Alert archive / Iowa / Severe Thunderstorm Watches in 2017

Severe Thunderstorm Watch 429

July 21, 20174 states

The Storm Prediction Center issued this severe thunderstorm watch at Jul 21, 2017, 4:52 PM CDT for 4 states. It was in force for 9 hr.

The area

The outline as issued.

The facts

Issued: Jul 21, 2017, 4:52 PM CDT (21:52 UTC)
Expired: Jul 22, 2017, 2:00 AM CDT
In force: 9 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 90 counties

Benton County, IA, Black Hawk County, IA, Boone County, IA, Bremer County, IA, Buchanan County, IA, Butler County, IA, Cedar County, IA, Clayton County, IA, Clinton County, IA, Dallas County, IA, Delaware County, IA, Des Moines County, IA, Dubuque County, IA, Fayette County, IA, Grundy County, IA, Hamilton County, IA, Hardin County, IA, Henry County, IA, Iowa County, IA, Jackson County, IA, Jasper County, IA, Jefferson County, IA, Johnson County, IA, Jones County, IA, Keokuk County, IA, Linn County, IA, Louisa County, IA, Lucas County, IA, Mahaska County, IA, Marion County, IA, Marshall County, IA, Monroe County, IA, Muscatine County, IA, Polk County, IA, Poweshiek County, IA, Scott County, IA, Story County, IA, Tama County, IA, Wapello County, IA, Warren County, IA, Washington County, IA, Boone County, IL, Bureau County, IL, Carroll County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Ford County, IL, Grundy County, IL, Henderson County, IL, Henry County, IL, Iroquois County, IL, Jo Daviess County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Marshall County, IL, McHenry County, IL, Mercer County, IL, Ogle County, IL, Peoria County, IL, Putnam County, IL, Rock Island County, IL, Stark County, IL, Stephenson County, IL, Warren County, IL, Whiteside County, IL, Will County, IL, Winnebago County, IL, Woodford County, IL, Benton County, IN, Cass County, IN, Fulton County, IN, Jasper County, IN, Lake County, IN, LaPorte County, IN, Marshall County, IN, Miami County, IN, Newton County, IN, Porter County, IN, Pulaski County, IN, Saint Joseph County, IN, Starke County, IN, White County, IN, Berrien County, MI

The radar

The Quad Cities radar (KDVN), 39 km from the middle of the area, began a volume at 21:53 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 20%
One or more EF2 to EF5 tornadoes: 10%
Ten or more severe wind reports: 60%
One or more gusts of 65 knots or more: 20%
Ten or more severe hail reports: 40%
One or more hailstones of 2 inches or more: 30%
Six or more combined severe hail and wind reports: 90%

Warnings issued inside it

34 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Jul 21, 5:01 PM CDT	Severe Thunderstorm Warning	DVN	Cedar, Jones, Linn	59 min
Jul 21, 5:08 PM CDT	Severe Thunderstorm Warning	ARX	Clayton	35 min
Jul 21, 5:16 PM CDT	Flash Flood Warning	DVN	Cedar, Johnson, Jones, Linn	6 hr
Jul 21, 5:24 PM CDT	Severe Thunderstorm Warning	DVN	Dubuque	37 min
Jul 21, 5:39 PM CDT	Tornado Warning	DVN	Cedar, Johnson, Muscatine	51 min
Jul 21, 5:57 PM CDT	Severe Thunderstorm Warning	ARX	Clayton, Fayette	48 min
Jul 21, 6:10 PM CDT	Tornado Warning	DVN	Rock Island	50 min
Jul 21, 6:15 PM CDT	Severe Thunderstorm Warning	DVN	Stephenson	45 min
Jul 21, 6:20 PM CDT	Severe Thunderstorm Warning	ARX	Fayette	25 min
Jul 21, 6:30 PM CDT	Severe Thunderstorm Warning	LOT	Ogle	45 min
Jul 21, 6:39 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, Kankakee, Livingston, Will	51 min
Jul 21, 6:54 PM CDT	Flash Flood Warning	ARX	Clayton	15 hr
Jul 21, 7:18 PM CDT	Tornado Warning	DVN	Carroll, Whiteside	42 min
Jul 21, 7:23 PM CDT	Tornado Warning	DVN	Whiteside	22 min
Jul 21, 7:33 PM CDT	Severe Thunderstorm Warning	DVN	Carroll, Rock Island, Whiteside	57 min
Jul 21, 7:33 PM CDT	Severe Thunderstorm Warning	DVN	Bureau, Henry, Mercer, Rock Island	57 min
Jul 21, 7:36 PM CDT	Flash Flood Warning	LOT	Ogle	6 hr
Jul 21, 7:51 PM CDT	Flash Flood Warning	DVN	Jo Daviess, Stephenson	6 hr
Jul 21, 7:58 PM CDT	Severe Thunderstorm Warning	LOT	Iroquois, Kankakee	47 min
Jul 21, 8:00 PM CDT	Severe Thunderstorm Warning	LOT	Lee, Ogle	45 min
Jul 21, 8:01 PM CDT	Severe Thunderstorm Warning	LOT	Kendall, LaSalle	44 min
Jul 21, 8:16 PM CDT	Tornado Warning	LOT	Iroquois	29 min
Jul 21, 8:33 PM CDT	Flash Flood Warning	LOT	Boone, McHenry, Winnebago	6 hr
Jul 21, 8:33 PM CDT	Severe Thunderstorm Warning	LOT	DeKalb, Lee	27 min
Jul 21, 9:06 PM CDT	Flash Flood Warning	DVN	Carroll, Whiteside	4 hr
Jul 21, 10:18 PM CDT	Flash Flood Warning	ARX	Chickasaw, Clayton, Fayette	12 hr
Jul 21, 10:24 PM CDT	Flash Flood Warning	DMX	Bremer	15 hr
Jul 21, 11:10 PM CDT	Severe Thunderstorm Warning	DVN	Carroll, Jo Daviess, Stephenson	65 min
Jul 22, 12:09 AM CDT	Flash Flood Warning	DVN	Buchanan, Delaware, Dubuque, Jackson	6 hr
Jul 22, 12:36 AM CDT	Severe Thunderstorm Warning	LOT	Iroquois	24 min
Jul 22, 12:37 AM CDT	Flash Flood Warning	DVN	Carroll	6 hr
Jul 22, 12:54 AM CDT	Severe Thunderstorm Warning	IWX	White	51 min
Jul 22, 12:59 AM CDT	Severe Thunderstorm Warning	LOT	Benton, Jasper	31 min
Jul 22, 1:45 AM CDT	Flash Flood Warning	DVN	Jo Daviess	6 hr

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 9.9 hours before the alert went out and 40 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 81 J/kg
Mixed-layer CIN: -302 J/kg
Mixed-layer LCL: 1173 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 125 m²/s²
0-3 km storm-relative helicity: 192 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 21, 1:11 AM CDT	Mesoscale Discussion	SPC	Bureau, Ford, Grundy, Iroquois, Kankakee, LaSalle and 7 more	94 min
Jul 21, 1:32 PM CDT	Mesoscale Discussion	SPC	Carroll, Henry, Jo Daviess, Lee, Mercer, Ogle and 2 more	2 hr
Jul 21, 6:28 PM CDT	Mesoscale Discussion	SPC	Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 23 more	92 min

Nearby

Severe Thunderstorm Watches in Iowa, 2017 Severe Thunderstorm Watches in Illinois, 2017 Severe Thunderstorm Watches in Indiana, 2017 Every severe thunderstorm watch 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.