Alert archive / Louisiana / Mesoscale Discussions in 2012
Mesoscale Discussion 313
The Storm Prediction Center issued this mesoscale discussion at Mar 21, 2012, 2:17 AM CDT for Ashley County, Arkansas; 23 parishes in Louisiana. It was in force for 118 min.
The area
The outline as issued.
The facts
- Issued
- Mar 21, 2012, 2:17 AM CDT (07:17 UTC)
- Expired
- Mar 21, 2012, 4:15 AM CDT
- In force
- 118 min
- Issued by
- the Storm Prediction Center
All 24 counties
Ashley County, AR, Acadia Parish, LA, Avoyelles Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, Evangeline Parish, LA, Franklin Parish, LA, Grant Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Lafayette Parish, LA, LaSalle Parish, LA, Morehouse Parish, LA, Ouachita Parish, LA, Pointe Coupee Parish, LA, Rapides Parish, LA, Richland Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, St. Mary Parish, LA, Vermilion Parish, LA, West Carroll Parish, LA, West Feliciana Parish, LA
The watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Jackson, MS (KJAN), launched 00:00Z, 7.3 hours before the alert went out and 226 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
- 267 J/kg
- Mixed-layer CIN
- -21 J/kg
- Mixed-layer LCL
- 1256 m above ground
- 0-6 km bulk shear
- 24 kt
- 0-1 km storm-relative helicity
- 36 m²/s²
- 0-3 km storm-relative helicity
- 145 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
978
ACUS11 KWNS 210718
SWOMCD
SPC MCD 210717
LAZ000-ARZ000-MSZ000-210915-
MESOSCALE DISCUSSION 0313
NWS STORM PREDICTION CENTER NORMAN OK
0217 AM CDT WED MAR 21 2012
AREAS AFFECTED...SW/S CNTRL LA INTO SERN AR
CONCERNING...TORNADO WATCH 95...
VALID 210717Z - 210915Z
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 95 CONTINUES.
IT IS POSSIBLE THAT A NEW WW MAY BE NEEDED EAST OF WW 95 BEFORE
DAYBREAK.
EAST OF THE QUASI-STATIONARY CLOSED LOW CENTERED OVER THE TEXAS
SOUTH PLAINS...MODELS INDICATE LITTLE CHANGE TO THE KINEMATIC
ENVIRONMENT ACROSS MUCH OF THE LOWER MISSISSIPPI VALLEY INTO AT
LEAST THE MID TO LATE MORNING HOURS. DEEP LAYER SOUTHERLY FLOW WILL
PERSIST...BROADLY CONFLUENT AT LOW-LEVELS...AND DIFLUENT ALOFT. A
GRADUAL WEAKENING OF 850 MB FLOW TO 30-40+ KT MAY OCCUR BETWEEN NOW
AND 10-12Z...BUT THIS WILL STILL CONTRIBUTE TO SIZABLE LOW-LEVEL
HODOGRAPHS IN THE PRESENCE OF A GENERALLY SATURATED AND SEASONABLY
HIGH MOISTURE CONTENT AIR MASS.
WHILE THERE IS LITTLE INDICATION OF SUPPORT FOR EASTWARD
ACCELERATION OF THE SURFACE FRONT/CONVECTIVE OUTFLOW BOUNDARY ALONG
WHICH THE MOST VIGOROUS CONVECTION CONTINUES TO FORM... SURFACE DATA
AND LONGER TERM RADAR LOOPS DO INDICATE A SLOW 10 KT +/- EASTWARD
ADVANCEMENT OF THE LINE ACROSS LOUISIANA AND SOUTHERN ARKANSAS. AT
THIS RATE ACTIVITY MAY PROGRESS ACROSS THE MONTICELLO AR AREA...AND
MONROE/ALEXANDRIA AREAS OF LOUISIANA...BY 11-12Z...WHILE STILL
REMAINING WEST OF LAFAYETTE.
WEAK LAPSE RATES ARE NOW LIMITING CAPE AND THE VIGOR OF THE
UPDRAFTS...WHICH APPEARS TO BE CONTRIBUTING TO DIMINISHING PEAK
HOURLY RAINFALL RATES. HOWEVER...SLOW MOVING/TRAINING CONVECTION
COULD STILL YIELD LOCALLY EXCESSIVE RAIN TOTALS. AND LOW-LEVEL
SHEAR REMAINS STRONG ENOUGH TO SUPPORT OCCASIONAL MESOCYCLONES
CAPABLE OF PRODUCING AT LEAST BRIEF TORNADOES...MAINLY WITHIN THE
NARROW WEDGE OF MID/UPPER 60S SURFACE DEW POINTS WHICH HAVE ADVECTED
NORTHWARD THROUGH LOUISIANA...PERHAPS PARTS OF SOUTHEAST ARKANSAS.
..KERR.. 03/21/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...JAN...LIX...LZK...LCH...SHV...
LAT...LON 29379294 30259248 30829263 31719256 32769235 33519211
33509176 33159142 32519130 31349140 30209133 29539138
28819246 29379294SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Mar 20, 9:27 PM CDT | Mesoscale Discussion | SPC | Arkansas, Desha, Independence, Jackson, Lawrence, Monroe and 4 more | 33 min |
| Mar 20, 10:59 PM CDT | Tornado Watch | SPC | Union | 7 hr |
| Mar 20, 8:02 PM CDT | Tornado Watch | SPC | Beauregard, Calcasieu, Cameron, Vernon | 4 hr |
| Mar 20, 10:23 PM CDT | Mesoscale Discussion | SPC | Allen, Beauregard, Calcasieu, Jefferson Davis, Natchitoches, Vernon | 67 min |
| Mar 21, 4:38 AM CDT | Mesoscale Discussion | SPC | Ascension, Assumption, Avoyelles, Catahoula, Concordia, East Baton Rouge and 19 more | 97 min |
| Mar 21, 5:04 AM CDT | Tornado Watch | SPC | Acadia, Ascension, Assumption, Avoyelles, Caldwell, Catahoula and 33 more | 7 hr |
| Mar 21, 7:48 AM CDT | Mesoscale Discussion | SPC | Ascension, Assumption, Avoyelles, East Baton Rouge, East Feliciana, Iberville and 10 more | 87 min |
| Mar 21, 9:25 AM CDT | Mesoscale Discussion | SPC | Ascension, Concordia, East Baton Rouge, East Carroll, East Feliciana, Franklin and 17 more | 95 min |
| Mar 21, 10:07 AM CDT | Tornado Watch | SPC | Ascension, East Carroll, East Feliciana, Franklin, Jefferson, Lafourche and 17 more | 8 hr |
| Mar 21, 12:19 PM CDT | Mesoscale Discussion | SPC | Jefferson, Lafourche, Orleans, Plaquemines, Saint Bernard, Saint Tammany and 1 more | 86 min |
| Mar 21, 3:47 PM CDT | Mesoscale Discussion | SPC | Saint Bernard | 88 min |
| Mar 21, 5:40 PM CDT | Mesoscale Discussion | SPC | Orleans, Plaquemines, Saint Bernard | 35 min |
| Mar 21, 6:02 PM CDT | Tornado Watch | SPC | Plaquemines, Saint Bernard | 9 hr |
Nearby
Mesoscale Discussions in Louisiana, 2012Mesoscale Discussions in Arkansas, 2012Every 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.