Alert archive / Mississippi / Mesoscale Discussions in 2011
Mesoscale Discussion 2002
The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2011, 1:04 PM CDT for 26 parishes in Louisiana; 40 counties in Mississippi. It was in force for 116 min.
The area
The outline as issued.
The facts
- Issued
- Aug 18, 2011, 1:04 PM CDT (18:04 UTC)
- Expired
- Aug 18, 2011, 3:00 PM CDT
- In force
- 116 min
- Issued by
- the Storm Prediction Center
All 66 counties
Ascension Parish, LA, Assumption Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Franklin Parish, LA, Iberville Parish, LA, Lafayette Parish, LA, Livingston Parish, LA, Madison Parish, LA, Orleans Parish, LA, Pointe Coupee Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Tensas Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Claiborne County, MS, Clarke County, MS, Copiah County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Hinds County, MS, Issaquena County, MS, Jasper County, MS, Jefferson County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lauderdale County, MS, Lawrence County, MS, Leake County, MS, Lincoln County, MS, Madison County, MS, Marion County, MS, Neshoba County, MS, Newton County, MS, Pearl River County, MS, Perry County, MS, Pike County, MS, Rankin County, MS, Scott County, MS, Simpson County, MS, Smith County, MS, Stone County, MS, Walthall County, MS, Warren County, MS, Wayne County, MS, Wilkinson County, MS, Yazoo County, MS
The nearest sounding before it
Slidell Radar S, LA (KSIL), launched 12:00Z, 6.1 hours before the alert went out and 117 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
- 2124 J/kg
- Mixed-layer CIN
- -12 J/kg
- Mixed-layer LCL
- 941 m above ground
- 0-6 km bulk shear
- 17 kt
- 0-1 km storm-relative helicity
- -17 m²/s²
- 0-3 km storm-relative helicity
- 106 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
021
ACUS11 KWNS 181804
SWOMCD
SPC MCD 181804
MSZ000-LAZ000-182000-
MESOSCALE DISCUSSION 2002
NWS STORM PREDICTION CENTER NORMAN OK
0104 PM CDT THU AUG 18 2011
AREAS AFFECTED...CNTRL/SRN MS...ERN/S-CNTRL LA
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 181804Z - 182000Z
A FEW STORMS COULD PRODUCE DMGG WIND GUSTS THIS AFTERNOON.
HOWEVER...THE ISOLATED NATURE OF THE SVR THREAT IS EXPECTED TO
PRECLUDE THE NEED FOR A WW.
MESOANALYSIS AT 17Z DEPICTS A REMNANT/DIFFUSE FRONT DRAPED ACROSS
SRN AR AND EXTENDING INTO W-CNTRL/SWRN MS AND FARTHER SOUTH INTO
S-CNTRL LA. THE SWD-SURGING COLD POOL ATTENDANT TO A DECAYING MCS IS
FORCING THE FRONT SWD OVER CNTRL MS AND NERN LA...WITH THE EFFECTIVE
BOUNDARY /I.E. COMPOSITE REMNANT FRONT - OUTFLOW BOUNDARY/ NOW
APPROACHING THE INTERSTATE 20 CORRIDOR NORTH OF A
MONROE-VICKSBURG-JACKSON LINE. WHILE JACKSON WSR-88D 0.5-DEGREE
REFLECTIVITY DATA SUGGEST THE BOUNDARY UNDERCUTTING ONGOING
CONVECTION...SLY FLOW OF 5-10 KT BELOW 0.5 KM AGL PER VWP DATA
SHOULD ENHANCE LOW-LEVEL CONVERGENCE ALONG THE LEADING EDGE OF THE
COLD POOL /SUCCEEDED BY 2-HR SFC PRESSURE RISES OF 2-3 MB/ AS IT
IMPINGES UPON CNTRL/SRN MS AND PORTIONS OF ERN LA. FURTHERMORE...12Z
JACKSON/SLIDELL RAOBS MODIFIED FOR CURRENT OBSERVATIONS SUGGEST THAT
MLCAPE VALUES HAVE INCREASED TO AROUND 2500-3000 J/KG AHEAD OF THE
BOUNDARY...WHICH MAY ALSO SUPPORT THE DEVELOPMENT OF VIGOROUS
CONVECTION ALONG AND SOUTH OF THE INTERSTATE 20 CORRIDOR. ALSO OF
NOTE...THE SRN BRANCH OF THE REMNANT FRONT INTERSECTS THE EFFECTIVE
BOUNDARY NEARLY ORTHOGONALLY 45 WNW JAN...WHERE MESOSCALE
CONVERGENCE IS LOCALLY ENHANCED. THIS INTERSECTION WILL SHIFT SWD
DURING THE NEXT FEW HOURS IN TANDEM WITH THE PROGRESSION OF THE
EFFECTIVE BOUNDARY...AND COULD FOCUS ENHANCED CONVECTIVE
POTENTIAL...IN ADDITION TO AREAS FARTHER SOUTH ALONG THE REMNANT
FRONT.
VERY MODEST NLY FLOW IS CONTRIBUTING TO 20-25 KT OF EFFECTIVE BULK
SHEAR...WHICH COULD SUPPORT PULSE TO OCCASIONALLY MULTICELLULAR
CONVECTION. DCAPE VALUES OF 1000-1300 J/KG MAY SUPPORT ISOLATED
INSTANCES OF DMGG WIND GUSTS WITH THE STRONGEST STORMS...AIDED BY
WATER-LOADING PROCESSES OWING TO PW VALUES OF 1.7-1.9 INCHES PER GPS
DATA. HOWEVER...THE LACK OF DEEP-LAYER VERTICAL SHEAR SHOULD LARGELY
MITIGATE A MORE ORGANIZED/WIDESPREAD SVR THREAT AS ACTIVITY
POTENTIALLY REACHES THE GULF COAST LATER THIS AFTERNOON. AS
SUCH...THE ISSUANCE OF A WW IS UNLIKELY UNLESS A LARGER OR MORE
INTENSE SVR THREAT EVOLVES.
..COHEN.. 08/18/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...MOB...JAN...LIX...LCH...
LAT...LON 29539026 29589161 30079233 31199188 32019174 32689139
32859065 32838970 32978870 32208857 31088856 30428863
29848907 29539026SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 18, 3:46 PM CDT | Mesoscale Discussion | SPC | Bienville, Bossier, Caddo, Caldwell, De Soto, Grant and 10 more | 89 min |
| Aug 18, 7:41 AM CDT | Mesoscale Discussion | SPC | Coahoma, DeSoto, Panola, Quitman, Tallahatchie, Tate and 1 more | 3 hr |
Nearby
Mesoscale Discussions in Mississippi, 2011Mesoscale Discussions in Louisiana, 2011Every mesoscale discussion in 2011
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.