Alert archive / Alabama / Mesoscale Discussions in 2011
Mesoscale Discussion 646
The Storm Prediction Center issued this mesoscale discussion at Apr 27, 2011, 9:20 PM CDT for 35 counties in Alabama; 4 counties in Mississippi. It was in force for 25 min.
The area
The outline as issued.
The facts
- Issued
- Apr 27, 2011, 9:20 PM CDT (02:20 UTC)
- Expired
- Apr 27, 2011, 9:45 PM CDT
- In force
- 25 min
- Issued by
- the Storm Prediction Center
All 39 counties
Autauga County, AL, Bibb County, AL, Blount County, AL, Butler County, AL, Calhoun County, AL, Cherokee County, AL, Chilton County, AL, Choctaw County, AL, Clarke County, AL, Clay County, AL, Cleburne County, AL, Conecuh County, AL, Coosa County, AL, Covington County, AL, Crenshaw County, AL, Dallas County, AL, DeKalb County, AL, Elmore County, AL, Escambia County, AL, Etowah County, AL, Greene County, AL, Hale County, AL, Jefferson County, AL, Lowndes County, AL, Marengo County, AL, Marshall County, AL, Monroe County, AL, Perry County, AL, Shelby County, AL, St. Clair County, AL, Sumter County, AL, Talladega County, AL, Tuscaloosa County, AL, Washington County, AL, Wilcox County, AL, George County, MS, Greene County, MS, Perry County, MS, Wayne County, MS
The radar
The Birmingham radar (KBMX), 150 km from the middle of the area, began a volume at 02:21 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
Birmingham, AL (KBMX), launched 00:00Z, 2.3 hours before the alert went out and 150 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
- 3065 J/kg
- Mixed-layer CIN
- -4 J/kg
- Mixed-layer LCL
- 711 m above ground
- 0-6 km bulk shear
- 73 kt
- 0-1 km storm-relative helicity
- 448 m²/s²
- 0-3 km storm-relative helicity
- 480 m²/s²
- Significant tornado parameter
- 9.6
- Supercell composite
- 33.6
The text
As transmitted, in the capitals the NWS used until 2016.
318
ACUS11 KWNS 280220
SWOMCD
SPC MCD 280220
ALZ000-TNZ000-FLZ000-MSZ000-280245-
MESOSCALE DISCUSSION 0646
NWS STORM PREDICTION CENTER NORMAN OK
0920 PM CDT WED APR 27 2011
AREAS AFFECTED...AL AND FAR SERN MS
CONCERNING...TORNADO WATCH 235...
VALID 280220Z - 280245Z
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 235 CONTINUES.
A NEW TORNADO WATCH WILL BE COORDINATED SOON FOR ERN...CENTRAL AND
SRN AL...AND FAR SERN MS GIVEN A TORNADO THREAT EXPECTED TO PERSIST
THROUGH THE REST OF THE EVENING AND EARLY OVERNIGHT PERIOD.
MID EVENING REGIONAL RADAR IMAGERY SHOWED STRONG TO SEVERE STORMS
OVER SERN TO ERN AL WITH THIS ACTIVITY LOCATED ALONG A PRE-FRONTAL
CONFLUENCE ZONE. ADDITIONAL DISCRETE STORMS CONTINUE TO DEVELOP
ALONG THE COLD FRONT MOVING INTO CENTRAL AL TO SERN MS. WARM SECTOR
AIR MASS WILL REMAIN MODERATELY UNSTABLE WITH EFFECTIVE BULK SHEAR
IN EXCESS OF 50 KT MAINTAINING LIKELIHOOD FOR DISCRETE SUPERCELLS.
WSR-88D VADS OVER SERN AL INDICATED STRENGTHENING LOW LEVEL JET /50+
KT/ WHICH IS SUPPORTING ENHANCED LOW LEVEL SHEAR /0-1 KM SRH 475 M2
PER S2/. GIVEN THE INSTABILITY/SHEAR VALUES...A CONTINUED TORNADO
THREAT IS EXPECTED AS STORMS DEVELOP ALONG AND AHEAD OF THE COLD
FRONT ADVANCING EWD.
..PETERS.. 04/28/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...MRX...BMX...HUN...MOB...JAN...LIX...
LAT...LON 30978939 32748813 35008569 33518540 32138641 31448619
31048642 30828821 30888918 30978939SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 27, 7:55 PM CDT | Mesoscale Discussion | SPC | Autauga, Bibb, Blount, Butler, Calhoun, Cherokee and 27 more | 65 min |
| Apr 27, 9:42 PM CDT | Tornado Watch | SPC | Autauga, Bibb, Butler, Calhoun, Cherokee, Chilton and 19 more | 4 hr |
| Apr 27, 11:09 PM CDT | Mesoscale Discussion | SPC | Barbour, Bullock, Chambers, Clay, Cleburne, Elmore and 7 more | 36 min |
| Apr 28, 1:22 AM CDT | Mesoscale Discussion | SPC | Dale, Geneva, Henry, Houston | 83 min |
Nearby
Mesoscale Discussions in Alabama, 2011Mesoscale Discussions in Mississippi, 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; radar from the NEXRAD Level II archive.