A fairly unremarkable day setup-wise resulted in a few strong storms during the evening hours that produced a small handful of damaging winds and wind gust reports. A frontal boundary was positioned well west/northwest of the state, leaving Iowa firmly within the warm sector.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS DMX wrote it up.
A fairly unremarkable day setup-wise resulted in a few strong storms during the evening hours that produced a small handful of damaging winds and wind gust reports.
A frontal boundary was positioned well west/northwest of the state, leaving Iowa firmly within the warm sector. Surface observations reflected at least as much with temperatures into the low 90s concurrent with dew points in the low to mid 70s. MUCAPE values, as one might expect, approached the 2000-3000 J/kg range but was devoid of supportive shear and any concentrated lift. Lingering morning showers and convection were working their way up from northeast Kansas, traveling to the northeast, before tapping into the moist, unstable Iowa air mass. Fortunately, with the lack of supportive shear profiles and hail CAPE (under 500 j/kg), severe weather was hard to come by. Though with DCAPE values around 1000 J/kg, a few storms were able to produce severe downdrafts and gust fronts leading to some minor to moderate tree damage and recorded wind gusts.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Des Moines, IA wrote its last area forecast discussion before the first event at Jun 17, 2:56 PM CST, 1 hour 6 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 356 PM CDT Sun Jun 17 2018 .DISCUSSION.../Tonight through Sunday/ Issued at 354 PM CDT Sun Jun 17 2018 Spotty showers beneath areas of clouds are traversing northwest and north central Iowa at mid-afternoon. With these, haven't seen any lightning and GOES-East Day Cloud Phase Distinction shows limited if any ice introduction up to this point. A few thunderstorms though have recently formed and moving into the Omaha metro. All of this activity is being forced by a subtle shortwave trough moving through the area now. Better chance for widespread storms will generally be north of the state along the front that will eventually slip into Iowa, but still likely to see rain and storms over our far northern counties tonight. Precipitable water values will be over 2 inches to near 2.5 inches with warm cloud depths of 13000 to 14500 feet. Mean flow of 25 to 30 knots will keep storms moving, but may end up parallel to the front yielding training storms. Rainfall amounts were increased using a blend of the HREF, NBM, and Superblend guidance, which puts amounts near 1 inch toward Estherville. Locally higher values still possible. SPC still has our northern counties with a marginal risk of hail or damaging wind gusts and while MLCAPE of 1000 J/kg is sufficient for storms, better organization will be limited by deep layer shear of less than 30 knots. The front will slowly drop into the state on Monday with an overall lull in the convection. The heat advisory will be allowed to expire for the northern part of the state this evening as clouds or showers will bring relatively cooler weather on Monday. For the I-80 counties and points south, will extend advisory as warm and quite humid air will continue. There is still potential, especially near I- 80 counties, that showers and storms will reach this area before peak heating and highest heat index values are realized. However, boundary will be close by so could have additional moisture pooling/higher dewpoints leading to heat index values edging over 100 degrees. The next round of storms as alluded to above will begin to develop Monday afternoon as better Q-vector convergence moves across the area later Monday afternoon into Monday night. The highest chances will be north of Highway 30. Precipitable water values will be around or above 2 inches once again with warm clouds depths of 13000 to near 15000 feet across central Iowa. Mean layer flow won't be as strong at 15 to 20 knots so better chance for slower moving, efficient rain producing storms than tonight. Similar adjustments were made for rain amounts Monday night as tonight, which bring a general 1 to 1.5 inches across many areas south of Highway 3 and north of I-80 roughly with locally higher amounts expected. Rain is expected to linger into Tuesday as the front continues to slowly move/meander southward into northern Missouri. While precipitable water values may be slightly lower, the rest of the heavy rainfall parameters stay on point, just more so focused over southern Iowa. Additional discussion on hydrology concerns is below in the hydrology discussion. Wednesday into Saturday, chances for showers and storms will continue across the state with the best chances over central to southern Iowa. High temperatures will be more seasonal with highs in the upper 70s to low 80s. A more substantial trough moves toward the area on Thursday with the GFS and now the ECMWF showing it propagating through on Friday into Saturday with drier air perhaps by later Saturday. && .AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/ Issued at 1229 PM CDT Sun Jun 17 2018 Official TAFs have VFR conditions throughout this period with gusty winds from the southwest decreasing this afternoon. However, challenges remain on impacts of storms later tonight over northern Iowa. There are some showers crossing into western Iowa possibly arriving between 19-20z at FOD, but confidence is too low to even include VCSH at this time. Better chance for showers and storms with MVFR or perhaps IFR conditions will be tonight as a cold front sinks into the state with focus on FOD and MCW. They may also impact ALO, but this is a lower chance so decided not to include. Lastly, a period of low level wind shear is possible tonight across northern and central Iowa. && .HYDROLOGY... Issued at 354 PM CDT Sun Jun 17 2018 Over the last 7 days, there have been several rounds of heavy rainfall across parts of central Iowa. Doppler radar estimates show a general 2 to 4 inches has fallen in an area roughly bounded by a polygon from Emmetsburg to Grinnell to Oskaloosa to Osceola to Atlantic to Carroll and back to Emmetsburg. Estimates within this polygon have local maxima of 5 to 6 inches. Ames COOP observer 5 miles southeast of the city recorded 7.56 inches for this same time period. This doesn't include the rain that fell the first full week of June over north central Iowa with flooding in Mason City along Willow Creek and the Winnebago River as well as along the Shell Rock River in Clarksville and Greene, which lingered into last weekend and early this week. Current forecast rainfall through Tuesday night has 1.5 to 2 inches average north of I-80. Still expecting some higher end totals closer to 4 or 5 inches from various deterministic models. With antecedent conditions setting the stage and expected rainfall, isolated flash flooding will be possible with WPC Excessive Rainfall Outlook over parts of our area the next three days. While river forecast center ensemble hydrographs using best estimate 72 hour rainfall would keep most rivers below flood stage, the higher end rain totals could lead to minor or perhaps moderate flooding as some gauges. Will continue to monitor in future forecast cycles if conditions warrant issuance of any watches. && .DMX WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 7 PM CDT Monday for IAZ057>062-070>075- 081>086-092>097. Heat Advisory until 7 PM CDT this evening for IAZ004>007-015>017- 023>028-033>039-044>050. && DISCUSSION...Ansorge AVIATION...Ansorge HYDROLOGY...Ansorge
Hazardous Weather Outlook National Weather Service Des Moines IA 301 PM CDT Sun Jun 17 2018 IAZ004>007-015>017-023>028-033>039-044>050-182015- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene- Boone-Story-Marshall-Tama- 301 PM CDT Sun Jun 17 2018 This Hazardous Weather Outlook is for portions of central and north central Iowa. .DAY ONE...This afternoon and tonight An isolated severe storm and locally heavy rainfall may occur overnight. A Heat Advisory remains in effect for the area through 7 pm this evening. Please refer to the National Weather Service website at weather.gov/desmoines for further details. .DAYS TWO THROUGH SEVEN...Monday through Saturday Strong to severe storms are forecast for Monday afternoon into early Tuesday. Large hail and damaging wind gusts are the primary threats. Heavy rain may also occur. Additional storms are forecast at times through the week, however, the predictability of severe weather remains low at this time from mid to late week. .SPOTTER INFORMATION STATEMENT... Spotters might be needed at times tonight into Monday. IAZ057>062-070>075-081>086-092>097-182015- Audubon-Guthrie-Dallas-Polk-Jasper-Poweshiek-Cass-Adair-Madison- Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas-Monroe-Wapello- Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis- 301 PM CDT Sun Jun 17 2018 This Hazardous Weather Outlook is for portions of central and south central Iowa. .DAY ONE...This afternoon and tonight A Heat Advisory remains in effect for the area through Monday. Please refer to the National Weather Service website at weather.gov/desmoines for further details. .DAYS TWO THROUGH SEVEN...Monday through Saturday Strong to severe storms are forecast Monday afternoon into early Tuesday. Large hail and damaging wind gusts are the primary threats. Heavy rain may also occur. Locally heavy rainfall will be possible again across southern Iowa Tuesday into Wednesday. More storms are forecast Thursday and Friday, however, the predictability of severe weather remains low at this time from mid to late week. .SPOTTER INFORMATION STATEMENT... Spotters might be needed at times Monday into Monday night.
Special Weather Statement
National Weather Service Des Moines IA
442 PM CDT SUN JUN 17 2018
IAZ044-172215-
Crawford IA-
442 PM CDT SUN JUN 17 2018
...Storms may produce strong winds in Crawford County...
At 441 PM CDT, Doppler radar was tracking a strong thunderstorm near
Dunlap, or 17 miles southwest of Denison, moving northeast at 40 mph.
Wind gusts up to 50 mph will be possible with this storm.
Locations impacted include...
Denison, Dunlap, Manilla, Dow City, Arion, Buck Grove and Denison
Municipal Airport.
LAT...LON 4205 9567 4205 9509 4187 9518 4186 9519
4186 9565 4187 9567
TIME...MOT...LOC 2141Z 227DEG 34KT 4180 9554
MartinThe Omaha radar (KOAX), 108 km away, was scanning. The volume nearest the first event began at 22:00 UTC.
3 thunderstorm wind. Local standard time, as filed.
Iowa DOT RWIS site recorded a 63 mph wind gust about 6 miles south of Denison.
Trained spotter reported large tree limbs broken. Time estimated from radar.
Trained spotter reported approximately 5 inch diameter tree branches down.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2018Every state in 2018This day in weather historyWarnings in Iowa, June 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 762542, 762541, 762543.