Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 1159
The Storm Prediction Center issued this mesoscale discussion at Jul 5, 2021, 10:49 PM MDT for Liberty County, Toole County, Montana. It was in force for 116 min.
The area
The outline as issued.
The facts
- Issued
- Jul 5, 2021, 10:49 PM MDT (04:49 UTC)
- Expired
- Jul 6, 2021, 12:45 AM MDT
- In force
- 116 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
Counties Liberty County, MT, Toole County, MT
The radar
The Great Falls radar (KTFX), 114 km from the middle of the area, began a volume at 04:50 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 00:00Z, 4.8 hours before the alert went out and 112 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
- 435 J/kg
- Mixed-layer CIN
- -65 J/kg
- Mixed-layer LCL
- 1792 m above ground
- 0-6 km bulk shear
- 43 kt
- 0-1 km storm-relative helicity
- 26 m²/s²
- 0-3 km storm-relative helicity
- 159 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.8
The text
As transmitted.
134 ACUS11 KWNS 060449 SWOMCD SPC MCD 060449 MTZ000-060645- Mesoscale Discussion 1159 NWS Storm Prediction Center Norman OK 1149 PM CDT Mon Jul 05 2021 Areas affected...Parts of north central Montana Concerning...Severe potential...Watch unlikely Valid 060449Z - 060645Z Probability of Watch Issuance...5 percent SUMMARY...A small cluster of strong storms may persist into the 2-4 AM MDT time frame, progressing east-southeastward across parts of north central Montana. This may include continuing risk to produce some hail and locally strong surface gusts, but potential for substantive intensification appears low. DISCUSSION...A small, but organized cluster of storms, with an embedded MCV, has crossed the international border to the north of Cutbank. This activity appears supported by forcing for ascent associated with warm advection along a baroclinic zone around 700 mb, ahead of a low amplitude wave within the westerlies. Latest Rapid Refresh suggests that this could persist east-southeastward across parts of north central Montana, north through northeast of Great Falls, into the 08-10Z time frame, before weakening. The deep-layer westerly mean wind vector across this region is rather weak (10-20 kt), but shear is strong due to profiles characterized by veering of low-level easterlies to modest westerlies at mid-levels. So, despite inflow of only weakly unstable air (up to 500+ J/kg), and the tendency for this inflow to become even less unstable as activity progresses eastward, a risk for hail and strong wind gusts may linger until storms dimimish. ..Kerr/Hart.. 07/06/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...TFX... LAT...LON 48921144 48110923 47830992 48311132 48581230 48921144
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 6, 2:37 PM MDT | Mesoscale Discussion | SPC | Big Horn, Fergus, Golden Valley, Judith Basin, Musselshell, Petroleum and 6 more | 83 min |
| Jul 6, 5:00 PM MDT | Severe Thunderstorm Watch | SPC | Big Horn, Custer, Musselshell, Powder River, Rosebud, Treasure and 1 more | 6 hr |
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.