Alert archive / Nebraska / Mesoscale Discussions in 2012

Mesoscale Discussion 1533

July 21, 2012Larimer County, Colorado; 10 counties in Nebraska; 4 counties in Wyoming

The Storm Prediction Center issued this mesoscale discussion at Jul 21, 2012, 5:12 PM MDT for Larimer County, Colorado; 10 counties in Nebraska; 4 counties in Wyoming. It was in force for 78 min.

The area

The outline as issued.

The facts

Issued: Jul 21, 2012, 5:12 PM MDT (23:12 UTC)
Expired: Jul 21, 2012, 6:30 PM MDT
In force: 78 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Larimer County, CO, Banner County, NE, Box Butte County, NE, Brown County, NE, Cherry County, NE, Dawes County, NE, Grant County, NE, Morrill County, NE, Scotts Bluff County, NE, Sheridan County, NE, Sioux County, NE, Albany County, WY, Goshen County, WY, Laramie County, WY, Platte County, WY

The radar

The Cheyenne radar (KCYS), 137 km from the middle of the area, began a volume at 23:14 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

Denver, CO (KDNR), launched 12:00Z, 11.2 hours before the alert went out and 223 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: 3 J/kg
Mixed-layer CIN: -475 J/kg
Mixed-layer LCL: 2634 m above ground
0-6 km bulk shear: 17 kt
0-1 km storm-relative helicity: 24 m²/s²
0-3 km storm-relative helicity: 36 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.

585 
ACUS11 KWNS 212312
SWOMCD
SPC MCD 212312 COR
NEZ000-SDZ000-COZ000-WYZ000-220030-

MESOSCALE DISCUSSION 1533
NWS STORM PREDICTION CENTER NORMAN OK
0612 PM CDT SAT JUL 21 2012

AREAS AFFECTED...SE WY...WRN NEB...NRN CO

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 212312Z - 220030Z

CORRECTED TO TAKE SW SD OUT OF AREAS AFFECTED

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...AN ISOLATED SEVERE THREAT WILL PROBABLY CONTINUE EARLY
THIS EVENING ACROSS ERN WY AND MAY ALSO IMPACT WRN NEB. MARGINAL
WIND DAMAGE AND HAIL WILL LIKELY BE THE PRIMARY THREATS. DUE TO THE
ISOLATED NATURE OF SEVERE THREAT...WW ISSUANCE IS UNLIKELY ACROSS
THE CNTRL HIGH PLAINS.

DISCUSSION...SCATTERED THUNDERSTORMS ARE DEVELOPING ALONG AN AXIS OF
MODERATE INSTABILITY EXTENDING FROM NEAR NW NEB SWWD TO NEAR
CHEYENNE. MLCAPE VALUES ARE ESTIMATED IN THE 1000 TO 1500 J/KG RANGE
WITH 0-6 KM SHEAR OF 20 TO 25 KT WHICH SHOULD SUPPORT MULTICELL
DEVELOPMENT. IN ADDITION...SFC TEMPS ABOVE 100F WITH DEWPOINTS IN
THE 40S F ARE CREATING VERY LARGE TEMP-DEWPOINT SPREADS WHICH MAY
ENHANCE DOWNDRAFT ACCELERATION. AS THE STORMS GRADUALLY MOVE NEWD
INTO WRN NEB...ISOLATED STRONG DOWNBURSTS WILL BE POSSIBLE. IN SPITE
OF THE WARM AIR ALOFT...HAIL WILL ALSO BE POSSIBLE MAINLY WHERE THE
CONVECTION HAS ACCESS TO MODERATE INSTABILITY.

FURTHER TO THE EAST ACROSS NCNTRL NEB...CONVECTION HAS DEVELOPED
NEAR A SFC LOW TO THE EAST OF VALENTINE NEB. THIS STORM SHOULD MOVE
INTO INCREASING INSTABILITY AND MAY BE MAINTAINED FOR A FEW HOURS.
HOWEVER...WARM AIR ALOFT AND WEAK LARGE-SCALE ASCENT BENEATH A CNTRL
PLAINS UPPER-LEVEL RIDGE WILL LIKELY KEEP THE ACTIVITY VERY
ISOLATED. HAIL AND STRONG WIND GUSTS WILL LIKELY BE THE PRIMARY
THREATS.

..BROYLES/CARBIN.. 07/21/2012

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

ATTN...WFO...LBF...UNR...BOU...CYS...

LAT...LON   41180389 41820241 42010050 42299986 42639972 43020010
            43020100 42990236 42960417 42680528 42160623 41530676
            41080672 40320595 40320537 40580474 41180389

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 21, 1:54 PM MDT	Mesoscale Discussion	SPC	Campbell, Crook, Niobrara, Weston	96 min
Jul 21, 4:41 PM MDT	Severe Thunderstorm Watch	SPC	Crook, Weston	7 hr

Nearby

Mesoscale Discussions in Nebraska, 2012 Mesoscale Discussions in Wyoming, 2012 Mesoscale Discussions in Colorado, 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.