A cold front moved across the area on the evening of June 28th. Convection developed quickly along the front as the cap eroded, initially discrete but quickly growing upscale.
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The episode as NWS DMX wrote it up.
A cold front moved across the area on the evening of June 28th. Convection developed quickly along the front as the cap eroded, initially discrete but quickly growing upscale. Robust CAPE exceeding 3000 J/kg was in place with good directional shear to support rotating updrafts. This resulted in a handful of weak tornadoes in Cass county at the onset of storm development. After storms grew upscale they remained sub-severe.
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 28, 5:51 PM CST, 53 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Des Moines IA 651 PM CDT Fri Jun 28 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Showers and storms likely through the remainder of the day into the early overnight hours, including the potential for strong to severe storms and locally heavy rainfall. - Terrific weekend with seasonably comfortable temps and humidity, but weather pattern becomes active again early next week with increasing humidity and chances for storms, including the potential for strong to severe storms and heavy rainfall. - River flooding continues within the Des Moines and Cedar River basins in northern Iowa. && .DISCUSSION... Issued at 212 PM CDT Fri Jun 28 2024 19z GOES water vapor imagery shows a compact upper shortwave pushing off the northern Rockies into the high Plains. At the surface an area of low pressure was noted over far northeastern Nebraska, with an attendant cold front draped to the south/southwest and a warm front positioned southeast through Iowa. Morning shower/storm activity within a broad elevated warm air advection regime is finally exiting east, although widespread low cloud cover remains in it's wake as highly moist low levels are trapped beneath a very warm mid-level environment with 700mb temps pushing 14C. Elevated convection has managed to develop within a zone of mid-level convergence over northwest Iowa. This activity will generally ride the northern edge of the warmer mid-level air across northern Iowa this afternoon. Some model guidance suggests a few robust core may materialize and support a threat of large hail. The most favorable window for severe weather likely holds off until the stout mid-level cap erodes toward early to mid-evening, allowing for CI along the cold front as it moves into western Iowa. Hires models initially show discrete storm modes as updrafts work within effective shear values of 30-40 kts. All severe hazards could be on the table. Model soundings show steep mid-level lapse rates and ECAPE near 3000 J/kg which would be supportive of large hail. Low level winds gradually veer with height, and may be enough to squeeze out a tornado or two especially as the LLJ increases and enhances the low level shear profiles. Storms will eventually congeal into one or more convective complexes as cold pools merge and support a threat for damaging wind gusts before the severe weather risk begins to wane due to decreasing instability with time and eastward extent. The environment is primed for heavy rainfall rates given warm cloud depths pushing 4000m+ and PW 1.75-2"+. HREF LPMM product advertises pockets of 2-3"+ rainfall amounts. The good news is the convection should be progressive, limiting the extent and magnitude of the heavier rainfall amounts. The threat should also mostly remain south of the heavily saturated portions of northern Iowa. Cold front and any associated storm chances clear the CWA tonight. Model guidance suggests some patchy fog potential into the early morning hours within a zone of light winds behind the front. Beyond that it is shaping up to be a fantastic weekend as a cooler and dry Canadian airmass settles into the state with highs in the 70s and 80s and comfortable humidity levels. Pattern activity picks right back up as a broad upper level trough with numerous embedded lower amplitude waves is re-established over the northern Rockies into the northern Plains. A broad warm air advection wing should spur elevated shower/storm activity Sunday night into early Monday. 12z model guidance is a bit slower with pattern progression beyond that point as a surface low deepens over the Dakotas and a deep but narrow plume of moisture is pulled northward up the Plains. This may hold additional convection to our west until Monday night into Tuesday as a cold frontal boundary slowly pushes through the state, including the potential for strong to severe storms and heavy rainfall. Models are in fair agreement with stalling out the front just south of the state and serves as the primary focus for additional storm activity through mid-week. Should the boundary hang up a bit further north, then we would possibly face a threat of additional episodes of heavy rainfall and impacts to our ongoing river flood concerns. See the hydro section for more details. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 642 PM CDT Fri Jun 28 2024 Challenging aviation forecast for the next few hours with varying CIGs ranging from IFR to VFR and possibility for showers/storms to impact sites and bring temporary visibility reductions from heavy rain and sporadic gusty winds. Have lessened shower/storm mentions from previous TAFs with storm development struggling to develop overall, but will continue to monitor trends and adjust mentions as needed based on radar trends. Although any storms that do develop should wane through the later half of the evening, some patchy fog remains possible north or east but overall looks transient and thus keeping impacts to any TAF site more minimal. Otherwise, CIGs improve through the night with VFR conditions generally prevailing by Saturday morning. Winds out of the south tonight become light and variable overnight before settling out of the northwest and increasing through the afternoon hours Saturday. && .HYDROLOGY... Issued at 200 PM CDT Fri Jun 28 2024 The observed rainfall from Thursday night into Friday morning ended up being higher than expected in some areas which led to some adjustments to the river forecasts. The most drastic examples are the Shell Rock River where renewed flooding is now expected at Shell Rock with the river going back above flood stage this evening. In addition, renewed flooding is expected on the Winnebago River with the Mason City area going back above flood stage on Saturday. In other locations the adjustments primarily involved either keeping the stages steady for longer or slowing the fall. Concern in the short term then turns to later today into tonight. We may see some locally high QPF amounts however we are not expecting widespread heavy QPF amounts. Our river forecast updates this morning take into account the QPF through Saturday morning. In the longer term, concern is about QPF next week and its potential impact on rivers. Again, with our current river forecasts taking into account 24 hrs of QPF they do not include the QPF for next week. The last few meteorological model runs have been trending higher in QPF especially across the southeast half of the state. Our latest QPF ensemble hydrographs and Hydrologic Ensemble Forecast System (HEFS) runs are latching on to this QPF. Unlike the rainfall a week ago, the QPF next week will affect more of the state so additional river basins may come in to play. The Cedar/Iowa River basins look to be the most affected however our guidance is showing possible rises on tributaries to those rivers as well as portions of the Des Moines and Skunk River basins. At this point the most likely scenario will be slowing the rate of fall of our area rivers, however some ensemble members are suggesting the possibility of additional or new crests with additional minor flooding. Some of the lower probabilities are suggesting moderate to major flooding at some locations. We cannot totally rule out these possibilities. Ultimately the location, amount and timing of the rain next week will be the biggest factor. In addition to the river flooding, we will also need to monitor for flash flood potential next week given the favorable heavy rainfall parameters Monday night into Tuesday. Make sure to stay up to date on the latest forecasts and river information, avoid flooded areas and rivers, and never drive around barricades or through flooded areas. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && DISCUSSION...Martin AVIATION...KCM HYDROLOGY...Zogg
Hazardous Weather Outlook National Weather Service Des Moines IA 228 PM CDT Fri Jun 28 2024 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-291930- 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- 228 PM CDT Fri Jun 28 2024 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight Showers and thunderstorms chances continue through the afternoon and evening hours, including the risk of strong to severe storms with primary threats of damaging winds and large hail. A few tornadoes may be possible as well as isolated heavy rainfall to around 2 inches. .DAYS TWO THROUGH SEVEN...Saturday through Thursday There are additional chances for thunderstorms between Monday and Wednesday of next week. The potential for any associated heavy rain or severe weather risks will be better determined in the coming days. .SPOTTER INFORMATION STATEMENT... Spotters may be needed on this evening.
The Omaha radar (KOAX), 102 km away, was scanning. The volume nearest the first event began at 00:42 UTC.
4 tornado, 1 funnel cloud. Local standard time, as filed.
This tornado was observed by storm chasers and remained in rural cropland. No damage indicators were impacted, hence the EFU rating.
This weak tornado remained mostly in rural farmland but did impact some trees with minor damage.
No damage indicators were impacted, hence the EFU rating as the tornado remained in rural cropland.
This tornado remained in rural cropland. No damage indicators were impacted, hence the EFU rating.
Brief funnel cloud, however chaser reported structure becoming more ragged with time.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2024Every state in 2024This day in weather historyThe tornado archive for Iowa, 2024Warnings in Iowa, June 2024
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: 1190985, 1190987, 1190990, 1190991, 1190272.