Alert archive / Texas / Mesoscale Discussions in 2011

Mesoscale Discussion 12

January 9, 201114 counties in Arkansas; 6 parishes in Louisiana; 18 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Jan 9, 2011, 10:55 AM CST for 14 counties in Arkansas; 6 parishes in Louisiana; 18 counties in Texas. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Jan 9, 2011, 10:55 AM CST (16:55 UTC)
Expired: Jan 9, 2011, 5:00 PM CST
In force: 6 hr
Issued by: the Storm Prediction Center

All 38 counties

Bradley County, AR, Calhoun County, AR, Clark County, AR, Columbia County, AR, Dallas County, AR, Hempstead County, AR, Howard County, AR, Lafayette County, AR, Little River County, AR, Miller County, AR, Nevada County, AR, Ouachita County, AR, Sevier County, AR, Union County, AR, Bossier Parish, LA, Caddo Parish, LA, Claiborne Parish, LA, Lincoln Parish, LA, Union Parish, LA, Webster Parish, LA, Bowie County, TX, Camp County, TX, Cass County, TX, Delta County, TX, Fannin County, TX, Franklin County, TX, Gregg County, TX, Harrison County, TX, Hopkins County, TX, Hunt County, TX, Lamar County, TX, Marion County, TX, Morris County, TX, Rains County, TX, Red River County, TX, Titus County, TX, Upshur County, TX, Wood County, TX

The radar

The Shreveport radar (KSHV), 99 km from the middle of the area, began a volume at 16:58 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

Shreveport, LA (KSHV), launched 12:00Z, 4.9 hours before the alert went out and 96 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1700 m above ground
0-6 km bulk shear: 41 kt
0-1 km storm-relative helicity: 155 m²/s²
0-3 km storm-relative helicity: 191 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

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

458 
ACUS11 KWNS 091656
SWOMCD
SPC MCD 091655
LAZ000-ARZ000-TXZ000-OKZ000-092300-

MESOSCALE DISCUSSION 0012
NWS STORM PREDICTION CENTER NORMAN OK
1055 AM CST SUN JAN 09 2011

AREAS AFFECTED...PORTIONS NE TX...EXTREME SERN OK...SWRN/S-CENTRAL
AR...NWRN/N-CENTRAL LA.

CONCERNING...HEAVY SNOW

VALID 091655Z - 092300Z

POTENTIAL IS INCREASING FOR HEAVY SNOW RATES 1-2 INCH/HOUR FROM ERN
PORTIONS TX/OK BORDER REGION...SWD TO NEAR I-20...THROUGH ABOUT 20Z.
 HEAVY SNOW POTENTIAL THEN SHOULD SHIFT ENEWD ACROSS ARKLATEX REGION
INTO S-CENTRAL AR BY 00Z.  THIS WILL OCCUR ALONG NRN EDGE OF LARGE
REGIONAL PRECIP SHIELD...WITH SOME AREAS NOW EXPERIENCING RAIN OR
MIX OF SLEET AND FREEZING RAIN UNDERGOING TRANSITION TO SNOW.

SFC ANALYSES INDICATE SUBSTANTIAL COOLING ACROSS TX PORTIONS OF
DISCUSSION AREA DURING LAST 3-4 HOURS...WHICH WILL CONTINUE TO COOL
LOW-LEVEL AIR MASS AND SHUNT SFC FREEZING LINE FARTHER SWD IN
ASSOCIATION WITH THREE PROCESSES...
1. SUBLIMATIONAL/EVAPORATIONAL WET-BULB EFFECTS IN PRECIP CASCADE
2. DYNAMIC COOLING OF DEEP COLUMN RELATED TO LARGE-SCALE
DCVA/ASCENT...AS MID-UPPER LOW AND ACCOMPANYING SHORTWAVE TROUGH
APCH...AND
3. LOWER-ORDER PROCESS OF SENSIBLE COOLING OF AIR MASS FROM COLDER
PRECIP GENERATED ALOFT.

ELEVATED/LOW-LEVEL WAA CONVEYOR...SAMPLED IN LOW LEVELS BY 30-40 KT
SELY LLJ IN VWP/PROFILER WINDS OVER LA AND SE TX...IS SUPPLYING
MOISTURE FOR PRECIP GENERATION AND WILL OFFSET THAT COOLING SOMEWHAT
ABOVE BOUNDARY LAYER.  HOWEVER...PRIND TEMPS WILL REMAIN COLD ENOUGH
TO KEEP PREDOMINANT PRECIP TYPE AS SNOW IN THIS CORRIDOR.  RATES
SHOULD INCREASE AND SNOW AREA SHOULD EXPAND OVER NEXT FEW HOURS...IN
RESPONSE TO MOISTURE TRANSPORT INTO NWRN PORTIONS OF REGIME
CHARACTERIZED BY JUXTAPOSITION OF NWRN FRINGES OF STRONGEST 294-303K
ISENTROPIC LIFT...WRN PART OF ZONE OF MAX 600-750 MB LAYER
FRONTOGENESIS...AND THERMAL LAYERS SUPPORTING OPTIMAL DENDRITE
GROWTH.

..EDWARDS.. 01/09/2011

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

ATTN...WFO...JAN...LZK...SHV...TSA...FWD...OUN...

LAT...LON   33889589 34119495 34169341 34109273 33919236 33669209
            33209198 32849197 32529231 32359296 32309368 32439514
            33039619 33699633 33889589

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jan 9, 7:09 AM CST	Mesoscale Discussion	SPC	Ashley, Bradley, Calhoun, Chicot, Columbia, Lafayette and 5 more	5 hr
Jan 9, 1:28 AM CST	Mesoscale Discussion	SPC	Aransas, Bee, Brooks, Calhoun, Duval, Goliad and 9 more	2 hr
Jan 9, 2:11 AM CST	Severe Thunderstorm Watch	SPC	Aransas, Calhoun, Duval, Jim Wells, Kleberg, Nueces and 2 more	4 hr

Nearby

Mesoscale Discussions in Texas, 2011 Mesoscale Discussions in Arkansas, 2011 Mesoscale Discussions in Louisiana, 2011 Every 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.