Alert archive / North Dakota / Mesoscale Discussions in 2021
Mesoscale Discussion 1618
The Storm Prediction Center issued this mesoscale discussion at Aug 27, 2021, 2:55 PM MDT for 7 counties in Montana; 11 counties in North Dakota; Butte County, Harding County, Perkins County, South Dakota. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 27, 2021, 2:55 PM MDT (20:55 UTC)
- Expired
- Aug 27, 2021, 5:00 PM MDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 21 counties
Carter County, MT, Dawson County, MT, Fallon County, MT, Richland County, MT, Roosevelt County, MT, Sheridan County, MT, Wibaux County, MT, Adams County, ND, Billings County, ND, Bowman County, ND, Dunn County, ND, Golden Valley County, ND, Hettinger County, ND, McKenzie County, ND, Mountrail County, ND, Slope County, ND, Stark County, ND, Williams County, ND, Butte County, SD, Harding County, SD, Perkins County, SD
The radar
The Bismarck radar (KBIS), 223 km from the middle of the area, began a volume at 20:57 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
Bismarck Municip, ND (KBIS), launched 12:00Z, 8.9 hours before the alert went out and 227 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
- 234 J/kg
- Mixed-layer CIN
- -137 J/kg
- Mixed-layer LCL
- 475 m above ground
- 0-6 km bulk shear
- 46 kt
- 0-1 km storm-relative helicity
- 63 m²/s²
- 0-3 km storm-relative helicity
- 83 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 1.3
The text
As transmitted.
879
ACUS11 KWNS 272055
SWOMCD
SPC MCD 272055
NDZ000-SDZ000-MTZ000-WYZ000-272300-
Mesoscale Discussion 1618
NWS Storm Prediction Center Norman OK
0355 PM CDT Fri Aug 27 2021
Areas affected...Northern High Plains
Concerning...Severe potential...Watch possible
Valid 272055Z - 272300Z
Probability of Watch Issuance...40 percent
SUMMARY...Isolated thunderstorm development is possible late this
afternoon into early evening. The strongest storms will be capable
of large hail and locally severe wind gusts.
DISCUSSION...An mid/upper-level trough is moving across Montana this
afternoon. Multiple vorticity maxima are evident on WV imagery
within the larger-scale trough, but a lobe of ascent appears to
moving across eastern MT, in conjunction with a weak surface
boundary, and gradually deepening cumulus is noted across southeast
MT. While surface temperatures are not particularly warm, relatively
cool midlevel temperatures are supporting SBCAPE of 750-1500 J/kg
(per recent mesoanalyses), with weakening SBCINH. Effective shear is
generally 30-40 kt across the region, with locally higher values
across northwest SD/southwest ND/southeast MT, where surface winds
are locally backed.
Isolated thunderstorm development is expected sometime late this
afternoon/early evening, with the most likely area across northwest
SD/southwest ND, where somewhat greater surface confluence is noted.
Long hodographs will favor a conditional potential for supercells,
with large hail and locally severe wind gusts the primary threats.
The need for a watch remains uncertain at this time, due to
potentially sparse storm coverage.
..Dean/Dial.. 08/27/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BIS...UNR...BYZ...GGW...
LAT...LON 44660394 44830497 45350510 45720519 47670537 48440524
48730484 48760423 48710344 48680288 48540224 46650207
45980205 45470208 45070232 44840272 44680310 44680335
44660394SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 26, 6:25 PM MDT | Mesoscale Discussion | SPC | Aurora, Bennett, Bon Homme, Brule, Buffalo, Charles Mix and 22 more | 2 hr |
| Aug 26, 7:03 PM MDT | Severe Thunderstorm Watch | SPC | Aurora, Beadle, Bennett, Bon Homme, Brookings, Brule and 36 more | 7 hr |
| Aug 26, 9:45 PM MDT | Mesoscale Discussion | SPC | Union | 2 hr |
| Aug 27, 5:33 PM MDT | Mesoscale Discussion | SPC | Butte, Perkins, Ziebach | 117 min |
Nearby
Mesoscale Discussions in North Dakota, 2021Mesoscale Discussions in Montana, 2021Mesoscale Discussions in South Dakota, 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.