Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 1536
The Storm Prediction Center issued this mesoscale discussion at Aug 16, 2021, 2:49 PM MDT for 12 counties in Montana. It was in force for 116 min.
The area
The outline as issued.
The facts
- Issued
- Aug 16, 2021, 2:49 PM MDT (20:49 UTC)
- Expired
- Aug 16, 2021, 4:45 PM MDT
- In force
- 116 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Gallatin County, MT, Garfield County, MT, Golden Valley County, MT, Madison County, MT, Musselshell County, MT, Park County, MT, Petroleum County, MT, Stillwater County, MT, Sweet Grass County, MT, Treasure County, MT, Wheatland County, MT, Yellowstone County, MT
The radar
The Billings radar (KBLX), 72 km from the middle of the area, began a volume at 20:49 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, 8.8 hours before the alert went out and 169 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
- 3460 m above ground
- 0-6 km bulk shear
- 33 kt
- 0-1 km storm-relative helicity
- 170 m²/s²
- 0-3 km storm-relative helicity
- 190 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
456
ACUS11 KWNS 162049
SWOMCD
SPC MCD 162049
MTZ000-WYZ000-162245-
Mesoscale Discussion 1536
NWS Storm Prediction Center Norman OK
0349 PM CDT Mon Aug 16 2021
Areas affected...Southern Montana
Concerning...Severe potential...Watch unlikely
Valid 162049Z - 162245Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated thunderstorms will continue to strengthen through
the late afternoon and may be capable of sporadic, but severe,
downburst winds. However, this threat will likely remain too limited
spatially to warrant a watch.
DISCUSSION...Regional reflectivity has shown a gradual increase in
convective showers and weak thunderstorms over the past hour. GOES
IR imagery has shown increased cloud top cooling with a few storms,
and an uptick in lightning has also been noted. This
maturing/deepening trend is likely attributable to a slow increase
in instability and reducing in inhibition as boundary-layer heating
and mixing are maximized via diurnal warming. Storms should continue
to grow through the late afternoon hours as MUCAPE values increase
to near 500-1000 J/kg. Although instability will likely remain
modest, 20-30 knots of effective bulk shear combined with steep
low-level lapse rates will support a potential for severe downburst
winds. This potential will likely be maximized over southern MT
where 0-3 km lapse rates are approaching 10 C/km and 50-60 F
dewpoint depressions are noted. However, storm coverage will likely
remain isolated due to generally weak forcing for ascent and
spatially limited instability. Because of this a watch is not
expected at this time.
..Moore/Hart.. 08/16/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BYZ...GGW...RIW...TFX...MSO...
LAT...LON 46501096 47310876 47410741 47240667 46910628 46540642
45770785 45280955 44991066 44541206 45381273 45891205
46501096Nearby
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.