mesoscale Discussions in Louisiana, 2017 Every mesoscale discussion 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.