{"id":5658,"date":"2026-09-11T15:08:26","date_gmt":"2026-09-11T15:08:26","guid":{"rendered":"https:\/\/ialert.com\/blog\/?p=5658"},"modified":"2026-09-11T15:08:26","modified_gmt":"2026-09-11T15:08:26","slug":"upper-midwest-severe-thunderstorms","status":"publish","type":"post","link":"https:\/\/ialert.com\/blog\/news-events\/upper-midwest-severe-thunderstorms\/","title":{"rendered":"Upper Midwest Severe Thunderstorms: Slight Risk of Large Hail, Damaging Wind, and Tornadoes September 11, 2026"},"content":{"rendered":"<p> <iframe src=\"https:\/\/ialert.com\/blog_outlook.php?event=upper-midwest-severe-thunderstorms\" title=\"Upper Midwest Severe Thunderstorms: Slight \n  Risk of Large Hail, Damaging Wind, and Tornadoes September 11, 2026\" loading=\"lazy\" style=\"width:100%;border:0;\" height=\"660\"><\/iframe><\/p>\n<p>Upper Midwest severe thunderstorms are the headline threat on September 11, 2026. The NOAA Storm Prediction Center&#8217;s Day 1 Convective<br \/>\n  Outlook, issued at 12:26 UTC (8:26 am EDT \/ 7:26 am CDT), places Duluth, International Falls, Bemidji, Brainerd, Hibbing, and St. Cloud,<br \/>\n  Minnesota, and Superior, Wisconsin, inside a Slight Risk, the second of five severe-weather categories. Scattered storms capable of large<br \/>\n  hail, with isolated stones two inches or larger, damaging winds, and a couple of tornadoes are expected late this afternoon into tonight<br \/>\n  across northern and western Minnesota.<\/p>\n<p><strong>Key points:<\/strong><\/p>\n<ul>\n<li>Slight Risk (level 2 of 5) covers far northeast South Dakota and northern and western Minnesota, including Duluth, Bemidji, International<br \/>\n  Falls, Brainerd, Hibbing, and St. Cloud. The outlook is valid from 13Z (9:00 am EDT \/ 8:00 am CDT) September 11 through 12Z (8:00 am EDT \/<br \/>\n  7:00 am CDT) September 12.<\/li>\n<li>A 15% damaging wind probability from Upper Midwest severe thunderstorms covers 50,442 square miles and about 1.3 million people, matching<br \/>\n  the Slight Risk outline.<\/li>\n<li>A 15% large hail probability covers 35,997 square miles across western and north-central Minnesota, with a hatched Intensity Level 1 area<br \/>\n  where isolated hail of two inches or larger is possible.<\/li>\n<li>A 5% tornado probability is drawn over Bemidji, Brainerd, Hibbing, and Alexandria, with a 2% tornado probability reaching St. Cloud,<br \/>\n  Willmar, Fergus Falls, and International Falls.<\/li>\n<li>Storm development is expected between 22Z and 01Z (6:00 pm to 9:00 pm EDT \/ 5:00 pm to 8:00 pm CDT), with the wind threat waning across<br \/>\n  western Wisconsin late this evening.<\/li>\n<\/ul>\n<div style=\"background: #000000; padding: 20px 24px; margin: 20px 0; border-radius: 4px;\">\n<p style=\"color: #ffffff; font-size: 16px; font-weight: bold; margin: 0 0 6px 0;\">Get Severe Weather Alerts for Your Location<\/p>\n<p style=\"color: rgba(255,255,255,0.9); margin: 0 0 14px 0;\">When any NWS watch, warning, or advisory is issued for your area, iAlert sends<br \/>\n  you an immediate notification by email, text message, or phone call, 24 hours a day, 7 days a week.<\/p>\n<p>  <a href=\"https:\/\/ialert.com\/services\/severe-weather-alerts.php\" style=\"background: #C41226; color: #ffffff; padding: 10px 22px; \n  text-decoration: none; border-radius: 3px; font-weight: bold; display: inline-block;\">Sign Up for Severe Weather Alerts &rarr;<\/a>\n  <\/div>\n<h2>Where Upper Midwest Severe Thunderstorms Are Most Likely<\/h2>\n<p>The Slight Risk for Upper Midwest severe thunderstorms runs from Milbank, South Dakota, across western and northern Minnesota to the Lake<br \/>\n  Superior shore at Duluth and Superior, Wisconsin, and north to the Canadian border at International Falls and Baudette. Cities inside it<br \/>\n  include Duluth, Superior, International Falls, Bemidji, Brainerd, Hibbing, Grand Rapids, Ely, Cloquet, Alexandria, Fergus Falls, Detroit<br \/>\n  Lakes, Park Rapids, Willmar, Little Falls, and St. Cloud.<\/p>\n<p>The SPC puts the 15% damaging wind area at 50,442 square miles and 1,299,435 people, naming Duluth, St. Cloud, Superior, Willmar, and<br \/>\n  Hibbing. That 15% wind polygon matches the Slight Risk outline to within 3% of its area, so the wind threat alone earned the category across<br \/>\n  the whole zone.<\/p>\n<p>Large hail is the second hazard from Upper Midwest severe thunderstorms, and it splits the Slight Risk in two. A 15% large hail<br \/>\n  probability covers 35,997 square miles and 694,055 people across western and north-central Minnesota, including Bemidji, International Falls,<br \/>\n  Brainerd, Hibbing, Alexandria, Fergus Falls, Willmar, Detroit Lakes, Park Rapids, and Sartell.<\/p>\n<p>A hatched Intensity Level 1 area, the lowest of the SPC&#8217;s three conditional intensity groups, covers 45,454 square miles and reaches past<br \/>\n  the Slight Risk into the Marginal over Sioux Falls, Watertown, and Brookings, South Dakota. The SPC discussion ties that hatching to isolated<br \/>\n  hail of two inches or larger from the initial supercells. Duluth, Superior, St. Cloud, Ely, and Cloquet sit in the 5% hail area, so damaging<br \/>\n  wind is the lead hazard for those cities.<\/p>\n<figure class=\"wp-block-image size-full\" style=\"max-width:880px;margin:28px auto;padding:10px;border:1px solid \n  #dde3ec;border-radius:6px;background:#ffffff;\"><br \/>\n    <img decoding=\"async\" src=\"https:\/\/ialert.com\/blog\/wp-content\/uploads\/2026\/09\/ialert-upper-midwest-severe-thunderstorms-spc-wind-risk-september-11-2026.jpg\"\n  alt=\"Upper Midwest severe thunderstorms SPC damaging wind probability map for September 11, 2026, showing a 15% wind risk over northern and \n  western Minnesota including Duluth, St. Cloud, and Superior, Wisconsin, a 5% wind risk from Minneapolis through eastern South Dakota and \n  Nebraska, and a second 5% wind risk from Memphis and Nashville through Atlanta and the Carolinas to Virginia\" width=\"1600\" height=\"842\" \n  style=\"max-width:100%;height:auto;border-radius:4px;\" loading=\"lazy\" \/><figcaption style=\"font-size:0.86em;color:#1a3a5c;text-align:center;margin:12px 6px 2px;line-height:1.45;\">SPC damaging wind probabilities<br \/>\n  for September 11, 2026. The 15% area (yellow) traces the Slight Risk for Upper Midwest severe thunderstorms from Milbank, South Dakota, to<br \/>\n  Duluth and International Falls. The two 5% areas (brown) mark the Marginal Risk bands from Minneapolis through South Dakota and Nebraska and<br \/>\n  from Memphis through Atlanta and the Carolinas to Virginia. Source: NOAA Storm Prediction Center; iAlert.com.<\/figcaption><\/figure>\n<p>Two separate Marginal Risk areas, the first of five SPC categories, flank the Slight Risk for Upper Midwest severe thunderstorms. The<br \/>\n  northern band wraps the Slight Risk on its south and east sides, from Ashland, Hayward, Rice Lake, and Spooner in northwest Wisconsin through<br \/>\n  Minneapolis, St. Paul, Hutchinson, and Mankato, then southwest through Sioux Falls, Mitchell, Watertown, Brookings, and Yankton, South<br \/>\n  Dakota, and Sioux City, Iowa, to Norfolk, Columbus, Lincoln, Grand Island, Kearney, and Hastings, Nebraska. Every city in that band carries a<br \/>\n  5% damaging wind probability.<\/p>\n<p>A 5% large hail probability, 103,914 square miles and 5.2 million people, covers most of it, including Minneapolis, St. Paul, Sioux Falls,<br \/>\n  and Sioux City. Lincoln and the northwest Wisconsin cities sit outside the hail line and carry wind only.<\/p>\n<p>The southeastern Marginal band runs from Jonesboro, Arkansas, and Memphis through Jackson, Clarksville, Nashville, and Chattanooga,<br \/>\n  Tennessee, Florence and Huntsville, Alabama, Atlanta, Athens, and Augusta, Georgia, Greenville, Spartanburg, and Columbia, South Carolina,<br \/>\n  Charlotte, Winston-Salem, Greensboro, Raleigh, and Fayetteville, North Carolina, and Danville, Lynchburg, Roanoke, Charlottesville, and<br \/>\n  Richmond, Virginia. Unlike the Upper Midwest severe thunderstorms zone, it carries a 5% damaging wind probability and no hail or tornado<br \/>\n  probability. The two 5% wind areas together cover 260,428 square miles and 31.9 million people, with the SPC naming Memphis, Charlotte,<br \/>\n  Nashville, Atlanta, and Minneapolis. Knoxville, Asheville, Birmingham, Little Rock, Norfolk, Virginia Beach, and Wilmington sit in the<br \/>\n  general thunderstorm area with no severe probability.<\/p>\n<p>The tornado threat from Upper Midwest severe thunderstorms is narrower than the categorical outline. A 5% tornado probability covers<br \/>\n  14,556 square miles and 367,386 people in north-central Minnesota, with the SPC naming Hibbing, Brainerd, Bemidji, and Alexandria.<br \/>\n  Point-in-polygon checks against the frozen outlook also place Grand Rapids, Park Rapids, Walker, Little Falls, Wadena, Staples, and Sauk<br \/>\n  Centre inside it.<\/p>\n<p>A surrounding 2% tornado probability covers 34,757 square miles and 660,912 people, taking in St. Cloud, Sartell, Willmar, Fergus Falls,<br \/>\n  Detroit Lakes, Morris, Montevideo, International Falls, Baudette, Ely, and Cloquet. It spills past the Slight Risk line to Marshall,<br \/>\n  Minnesota, which sits in the Marginal Risk. Duluth, Superior, and Two Harbors carry no tornado probability.<\/p>\n<figure class=\"wp-block-image size-full\" style=\"max-width:880px;margin:28px auto;padding:10px;border:1px solid \n  #dde3ec;border-radius:6px;background:#ffffff;\"><br \/>\n    <img decoding=\"async\" \n  src=\"https:\/\/ialert.com\/blog\/wp-content\/uploads\/2026\/09\/ialert-upper-midwest-severe-thunderstorms-spc-tornado-risk-september-11-2026.jpg\" \n  alt=\"Upper Midwest severe thunderstorms SPC tornado probability map for September 11, 2026, showing a 5% tornado risk centered on Bemidji, \n  Brainerd, Hibbing, and Alexandria, Minnesota, inside a broader 2% tornado risk covering St. Cloud, Willmar, Fergus Falls, and International \n  Falls\" width=\"1600\" height=\"842\" style=\"max-width:100%;height:auto;border-radius:4px;\" loading=\"lazy\" \/><figcaption style=\"font-size:0.86em;color:#1a3a5c;text-align:center;margin:12px 6px 2px;line-height:1.45;\">SPC tornado probabilities for<br \/>\n  September 11, 2026. The 5% area (brown) covers Bemidji, Brainerd, Hibbing, and Alexandria in north-central Minnesota. The 2% area (green)<br \/>\n  extends from Marshall and St. Cloud to Fergus Falls and International Falls. Duluth carries no tornado probability from Upper Midwest severe<br \/>\n  thunderstorms today. Source: NOAA Storm Prediction Center; iAlert.com.<\/figcaption><\/figure>\n<h2>Meteorologist&#8217;s Take on Upper Midwest Severe Thunderstorms<\/h2>\n<p>The setup for Upper Midwest severe thunderstorms begins with large-scale upper troughing parked over central Canada. An embedded mid-level<br \/>\n  shortwave trough is forecast to eject eastward over the northern Plains into the Upper Midwest through the period. The SPC expects a modest<br \/>\n  surface response across South Dakota, with most guidance developing a sub-1000 mb low into eastern South Dakota by 00Z (8:00 pm EDT \/ 7:00 pm<br \/>\n  CDT). A cold front tied to that low and to the primary low over central Canada will push east-southeastward across the Upper Midwest, with a<br \/>\n  dryline extending south across the central Plains.<\/p>\n<p>Ahead of the front, a narrow corridor of 60s surface dewpoints will combine with daytime heating and steepened mid-level lapse rates to<br \/>\n  produce moderate destabilization for Upper Midwest severe thunderstorms. Recent NAM and RAP runs show minimal capping along and ahead of the<br \/>\n  front in far northeast South Dakota and western Minnesota by 22Z to 01Z (6:00 pm to 9:00 pm EDT \/ 5:00 pm to 8:00 pm CDT). The SPC calls<br \/>\n  convective development likely in that window, driven by low-level convergence along the front and ascent from the shortwave trough.<\/p>\n<p>Forecast soundings show strongly veering and gradually strengthening winds with height, and 35 to 45 knots of deep-layer shear will<br \/>\n  support organized convection. Initial supercells pose the large hail threat, including isolated stones of two inches or larger. Storm mode<br \/>\n  should trend toward clusters fairly quickly because of the cold front and a strengthening low-level jet this evening. Any supercells that<br \/>\n  stay at least semi-discrete into the early evening may also pose a tornado threat as low-level shear increases, but the SPC rates confidence<br \/>\n  in that scenario as fairly low because of the expected mode transition.<\/p>\n<p>Scattered damaging winds from Upper Midwest severe thunderstorms are expected with any clusters or bowing line segments that develop and<br \/>\n  spread east through the evening. The SPC expects the wind threat to wane with eastward extent across Minnesota into western Wisconsin by late<br \/>\n  this evening because the zone of destabilization is narrow. That is why the Marginal Risk, not the Slight Risk, covers Ashland, Hayward, and<br \/>\n  Rice Lake, Wisconsin.<\/p>\n<p>Farther south, from southeast South Dakota and southwest Minnesota into the central Plains, storm initiation and coverage are highly<br \/>\n  uncertain and conditional this afternoon and evening. The better forcing stays across western and northern Minnesota, along and northeast of<br \/>\n  the surface low. A favorable thermodynamic environment and 25 to 35 knots of deep-layer shear would still support severe hail and wind with<br \/>\n  any storm that develops and is sustained. Model guidance shows some signal for initiation across southern Nebraska into northern Kansas late<br \/>\n  this afternoon and evening where surface temperatures run hotter, and the SPC extended the southern end of the Marginal Risk to cover that<br \/>\n  possibility.<\/p>\n<p>In the Mid-South and Southeast, two weak mid-level perturbations, one over Arkansas and one along the central Gulf Coast, will track<br \/>\n  east-northeastward through the day. A stalled surface front from the ArkLaTex into the Tennessee Valley and northeastward to Virginia gives<br \/>\n  storms a focus. The SPC expects mostly disorganized, pulse-type convection with occasional damaging winds as heating steepens low-level lapse<br \/>\n  rates. Modestly enhanced mid-level flow across parts of the Mid-South and Virginia could promote loosely organized clusters with some<br \/>\n  damaging wind threat, which is why the 5% wind band extends from Memphis to Richmond.<\/p>\n<h2>How to Stay Safe During Upper Midwest Severe Thunderstorms<\/h2>\n<p>Large hail and damaging wind are the primary hazards from Upper Midwest severe thunderstorms in the Slight Risk. Large hail means stones<br \/>\n  at least one inch in diameter, the National Weather Service severe threshold, and the SPC notes isolated stones of two inches or larger are<br \/>\n  possible within the 15% hail area from Bemidji and International Falls to Alexandria and Willmar. Move vehicles into a garage or under a<br \/>\n  hard-sided roof before storms arrive. Hail that size cracks windshields and damages siding and roofs.<\/p>\n<p>Damaging wind, a gust of 58 mph or greater, is the one hazard drawn across the entire Slight Risk and both Marginal bands. Go indoors when<br \/>\n  thunder is heard, stay away from windows, and secure outdoor furniture and anything else wind can lift. If you are driving when a storm<br \/>\n  hits, pull off the road and park away from trees and power lines. Keep a <a href=\"https:\/\/ialert.com\/analysis.php#alerts\">close watch on<br \/>\n  active weather alerts<\/a> so you know the moment a Severe Thunderstorm Warning or Tornado Warning is issued for your county.<\/p>\n<p>The 5% tornado probability over Bemidji, Brainerd, Hibbing, and Alexandria, and the 2% probability reaching St. Cloud and International<br \/>\n  active weather alerts<\/a> so you know the moment a Severe Thunderstorm Warning or Tornado Warning is issued for your county.<\/p>\n<p>The 5% tornado probability over Bemidji, Brainerd, Hibbing, and Alexandria, and the 2% probability reaching St. Cloud and International<br \/>\n  Falls, mean rotating storms cannot be ruled out in the early evening. Identify a lowest-floor interior room now, before Upper Midwest severe<br \/>\n  thunderstorms develop, and keep a way to receive warnings after dark. SPC uses a five-tier system to communicate severe weather potential;<br \/>\n  see the <a href=\"https:\/\/ialert.com\/blog\/weather-articles\/severe-weather-outlook\/\">iAlert guide to SPC outlook risk categories<\/a> for a full<br \/>\n  explanation of each level, and check your <a href=\"https:\/\/ialert.com\/forecast.php\">local weather forecast<\/a> for storm timing in your<br \/>\n  area.<\/p>\n<h2>Upper Midwest Severe Thunderstorms FAQ<\/h2>\n<h3>Where is the highest risk of severe thunderstorms on September 11?<\/h3>\n<p>The Slight Risk covering far northeast South Dakota and western and northern Minnesota is the highest category today, with Duluth,<br \/>\n  Superior, International Falls, Bemidji, Brainerd, Hibbing, Alexandria, Willmar, and St. Cloud inside it. The SPC confined the Slight Risk to<br \/>\n  where it has the greatest confidence in organized thunderstorm development, and the 15% damaging wind probability covers all of it. The<br \/>\n  highest combined threat from Upper Midwest severe thunderstorms, with 15% wind, 15% hail, hatched hail intensity, and 5% tornado<br \/>\n  probabilities stacked together, sits over Bemidji, Brainerd, Hibbing, and Alexandria.<\/p>\n<h3>How large could hail get in today&#8217;s Upper Midwest severe thunderstorms?<\/h3>\n<p>The SPC discussion says initial supercells should pose a threat for large hail, with isolated stones of two inches or larger possible.<br \/>\n  That threat maps to the 15% hail probability and the hatched Intensity Level 1 area across western and north-central Minnesota, which the SPC<br \/>\n  puts at 45,454 square miles and about 1 million people, naming Sioux Falls, Watertown, Willmar, Brookings, and Hibbing.<\/p>\n<h3>Are tornadoes expected with Upper Midwest severe thunderstorms today?<\/h3>\n<p>The SPC forecasts a couple of tornadoes and draws a 5% tornado probability over Bemidji, Brainerd, Hibbing, and Alexandria, with 2%<br \/>\n  reaching St. Cloud, Willmar, Fergus Falls, and International Falls. The discussion ties the tornado threat to supercells that stay at least<br \/>\n  semi-discrete into the early evening, and it rates confidence in that scenario as fairly low because storms are expected to cluster quickly<br \/>\n  along the cold front. Duluth and Superior carry no tornado probability.<\/p>\n<h3>When will storms develop?<\/h3>\n<p>The SPC expects Upper Midwest severe thunderstorms to develop between 22Z and 01Z (6:00 pm to 9:00 pm EDT \/ 5:00 pm to 8:00 pm CDT) in far<br \/>\n  northeast South Dakota and western Minnesota, then spread east through the evening as clusters and bowing line segments. The wind threat<br \/>\n  should wane across Minnesota into western Wisconsin by late this evening. The outlook is valid through 12Z (8:00 am EDT \/ 7:00 am CDT)<br \/>\n  September 12.<\/p>\n<p><strong>Sources:<\/strong><\/p>\n<ul>\n<li><a href=\"https:\/\/www.spc.noaa.gov\/products\/outlook\/archive\/2026\/day1otlk_20260911_1300.html\" target=\"_blank\" rel=\"noopener\">NOAA Storm Prediction Center, Day 1<br \/>\n  Convective Outlook, issued 12:26 UTC (8:26 am EDT \/ 7:26 am CDT), September 11, 2026<\/a><\/li>\n<li><a href=\"https:\/\/www.spc.noaa.gov\/about\/outlooks\/\" target=\"_blank\" rel=\"noopener\">NOAA Storm Prediction Center, About the SPC Convective Outlooks:<br \/>\n  probability-to-category conversion and Conditional Intensity Groups<\/a><\/li>\n<\/ul>\n<div style=\"background: #000000; padding: 20px 24px; margin: 20px 0; border-radius: 4px;\">\n<p style=\"color: #ffffff; font-size: 16px; font-weight: bold; margin: 0 0 6px 0;\">Get Severe Weather Alerts for Your Location<\/p>\n<p style=\"color: rgba(255,255,255,0.9); margin: 0 0 14px 0;\">When any NWS watch, warning, or advisory is issued for your area, iAlert sends<br \/>\n  you an immediate notification by email, text message, or phone call, 24 hours a day, 7 days a week.<\/p>\n<p>  <a href=\"https:\/\/ialert.com\/services\/severe-weather-alerts.php\" style=\"background: #C41226; color: #ffffff; padding: 10px 22px; \n  text-decoration: none; border-radius: 3px; font-weight: bold; display: inline-block;\">Sign Up for Severe Weather Alerts &rarr;<\/a>\n  <\/div>\n","protected":false},"excerpt":{"rendered":"<p>Upper Midwest severe thunderstorms bring a Slight Risk to Duluth, Bemidji, and northern Minnesota Sept. 11, with large hail, damaging wind.<span class=\"more\"> <a href=\"https:\/\/ialert.com\/blog\/news-events\/upper-midwest-severe-thunderstorms\/\">Read More&#8230;<\/a><\/span><\/p>\n","protected":false},"author":6,"featured_media":5660,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":"","rank_math_focus_keyword":"Upper Midwest severe thunderstorms","rank_math_title":"Upper Midwest Severe Thunderstorms: 15% Wind Risk Today","rank_math_description":"Upper Midwest severe thunderstorms bring a Slight Risk to Duluth, Bemidji, and northern Minnesota Sept. 11, with large hail, damaging wind."},"categories":[719],"tags":[772],"class_list":["post-5658","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news-events","tag-spc-outlook"],"acf":[],"_links":{"self":[{"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/posts\/5658","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/comments?post=5658"}],"version-history":[{"count":2,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/posts\/5658\/revisions"}],"predecessor-version":[{"id":5663,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/posts\/5658\/revisions\/5663"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/media\/5660"}],"wp:attachment":[{"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/media?parent=5658"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/categories?post=5658"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/tags?post=5658"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}