Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1620
The Storm Prediction Center issued this mesoscale discussion at Aug 27, 2021, 5:30 PM CDT for 6 counties in Iowa. It was in force for 60 min.
The area
The outline as issued.
The facts
- Issued
- Aug 27, 2021, 5:30 PM CDT (22:30 UTC)
- Expired
- Aug 27, 2021, 6:30 PM CDT
- In force
- 60 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 465
Counties Allamakee County, IA, Cerro Gordo County, IA, Chickasaw County, IA, Floyd County, IA, Howard County, IA, Winneshiek County, IA
The radar
The La Crosse radar (KARX), 129 km from the middle of the area, began a volume at 22:34 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
Minneapolis, MN (KMPX), launched 12:00Z, 10.5 hours before the alert went out and 211 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
- 487 J/kg
- Mixed-layer CIN
- -63 J/kg
- Mixed-layer LCL
- 644 m above ground
- 0-6 km bulk shear
- 24 kt
- 0-1 km storm-relative helicity
- -9 m²/s²
- 0-3 km storm-relative helicity
- -16 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
607
ACUS11 KWNS 272230
SWOMCD
SPC MCD 272230
IAZ000-272330-
Mesoscale Discussion 1620
NWS Storm Prediction Center Norman OK
0530 PM CDT Fri Aug 27 2021
Areas affected...northeast IA
Concerning...Tornado Watch 465...
Valid 272230Z - 272330Z
The severe weather threat for Tornado Watch 465 continues.
SUMMARY...The severe threat in recently issued tornado watch #465
will likely focus primarily in northeast IA during the next 1-2
hours. The risk for supercell-related hazards will include hail,
severe gusts, and possibly a tornado.
DISCUSSION...Visible-satellite imagery shows an outflow boundary
situated west-east across far northeast IA into southwest WI.
Temperatures south of the boundary are in the low-mid 80s with mid
70s dewpoints. As a result, a very unstable airmass is located over
the upper MS Valley early this evening. It seems a messy supercell
mode may persist for the next few hours due in part to 1) only weak
forcing but 2) enlargement of the hodograph with a veer-back-veer
wind profile---leading to precipitation seeding near updrafts. RAP
forecast soundings depict this relative limitation in the wind
profile in the upper levels which is only partly observed by the La
Crosse, WI 88D VAD data.
..Smith.. 08/27/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...ARX...DMX...
LAT...LON 43219323 43479179 43279132 42959145 42849308 42989327
43219323SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 26, 8:03 PM CDT | Severe Thunderstorm Watch | SPC | Buena Vista, Cherokee, Clay, Dickinson, Ida, Lyon and 5 more | 7 hr |
| Aug 26, 10:45 PM CDT | Mesoscale Discussion | SPC | Bremer, Buena Vista, Butler, Calhoun, Cerro Gordo, Cherokee and 25 more | 2 hr |
| Aug 27, 1:53 PM CDT | Mesoscale Discussion | SPC | Black Hawk, Bremer, Butler, Calhoun, Cerro Gordo, Chickasaw and 18 more | 97 min |
| Aug 27, 4:01 PM CDT | Mesoscale Discussion | SPC | Allamakee, Black Hawk, Bremer, Butler, Calhoun, Cerro Gordo and 20 more | 59 min |
| Aug 27, 5:15 PM CDT | Tornado Watch | SPC | Allamakee, Bremer, Butler, Cerro Gordo, Chickasaw, Clayton and 12 more | 6 hr |
| Aug 27, 6:28 PM CDT | Mesoscale Discussion | SPC | Audubon, Calhoun, Carroll, Crawford, Greene, Guthrie and 6 more | 92 min |
Nearby
Mesoscale Discussions in Iowa, 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.