Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1368
The Storm Prediction Center issued this mesoscale discussion at Jul 27, 2021, 7:33 PM CDT for 17 counties in Iowa; 14 counties in Minnesota; 11 counties in Wisconsin. It was in force for 87 min.
The area
The outline as issued.
The facts
- Issued
- Jul 27, 2021, 7:33 PM CDT (00:33 UTC)
- Expired
- Jul 27, 2021, 9:00 PM CDT
- In force
- 87 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 60%
All 42 counties
Allamakee County, IA, Black Hawk County, IA, Bremer County, IA, Buchanan County, IA, Butler County, IA, Cerro Gordo County, IA, Chickasaw County, IA, Clayton County, IA, Delaware County, IA, Fayette County, IA, Floyd County, IA, Franklin County, IA, Grundy County, IA, Howard County, IA, Mitchell County, IA, Winneshiek County, IA, Worth County, IA, Dakota County, MN, Dodge County, MN, Fillmore County, MN, Freeborn County, MN, Goodhue County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Ramsey County, MN, Rice County, MN, Steele County, MN, Wabasha County, MN, Waseca County, MN, Winona County, MN, Buffalo County, WI, Crawford County, WI, Grant County, WI, Iowa County, WI, La Crosse County, WI, Monroe County, WI, Pierce County, WI, Richland County, WI, Sauk County, WI, Trempealeau County, WI, Vernon County, WI
The radar
The La Crosse radar (KARX), 69 km from the middle of the area, began a volume at 00:35 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Minneapolis, MN (KMPX), launched 00:00Z, 0.6 hours before the alert went out and 181 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
- 4029 J/kg
- Mixed-layer CIN
- -9 J/kg
- Mixed-layer LCL
- 1142 m above ground
- 0-6 km bulk shear
- 35 kt
- 0-1 km storm-relative helicity
- 5 m²/s²
- 0-3 km storm-relative helicity
- 65 m²/s²
- Significant tornado parameter
- 0.7
- Supercell composite
- 6.6
The text
As transmitted.
462
ACUS11 KWNS 280033
SWOMCD
SPC MCD 280033
WIZ000-IAZ000-MNZ000-280200-
Mesoscale Discussion 1368
NWS Storm Prediction Center Norman OK
0733 PM CDT Tue Jul 27 2021
Areas affected...portions of southern MN...southwest WI...northeast
IA
Concerning...Severe potential...Watch possible
Valid 280033Z - 280200Z
Probability of Watch Issuance...60 percent
SUMMARY...Thunderstorms may develop this evening with a risk for
potentially very large hail and damaging gusts. Trends are being
monitored and a Severe Thunderstorm Watch is possible prior to
02-03z.
DISCUSSION...A warm front has been gradually sharpening over
southern MN and southwest WI, with strong instability in place as
MLCAPE ranges from 2500 to 4000 J/kg based on latest objective
analysis. Early evening visible imagery and recent radar data
reveal attempts at convection initiation over southeast MN, and CAM
guidance continues to suggest development in the vicinity of the
MN/WI/IA border region over the next few hours, and possibly as far
north as the Twin Cities where towering cumulus was noted on the
last few 1-minute visible images. Modest height rises over the
discussion area during the past several hours casts some uncertainty
on the overall extent of thunderstorm development this evening,
however storms that do develop would likely possess supercell
structures initially and be capable of significant severe hail and
damaging winds. At least some risk for a tornado will exist in the
vicinity of the boundary where low-level SRH is locally enhanced.
Increasing storm coverage with time would result in a transition to
damaging winds as the primary severe threat.
Short-term observational trends will continue to be monitored for
the possibility of a watch prior to 02-03z.
..Bunting/Grams.. 07/28/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MKX...DVN...ARX...MPX...DMX...
LAT...LON 42099217 42289306 42959343 43809378 44249371 44749344
45029318 45029300 44729229 44549183 44329121 44089069
43769010 43428972 42958979 42479087 42099217SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 27, 8:03 PM CDT | Severe Thunderstorm Watch | SPC | Allamakee, Bremer, Buchanan, Chickasaw, Clayton, Delaware and 7 more | 6 hr |
| Jul 27, 10:35 PM CDT | Mesoscale Discussion | SPC | Allamakee, Bremer, Buchanan, Chickasaw, Clayton, Delaware and 5 more | 55 min |
| Jul 28, 12:50 AM CDT | Mesoscale Discussion | SPC | Benton, Buchanan, Clayton, Delaware, Dubuque, Jackson and 2 more | 55 min |
| Jul 28, 2:48 AM CDT | Mesoscale Discussion | SPC | Big Stone, Chippewa, Douglas, Grant, Kandiyohi, Lac qui Parle and 12 more | 2 hr |
| Jul 28, 10:28 AM CDT | Mesoscale Discussion | SPC | Aitkin, Beltrami, Cass, Clearwater, Hubbard, Itasca | 2 hr |
| Jul 28, 12:59 PM CDT | Mesoscale Discussion | SPC | Koochiching, Lake, Lake of the Woods, Saint Louis | 2 hr |
| Jul 28, 3:32 PM CDT | Mesoscale Discussion | SPC | Beltrami, Clearwater, Lake of the Woods, Mahnomen, Red Lake | 118 min |
| Jul 28, 5:09 PM CDT | Mesoscale Discussion | SPC | Aitkin, Anoka, Benton, Carlton, Chisago, Crow Wing and 7 more | 2 hr |
Nearby
Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Minnesota, 2021Mesoscale Discussions in Wisconsin, 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.