Alert archive / Louisiana / Mesoscale Discussions in 2012
Mesoscale Discussion 2247
The Storm Prediction Center issued this mesoscale discussion at Dec 28, 2012, 3:51 PM CST for 4 parishes in Louisiana. It was in force for 84 min.
The area
The outline as issued.
The facts
- Issued
- Dec 28, 2012, 3:51 PM CST (21:51 UTC)
- Expired
- Dec 28, 2012, 5:15 PM CST
- In force
- 84 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 20%
Counties Jefferson Parish, LA, Lafourche Parish, LA, Plaquemines Parish, LA, Terrebonne Parish, LA
The nearest sounding before it
Slidell Radar S, LA (KSIL), launched 12:00Z, 9.9 hours before the alert went out and 138 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 637 m above ground
- 0-6 km bulk shear
- 63 kt
- 0-1 km storm-relative helicity
- 430 m²/s²
- 0-3 km storm-relative helicity
- 349 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
742
ACUS11 KWNS 282152
SWOMCD
SPC MCD 282151
LAZ000-282315-
MESOSCALE DISCUSSION 2247
NWS STORM PREDICTION CENTER NORMAN OK
0351 PM CST FRI DEC 28 2012
AREAS AFFECTED...SERN LA
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 282151Z - 282315Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...THE THREAT FOR A BRIEF TORNADO AND/OR A FEW STRONG WIND
GUSTS PERSISTS ACROSS SERN LA LATE THIS AFTERNOON INTO THE EARLY
EVENING...WITH THE OVERALL THREAT ENDING BY 01-02Z.
DISCUSSION...MID AFTERNOON SURFACE ANALYSIS AND REGIONAL RADAR
IMAGERY SHOWED A BROKEN LINE OF TSTMS EXTENDING FROM E OF KBTR SWWD
THROUGH ST MARY PARISH /45 W KHUM/ AND OFFSHORE TO APPROXIMATELY 90
MILES SSW OF THE CENTRAL LA COAST. THIS ACTIVITY WAS LOCATED ALONG
A NNE-SSW ORIENTED WIND SHIFT...THOUGH THE STORMS FARTHER INLAND
TENDED TO BE LOCATED IN ADVANCE OF THE WIND SHIFT. THESE STORMS ARE
LIKELY BEING MAINTAINED BY DEEP LAYER CONVERGENCE ALONG THE SURFACE
BOUNDARY AND ATTENDANT TO FORCING FOR ASCENT AHEAD OF THE
PROGRESSIVE SRN PLAINS SHORT WAVE TROUGH. MEANWHILE...INCREASING
ASCENT WITH THE TROUGH APPEARS TO HAVE AIDED IN THE DEVELOPMENT OF
MORE RECENT WARM SECTOR DISCRETE OFFSHORE CELLS /THE NRN MOST ONES
WERE LOCATED 55-65 MILES S OF THE SERN LA COAST/.
DESPITE THE WARM SECTOR HAVING MOVED INLAND OVER SERN LA THIS
AFTERNOON...OBJECTIVE ANALYSES INDICATED THE GREATEST INSTABILITY TO
SUSTAIN ACTIVITY WAS LOCATED OFFSHORE. HOWEVER...STRONG DEEP LAYER
AND LOW LEVEL SHEAR /EFFECTIVE BULK SHEAR OF 30-40 KT AND EFFECTIVE
SRH OF 200-400 M2 PER S2/ IN THE WARM SECTOR OVER LAND REMAINS
CONDUCIVE FOR STORMS TO ROTATE. GIVEN MEAGER INSTABILITY OVER SERN
LA /MLCAPE AOB 250 J PER KG/ PRECLUDING GREATER STORM COVERAGE...A
WW IS NOT WARRANTED AT THIS TIME.
..PETERS/HART.. 12/28/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...LIX...LCH...
LAT...LON 28909168 29939104 29809017 29498920 29158891 28768900
28528944 28678993 28649047 28909168SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Dec 28, 6:31 AM CST | Mesoscale Discussion | SPC | Calcasieu, Cameron | 89 min |
| Dec 28, 9:41 AM CST | Mesoscale Discussion | SPC | Acadia, Calcasieu, Cameron, Iberia, Jefferson Davis, Lafayette and 3 more | 94 min |
Nearby
Mesoscale Discussions in Louisiana, 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.