Alert archive / South Dakota / Mesoscale Discussions in 2012

Mesoscale Discussion 1672

August 1, 201213 counties in Nebraska; 26 counties in South Dakota

The Storm Prediction Center issued this mesoscale discussion at Aug 1, 2012, 1:53 PM MDT for 13 counties in Nebraska; 26 counties in South Dakota. It was in force for 67 min.

The area

The outline as issued.

The facts

Issued: Aug 1, 2012, 1:53 PM MDT (19:53 UTC)
Expired: Aug 1, 2012, 3:00 PM MDT
In force: 67 min
Issued by: the Storm Prediction Center
Chance of a watch: 80%

All 39 counties

Arthur County, NE, Blaine County, NE, Boyd County, NE, Brown County, NE, Cherry County, NE, Grant County, NE, Hooker County, NE, Keya Paha County, NE, Logan County, NE, Loup County, NE, McPherson County, NE, Rock County, NE, Thomas County, NE, Aurora County, SD, Beadle County, SD, Bennett County, SD, Brule County, SD, Buffalo County, SD, Charles Mix County, SD, Clark County, SD, Codington County, SD, Davison County, SD, Douglas County, SD, Gregory County, SD, Haakon County, SD, Hand County, SD, Hughes County, SD, Hyde County, SD, Jackson County, SD, Jerauld County, SD, Jones County, SD, Lyman County, SD, Mellette County, SD, Sanborn County, SD, Spink County, SD, Stanley County, SD, Sully County, SD, Todd County, SD, Tripp County, SD

The radar

The North Platte radar (KLNX), 122 km from the middle of the area, began a volume at 19:56 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

N. Platte/Lee Bi, NE (KLBF), launched 12:00Z, 7.9 hours before the alert went out and 213 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: 756 J/kg
Mixed-layer CIN: -301 J/kg
Mixed-layer LCL: 1649 m above ground
0-6 km bulk shear: 27 kt
0-1 km storm-relative helicity: 212 m²/s²
0-3 km storm-relative helicity: 240 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

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

756 
ACUS11 KWNS 011953
SWOMCD
SPC MCD 011953 
SDZ000-NEZ000-012100-

MESOSCALE DISCUSSION 1672
NWS STORM PREDICTION CENTER NORMAN OK
0253 PM CDT WED AUG 01 2012

AREAS AFFECTED...CENTRAL/ERN SD AND NRN/CENTRAL NEB

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

VALID 011953Z - 012100Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...WW ISSUANCE IS LIKELY THIS AFTERNOON ACROSS PARTS OF
CENTRAL AND ERN SD AND SWD INTO NRN/CENTRAL NEB.  LARGE HAIL AND
DAMAGING WINDS WILL BE THE PRIMARY THREATS.

TSTMS WILL CONTINUE TO INCREASE IN COVERAGE AND INTENSITY ACROSS
CENTRAL INTO ERN SD THIS AFTERNOON...WITH ADDITIONAL TSTM
DEVELOPMENT ALSO UNDERWAY OVER THE NEB PANHANDLE.  THIS LATTER
ACTIVITY WILL MOVE EWD INTO CENTRAL AND NRN PARTS OF NEB.

DISCUSSION...REGIONAL RADARS INDICATED AN INCREASE IN TSTM
DEVELOPMENT ALONG AND N OF THE WRN EXTENT OF A SURFACE FRONT...WHICH
GENERALLY EXTENDED FROM EAST CENTRAL SD TO AN AREA OF LOW PRESSURE
INVOF OF PHP/PIR.  ADDITIONAL STORMS WERE INCREASING IN COVERAGE AND
INTENSITY ALONG A DRY LINE EXTENDING SSWWD INTO THE ERN NEB
PANHANDLE.  STRONG SURFACE HEATING ACROSS THIS REGION BENEATH COOLER
MIDLEVEL TEMPERATURES IS SUPPORTING MODERATE DESTABILIZATION AND A
STEEP LAPSE RATE ENVIRONMENT.  THE OVERALL INCREASE IN TSTM
DEVELOPMENT WILL PERSIST AS FORCING FOR ASCENT ATTENDANT TO A
MIDLEVEL SHORTWAVE TROUGH TRAVERSING THE DAKOTAS SPREADS EWD.
EFFECTIVE BULK SHEAR OF 35-45 KT WILL SUPPORT ROTATING UPDRAFTS WITH
STEEP MIDLEVEL LAPSE RATES SUPPORTING A HAIL THREAT.  DAMAGING WINDS
CAN ALSO BE EXPECTED AS DCAPE OF 1500-1900 J/KG AND STEEPENING LOW
LEVEL LAPSE RATES /9-9.5 C PER KM/ ENHANCE DOWNDRAFT WIND SPEEDS.

..PETERS/CARBIN.. 08/01/2012

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

ATTN...WFO...FSD...ABR...LBF...UNR...

LAT...LON   41520217 43270217 44530202 44979889 45169707 43709798
            42659895 41609961 41350126 41520217

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 1, 2:19 PM MDT	Severe Thunderstorm Watch	SPC	Arthur, Blaine, Brown, Cherry, Garden, Grant and 8 more	6 hr
Aug 1, 3:14 PM MDT	Mesoscale Discussion	SPC	Grant	91 min
Aug 1, 4:12 PM MDT	Severe Thunderstorm Watch	SPC	Brookings, Lake, Moody	5 hr

Nearby

Mesoscale Discussions in South Dakota, 2012 Mesoscale Discussions in Nebraska, 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.