Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1877
The Storm Prediction Center issued this mesoscale discussion at Oct 20, 2021, 7:39 AM CDT for 17 counties in Iowa; 8 counties in Minnesota. It was in force for 96 min.
The area
The outline as issued.
The facts
- Issued
- Oct 20, 2021, 7:39 AM CDT (12:39 UTC)
- Expired
- Oct 20, 2021, 9:15 AM CDT
- In force
- 96 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
All 25 counties
Buena Vista County, IA, Calhoun County, IA, Cherokee County, IA, Clay County, IA, Dickinson County, IA, Emmet County, IA, Humboldt County, IA, Ida County, IA, Kossuth County, IA, Lyon County, IA, O'Brien County, IA, Osceola County, IA, Palo Alto County, IA, Plymouth County, IA, Pocahontas County, IA, Sac County, IA, Sioux County, IA, Cottonwood County, MN, Jackson County, MN, Martin County, MN, Murray County, MN, Nobles County, MN, Pipestone County, MN, Rock County, MN, Watonwan County, MN
The radar
The Sioux Falls radar (KFSD), 115 km from the middle of the area, began a volume at 12:39 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, 0.7 hours before the alert went out and 224 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1107 m above ground
- 0-6 km bulk shear
- 34 kt
- 0-1 km storm-relative helicity
- 62 m²/s²
- 0-3 km storm-relative helicity
- 163 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
419
ACUS11 KWNS 201239
SWOMCD
SPC MCD 201239
IAZ000-MNZ000-SDZ000-201415-
Mesoscale Discussion 1877
NWS Storm Prediction Center Norman OK
0739 AM CDT Wed Oct 20 2021
Areas affected...southwest MN into northwest IA
Concerning...Severe potential...Watch unlikely
Valid 201239Z - 201415Z
Probability of Watch Issuance...5 percent
SUMMARY...Isolated strong thunderstorms may produce marginally
severe hail this morning.
DISCUSSION...Widely scattered elevated thunderstorms are ongoing
this morning near a surface low over western IA/MN in an area of low
level warm advection ahead of an upper trough and surface cold
front. While instability will remain weak across the region given a
cool surface temperatures and modest boundary-layer moisture, steep
midlevel lapse rates greater than 7.5 C/km are in place over the
region amid favorable effective shear. This should continue to
support briefly organized clusters/cells this morning. The strongest
cells may produce isolated hail stones up to 1 inch in diameter. The
overall severe threat is expected to remain limited and a watch is
not expected.
..Leitman/Guyer.. 10/20/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MPX...DMX...FSD...
LAT...LON 44139648 44199618 44159500 43909437 43479393 43049388
42669401 42409421 42319448 42319533 42549630 42649661
43449664 43909662 44139648Nearby
Mesoscale Discussions in Iowa, 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.