Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1621
The Storm Prediction Center issued this mesoscale discussion at Aug 27, 2021, 6:28 PM CDT for 12 counties in Iowa; Douglas County, Sarpy County, Washington County, Nebraska. It was in force for 92 min.
The area
The outline as issued.
The facts
- Issued
- Aug 27, 2021, 6:28 PM CDT (23:28 UTC)
- Expired
- Aug 27, 2021, 8:00 PM CDT
- In force
- 92 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Audubon County, IA, Calhoun County, IA, Carroll County, IA, Crawford County, IA, Greene County, IA, Guthrie County, IA, Harrison County, IA, Ida County, IA, Pottawattamie County, IA, Sac County, IA, Shelby County, IA, Webster County, IA, Douglas County, NE, Sarpy County, NE, Washington County, NE
The radar
The Omaha radar (KOAX), 95 km from the middle of the area, began a volume at 23:31 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
Omaha, NE (KOAX), launched 12:00Z, 11.5 hours before the alert went out and 96 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
- 956 J/kg
- Mixed-layer CIN
- -243 J/kg
- Mixed-layer LCL
- 1443 m above ground
- 0-6 km bulk shear
- 30 kt
- 0-1 km storm-relative helicity
- 190 m²/s²
- 0-3 km storm-relative helicity
- 165 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.6
The text
As transmitted.
292
ACUS11 KWNS 272329
SWOMCD
SPC MCD 272328
IAZ000-NEZ000-280100-
Mesoscale Discussion 1621
NWS Storm Prediction Center Norman OK
0628 PM CDT Fri Aug 27 2021
Areas affected...far eastern NE...west-central IA
Concerning...Severe potential...Watch possible
Valid 272328Z - 280100Z
Probability of Watch Issuance...40 percent
SUMMARY...Isolated large hail and severe gusts are possible with the
more intense thunderstorms this evening. Overall storm coverage is
still uncertain (i.e., isolated) and the lower storm coverage may
preclude a severe thunderstorm watch being issued, although the
stronger storms will potentially be capable of severe weather given
the favorable environment.
DISCUSSION...Visible-satellite imagery shows developing convection
over far eastern NE into west-central IA on the trailing portion of
a mid-level shortwave trough migrating east-northeastward over the
Upper Midwest. Surface conditions are hot and humid with
temperatures in the lower 90s with lower 70s dewpoints. The RAP
forecast sounding for Omaha, NE shows a good depiction of the
surface conditions and it indicates around 3300 J/kg MLCAPE.
Although flow is relatively modest in the lowest 9 km per KOAX 88D
VAD data (sub 30 kt), 25-30 kt effective shear is indicated and
would in turn support organized storm structures this evening. The
main threats with the stronger storms would be a hail/wind threat.
..Smith/Bunting.. 08/27/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...DMX...FSD...OAX...
LAT...LON 41319663 42129588 42589525 42659446 42359396 41819414
41149559 40929619 41319663SPC 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, 5:30 PM CDT | Mesoscale Discussion | SPC | Allamakee, Cerro Gordo, Chickasaw, Floyd, Howard, Winneshiek | 60 min |
| Aug 26, 7:25 PM CDT | Mesoscale Discussion | SPC | Boyd, Brown, Cherry, Holt, Keya Paha, Rock | 2 hr |
Nearby
Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Nebraska, 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.