On May 20th, isolated severe thunderstorms produced large hail up to half dollar size across southeast Minnesota. Additionally, two brief landspout tornadoes occurred in Dodge county during the evening hours.
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 ARX wrote it up.
On May 20th, isolated severe thunderstorms produced large hail up to half dollar size across southeast Minnesota. Additionally, two brief landspout tornadoes occurred in Dodge county during the evening hours.
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 La Crosse, WI wrote its last area forecast discussion before the first event at May 20, 2:05 PM CST, 3 hours 5 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service La Crosse WI 305 PM CDT Mon May 20 2024 .KEY MESSAGES... - Storms begin to move in late evening/overnight and into the morning tomorrow bringing heavy rainfall and an isolated threat for damaging wind gusts and large hail. - A significant severe weather event with an enhanced risk (Threat level 3 of 5) for severe storms locally for Tuesday. Multiple rounds of storms continue from the morning into evening on Tuesday. The highest severe threat appears to begin late afternoon and into the evening with damaging wind gusts and tornadoes being the primary threats, large hail is a secondary threat. With multiple rounds of storms expected, flood prone areas should be on alert for possible river rises. - Quieter conditions expected to return beginning on Wednesday with some shower/storm chances into the weekend. && .DISCUSSION... Issued at 305 PM CDT Mon May 20 2024 This Evening - Tuesday Morning: Storms With Isolated Severe Threat Storms will begin to initiate across portions of southern MN as a piece of shortwave energy passes through late this evening. As storms develop they will have minimal 0-6 km shear (20-30 kts) but fairly robust MLCAPE (1000-1500 J/kg) shown in the 20.15z RAP late this evening. With steeper low-level lapse rates across southeast MN later this evening, some severe hail will possible. Furthermore, one thing of note is much of the 0-6 km shear is suspended aloft with winds closer to the surface remaining fairly light at model soundings for KRST this evening. As a result, storms may have some trouble maintaining themselves with unorganized cold pools. Overnight, a surface low begins to approach associated with increasingly negatively tilted upper-level low. This surface low will feature a warm front that will progress into the region during the day Tuesday. As it progresses, instability will begin to be advected into our region during into the morning hours which with the forcing from the warm front help develop an mesoscale convective system from some of the aforementioned convection across our forecast area. Initially the 20.15z RAP effective bulk shear (20-30 kts) and MLCAPE values (500-1000 J/kg) are fairly minimal during the morning hours with the warm front hanging out to our south. However, one signal some of the CAMs have been showing is hints at some gravity wave convection north of the front with elevated instability profiles somewhat more favorable (MUCAPE of 1000-2000 J/kg). As a result, some of this morning convection could pose some damaging wind threat into early afternoon even if much of the severe parameters are on the marginal side initially, however this would be fairly isolated in nature with the 20.12z HRRR Machine learning probabilities having some potential (15-30% probabilities) with the morning and early afternoon convection for damaging wind gusts of 58 mph or greater south of I-90. Tuesday Afternoon - Evening: Impactful Severe Weather Event As we continue throughout the day, the warm front will slowly push its way into the region as the parent surface low progresses, convection will continue to develop along and north of the front which will provide continuous thunderstorm activity across the region throughout the day. With the persistent convection over the region, flash flooding will be a consideration. Generally, the 20.12z HREF shows mean QPF across the region of 1 to 2 inches with 75th percentile values eclipsing 3 to 4 inches in areas. Precipitable waters really surge quickly during the afternoon with values in the 20.12z NAM/GFS/CAMs of over 1.5" which is around the climatological maximum at KDVN. While storm motions will be fairly progressive, the greater concern would be more the persistent training of storms over a given area. Consequently, the WPC has our region in a slight risk (level 2 of 4) for excessive rainfall when considering that 3-hr flash flood guidance is around 2 inches across much of the forecast area. Therefore, would expect some flooding is possible, primarily in areas that are prone to river rises. The severe threat then really begins to ramp up by later afternoon and into the evening, which by this time the surface low begins to lift northwest of the local area. As this occurs, 850mb moisture transport sharply increases allowing for instability to quickly be advected into our region. MLCAPE values will increase to around 2000-2500 J/kg with the most robust instability profiles presenting mainly south of I-90. Our region becomes subjected to more favorable synoptic winds Tuesday evening allowing bulk shear profiles to become more optimal as 0-6km shear values in the 20.15z RAP increase to 40- 60 kts. Ahead of the cold front, storm mode may be fairly messy with multi-cells, linear segments and isolated supercells (mainly southern portions of our forecast area) ahead of an incoming cold front throughout the day with some clearing possible during the afternoon as some of the CAMs try to show. Eventually during the evening, the cold front approaches and more robust ascent accompanied with a strong 850mb low-level jet to 60-70 kts will allow for an organized QLCS (Quasi-Linear Convective System) along the cold pool. The passage of the cold front will usher in a more stable airmass ending convective concerns with it from west to east during the late evening hours. Damaging wind gusts will be the most widespread severe threat during this period with the aforementioned low-level jet and DCAPE values of 1000-1300 J/kg along the cold front shown in the 20.15z RAP. Consequently, expecting more widespread gusts to 60-70 mph with the QLCS as reflected in the 20.12z HRRR Machine Learning Probabilities with high values (60-80% chance). Cannot rule out higher gusts to 80 mph in any localized bows/surges. As a result, SPC has an enhanced risk (Threat level 3 of 5) for most of our area. Increasing low-level shear and 0-1km storm relative helicity into the evening shows an environment where a few QLCS tornadoes may occur, especially along and south of I-90 where low-level curvature in model hodographs is most apparent. Some uncertainty remains in how far north the QLCS tornado threat will extend due to waning instability gradient as you head north. Large hail appears to be more a secondary threat for our region, much of the godzilla CAPE appears to be south of our local area that would be more favorable for severe hail, cannot rule out some severe hail across northeast Iowa and southwestern Wisconsin with MUCAPE values of up to 3000 J/kg and steeper mid-level lapse rates. Some sources of uncertainty still remain as there appears to be questions remaining as to where exactly the surface low is positioned which may have implications for how far north the favorable instability is able to be advected into our region. This uncertainty can be best seen between the 20.06z and 20.12z runs of the HRRR which has different ideas of where the surface low is situated. Additionally, with the warm front positioned south of the region initially, widespread convection throughout the day may limit the amount of instability that can build in across the region. Consequently, it will be very important to continue to monitor the forecast over the next 24-36 hours for changes. In any case, Tuesday has the potential to be a very impactful severe weather day for our forecast area with multiple rounds of storms throughout the day, all of which pose some level of severe potential. Be sure to have multiple ways of receiving warnings as power outages are possible with the increased damaging wind and tornado threat. Remember, this environment is fairly favorable for QLCS tornadoes which can spin up very quickly and are difficult to see so it is important to get to your safe location promptly when a warning is issued. Wednesday & Beyond: Quieter Conditions Conditions certainly begin to calm down by Wednesday as the aforementioned trough swings north of the Great Lakes region allowing for some upper-level ridging to work its way in later Wednesday into Thursday allowing for some drier conditions. There is some signal later Friday and into the weekend for some shortwaves pass to our north which will increase our shower/storm chances during this period but any severe threat is unknown at this time. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1238 PM CDT Mon May 20 2024 Early convection is clearing the area with a mix of VFR and MVFR ceilings across the area. Short period of VFR conditions expected between systems this afternoon into the early evening, but as next short wave approaches, and instability builds to the west, expecting the next round of convection to start impacts areas later this evening. Speaking of which, convection will drive the aviation forecasts through the overnight and into much of Tuesday. Hard to narrow down specifics quite yet, but the probabilities of more widespread storm activity increase dramatically this evening and peak overnight into Tuesday morning. This period could see wave after wave of impact at TAF sites likely leading to periodic IFR with both ceilings and visibilities. Could see some breaks between convection on Tuesday as well but hard to work out those specifics this far out. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && DISCUSSION...Naylor AVIATION...EMS
Hazardous Weather Outlook National Weather Service La Crosse WI 132 PM CDT Mon May 20 2024 IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029- 032>034-041>044-053>055-061-211200- Mitchell-Howard-Winneshiek-Allamakee-Floyd-Chickasaw-Fayette- Clayton-Wabasha-Dodge-Olmsted-Winona-Mower-Fillmore-Houston- Taylor-Clark-Buffalo-Trempealeau-Jackson-La Crosse-Monroe-Juneau- Adams-Vernon-Crawford-Richland-Grant- 132 PM CDT Mon May 20 2024 This Hazardous Weather Outlook is for parts of southeast Minnesota...northeast Iowa and southwest into central Wisconsin. .DAY ONE...Tonight Storms will redevelop, especially across parts of southeast Minnesota and northern Iowa. Strong to severe storms could develop overnight with large hail and damaging winds. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Multiple rounds of storms are expected Tuesday. Storms could impact the area Tuesday morning, with more redevelopment expected Tuesday afternoon and evening / 3-9pm / when the highest potential for severe storms exists. Storm activity later in the day will depend on where morning storms track. All hazards are possible Tuesday with damaging wind gusts and tornadoes being the primary threats, large hail is also possible with some storms. With the consecutive rounds of thunderstorms, localized areas may recieve several inches of rain. As a result, the threat for river rises and flooding will be on the increase. Those with interests along area creeks, streams, and rivers should monitor conditions closer to start the week. More thunderstorms are possible later in the week / Friday and Saturday / but it is too early to discern the severe weather threat at this time. .SPOTTER INFORMATION STATEMENT... Spotters should monitor the weather closely tonight through Tuesday. Tuesday afternoon and evening look like the highest potential for severe weather but please report any hail, gusty winds, or other severe weather if observed. Activation could be needed at times. .EMERGENCY MANAGEMENT COORDINATION... No webinar is scheduled. Naylor/Shea
The Minneapolis radar (KMPX), 112 km away, was scanning. The volume nearest the first event began at 23:08 UTC.
5 hail, 2 tornado. Local standard time, as filed.
Brief touchdown in open field. Witnessed by multiple sources and path documented via satellite imagery.
Brief touchdown in open field. Witnessed by multiple sources and path documented via satellite imagery.
The public reported pea to dime sized hail in Byron.
State officials reported quarter sized hail 4 miles north of Hayfield. Reported that hail was covering the ground.
Law enforcement reported quarter sized hail 3 miles west northwest of Hayfield. Reported that hail was covering the ground.
The public reported half dollar sized hail near Hayfield.
The public reported half dollar sized hail near Rock Dell.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Minnesota in 2024Every state in 2024This day in weather historyThe tornado archive for Minnesota, 2024Warnings in Minnesota, May 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: 1177645, 1177646, 1177439, 1177443, 1177447, 1183048, 1183049.