Alert archive / Alabama / Mesoscale Discussions in 2012

Mesoscale Discussion 1659

July 31, 201216 counties in Alabama

The Storm Prediction Center issued this mesoscale discussion at Jul 31, 2012, 1:02 AM CDT for 16 counties in Alabama. It was in force for 88 min.

The area

The outline as issued.

The facts

Issued: Jul 31, 2012, 1:02 AM CDT (06:02 UTC)
Expired: Jul 31, 2012, 2:30 AM CDT
In force: 88 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

Counties Bibb County, AL, Blount County, AL, Chilton County, AL, Cullman County, AL, Fayette County, AL, Hale County, AL, Jefferson County, AL, Lamar County, AL, Marion County, AL, Perry County, AL, Shelby County, AL, St. Clair County, AL, Talladega County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL

The radar

The Birmingham radar (KBMX), 57 km from the middle of the area, began a volume at 06:02 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.

Severe Thunderstorm Watch 542Jul 31, 1:25 AM CDT

The nearest sounding before it

Birmingham, AL (KBMX), launched 00:00Z, 6.0 hours before the alert went out and 55 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 771 J/kg
Mixed-layer CIN: -144 J/kg
Mixed-layer LCL: 1852 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 39 m²/s²
0-3 km storm-relative helicity: 145 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.5

Open this sounding in Storm Lab

The text

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

277 
ACUS11 KWNS 310602
SWOMCD
SPC MCD 310602 
ALZ000-310730-

MESOSCALE DISCUSSION 1659
NWS STORM PREDICTION CENTER NORMAN OK
0102 AM CDT TUE JUL 31 2012

AREAS AFFECTED...NW AND CENTRAL AL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 310602Z - 310730Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...DEVELOPMENT OF A SMALL MCS APPEARS LIKELY ACROSS
NW/CENTRAL AL THE NEXT FEW HOURS...BUT AN APPROACHING OUTFLOW FROM
THE S ADDS UNCERTAINTY TO THE LONGER-TERM THREAT FOR DAMAGING
WINDS/HAIL.

DISCUSSION...CONVECTION HAS BEEN INCREASING IN COVERAGE ACROSS
NW/CENTRAL AL THE PAST 1-2 HOURS IN A ZONE OF LOW-LEVEL WAA FROM THE
W...ON THE NE EDGE OF A RESERVOIR OF MODERATE-STRONG INSTABILITY
EXTENDING EWD FROM CENTRAL MS.  LARGE SCALE SUPPORT FOR STORM
DEVELOPMENT WILL PERSIST WITH A WEAK WLY LLJ AND THE APPROACH OF A
MIDLEVEL TROUGH FROM THE NNW...AND EFFECTIVE BULK SHEAR OF 30-35 KT
WILL SUPPORT ORGANIZED STORMS/CLUSTERS.  HOWEVER...OUTFLOW FROM
EARLIER CONVECTION ACROSS SE AL IS ADVANCING NWD/NNWWD ACROSS
CENTRAL AL AND WILL ENCOUNTER THE DEVELOPING STORMS IN THE NEXT HOUR
NEAR BHM...AND IN THE NEXT 2-3 HOURS FARTHER W INTO W CENTRAL AL.  A
SHORT-TERM INCREASE IN STORM INTENSITY MAY OCCUR WITH THE
OUTFLOW/STORM MERGERS...BUT A COOLER/MORE STABLE AIR MASS TO THE S
OF THE BOUNDARY MAY LIMIT THE SEWD EXTENT OF THE DAMAGING WIND AND
LARGE HAIL RISK.  GIVEN THE SOMEWHAT CONFINED EXTENT OF THE SEVERE
THREAT IN AL...THE NEED FOR A WATCH IS UNCLEAR...BUT THIS AREA WILL
CONTINUE TO BE MONITORED.

..THOMPSON.. 07/31/2012

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

ATTN...WFO...BMX...HUN...

LAT...LON   33818625 33298606 33058612 32788669 32438724 32438752
            32678790 33178800 33728814 34008819 34188804 34358784
            34418743 34258700 33818625

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 30, 11:21 PM CDT	Mesoscale Discussion	SPC	Fayette, Franklin, Greene, Jefferson, Lamar, Marion and 5 more	114 min
Jul 31, 1:23 AM CDT	Severe Thunderstorm Watch	SPC	Autauga, Bibb, Bullock, Chambers, Chilton, Clay and 19 more	6 hr
Jul 31, 5:48 AM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Bullock, Chambers, Chilton, Clay and 19 more	57 min
Jul 31, 7:47 AM CDT	Mesoscale Discussion	SPC	Choctaw, Clarke, Conecuh, Covington, Escambia, Geneva and 3 more	58 min
Jul 31, 11:01 AM CDT	Mesoscale Discussion	SPC	Baldwin, Clarke, Mobile, Washington	59 min

Nearby

Mesoscale Discussions in Alabama, 2012 Every 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.