Alert archive / Arkansas / Mesoscale Discussions in 2017
Mesoscale Discussion 96
The Storm Prediction Center issued this mesoscale discussion at Jan 21, 2017, 5:32 PM CST for 4 states. It was in force for 118 min.
The area
The outline as issued.
The facts
- Issued
- Jan 21, 2017, 5:32 PM CST (23:32 UTC)
- Expired
- Jan 21, 2017, 7:30 PM CST
- In force
- 118 min
- Issued by
- the Storm Prediction Center
All 77 counties
Arkansas County, AR, Ashley County, AR, Bradley County, AR, Calhoun County, AR, Chicot County, AR, Clark County, AR, Cleveland County, AR, Columbia County, AR, Dallas County, AR, Desha County, AR, Drew County, AR, Garland County, AR, Grant County, AR, Hempstead County, AR, Hot Spring County, AR, Howard County, AR, Jefferson County, AR, Lafayette County, AR, Lincoln County, AR, Little River County, AR, Lonoke County, AR, Miller County, AR, Monroe County, AR, Montgomery County, AR, Nevada County, AR, Ouachita County, AR, Phillips County, AR, Pike County, AR, Pulaski County, AR, Saline County, AR, Sevier County, AR, Union County, AR, Avoyelles Parish, LA, Bienville Parish, LA, Bossier Parish, LA, Caddo Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Claiborne Parish, LA, Concordia Parish, LA, De Soto Parish, LA, East Carroll Parish, LA, Franklin Parish, LA, Grant Parish, LA, Jackson Parish, LA, LaSalle Parish, LA, Lincoln Parish, LA, Madison Parish, LA, Morehouse Parish, LA, Natchitoches Parish, LA, Ouachita Parish, LA, Rapides Parish, LA, Red River Parish, LA, Richland Parish, LA, Sabine Parish, LA, Tensas Parish, LA, Union Parish, LA, Vernon Parish, LA, Webster Parish, LA, West Carroll Parish, LA, Winn Parish, LA, Adams County, MS, Bolivar County, MS, Claiborne County, MS, Coahoma County, MS, Humphreys County, MS, Issaquena County, MS, Jefferson County, MS, Leflore County, MS, Sharkey County, MS, Sunflower County, MS, Tallahatchie County, MS, Warren County, MS, Washington County, MS, Yazoo County, MS, Bowie County, TX, Cass County, TX
The radar
The Shreveport radar (KSHV), 135 km from the middle of the area, began a volume at 23:34 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Shreveport, LA (KBAD), launched 12:00Z, 11.5 hours before the alert went out and 126 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
- 20 J/kg
- Mixed-layer CIN
- -323 J/kg
- Mixed-layer LCL
- 1223 m above ground
- 0-6 km bulk shear
- 53 kt
- 0-1 km storm-relative helicity
- 12 m²/s²
- 0-3 km storm-relative helicity
- 81 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.1
The text
As transmitted.
768
ACUS11 KWNS 212333
SWOMCD
SPC MCD 212332
MSZ000-ARZ000-LAZ000-TXZ000-220130-
Mesoscale Discussion 0096
NWS Storm Prediction Center Norman OK
0532 PM CST Sat Jan 21 2017
Areas affected...Portions of far northeast Texas...northern
Louisiana...southern/central Arkansas...and western Mississippi
Concerning...Tornado Watch 16...
Valid 212332Z - 220130Z
The severe weather threat for Tornado Watch 16 continues.
SUMMARY...The threat for tornadoes, very large hail, and damaging
wind gusts continues across much of Watch 16. Additionally,
downstream watch issuance will likely be needed across northeastern
LA, southeastern AR, and western MS within 2-3 hours.
DISCUSSION...Multiple supercells have formed late this afternoon
across west-central portions of Watch 16, in response to low-level
confluence near a surface trough/warm front and mid/upper-level
ascent on the nose of an impulse over eastern TX. A surface low was
analyzed near the TX/LA border at 23Z, with a warm front extending
to its southeast towards New Orleans. Near this boundary, backed
surface winds are enhancing storm-relative helicity sufficiently for
low-level mesocyclogenesis. Indeed, a fairly prominent tornadic
debris signature was noted across far northeast Marion County / far
southeast Cass County in TX over the last 20-30 minutes and another
recently observed over northeast Bossier Parish.
More supercells are likely to form farther south, with the potential
for tornadoes continuing as they progress northeast, especially when
these cells approach the aforementioned surface front. Moreover,
steep mid-level lapse rates noted in 18/20Z regional soundings and
ample effective shear will maintain the potential for robust
organized updrafts capable of very large hail. Indeed, recent KSHV
data have depicted several broad/deep ZDR column and ring structures
aloft, suggesting hailstone growth should be quite efficient.
..Picca.. 01/21/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MEG...JAN...LIX...LZK...LCH...SHV...
LAT...LON 32369408 32919442 33269455 34399421 34879347 34799137
34529059 34129016 33229009 31449098 31139176 30909226
30989325 32369408SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jan 21, 2:33 PM CST | Mesoscale Discussion | SPC | Calhoun, Clark, Columbia, Dallas, Hempstead, Howard and 9 more | 2 hr |
| Jan 21, 3:41 PM CST | Tornado Watch | SPC | Bradley, Calhoun, Clark, Cleveland, Columbia, Dallas and 22 more | 7 hr |
| Jan 20, 6:37 PM CST | Mesoscale Discussion | SPC | Acadia, Allen, Beauregard, Calcasieu, Cameron, Evangeline and 3 more | 113 min |
| Jan 20, 7:32 PM CST | Tornado Watch | SPC | Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 9 more | 6 hr |
| Jan 20, 10:04 PM CST | Mesoscale Discussion | SPC | Acadia, Allen, Avoyelles, Calcasieu, Cameron, Evangeline and 7 more | 116 min |
| Jan 20, 10:44 PM CST | Mesoscale Discussion | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Jefferson, Lafourche and 12 more | 61 min |
| Jan 20, 11:00 PM CST | Tornado Watch | SPC | Ascension, Assumption, Concordia, East Baton Rouge, East Feliciana, Iberville and 17 more | 8 hr |
| Jan 21, 1:41 AM CST | Mesoscale Discussion | SPC | Acadia, Avoyelles, Cameron, Evangeline, Iberia, Jefferson Davis and 5 more | 64 min |
| Jan 21, 2:55 AM CST | Mesoscale Discussion | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Iberville, Jefferson and 16 more | 2 hr |
| Jan 21, 6:35 AM CST | Mesoscale Discussion | SPC | Jefferson, Lafourche, Orleans, Plaquemines, Saint Bernard, Saint Charles and 1 more | 55 min |
| Jan 21, 2:34 PM CST | Mesoscale Discussion | SPC | Allen, Ascension, Avoyelles, Catahoula, Concordia, East Baton Rouge and 16 more | 2 hr |
| Jan 21, 3:29 PM CST | Tornado Watch | SPC | Acadia, Ascension, Avoyelles, Catahoula, Concordia, East Baton Rouge and 22 more | 6 hr |
| Jan 20, 10:07 PM CST | Mesoscale Discussion | SPC | Brazoria, Chambers, Fort Bend, Hardin, Harris, Jasper and 10 more | 113 min |
Nearby
Mesoscale Discussions in Arkansas, 2017Mesoscale Discussions in Louisiana, 2017Mesoscale Discussions in Mississippi, 2017Every 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.