Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 1419
The Storm Prediction Center issued this mesoscale discussion at Aug 4, 2021, 4:25 PM MDT for Liberty County, Toole County, Montana. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 4, 2021, 4:25 PM MDT (22:25 UTC)
- Expired
- Aug 4, 2021, 6:30 PM MDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Liberty County, MT, Toole County, MT
The radar
The Great Falls radar (KTFX), 133 km from the middle of the area, began a volume at 22:25 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, 10.4 hours before the alert went out and 146 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
- 3035 m above ground
- 0-6 km bulk shear
- 24 kt
- 0-1 km storm-relative helicity
- -14 m²/s²
- 0-3 km storm-relative helicity
- 45 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
331
ACUS11 KWNS 042225
SWOMCD
SPC MCD 042225
MTZ000-050030-
Mesoscale Discussion 1419
NWS Storm Prediction Center Norman OK
0525 PM CDT Wed Aug 04 2021
Areas affected...Parts of northwestern into north central Montana
Concerning...Severe potential...Watch unlikely
Valid 042225Z - 050030Z
Probability of Watch Issuance...20 percent
SUMMARY...Strong thunderstorm development, including a few supercell
structures, probably will continue near and north through east of
Cut Bank into 6-8 PM MDT time frame, posing a risk for severe hail
and locally strong surface gusts.
DISCUSSION...Vigorous thunderstorm development appears underway to
the northwest and north of Cut Bank. This is occurring within the
crest of large-scale mid-level ridging, where forcing for ascent,
associated with weak low-level upslope flow and an approaching
mid-level short wave trough migrating through the broader-scale
anticyclonic flow, may support the maintenance of convection into
the 00-02Z time frame.
A seasonably warm and deeply-mixed boundary layer (with 40+ F
surface temp/dew point spreads) across this region appears
characterized by modest CAPE on the order of 500-1000 J/kg.
However, within the cloud-bearing layer, mean flow may be in excess
of 30 kt, with unidirectional but strong westerly shear.
This environment may remain supportive of the formation of
additional splitting supercell structures with the potential to
produce severe hail and at least locally strong downbursts. It is
possible that consolidating surface cold pools could begin to
support some upscale convective growth, with a tendency to propagate
south-southeastward accompanied by a bit more substantive risk for
strong surface gusts by early evening.
..Kerr/Hart.. 08/04/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...TFX...
LAT...LON 49261184 48921021 48180998 47931089 48391200 48671305
49261184Nearby
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.