Alert archive / Montana / Mesoscale Discussions in 2021

Mesoscale Discussion 849

June 4, 2021Lemhi County, Idaho; 13 counties in Montana

The Storm Prediction Center issued this mesoscale discussion at Jun 4, 2021, 1:59 PM MDT for Lemhi County, Idaho; 13 counties in Montana. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Jun 4, 2021, 1:59 PM MDT (19:59 UTC)
Expired: Jun 4, 2021, 4:00 PM MDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 40%

Counties Lemhi County, ID, Beaverhead County, MT, Broadwater County, MT, Deer Lodge County, MT, Gallatin County, MT, Granite County, MT, Jefferson County, MT, Madison County, MT, Meagher County, MT, Park County, MT, Silver Bow County, MT, Stillwater County, MT, Sweet Grass County, MT, Wheatland County, MT

The radar

The Missoula radar (KMSX), 212 km from the middle of the area, began a volume at 19:59 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 237Jun 4, 4:00 PM MDT

The nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 8.0 hours before the alert went out and 238 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: 86 J/kg
Mixed-layer CIN: -225 J/kg
Mixed-layer LCL: 2278 m above ground
0-6 km bulk shear: 18 kt
0-1 km storm-relative helicity: 6 m²/s²
0-3 km storm-relative helicity: 46 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

743 
ACUS11 KWNS 042000
SWOMCD
SPC MCD 041959 
MTZ000-WYZ000-IDZ000-042200-

Mesoscale Discussion 0849
NWS Storm Prediction Center Norman OK
0259 PM CDT Fri Jun 04 2021

Areas affected...Far East-Central ID...Southwest MT

Concerning...Severe potential...Watch possible 

Valid 041959Z - 042200Z

Probability of Watch Issuance...40 percent

SUMMARY...Thunderstorm coverage is expected to increase throughout
the afternoon. Some strong to severe storms are possible, with
damaging wind gusts and isolated hail as the primary threats.

DISCUSSION...Visible satellite imagery has shown increasingly deep
cumulus developing over the high terrain of east-central ID and
adjacent southwest MT over the last two hours. This deepening
appears to be associated with gradually increasing ascent attendant
to the approaching low-amplitude shortwave trough approaching the
region. This ascent is not overly strong, but it is favorable timed
with diurnal destabilization and the erosion of any convective
inhibition. Lightning has already been observed in a few cells
across the region.

The expectation is for the overall thunderstorm coverage to
gradually increase over the next few hours as ascent persists and
the atmosphere further destabilizes. Current mesoanalysis estimates
MLCAPE from 500 to 1000 J/kg across the region, and this modest
buoyancy is forecast to continue throughout the afternoon. This
instability coupled with moderate vertical shear will likely support
strong updrafts, a few of which could produce hail. Additionally,
given the high-based storm bases and deeply mixed boundary layer,
strong thunderstorm outflow is also anticipated. Overall storm
coverage may necessitate watch issuance over eastern portions of the
region within the next hour or two.

..Mosier/Guyer.. 06/04/2021

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

ATTN...WFO...BYZ...RIW...TFX...PIH...MSO...

LAT...LON   45331466 46631329 46980986 45950914 44930996 44121360
            45331466

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 4, 4:01 PM MDT	Severe Thunderstorm Watch	SPC	Custer, Dawson, Fallon, Fergus, Garfield, Golden Valley and 13 more	7 hr

Nearby

Mesoscale Discussions in Montana, 2021 Mesoscale Discussions in Idaho, 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.