Alert archive / Iowa / Mesoscale Discussions in 2017

Mesoscale Discussion 1522

August 18, 201722 counties in Iowa; 21 counties in Minnesota; 9 counties in South Dakota

The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2017, 2:54 PM CDT for 22 counties in Iowa; 21 counties in Minnesota; 9 counties in South Dakota. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued
Aug 18, 2017, 2:54 PM CDT (19:54 UTC)
Expired
Aug 18, 2017, 5:30 PM CDT
In force
3 hr
Issued by
the Storm Prediction Center
Chance of a watch
40%
All 52 counties

Buena Vista County, IA, Calhoun County, IA, Carroll County, IA, Cherokee County, IA, Clay County, IA, Crawford County, IA, Dickinson County, IA, Emmet County, IA, Hancock 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, Webster County, IA, Winnebago County, IA, Big Stone County, MN, Blue Earth County, MN, Brown County, MN, Chippewa County, MN, Cottonwood County, MN, Faribault County, MN, Jackson County, MN, Lac qui Parle County, MN, Lincoln County, MN, Lyon County, MN, Martin County, MN, Murray County, MN, Nicollet County, MN, Nobles County, MN, Pipestone County, MN, Redwood County, MN, Renville County, MN, Rock County, MN, Swift County, MN, Watonwan County, MN, Yellow Medicine County, MN, Brookings County, SD, Codington County, SD, Deuel County, SD, Grant County, SD, Hamlin County, SD, Lincoln County, SD, Minnehaha County, SD, Moody County, SD, Roberts County, SD

The radar

The Sioux Falls radar (KFSD), 103 km from the middle of the area, began a volume at 19:54 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 12:00Z, 7.9 hours before the alert went out and 185 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.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 12:00Z on 2017-08-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 23 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Minneapolis, MN at 12:00Z on 2017-08-18The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -47 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
23 J/kg
Mixed-layer CIN
-139 J/kg
Mixed-layer LCL
1090 m above ground
0-6 km bulk shear
18 kt
0-1 km storm-relative helicity
-47 m²/s²
0-3 km storm-relative helicity
-32 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Aug 18, 4:51 PM CDTSevere Thunderstorm WatchSPCAdair, Audubon, Boone, Buena Vista, Butler, Calhoun and 37 more8 hr
Aug 18, 6:58 PM CDTMesoscale DiscussionSPCAdair, Audubon, Boone, Buena Vista, Calhoun, Carroll and 34 more62 min

Nearby

Mesoscale Discussions in Iowa, 2017Mesoscale Discussions in Minnesota, 2017Mesoscale Discussions in South Dakota, 2017Every mesoscale discussion in 2017

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.