Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 1173
The Storm Prediction Center issued this mesoscale discussion at Jul 6, 2021, 10:27 PM MDT for 5 counties in Montana. It was in force for 93 min.
The area
The outline as issued.
The facts
- Issued
- Jul 6, 2021, 10:27 PM MDT (04:27 UTC)
- Expired
- Jul 7, 2021, 12:00 AM MDT
- In force
- 93 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 339
Counties Custer County, MT, Garfield County, MT, Phillips County, MT, Powder River County, MT, Rosebud County, MT
The radar
The Glasgow radar (KGGW), 111 km from the middle of the area, began a volume at 04:28 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
Glasgow Intl Airport, MT (KGGW), launched 00:00Z, 4.5 hours before the alert went out and 114 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
- 20 J/kg
- Mixed-layer CIN
- -155 J/kg
- Mixed-layer LCL
- 1401 m above ground
- 0-6 km bulk shear
- 54 kt
- 0-1 km storm-relative helicity
- -5 m²/s²
- 0-3 km storm-relative helicity
- 134 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.1
The text
As transmitted.
835
ACUS11 KWNS 070427
SWOMCD
SPC MCD 070427
MTZ000-WYZ000-070600-
Mesoscale Discussion 1173
NWS Storm Prediction Center Norman OK
1127 PM CDT Tue Jul 06 2021
Areas affected...Parts of eastern Montana and adjacent northwestern
Wyoming
Concerning...Severe Thunderstorm Watch 339...
Valid 070427Z - 070600Z
The severe weather threat for Severe Thunderstorm Watch 339
continues.
SUMMARY...Widely scattered ongoing storms are expected to begin
diminishing within the next couple of hours. Until then, they may
continue to pose a risk for hail and locally strong surface gusts.
A new severe weather watch does not appear necessary, but remaining
portions of Severe Thunderstorm Watch 339 could be locally extended
an hour or two.
DISCUSSION...Despite considerable stabilization of low-level lapse
rates to the lee of the northern Rockies. Four widely scattered
supercells have been maintained along a corridor of higher
precipitable water coinciding with weak lower/mid-level warm
advection, from southeastern Saskatchewan into northwestern Wyoming.
This likely has been most prominently supported by the strong
deep-layer shear, and storm-scale dynamic forcing, but seems
unlikely to continue much beyond another hour or two due to the
stabilizing environment.
..Kerr.. 07/07/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...UNR...BYZ...GGW...TFX...
LAT...LON 49260962 49450859 48680761 47480643 45180440 44670595
45540694 46430731 47940837 49260962SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 6, 6:40 PM MDT | Mesoscale Discussion | SPC | Blaine, Fergus, Garfield, Hill, Musselshell, Petroleum and 4 more | 95 min |
| Jul 7, 2:03 PM MDT | Mesoscale Discussion | SPC | Broadwater, Cascade, Custer, Fergus, Garfield, Golden Valley and 13 more | 117 min |
| Jul 7, 3:03 PM MDT | Severe Thunderstorm Watch | SPC | Big Horn, Broadwater, Carbon, Carter, Cascade, Chouteau and 19 more | 8 hr |
| Jul 7, 5:48 PM MDT | Mesoscale Discussion | SPC | Big Horn, Carbon, Custer, Fergus, Garfield, Golden Valley and 8 more | 117 min |
Nearby
Mesoscale Discussions in Montana, 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.