Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 1069
The Storm Prediction Center issued this mesoscale discussion at Jun 23, 2021, 4:33 PM MDT for 9 counties in Montana. It was in force for 117 min.
The area
The outline as issued.
The facts
- Issued
- Jun 23, 2021, 4:33 PM MDT (22:33 UTC)
- Expired
- Jun 23, 2021, 6:30 PM MDT
- In force
- 117 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
Counties Big Horn County, MT, Carbon County, MT, Golden Valley County, MT, Musselshell County, MT, Rosebud County, MT, Stillwater County, MT, Sweet Grass County, MT, Treasure County, MT, Yellowstone County, MT
The radar
The Billings radar (KBLX), 26 km from the middle of the area, began a volume at 22:37 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, 10.6 hours before the alert went out and 251 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
- 2470 m above ground
- 0-6 km bulk shear
- 19 kt
- 0-1 km storm-relative helicity
- 100 m²/s²
- 0-3 km storm-relative helicity
- 82 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
679
ACUS11 KWNS 232233
SWOMCD
SPC MCD 232233
MTZ000-WYZ000-240030-
Mesoscale Discussion 1069
NWS Storm Prediction Center Norman OK
0533 PM CDT Wed Jun 23 2021
Areas affected...South Central Montana
Concerning...Severe potential...Watch unlikely
Valid 232233Z - 240030Z
Probability of Watch Issuance...5 percent
SUMMARY...Isolated thunderstorms may pose a hail/wind risk this
evening, but the overall threat will remain spatially limited. A
watch is not expected.
DISCUSSION...A single thunderstorm has developed over south-central
MT over the past 30-45 minutes within a broad cluster of agitated
cumulus. This storm has been slow to mature, owing mainly to weak
instability (generally near 500 J/kg per RAP forecast soundings and
mesoanalysis estimates). However, nearly 40 knots of 0-6 km bulk
shear was recently sampled from the KBLX VWP, which matches well
with mesoanalysis estimates of around 40-50 knots of effective bulk
shear. The favorable deep shear coupled with a nearly
uni-directional wind profile may compensate for the limited
instability and support some storm organization. A severe hail
threat is possible with any storm that can manage to mature, and
steep low-level lapse rates near 9 C/km will support strong storm
outflow and a damaging wind risk. GOES visible imagery shows several
clusters of deepening cumulus, but weak forcing for ascent will
likely result in isolated storm coverage. Given the low potential
for a widespread severe threat a watch is not expected.
..Moore/Grams.. 06/23/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BYZ...GGW...TFX...
LAT...LON 45591020 46041020 46700968 46920894 46900815 46490704
45610593 45280591 45060626 44980728 45230948 45591020Nearby
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.