Alert archive / Montana / Mesoscale Discussions in 2021

Mesoscale Discussion 903

June 9, 20218 counties in Montana

The Storm Prediction Center issued this mesoscale discussion at Jun 9, 2021, 5:05 PM MDT for 8 counties in Montana. It was in force for 85 min.

The area

The outline as issued.

The facts

Issued: Jun 9, 2021, 5:05 PM MDT (23:05 UTC)
Expired: Jun 9, 2021, 6:30 PM MDT
In force: 85 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 60%

Counties Blaine County, MT, Cascade County, MT, Chouteau County, MT, Fergus County, MT, Hill County, MT, Judith Basin County, MT, Liberty County, MT, Petroleum County, MT

The radar

The Great Falls radar (KTFX), 124 km from the middle of the area, began a volume at 23:05 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 250Jun 9, 6:40 PM MDT

The nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 11.1 hours before the alert went out and 79 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: 910 m above ground
0-6 km bulk shear: 54 kt
0-1 km storm-relative helicity: 54 m²/s²
0-3 km storm-relative helicity: 147 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

835 
ACUS11 KWNS 092305
SWOMCD
SPC MCD 092305 
MTZ000-100030-

Mesoscale Discussion 0903
NWS Storm Prediction Center Norman OK
0605 PM CDT Wed Jun 09 2021

Areas affected...North-central MT

Concerning...Severe potential...Watch possible 

Valid 092305Z - 100030Z

Probability of Watch Issuance...60 percent

SUMMARY...Isolated but intense thunderstorm development is possible
by 00Z. Very large hail, severe wind gusts, and perhaps a tornado or
two will be possible this evening.

DISCUSSION...At 23Z, cumulus is increasing across portions of
central MT, with attempts at initiation apparently underway across
portions of Cascade and Judith Basin counties. At least isolated
thunderstorm development is expected by early evening, as a
shortwave midlevel trough currently over southern ID moves into the
region and convective inhibition continues to erode. 

Steep midlevel lapse rates and sufficient low-level moisture are
supporting at least weak buoyancy across the region, with somewhat
larger buoyancy (MLCAPE of 1000-1500 J/kg) noted where stronger
heating has occurred across central MT. As midlevel southwesterly
flow continues to strengthen, effective shear will increase to 40-50
kt, supporting the potential for isolated supercells. 

Very large hail (potentially exceeding 2 inches in diameter) will be
the primary initial threat. A tornado will also be possible with any
sustained supercell near and just north of a surface boundary across
central MT, where low-level moisture and shear will be locally
maximized. The threat for isolated severe wind gusts will also be
present with any supercell, and also with any outflow-dominant
cluster that may develop later this evening. 

While the coverage of storms this evening remains uncertain, watch
issuance may be required given the potential for potentially
significant hail and wind with isolated supercells.

..Dean/Dial.. 06/09/2021

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

ATTN...WFO...BYZ...GGW...TFX...

LAT...LON   48910832 47100798 46541030 46921164 47871223 48921082
            48910992 48910832

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 8, 6:15 PM MDT	Mesoscale Discussion	SPC	Carter, Custer, Daniels, Dawson, Fallon, McCone and 8 more	90 min
Jun 9, 4:43 PM MDT	Mesoscale Discussion	SPC	Deer Lodge, Granite, Lake, Lewis and Clark, Missoula, Powell and 2 more	92 min

Nearby

Mesoscale Discussions in Montana, 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.