Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1434
The Storm Prediction Center issued this mesoscale discussion at Aug 7, 2021, 3:46 PM CDT for 13 counties in Iowa; 8 counties in Minnesota; 11 counties in Wisconsin. It was in force for 119 min.
The area
The outline as issued.
The facts
- Issued
- Aug 7, 2021, 3:46 PM CDT (20:46 UTC)
- Expired
- Aug 7, 2021, 5:45 PM CDT
- In force
- 119 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 32 counties
Allamakee County, IA, Bremer County, IA, Butler County, IA, Cerro Gordo County, IA, Chickasaw County, IA, Clayton County, IA, Fayette County, IA, Floyd County, IA, Howard County, IA, Mitchell County, IA, Winnebago County, IA, Winneshiek County, IA, Worth County, IA, Dodge County, MN, Fillmore County, MN, Freeborn County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Steele County, MN, Waseca County, MN, Columbia County, WI, Crawford County, WI, Dane County, WI, Grant County, WI, Green County, WI, Iowa County, WI, Lafayette County, WI, Richland County, WI, Rock County, WI, Sauk County, WI, Vernon County, WI
The radar
The La Crosse radar (KARX), 73 km from the middle of the area, began a volume at 20:50 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Davenport, (KDVN), launched 12:00Z, 8.8 hours before the alert went out and 217 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
- 1645 J/kg
- Mixed-layer CIN
- -79 J/kg
- Mixed-layer LCL
- 1006 m above ground
- 0-6 km bulk shear
- 20 kt
- 0-1 km storm-relative helicity
- 39 m²/s²
- 0-3 km storm-relative helicity
- 37 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
593
ACUS11 KWNS 072046
SWOMCD
SPC MCD 072046
WIZ000-IAZ000-MNZ000-072245-
Mesoscale Discussion 1434
NWS Storm Prediction Center Norman OK
0346 PM CDT Sat Aug 07 2021
Areas affected...Portions of southern MN...northeastern IA...and
southern WI
Concerning...Severe potential...Watch possible
Valid 072046Z - 072245Z
Probability of Watch Issuance...40 percent
SUMMARY...All severe hazards remain possible this afternoon, but
overall storm coverage is uncertain. Watch issuance is still
possible.
DISCUSSION...Storms occurring through much of the day across
southern MN into southwestern WI have largely remained elevated
while posing an isolated hail/wind threat. Recent visible and
satellite imagery suggests that some attempt at surface-based storm
development is underway across south-central MN along a convectively
reinforced warm front. If this activity can strengthen over the next
couple of hours, then it would pose a threat for all severe hazards,
as MLCAPE of 2000-3000 J/kg and 35-40 kt of effective bulk shear
present across the warm sector will be favorable for organized
updrafts. A small cluster is also present across southwestern WI,
and this activity should pose mainly an isolated damaging wind
threat in the short term as it moves eastward. The main uncertainty
is overall coverage of surface-based storms, as large-scale forcing
behind an MCV moving into WI remains unclear. Any tornado potential
will likely remain focused along the warm front where the greatest
low-level shear is present owing to backed surface winds. At this
point, watch issuance remains possible, and will largely be
dependent on the development of additional surface-based storms
along the front.
..Gleason/Thompson.. 08/07/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MKX...DVN...ARX...MPX...DMX...
LAT...LON 44239353 43759025 43338872 42578894 42539078 42579277
42989364 43789392 44239353SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 6, 11:54 PM CDT | Mesoscale Discussion | SPC | Lyon, Sioux | 2 hr |
| Aug 7, 2:10 AM CDT | Mesoscale Discussion | SPC | Lyon, Osceola | 2 hr |
| Aug 7, 11:03 AM CDT | Mesoscale Discussion | SPC | Allamakee, Black Hawk, Bremer, Buchanan, Butler, Cerro Gordo and 11 more | 2 hr |
| Aug 7, 6:35 PM CDT | Severe Thunderstorm Watch | SPC | Fremont, Harrison, Mills, Montgomery, Page, Pottawattamie and 1 more | 6 hr |
| Aug 7, 4:36 PM CDT | Severe Thunderstorm Watch | SPC | Columbia, Dane, Dodge, Green, Iowa, Jefferson and 5 more | 4 hr |
| Aug 7, 5:02 PM CDT | Mesoscale Discussion | SPC | Green, Iowa, Rock, Walworth | 58 min |
Nearby
Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Wisconsin, 2021Mesoscale Discussions in Minnesota, 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.