Seasonally cool conditions prevailed throughout the day with temperatures only into the 70s in many cases and dew points in the 60s. With low pressure located over Minnesota, weak warm frontal and cold frontal boundary reflections resided over western Iowa and northern Nebraska respectively.
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.
Seasonally cool conditions prevailed throughout the day with temperatures only into the 70s in many cases and dew points in the 60s. With low pressure located over Minnesota, weak warm frontal and cold frontal boundary reflections resided over western Iowa and northern Nebraska respectively. In the afternoon, storms initiated within 1000-2000 J/kg MUCAPE and effective bulk shear generally under 30 kts. Resulting storms were unorganized and sub-severe in nature for the most part. A pair of quarter sized hail reports were received near Pocahontas, otherwise periods of heavy rain most often prevailed.
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 Aug 26, 5:39 AM CST, 4 hours 21 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 639 AM CDT Sat Aug 26 2017 .SHORT TERM.../Today through Tonight/ Issued at 313 AM CDT Sat Aug 26 2017 Similar to previous overnights...area of showers and thunderstorms is evolving over northwest Iowa and eastern Nebraska...slowly weakening as it moves to the east with the stronger portion of the line sagging south toward southeast Nebraska now. Weak low pressure trough still expected to move east across the area by tonight. Current storms should continue to diminish through the morning hours with lingering showers/isolated thunder mainly west and north with showers east of the weakening area. Some uncertainty as to whether much will happen until late afternoon after the morning showers and weakening convection further dissipates. Little overall synoptic forcing and surface convergence will inhibit any organization or trigger until instability increases again by late afternoon/early evening. Currently SPC outlook for the south/southwest for slight risk this afternoon/evening. Though instability of 2000 to 2500 j/kg does support stronger storms...wind shear lacking to any great extent and little in terms of overall sfc convergence so coverage of any strong storms likely to be very limited. Wind/hail would be the main concerns. As the trough/cool front moves southeast tonight expect that the scattered areas of thunderstorms will continue but weaken overnight toward morning. Highs today will again reach the 70s to lower 80s with lows tonight a bit warmer south in the mid 60s due in part to cloud cover and storm potential as well as southwest winds south of the boundary. Northern areas will brush with 60 with cooler air beginning to filter in from the northwest. .LONG TERM.../Sunday through Friday/ Issued at 313 AM CDT Sat Aug 26 2017 An upper level ridge will prevail over the western US through the remainder of the weekend into early next week. During this time, an upper area of low pressure will drop out of central Canada moving over eastern Iowa into the Ohio Valley. This upper low will essentially cut off what could have been an exit for present Hurricane Harvey, which will remain over the southeastern part of Texas through the week as steering currents remain weak. While we're far removed from the impacts of Harvey tonight, our thoughts are with those impacted by Hurricane Harvey, including our NWS colleagues. Back closer to central Iowa, the aforementioned upper low drops into Minnesota on Sunday with a surface cold front sweeping through most of the forecast area by the afternoon. This will confine the best shower and stronger thunderstorm chances to eastern and far southern Iowa where better instability and lift will be located. Behind the cold front, isolated showers and thunderstorms will be possible as the cooler temperatures aloft begin to arrive, making it favorable for air parcels to rise with steep low level and modest mid-level lapse rates. As the new work week begins, the upper low will arrive over eastern Iowa with diurnal showers and perhaps isolated thunderstorms Monday afternoon into early evening. The most favored areas for any rainfall will be east of a Waterloo to Ottumwa line, or roughly east of Highway 63, which is closer to the upper low. Overall, forecast soundings for KALO and KOTM show rather meager values of CAPE so thunder should be isolated. With breezy northerly winds on Monday, did adjust highs down a degree or so from Superblend over northern Iowa. Overall, Monday's highs will be below normal by a few to several degrees. As surface high pressure builds in Monday night into Tuesday morning, clear skies and light north winds should allow decent cooling so have lowered temperatures a few degrees outside of urban areas. Tuesday through the end of the week will feature highs mainly in the upper 70s to lower 80s (near normal) with lows in the upper 50s to lower 60s as low return to normal in the latter part of the week. Rain chances will remain low through the middle part of the week as the high moves across the region. Any rain chances will be relegated to northeast Iowa later Thursday and again later Friday as a weak shortwave comes across the western US ridge. && .AVIATION.../For the 12Z TAFS through 12Z Sunday morning/ Issued at 638 AM CDT Sat Aug 26 2017 Main concern will be possible convection and lowering cigs aft 09z Sunday. Diminishing area of -shra and iso thunder over northern Iowa near KFOD and KMCW will further weaken by 15z. A few showers are also located along US 30 closer to KDSM. Winds will increase to south southwest 12G20 by 15z and remain through 23z. Additional showers/sct thunder will increase again aft 21z with best areal coverage north of US 20 and south/southwest of I80 affecting KMCW and possibly KDSM. Elsewhere more spotty coverage is anticipated. May need to refine forecast with next package. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...REV LONG TERM...Ansorge AVIATION...REV
Hazardous Weather Outlook National Weather Service Des Moines IA 1017 AM CDT Sat Aug 26 2017 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-271530- 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-Audubon-Guthrie-Dallas-Polk-Jasper- Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union- Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne- Appanoose-Davis- 1017 AM CDT Sat Aug 26 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Isolated thunderstorms are expected throughout the day today into the evening. The severe weather threat is low, but a brief stronger storm is possible with hail and gusty wind threat. .DAYS TWO THROUGH SEVEN...Sunday through Friday Isolated thunderstorms are possible Sunday with the better chances over eastern and far southern Iowa. The risk of severe storms is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated. KLP
Special Weather Statement National Weather Service Des Moines IA 1028 AM CDT SAT AUG 26 2017 IAZ015-023-261615- Palo Alto IA-Pocahontas IA- 1028 AM CDT SAT AUG 26 2017 ...SPECIAL WEATHER STATEMENT... At 1028 AM CDT, Doppler radar was tracking strong thunderstorms along a line extending from 6 miles northeast of Lost Island Lake to near Emmetsburg to near Albert City. Movement was east at 30 mph. Half inch hail and winds in excess of 30 mph will be possible with these storms. Locations impacted include... Emmetsburg, Pocahontas, Laurens, Five Island Lake, Silver Lake, Rush Lake, Lost Island Lake, Graettinger, West Bend, Ruthven, Rolfe, Mallard, Ayrshire, Havelock, Cylinder, Plover, Curlew, Rodman, Kearney State Park and Pocahontas Municipal Airport. LAT...LON 4325 9445 4274 9444 4267 9491 4325 9492 TIME...MOT...LOC 1528Z 263DEG 26KT 4325 9485 4314 9477 4270 9492 Beerends
The Des Moines radar (KDMX), 172 km away, was scanning. The volume nearest the first event began at 16:00 UTC.
2 hail, 1 heavy rain. Local standard time, as filed.
Coop observer recorded heavy rainfall of 1.35 inches over a 30 minute period from 11 am to 11:30 am CDT.
Trained spotter reported quarter sized hail.
Trained spotter reported quarter sized hail.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2017Every state in 2017This day in weather historyWarnings in Iowa, August 2017
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: 714670, 714671, 714672.