Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 1165
The Storm Prediction Center issued this mesoscale discussion at Jul 6, 2021, 2:37 PM MDT for 12 counties in Montana; Johnson County, Sheridan County, Wyoming. It was in force for 83 min.
The area
The outline as issued.
The facts
- Issued
- Jul 6, 2021, 2:37 PM MDT (20:37 UTC)
- Expired
- Jul 6, 2021, 4:00 PM MDT
- In force
- 83 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Big Horn County, MT, Fergus County, MT, Golden Valley County, MT, Judith Basin County, MT, Musselshell County, MT, Petroleum County, MT, Powder River County, MT, Rosebud County, MT, Stillwater County, MT, Treasure County, MT, Wheatland County, MT, Yellowstone County, MT, Johnson County, WY, Sheridan County, WY
The radar
The Billings radar (KBLX), 44 km from the middle of the area, began a volume at 20:41 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
Great_falls, MT (KTFX), launched 12:00Z, 8.6 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.
- Mixed-layer CAPE
- 103 J/kg
- Mixed-layer CIN
- -251 J/kg
- Mixed-layer LCL
- 1154 m above ground
- 0-6 km bulk shear
- 27 kt
- 0-1 km storm-relative helicity
- 37 m²/s²
- 0-3 km storm-relative helicity
- 134 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.2
The text
As transmitted.
404
ACUS11 KWNS 062037
SWOMCD
SPC MCD 062037
MTZ000-WYZ000-062200-
Mesoscale Discussion 1165
NWS Storm Prediction Center Norman OK
0337 PM CDT Tue Jul 06 2021
Areas affected...southern Montana far northern Wyoming.
Concerning...Severe potential...Watch possible
Valid 062037Z - 062200Z
Probability of Watch Issuance...40 percent
SUMMARY...Isolated storms including a few supercells may pose a risk
for damaging winds and hail this evening. A weather watch is
possible but uncertain.
DISCUSSION...Afternoon visible satellite imagery showed towering
cumulus developing off the higher terrain of southern Montana and
northern Wyoming. Along the western fringes of a northwesterly flow
shortwave trough, storm development appears probable in the next
hour or two as remaining inhibition weakens. Within a warming and
destabilizing environment with around 1000 J/kg of MLCAPE, and 30-40
kts of effective shear, supercells are expected to be the primary
storm mode. Mid-level lapse rates while not overly steep around
7-7.5 C/km should be sufficient for the development of large hail,
especially with stronger supercells. Damaging wind gusts will also
be likely given the well-mixed boundary layer with temperature
dewpoint spreads near 30 degrees F.
High-res guidance has been inconsistent on the coverage of storms
that develop later this evening. This is likely due to weak forcing
for ascent within the upslope flow regime limiting model-based
convective initiation. Given satellite trends, it appears possible
that isolated to widely scattered storms may develop and track
southeastward across Montana and portions of northern Wyoming. The
convective parameter space suggests a weather watch is possible,
though uncertainty remains.
..Lyons/Guyer.. 07/06/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...UNR...BYZ...GGW...RIW...TFX...
LAT...LON 47641009 47650935 47610845 46540611 46150563 44620512
43840600 44030686 44670763 45590952 46251061 47171080
47641009SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 5, 10:49 PM MDT | Mesoscale Discussion | SPC | Liberty, Toole | 116 min |
| Jul 6, 5:00 PM MDT | Severe Thunderstorm Watch | SPC | Big Horn, Custer, Musselshell, Powder River, Rosebud, Treasure and 1 more | 6 hr |
Nearby
Mesoscale Discussions in Montana, 2021Mesoscale Discussions in Wyoming, 2021Every 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.