{"id":5762,"date":"2026-10-21T13:43:13","date_gmt":"2026-10-21T13:43:13","guid":{"rendered":"https:\/\/ialert.com\/blog\/?p=5762"},"modified":"2026-10-21T13:43:13","modified_gmt":"2026-10-21T13:43:13","slug":"arizona-severe-thunderstorms-oct-21","status":"publish","type":"post","link":"https:\/\/ialert.com\/blog\/news-events\/arizona-severe-thunderstorms-oct-21\/","title":{"rendered":"Arizona Severe Thunderstorms: SPC Enhanced Risk for Flagstaff and Prescott on October 21, 2026"},"content":{"rendered":"<p>  <iframe src=\"https:\/\/ialert.com\/blog_outlook.php?event=arizona-severe-thunderstorms-oct-21\" title=\"Arizona Severe Thunderstorms: SPC Enhanced Risk for Flagstaff and Prescott on\n  October 21, 2026\" loading=\"lazy\" style=\"width:100%;border:0;\" height=\"660\"><\/iframe><\/p>\n<p>Arizona severe thunderstorms are the headline threat in the NOAA Storm Prediction Center&#8217;s updated Day 1 Convective Outlook for Wednesday, October 21, 2026, issued 12:30 UTC<br \/>\n  (5:30 am MST \/ 8:30 am EDT). The outlook places an Enhanced Risk, the third of five severe categories (level 3 of 5), over Flagstaff, Prescott, Sedona, and Payson, with Phoenix<br \/>\n  in the Slight Risk just to the south. The SPC expects large hail, damaging winds, and a tornado risk across parts of Arizona today and tonight, and it flags a conditional risk<br \/>\n  for hail 2 inches or larger in diameter with splitting supercells.<\/p>\n<p><strong>Key points:<\/strong><\/p>\n<ul>\n<li>Enhanced Risk (level 3 of 5) covers Flagstaff, Prescott, Sedona, Payson, and Cottonwood.<\/li>\n<li>Phoenix, Mesa, Scottsdale, Show Low, Kingman, and St. George, Utah sit in the Slight Risk (level 2 of 5).<\/li>\n<li>The SPC carries a 30% large hail probability in the Enhanced Risk, with hail 2 inches or larger possible.<\/li>\n<li>Tornado probability is 5% at Flagstaff and Prescott; tornadoes are possible this afternoon and early evening.<\/li>\n<li>A Marginal Risk reaches Las Vegas, Tucson, Cedar City, Utah, and the Los Angeles coast.<\/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 you an immediate notification by<br \/>\n  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; text-decoration: none; border-radius: 3px; \n  font-weight: bold; display: inline-block;\">Sign Up for Severe Weather Alerts &rarr;<\/a>\n  <\/div>\n<h2>Where Arizona severe thunderstorms pose the greatest threat<\/h2>\n<p>The Enhanced Risk is drawn over north-central Arizona along and below the Mogollon Rim, taking in Flagstaff, Prescott, Sedona, Payson, Cottonwood, and Williams. The SPC risk<br \/>\n  tables put about 283,000 people inside it. SPC uses a five-tier system to communicate severe weather potential, and you can read more in our <a \n  href=\"https:\/\/ialert.com\/blog\/weather-articles\/severe-weather-outlook\/\">severe weather outlook explainer<\/a>.<\/p>\n<p>The Slight Risk (level 2 of 5) wraps around that core and covers most of central and northern Arizona. It includes Phoenix, Mesa, Scottsdale, Show Low, Globe, Winslow,<br \/>\n  Holbrook, Kingman, Page, and Grand Canyon Village, and it reaches into St. George and Kanab, Utah and Mesquite, Nevada. The 12:30 UTC update extended the Slight Risk westward<br \/>\n  across northwest Arizona, southeast Nevada, and southwest Utah, mainly for large hail with supercells this afternoon and evening.<\/p>\n<p>A Marginal Risk (level 1 of 5) covers two separate areas. The larger one rings the Slight Risk across southern Arizona, southern Nevada, southwest Utah, and northwest New<br \/>\n  Mexico, including Tucson, Las Vegas, Henderson, Cedar City, Gallup, and Farmington. The second runs along the central and southern California coast from San Luis Obispo through<br \/>\n  Santa Barbara to Los Angeles.<\/p>\n<p>Outside the severe risk areas, a broad general thunderstorm area covers much of the West, including Albuquerque, Salt Lake City, Reno, Fresno, San Diego, and Boise, along<br \/>\n  with a separate area on the South Texas coast near Corpus Christi.<\/p>\n<h2>SPC hazard probabilities, city by city<\/h2>\n<p><strong>Large hail.<\/strong> For Arizona severe thunderstorms, the SPC draws a 30% hail probability over Flagstaff, Prescott, Sedona, Payson, and Cottonwood, a 15%<br \/>\n  probability over Phoenix, Mesa, Show Low, Kingman, and St. George, Utah, and a 5% probability over Tucson, Las Vegas, and Cedar City, Utah. Los Angeles has no hail probability<br \/>\n  drawn. The Enhanced Risk outline is identical to the 30% hail area, so hail alone earned the level 3 rating today.<\/p>\n<p>A hatched hail area, the SPC&#8217;s Conditional Intensity Group 1, covers 68,592 square miles and roughly 4.9 million people, from Flagstaff and Prescott south through Phoenix and<br \/>\n  west to Kingman and St. George. Hatching marks where Arizona severe thunderstorms that do form could reach the high end of the hail scale; the SPC discussion ties it to a<br \/>\n  conditional risk for 2 inch or larger hail.<\/p>\n<p><strong>Damaging wind.<\/strong> The top 15% wind probability with Arizona severe thunderstorms covers Flagstaff, Show Low, Sedona, Payson, Winslow, Globe, and Holbrook. A 5%<br \/>\n  wind probability covers Prescott, Phoenix, Tucson, Las Vegas, Kingman, and Cedar City, and separately the California coast around Los Angeles. Show Low deserves a plain word of<br \/>\n  caution: it sits in the Slight Risk but shares the top 15% wind probability with Flagstaff, while Prescott, inside the Enhanced Risk, carries only 5%.<\/p>\n<p><strong>Tornado risk.<\/strong> The 5% tornado probability for Arizona severe thunderstorms covers Flagstaff, Prescott, Sedona, Payson, Williams, Winslow, and Grand Canyon<br \/>\n  Village, an area of about 931,000 people. A 2% probability covers Phoenix, Mesa, Show Low, Kingman, Page, and St. George and Cedar City, Utah, and separately the coast from San<br \/>\n  Luis Obispo to Los Angeles. Tucson has no tornado probability drawn. These percentages are the chance of a report within 25 miles of a point, not a measure of storm<br \/>\n  strength.<\/p>\n<h2>California coast: isolated wind and tornado risk<\/h2>\n<p>The SPC also highlights coastal central and southern California. A large, closed upper low over the eastern Pacific will approach the central California coast, with a belt of<br \/>\n  strong southerly flow at mid levels spreading over the coast through the day. A low-topped line of convection may develop in response during the afternoon and evening.<\/p>\n<p>Instability is forecast to stay minimal and shallow, and the SPC notes this line may struggle to grow tall enough to produce lightning. Even so, modestly enhanced flow and<br \/>\n  low-level shear support an isolated risk for severe gusts and perhaps a tornado as the line moves onshore.<\/p>\n<p>\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/ialert.com\/blog\/wp-content\/uploads\/2026\/10\/ialert-arizona-severe-thunderstorms-hail-risk-october-21-2026.jpg\" alt=\"Arizona severe thunderstorms hail risk map: \n  SPC 30% large hail probability at Flagstaff and Prescott, October 21, 2026\" width=\"1424\" height=\"747\" class=\"aligncenter size-full wp-image-5765\" srcset=\"https:\/\/ialert.com\/blog\/wp-content\/uploads\/2026\/10\/ialert-arizona-severe-thunderstorms-hail-risk-october-21-2026.jpg 1424w, https:\/\/ialert.com\/blog\/wp-content\/uploads\/2026\/10\/ialert-arizona-severe-thunderstorms-hail-risk-october-21-2026-300x157.jpg 300w, https:\/\/ialert.com\/blog\/wp-content\/uploads\/2026\/10\/ialert-arizona-severe-thunderstorms-hail-risk-october-21-2026-1024x537.jpg 1024w\" sizes=\"auto, (max-width: 1424px) 100vw, 1424px\" \/><\/p>\n<h2>Meteorologist&#8217;s take<\/h2>\n<p>The setup started early. Thunderstorms were already ongoing across central and northern Arizona this morning, aided by large-scale lift beneath a strong southwesterly jet at<br \/>\n  mid and upper levels. The SPC says those storms carry mainly an isolated severe hail threat in the short term, with 40 to 50 knots of effective bulk shear supporting supercells<br \/>\n  even though instability is weak (MUCAPE 500 to 1,000 J\/kg).<\/p>\n<p>The bigger round of Arizona severe thunderstorms comes this afternoon. An unseasonably moist low-level airmass over southern and central Arizona will spread north across the<br \/>\n  lower Colorado River Valley and the Mogollon Rim. Even under widespread cloud cover, filtered sunshine will build up to 1,000 to 1,500 J\/kg of MLCAPE, locally more in central<br \/>\n  Arizona, and convective inhibition (the warm lid that holds storms back) should be minimal by 18 to 20 UTC, or 11 am to 1 pm MST. New storms are likely to form across central<br \/>\n  and northern Arizona in that window.<\/p>\n<p>Deep-layer shear of 40 to 55 knots or more will easily support supercells, the rotating storms that produce the largest hail. The SPC points to splitting supercells and long,<br \/>\n  nearly straight hodographs at mid and upper levels, the pattern behind its conditional risk for 2 inch or larger hail. Arizona severe thunderstorms should stay mostly discrete,<br \/>\n  which favors hail over widespread wind damage, though occasional damaging gusts are still possible.<\/p>\n<p>The tornado question is less certain. Temperatures will stay fairly cool across northern Arizona, but the SPC says a tornado risk may focus over northwest and north-central<\/p>\n<p>The tornado question is less certain. Temperatures will stay fairly cool across northern Arizona, but the SPC says a tornado risk may focus over northwest and north-central<br \/>\n  Arizona this afternoon and early evening, where east-southeasterly low-level winds add more low-level shear. The detail that matters most for anyone tracking Arizona severe<br \/>\n  thunderstorms today: the SPC expects multiple rounds of strong to severe storms into tonight. A lull after the morning storms is not the all clear.<\/p>\n<h2>How to Stay Safe in Arizona Severe Thunderstorms<\/h2>\n<p>Hail that large is a vehicle and roof hazard first. If you live or work between Prescott, Flagstaff, and Show Low, park under cover before storms build this afternoon, and<br \/>\n  move indoors and away from skylights and windows when Arizona severe thunderstorms approach.  The National Weather Service classifies a thunderstorm as severe when it produces hail 1 inch or larger in diameter, wind gusts of 58 mph or greater, or a tornado.<\/p>\n<p>Because the strongest supercells carry a tornado risk, identify your safest room now: an interior room on the lowest floor, away from windows. Mobile homes and RVs do not<br \/>\n  offer protection from tornadoes or severe wind, so plan where you will go instead. Anyone driving Interstate 17 or Interstate 40 through the risk area should be ready to delay<br \/>\n  the trip rather than push through a hail core.<\/p>\n<p>Watch trends on <a href=\"https:\/\/ialert.com\/analysis.php?tab=radar\">live radar and alerts<\/a> and make sure warnings can reach you with sound. Repeated rounds of storms over<br \/>\n  the Mogollon Rim can also drop heavy rain on burn scars and dry washes, so never drive into water covering a road.<\/p>\n<h2>Arizona severe thunderstorms FAQ<\/h2>\n<h3>Where is the highest risk today?<\/h3>\n<p>The Enhanced Risk, level 3 of 5, covers north-central Arizona, including Flagstaff, Prescott, Sedona, and Payson. Phoenix, Show Low, and Kingman sit in the Slight Risk, and<br \/>\n  Show Low shares the top 15% damaging wind probability.<\/p>\n<h3>How large could the hail get?<\/h3>\n<p>The SPC flags a conditional risk for hail 2 inches or larger in diameter with splitting supercells. Flagstaff and Prescott carry a 30% large hail probability, Phoenix and<br \/>\n  Show Low 15%, and Tucson, Las Vegas, and Cedar City 5%.<\/p>\n<h3>Is there a tornado risk?<\/h3>\n<p>Yes. The SPC draws a 5% tornado probability over Flagstaff, Prescott, Sedona, and Payson, focused on northwest and north-central Arizona this afternoon and early evening. A<br \/>\n  2% probability covers Phoenix, Show Low, Kingman, St. George, Cedar City, and the Los Angeles coast.<\/p>\n<h3>When will storms arrive?<\/h3>\n<p>Storms were already active this morning. A second round of Arizona severe thunderstorms is likely to develop across central and northern Arizona around 11 am to 1 pm MST, and<br \/>\n  the SPC expects multiple rounds of strong to severe thunderstorms into tonight.<\/p>\n<p>Arizona severe thunderstorms today hinge on afternoon heating after the morning storms clear, so check your <a href=\"https:\/\/ialert.com\/forecast.php\">local weather<br \/>\n  forecast<\/a> and keep alerts enabled through the evening hours.<\/p>\n<p><strong>Sources:<\/strong><\/p>\n<ul>\n<li><a href=\"https:\/\/www.spc.noaa.gov\/products\/outlook\/archive\/2026\/day1otlk_20261021_1300.html\" target=\"_blank\" rel=\"noopener\">NOAA Storm Prediction Center, Day 1 Convective Outlook, issued 12:30 UTC (5:30<br \/>\n  am MST \/ 8:30 am EDT), October 21, 2026<\/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 you an immediate notification by<br \/>\n  email, text message, or phone call, 24 hours a day, 7 days a week.<\/p>\n<p>  <a href\n<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Arizona severe thunderstorms: SPC issues an Enhanced Risk for Flagstaff and Prescott Oct 21, with hail over 2 inches and tornadoes.<span class=\"more\"> <a href=\"https:\/\/ialert.com\/blog\/news-events\/arizona-severe-thunderstorms-oct-21\/\">Read More&#8230;<\/a><\/span><\/p>\n","protected":false},"author":6,"featured_media":5766,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":"","rank_math_focus_keyword":"Arizona severe thunderstorms","rank_math_title":"Arizona Severe Thunderstorms: Dangerous 2-Inch Hail Risk","rank_math_description":"Arizona severe thunderstorms Oct 21: SPC Enhanced Risk for Flagstaff and Prescott, hail over 2 inches possible, plus a tornado risk."},"categories":[719],"tags":[772],"class_list":["post-5762","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\/5762","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=5762"}],"version-history":[{"count":6,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/posts\/5762\/revisions"}],"predecessor-version":[{"id":5770,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/posts\/5762\/revisions\/5770"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/media\/5766"}],"wp:attachment":[{"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/media?parent=5762"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/categories?post=5762"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ialert.com\/blog\/wp-json\/wp\/v2\/tags?post=5762"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}