Alert archive / Alabama / Mesoscale Discussions in 2012

Mesoscale Discussion 2187

December 20, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Dec 20, 2012, 7:09 AM CST for 4 states. It was in force for 96 min.

The area

The outline as issued.

The facts

Issued
Dec 20, 2012, 7:09 AM CST (13:09 UTC)
Expired
Dec 20, 2012, 8:45 AM CST
In force
96 min
Issued by
the Storm Prediction Center
All 55 counties

Autauga County, AL, Baldwin County, AL, Bibb County, AL, Butler County, AL, Chilton County, AL, Choctaw County, AL, Clarke County, AL, Conecuh County, AL, Coosa County, AL, Covington County, AL, Crenshaw County, AL, Dallas County, AL, Elmore County, AL, Escambia County, AL, Greene County, AL, Hale County, AL, Lowndes County, AL, Marengo County, AL, Mobile County, AL, Monroe County, AL, Montgomery County, AL, Perry County, AL, Pickens County, AL, Sumter County, AL, Tallapoosa County, AL, Tuscaloosa County, AL, Washington County, AL, Wilcox County, AL, Escambia County, FL, Okaloosa County, FL, Santa Rosa County, FL, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, Clarke County, MS, Covington County, MS, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Jasper County, MS, Jones County, MS, Kemper County, MS, Lamar County, MS, Lauderdale County, MS, Marion County, MS, Noxubee County, MS, Pearl River County, MS, Perry County, MS, Stone County, MS, Wayne County, MS

The radar

The Mobile radar (KMOB), 45 km from the middle of the area, began a volume at 13:10 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

Slidell Radar S, LA (KSIL), launched 12:00Z, 1.2 hours before the alert went out and 136 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-pSkew-T log-p diagram, Slidell Radar S, LA at 12:00Z on 2012-12-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1181 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Slidell Radar S, LA at 12:00Z on 2012-12-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 275 square meters per square second.1939587897Sfc1 km3 km6 km9 kmRMLM
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
1181 J/kg
Mixed-layer CIN
-4 J/kg
Mixed-layer LCL
506 m above ground
0-6 km bulk shear
47 kt
0-1 km storm-relative helicity
275 m²/s²
0-3 km storm-relative helicity
310 m²/s²
Significant tornado parameter
2.0
Supercell composite
9.6

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

172 
ACUS11 KWNS 201310
SWOMCD
SPC MCD 201309
ALZ000-FLZ000-MSZ000-LAZ000-201445-

MESOSCALE DISCUSSION 2187
NWS STORM PREDICTION CENTER NORMAN OK
0709 AM CST THU DEC 20 2012

AREAS AFFECTED...ERN/SRN MS...SERN LA...CENTRAL/SRN AL...AND WRN FL
PANHANDLE

CONCERNING...TORNADO WATCH 689...

VALID 201309Z - 201445Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 689 CONTINUES.

SUMMARY...ENVIRONMENT ACROSS WW 689 WILL REMAIN CONDUCIVE FOR A
TORNADO THREAT AND DAMAGING WINDS UNTIL 14-15Z IN THE MS/SERN LA
PORTION OF THIS WW...AND UNTIL 15-17Z ACROSS THE CENTRAL/SRN AL AND
WRN FL PANHANDLE PORTION.

DISCUSSION...AT 12Z...SURFACE MESOANALYSIS SHOWED A WIND
SHIFT...ALSO DEPICTED BY RADAR IMAGERY AS LOW TOPPED /NON-LIGHTNING
PRODUCING/ CONVECTION...EXTENDING FROM WRN TN SWD TO ALONG THE NERN
MS/NWRN AL BORDER...AND THEN SSWWD THROUGH E-CENTRAL TO SWRN MS
THROUGH SERN LA BETWEEN KBTR AND KMSY. A WARM FRONT EXTENDED SEWD
FROM KCBM THROUGH SWRN AL TO THE WRN FL PANHANDLE.  SURFACE
DEWPOINTS IN THE WARM SECTOR ARE IN THE 60S...EXCEPT FOR VALUES
AROUND 70 F IN SERN LA TO THE MS COAST WHERE INSTABILITY REMAINS THE
GREATEST.

TRENDS IN LOW LEVEL WINDS HAVE INDICATED VEERING TO SWLY.
HOWEVER...AREA WSR-88D VWPS ALSO SHOWED STRENGTHENING DEEP LAYER
WIND FIELDS AS THE WELL-DEFINED SHORTWAVE TROUGH PROGRESSES EWD INTO
THE MID AND LOWER MS VALLEY REGION.  THIS IS MAINTAINING AND/OR
SLIGHTLY ENHANCING LOW LEVEL SHEAR /SFC-1 KM OF 35-40 KT AT SLIDELL
LA AND MOBILE AL/.  DEEP LAYER SHEAR OF 35-45 KT WILL CONTINUE TO
FAVOR THE DEVELOPMENT OF DISCRETE CELLS AHEAD OF THE AFOREMENTIONED
PRIMARY WIND SHIFT...WITH THE TORNADO THREAT CONTINUING AS FORECAST
IN THE SUMMARY SECTION ABOVE.

..PETERS.. 12/20/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...TAE...BMX...MOB...JAN...LIX...

LAT...LON   30139082 32108925 33718823 33588738 33118671 33098555
            31828607 30888637 30078651 29848813 29928834 30178841
            30198902 30068947 30108987 30029022 29899053 29869087
            30139082

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Dec 20, 4:08 AM CSTMesoscale DiscussionSPCChoctaw, Colbert, Fayette, Franklin, Greene, Lamar and 5 more67 min
Dec 20, 4:23 AM CSTTornado WatchSPCAutauga, Baldwin, Barbour, Bibb, Bullock, Butler and 34 more9 hr
Dec 20, 8:49 AM CSTMesoscale DiscussionSPCDale, Geneva, Henry, Houston56 min
Dec 20, 9:19 AM CSTTornado WatchSPCCoffee, Dale, Geneva, Henry, Houston9 hr
Dec 20, 9:56 AM CSTMesoscale DiscussionSPCAutauga, Baldwin, Bibb, Butler, Chambers, Chilton and 22 more64 min
Dec 20, 1:31 PM CSTMesoscale DiscussionSPCBarbour, Coffee, Dale, Geneva, Henry, Houston and 1 more59 min
Dec 20, 5:22 PM CSTMesoscale DiscussionSPCAlachua, Baker, Bradford, Clay, Columbia, Dixie and 7 more53 min
Dec 19, 9:56 PM CSTSevere Thunderstorm WatchSPCBossier, Caddo, De Soto5 hr
Dec 19, 11:55 PM CSTMesoscale DiscussionSPCAllen, Avoyelles, Beauregard, Bienville, Bossier, Caddo and 28 more95 min
Dec 20, 12:50 AM CSTMesoscale DiscussionSPCBienville, Caldwell, Claiborne, East Carroll, Franklin, Jackson and 10 more55 min
Dec 20, 1:07 AM CSTSevere Thunderstorm WatchSPCAvoyelles, Bienville, Caldwell, Catahoula, Claiborne, Concordia and 20 more5 hr

Nearby

Mesoscale Discussions in Alabama, 2012Mesoscale Discussions in Mississippi, 2012Mesoscale 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; radar from the NEXRAD Level II archive.