Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 855
The Storm Prediction Center issued this mesoscale discussion at Jun 5, 2021, 2:27 PM MDT for 10 counties in Montana; Park County, Wyoming. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Jun 5, 2021, 2:27 PM MDT (20:27 UTC)
- Expired
- Jun 5, 2021, 4:30 PM MDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Carbon County, MT, Gallatin County, MT, Golden Valley County, MT, Musselshell County, MT, Park County, MT, Stillwater County, MT, Sweet Grass County, MT, Treasure County, MT, Wheatland County, MT, Yellowstone County, MT, Park County, WY
The radar
The Billings radar (KBLX), 73 km from the middle of the area, began a volume at 20:26 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
Great_falls, MT (KTFX), launched 12:00Z, 8.5 hours before the alert went out and 222 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 3187 m above ground
- 0-6 km bulk shear
- 41 kt
- 0-1 km storm-relative helicity
- 102 m²/s²
- 0-3 km storm-relative helicity
- 83 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
581
ACUS11 KWNS 052027
SWOMCD
SPC MCD 052027
MTZ000-WYZ000-052230-
Mesoscale Discussion 0855
NWS Storm Prediction Center Norman OK
0327 PM CDT Sat Jun 05 2021
Areas affected...the south-central Montana/northwestern Wyoming
vicinity
Concerning...Severe potential...Watch possible
Valid 052027Z - 052230Z
Probability of Watch Issuance...40 percent
SUMMARY...Gradually increasing convection over the south-central
Montana vicinity will pose a risk for very isolated, strong wind
gusts. Need for potential WW remains uncertain.
DISCUSSION...Afternoon heating/mixing of a marginally moist boundary
layer has led to a general decrease surface dewpoints across the
region. Still, gradual destabilization is ongoing, with mixed-layer
CAPE now around 500 J/kg per objective analyses over portions of
south-central Montana near and west of Billings.
TCU/CB development is ongoing over the higher terrain of
southwestern Montana, with a few stronger updrafts now spreading
into lower elevation areas. Activity remain isolated however, with
any potential for gusty winds largely dependent upon evaporative
assistance within the dry/well-mixed boundary layer.
With time, greater wind risk would likely be contingent upon
clustering/upscale growth of convection, and with limited
instability with eastward/northeastward extent into eastern Montana,
coverage/intensity of convection remains uncertain, despite ample
deep-layer shear supported by enhanced southwesterly mid-level flow
atop the region.
..Goss/Guyer.. 06/05/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BYZ...GGW...RIW...TFX...
LAT...LON 44971138 45381155 46671022 47060916 46950712 46100688
44910864 44880845 44301010 44971138SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jun 4, 8:10 PM MDT | Mesoscale Discussion | SPC | Custer, Dawson, Garfield, Golden Valley, Judith Basin, Musselshell and 8 more | 2 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.