Alert archive / South Dakota / Mesoscale Discussions in 2007

Mesoscale Discussion 849

May 21, 200719 counties in South Dakota

The Storm Prediction Center issued this mesoscale discussion at May 21, 2007, 2:34 PM CDT for 19 counties in South Dakota. It was in force for 86 min.

The area

The outline as issued.

The facts

Issued: May 21, 2007, 2:34 PM CDT (19:34 UTC)
Expired: May 21, 2007, 4:00 PM CDT
In force: 86 min
Issued by: the Storm Prediction Center

Counties Campbell County, SD, Corson County, SD, Dewey County, SD, Haakon County, SD, Hughes County, SD, Jackson County, SD, Jones County, SD, Lyman County, SD, Meade County, SD, Mellette County, SD, Oglala Lakota County, SD, Pennington County, SD, Perkins County, SD, Potter County, SD, Stanley County, SD, Sully County, SD, Tripp County, SD, Walworth County, SD, Ziebach County, SD

The radar

The Rapid City radar (KUDX), 88 km from the middle of the area, began a volume at 19:38 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 283May 21, 2:55 PM CDT

The nearest sounding before it

Rapid City, SD (KUNR), launched 12:00Z, 7.6 hours before the alert went out and 94 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: 222 J/kg
Mixed-layer CIN: -453 J/kg
Mixed-layer LCL: 1556 m above ground
0-6 km bulk shear: 21 kt
0-1 km storm-relative helicity: 186 m²/s²
0-3 km storm-relative helicity: 193 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.

000 
ACUS11 KWNS 211934
SWOMCD
SPC MCD 211934 
SDZ000-212100-

MESOSCALE DISCUSSION 0849
NWS STORM PREDICTION CENTER NORMAN OK
0234 PM CDT MON MAY 21 2007

AREAS AFFECTED...CNTRL/WRN SD

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

VALID 211934Z - 212100Z

THERE WILL BE AN INCREASING THREAT FOR TSTMS...SOME POSSIBLY
SVR...ACROSS WRN/CNTRL SD LATE AFTN/EVE...LIKELY REQUIRING WW
ISSUANCE.

LATEST MESOANALYSIS WAS SHOWING A DEEPENING SFC LOW OVER WRN SD WITH
A PRE-FRONTAL TROUGH EXTENDING SWD TO VCNTY RAP.  AIR MASS AHEAD OF
THIS FEATURE HAS BECOME VERY WARM WITH SFC TEMPERATURES SOARING INTO
THE MID 80S WHILE MAINTAINING BOUNDARY LAYER DEW POINTS IN THE MID
50S TO LOWER 60S. 

INITIAL TSTMS WILL LIKELY DEVELOP ACROSS WRN ND...CLOSER TO THE
STRONGER LARGE SCALE HEIGHT FALL AXIS.  BUT...LATER IN THE
AFTN...COMBINATION OF ADDITIONAL HEATING AND SRN PERIPHERY OF THE
HEIGHT FALLS SKIRTING ACROSS THE REGION WILL BE FAVORABLE FOR TSTM
INITIATION FARTHER S ACROSS SD.  

TROPOSPHERIC FLOW WILL BE CHARACTERIZED BY A DEEP SSWLY COMPONENT
WITH RELATIVELY WEAK SHEAR NOTED IN THE LOWEST 6KM.  AS A
RESULT...MULTICELL STORMS MAY TAKE ON A LINEAR MODE QUICKLY WITH
LARGE HAIL THE PREDOMINANT THREAT GIVEN STEEP LAPSE RATES ALOFT. 
ACTIVITY SHOULD MOVE EWD SLOWLY INTO CNTRL SD/SCNTRL ND DURING THE
EVENING AS THE FLOW REGIME REMAINS PARALLEL TO THE INITIATING
BOUNDARIES.

..RACY.. 05/21/2007

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

ATTN...WFO...ABR...BIS...UNR...

43160334 45930297 45919928 43249978

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 20, 7:48 PM CDT	Mesoscale Discussion	SPC	Butte, Lawrence	87 min
May 21, 1:07 PM CDT	Mesoscale Discussion	SPC	Roberts	83 min
May 21, 2:52 PM CDT	Severe Thunderstorm Watch	SPC	Bennett, Butte, Campbell, Corson, Custer, Dewey and 18 more	8 hr
May 21, 6:17 PM CDT	Mesoscale Discussion	SPC	Butte, Campbell, Corson, Custer, Dewey, Haakon and 9 more	88 min

Nearby

Mesoscale Discussions in South Dakota, 2007 Every mesoscale discussion in 2007

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.