Alert archive / Montana / Mesoscale Discussions in 2021

Mesoscale Discussion 1214

July 9, 20216 counties in Montana; 5 counties in Wyoming

The Storm Prediction Center issued this mesoscale discussion at Jul 9, 2021, 2:20 PM MDT for 6 counties in Montana; 5 counties in Wyoming. It was in force for 85 min.

The area

The outline as issued.

The facts

Issued: Jul 9, 2021, 2:20 PM MDT (20:20 UTC)
Expired: Jul 9, 2021, 3:45 PM MDT
In force: 85 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Big Horn County, MT, Carbon County, MT, Golden Valley County, MT, Stillwater County, MT, Sweet Grass County, MT, Yellowstone County, MT, Campbell County, WY, Crook County, WY, Johnson County, WY, Sheridan County, WY, Weston County, WY

The radar

The Billings radar (KBLX), 180 km from the middle of the area, began a volume at 20:23 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 357Jul 9, 5:35 PM MDT

The nearest sounding before it

Riverton, WY (KRIW), launched 12:00Z, 8.3 hours before the alert went out and 228 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: 2505 m above ground
0-6 km bulk shear: 65 kt
0-1 km storm-relative helicity: 219 m²/s²
0-3 km storm-relative helicity: 312 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

438 
ACUS11 KWNS 092020
SWOMCD
SPC MCD 092020 
SDZ000-WYZ000-MTZ000-092145-

Mesoscale Discussion 1214
NWS Storm Prediction Center Norman OK
0320 PM CDT Fri Jul 09 2021

Areas affected...southeast Montana into northeast Wyoming

Concerning...Severe potential...Watch unlikely 

Valid 092020Z - 092145Z

Probability of Watch Issuance...20 percent

SUMMARY...Storms are likely to develop southeastward into northeast
Wyoming this evening, with areas of strong wind gusts or marginal
hail.

DISCUSSION...A few storms have formed northwest of Billings MT over
the higher terrain, and on the north side of a cyclonic speed max
aloft with cooler 500 mb temperatures. Meanwhile farther south,
increasing CU is noted over the Big Horns, with strong heating
occurring area-wide.

Surface analysis shows a trough over eastern WY, which is also
coincident with the theta-e axis. Though low-level winds are weak,
steepening deep-layer lapse rates and sufficient moisture should
sustain cells across southeast MT, with new development expected
around 21-22Z across northeastern WY.

The combination of very steep lapse rates and long hodographs will
support cells capable of marginal hail, and perhaps severe hail
later tonight into eastern WY where moisture is more abundant. With
time, locally severe gusts may occur as outflow become more
prominent.

..Jewell/Bunting.. 07/09/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...UNR...CYS...BYZ...RIW...TFX...

LAT...LON   43730409 43490470 43480615 43840681 44500768 44940872
            45441026 45821067 46251050 46450942 46020754 45420610
            44880481 44650427 44090395 43730409

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 9, 1:38 PM MDT	Mesoscale Discussion	SPC	Goshen, Laramie, Platte	97 min
Jul 9, 2:16 PM MDT	Severe Thunderstorm Watch	SPC	Goshen, Laramie, Niobrara, Platte	9 hr
Jul 9, 5:33 PM MDT	Severe Thunderstorm Watch	SPC	Campbell, Crook, Weston	4 hr

Nearby

Mesoscale Discussions in Montana, 2021 Mesoscale Discussions in Wyoming, 2021 Every mesoscale discussion in 2021

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.