Alert archive / Tennessee / Mesoscale Discussions in 2012

Mesoscale Discussion 2143

December 9, 20129 counties in Arkansas; 10 counties in Tennessee

The Storm Prediction Center issued this mesoscale discussion at Dec 9, 2012, 8:02 PM CST for 9 counties in Arkansas; 10 counties in Tennessee. It was in force for 58 min.

The area

The outline as issued.

The facts

Issued: Dec 9, 2012, 8:02 PM CST (02:02 UTC)
Expired: Dec 9, 2012, 9:00 PM CST
In force: 58 min
Issued by: the Storm Prediction Center

Counties Arkansas County, AR, Crittenden County, AR, Cross County, AR, Lee County, AR, Mississippi County, AR, Monroe County, AR, Phillips County, AR, Prairie County, AR, St. Francis County, AR, Crockett County, TN, Dyer County, TN, Fayette County, TN, Gibson County, TN, Haywood County, TN, Lauderdale County, TN, Obion County, TN, Shelby County, TN, Tipton County, TN, Weakley County, TN

The radar

The Memphis radar (KNQA), 43 km from the middle of the area, began a volume at 02:01 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 nearest sounding before it

Little Rock, AR (KLZK), launched 00:00Z, 2.0 hours before the alert went out and 53 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: 715 J/kg
Mixed-layer CIN: -6 J/kg
Mixed-layer LCL: 646 m above ground
0-6 km bulk shear: 57 kt
0-1 km storm-relative helicity: 245 m²/s²
0-3 km storm-relative helicity: 262 m²/s²
Significant tornado parameter: 1.1
Supercell composite: 6.7

Open this sounding in Storm Lab

The text

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

011 
ACUS11 KWNS 100202
SWOMCD
SPC MCD 100202 
TNZ000-KYZ000-MOZ000-ARZ000-MSZ000-100300-

MESOSCALE DISCUSSION 2143
NWS STORM PREDICTION CENTER NORMAN OK
0802 PM CST SUN DEC 09 2012

AREAS AFFECTED...ERN AR THROUGH WRN TN AND SWRN KY

CONCERNING...TORNADO WATCH 677...

VALID 100202Z - 100300Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 677 CONTINUES.

SUMMARY...TORNADO WATCH 677 IS SCHEDULED TO EXPIRE AT 03Z. THE
TORNADO THREAT IS EXPECTED TO GRADUALLY DECREASE THROUGH
EVENING...BUT A NON ZERO TORNADO OR SEVERE THREAT WILL PERSIST
THROUGH 05Z FROM ERN AR INTO WRN TN. AS A RESULT...DEPENDING ON
CONVECTIVE TRENDS...WW 677 COULD BE LOCALLY EXTENDED IN TIME AND
SPACE TO INCLUDE A PORTION OF WRN TN. SPC WILL CONTACT AFFECTED
OFFICES SOON TO DISCUSS THE COURSE OF ACTION REGARDING THE
EXPIRATION OF WW 677.

DISCUSSION...STORMS HAVE EVOLVED INTO A PREDOMINANT LINEAR MODE FROM
SWRN KY THROUGH ERN AR. TRENDS IN CONVECTIVE MODE...A STABILIZING
BOUNDARY LAYER...INCREASINGLY MARGINAL INSTABILITY...AND A TENDENCY
FOR THE LLJ TO GRADUALLY SHIFT EAST OF THE SFC MOIST AXIS SUGGEST
THE TORNADO THREAT SHOULD GRADUALLY DECREASE WITH TIME.
HOWEVER...LATEST VWP DATA FROM MEMPHIS STILL SHOW STRONG LOW LEVEL
SHEAR WITH 0-1 KM STORM RELATIVE HELICITY AROUND 250 M2/S2. GIVEN
THE FAVORABLE SHEAR ENVIRONMENT...EMBEDDED SUPERCELLS AND A TORNADO
OR TWO CANNOT BE COMPLETELY RULED OUT NEXT 2-3 HOURS AS ACTIVITY
CONTINUES THROUGH THE REMAINDER OF THE WEAK INSTABILITY AXIS.

OTHERWISE...STORMS DEVELOPING FARTHER EAST WITHIN WARM ADVECTION
REGIME OVER WRN TN ARE MORE DISCRETE IN CHARACTER...BUT ARE WITHIN A
WEAK INSTABILITY ENVIRONMENT AND APPEAR TO BE AT LEAST SLIGHTLY
ELEVATED.

..DIAL.. 12/10/2012

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

ATTN...WFO...PAH...MEG...LZK...

LAT...LON   34319237 35709026 36828848 36148845 35138934 34989022
            34239099 34319237

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 9, 8:38 PM CST	Mesoscale Discussion	SPC	Ashley, Bradley, Calhoun, Chicot, Cleveland, Columbia and 10 more	67 min

Nearby

Mesoscale Discussions in Tennessee, 2012 Mesoscale Discussions in Arkansas, 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.