{"id":4839,"date":"2026-08-28T17:52:56","date_gmt":"2026-08-28T17:52:56","guid":{"rendered":"https:\/\/discussions.weather.arizona.edu\/?p=4839"},"modified":"2026-08-28T18:03:24","modified_gmt":"2026-08-28T18:03:24","slug":"august-28th-2026-scattered-weaker-thunderstorms-today-tomorrow-theres-potential-for-strong-storms-in-tucson-and-phoenix-a-passing-trough-will-keep-the-act","status":"publish","type":"post","link":"https:\/\/discussions.weather.arizona.edu\/?p=4839","title":{"rendered":"August 28th, 2026: Scattered\u00a0weaker thunderstorms today; tomorrow\u00a0there&#8217;s\u00a0potential for strong\u00a0storms in Tucson and\u00a0Phoenix. A passing trough\u00a0will\u00a0keep\u00a0the active period going through Monday."},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Two tropical storms, Lowell and Karina, have recently developed in the Pacific, with Karina potentially affecting the Southwest U.S. if it moves northeast. Moisture is flowing into the region from remnants of tropical storm Iselle and the easterly monsoonal transport around the subtropical high. Surface dewpoint observations indicate a continuing moisture surge, with similar values and spatial pattern to yesterday.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Forecasts predict weaker thunderstorm activity today compared to yesterday. Tomorrow, severe storms are expected in Tucson and Phoenix, with heavy rainfall, strong winds, blowing dust, and a possible haboob. A polar low and the associated jet stream will drive storm activity from Saturday night through Monday, allowing storms to develop at any time of day. A break in precipitation is forecast from Tuesday on, though high temperatures are expected to drop below triple digits next week.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Yesterday&#8217;s Weather<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Yesterday, we debated between the HRRR-UA WRF 12Z (below, left) and the 15Z, trying to determine which forecast was more likely.<\/p>\n\n\n\n<figure class=\"wp-block-video aligncenter\"><video height=\"822\" style=\"aspect-ratio: 1688 \/ 822;\" width=\"1688\" autoplay controls loop muted src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/20260828-1616-50.8952568.mp4\" playsinline><\/video><figcaption class=\"wp-element-caption\">12Z HRRR-UA WRF simulated radar reflectivity (left) and corresponding MRMS radar mosaic (right) from 12 pm yesterday to 1 am today<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">We decided on the more aggressive 15Z forecast (below, left). What happened (right) was a blend between the two, with isolated storms more like the 12Z forecast, but with the intensity of the 15Z forecast.&nbsp;<\/p>\n\n\n\n<figure class=\"wp-block-video aligncenter\"><video height=\"818\" style=\"aspect-ratio: 1684 \/ 818;\" width=\"1684\" autoplay controls loop muted src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/20260828-1619-47.4652596.mp4\" playsinline><\/video><figcaption class=\"wp-element-caption\">15Z HRRR-UA WRF simulated radar reflectivity (left) and corresponding MRMS radar mosaic (right) from 12 pm yesterday to 1 am today<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The observed radar reflectivity shows a storm at 5:30 pm (left)&nbsp;that&nbsp;produced a 67-mph microburst at Tucson International Airport; outflow from this storm helped develop the storm that produced over an inch of rain near downtown Tucson&nbsp;at 6 pm (right). Again, a&nbsp;blend of 12Z and 15Z forecasts:&nbsp;isolated, but more intense storms.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"319\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-203-1024x319.png\" alt=\"\" class=\"wp-image-4914\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-203-1024x319.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-203-300x94.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-203-768x239.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-203-1536x479.png 1536w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-203.png 1732w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Observed radar reflectivity from yesterday at 5:30 pm (left) and 6 pm (right).<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Visible satellite imagery at 5:30 pm, overlaid with lightning data, shows thunderstorms in southeast Arizona and northeast New Mexico. Most of the clouds in western and northern Arizona and parts of New Mexico were mid- and high-level clouds from former Tropical Storm Iselle.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"680\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-199-1024x680.png\" alt=\"\" class=\"wp-image-4908\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-199-1024x680.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-199-300x199.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-199-768x510.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-199.png 1207w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">GOES-19 visible satellite imagery and GLM lightning data from August 27th at 5:30 pm, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">The HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) are shown below.&nbsp;The forecast precipitation was close to observed in New Mexico. The&nbsp;forecast&nbsp;still underestimated&nbsp;precipitation in northern Mexico south of Douglas. Surge moisture resulted in more precipitation&nbsp;in the mountains east of Puerto Pe\u00f1asco and&nbsp;in&nbsp;southeast Pinal County.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"335\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-200-1024x335.png\" alt=\"\" class=\"wp-image-4909\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-200-1024x335.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-200-300x98.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-200-768x251.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-200-1536x502.png 1536w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-200.png 1732w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) for August 27th.<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Pima County Flood Control alert gauges below show the rain was isolated but heavy. Other than the microburst over&nbsp;downtown Tucson, most other rain fell near the mountains. Only a few gauges in Maricopa County had light&nbsp;precipitation.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"631\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-201-1024x631.png\" alt=\"\" class=\"wp-image-4910\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-201-1024x631.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-201-300x185.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-201-768x473.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-201.png 1322w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">24-hour precipitation totals from Pima County Regional Flood Control District gauges, <a href=\"https:\/\/alertmap.rfcd.pima.gov\/gmap\/gmap.html\">Alert Map<\/a>.<\/figcaption><\/figure>\n<\/div>\n\n\n<h2 class=\"wp-block-heading\">Analysis<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The National Hurricane Center (NHC) tropical weather outlook&nbsp;shows&nbsp;Tropical Storms Lowell and Karina formed yesterday.&nbsp;The&nbsp;tropics are a&nbsp;source of late-monsoon moisture, and any tropical systems near the southern tip of Baja could push moisture into Arizona.&nbsp;Lowell is too far west to affect Arizona, but Karina may affect the Southwest United States depending upon its movement.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1032\" height=\"626\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-205-edited.png\" alt=\"\" class=\"wp-image-4918\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-205-edited.png 1032w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-205-edited-300x182.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-205-edited-1024x621.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-205-edited-768x466.png 768w\" sizes=\"auto, (max-width: 1032px) 100vw, 1032px\" \/><figcaption class=\"wp-element-caption\">National Hurricane Center <a href=\"https:\/\/www.nhc.noaa.gov\/\">outlook<\/a> for the Pacific basin<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">The Tropical Upper Tropospheric Trough (TUTT)&nbsp;has moved further west with a trough extending east into the Gulf of Mexico. The polar&nbsp;low&nbsp;is west of the California low, and the associated&nbsp;jet stream extends into Montana.&nbsp;Two other moisture flows come from the remains of Tropical Storm Iselle, and the flow&nbsp;to its&nbsp;south (green arrow) is around the subtropical&nbsp;high-pressure.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"626\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094001-1024x626.png\" alt=\"\" class=\"wp-image-4919\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094001-1024x626.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094001-300x183.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094001-768x469.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094001.png 1100w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">GOES-19 upper-level water vapor image August 27th at 8 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">The Velocity Azimuth Display Wind Profile from Yuma shows the surge is continuing with a depth of 3000 feet.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"717\" height=\"776\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-206.png\" alt=\"\" class=\"wp-image-4921\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-206.png 717w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-206-277x300.png 277w\" sizes=\"auto, (max-width: 717px) 100vw, 717px\" \/><figcaption class=\"wp-element-caption\">Velocity Azimuth Display wind profile from Yuma radar KYUM from 4:32 am to 6 am.<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">The visible satellite picture taken at 8 am shows scattered mid- and high-level clouds over Arizona, while New Mexico is mostly clear.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"673\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-207-1024x673.png\" alt=\"\" class=\"wp-image-4923\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-207-1024x673.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-207-300x197.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-207-768x505.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-207.png 1217w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">GOES-19 visible satellite imagery from August 28th at 8 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">There has been no significant change in surface dewpoints&nbsp;since yesterday,&nbsp;as surge moisture is being balanced by vertical mixing of dry air aloft.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"551\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094716-1024x551.png\" alt=\"\" class=\"wp-image-4925\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094716-1024x551.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094716-300x161.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094716-768x413.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094716.png 1472w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Surface weather station observations for Arizona and New Mexico at 7:00 am, <a href=\"https:\/\/www.weather.gov\/wrh\/hazards?&amp;zoom=8&amp;scroll_zoom=false&amp;center=32.656025851099066,-110.76888628244107&amp;boundaries=false,true,false,false,false,false,false,false,false,false,false&amp;tab=observation&amp;hazard=true&amp;hazard_type=all&amp;hazard_opacity=80&amp;obs=true&amp;obs_type=weather&amp;elements=temp,wind,gust&amp;temp_filter=-80,130&amp;gust_filter=0,150&amp;rh_filter=0,100&amp;elev_filter=-300,14000&amp;precip_filter=0.01,30&amp;obs_popup=false&amp;obs_density=60&amp;obs_provider=ALL\">NWS<\/a><\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">The HRRR-UA WRF 12Z initialization (left) and observed (right) sounding for Phoenix at 5 am are shown below.&nbsp;The forecast initialization&nbsp;captures the&nbsp;surge of moisture from 880 mb down to the surface&nbsp;with a little warming aloft just above 420 mb.&nbsp;The observed sounding better captures the mid-level moisture between 550&nbsp;mb and 680&nbsp;mb.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"575\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094912-1024x575.png\" alt=\"\" class=\"wp-image-4926\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094912-1024x575.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094912-300x168.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094912-768x431.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-094912.png 1408w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">HRRR-UA WRF 12Z (left) initialization and observed sounding (right) at Phoenix for 5 am this morning.<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">At&nbsp;250mb, the ridge is just south of Nogales, with anticyclonic (clockwise) flow around it. The jet associated with the polar low&nbsp;off the West Coast is&nbsp;from California to Montana.&nbsp;The jet stream will continue to move east into the western United States over the weekend.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"837\" height=\"852\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095322.png\" alt=\"\" class=\"wp-image-4927\" style=\"aspect-ratio:0.9823980815306224;width:569px;height:auto\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095322.png 837w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095322-295x300.png 295w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095322-768x782.png 768w\" sizes=\"auto, (max-width: 837px) 100vw, 837px\" \/><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">The&nbsp;high-pressure ridge in west-central New Mexico has a broad circulation over the western United States&nbsp;at 500 mb. Temperatures have cooled in California and Oregon due to&nbsp;the trough off the West Coast.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"855\" height=\"857\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095850.png\" alt=\"\" class=\"wp-image-4928\" style=\"aspect-ratio:0.9976641892564885;width:611px;height:auto\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095850.png 855w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095850-300x300.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095850-150x150.png 150w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-095850-768x770.png 768w\" sizes=\"auto, (max-width: 855px) 100vw, 855px\" \/><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">At 700mb,&nbsp;the monsoon high&nbsp;is over northeast Arizona with a ridge axis extending southeast to&nbsp;the El Paso area.&nbsp;A trough extends south from Douglas into Mexico.&nbsp;The&nbsp;circulation and&nbsp;moisture transport&nbsp;are weak across&nbsp;Mexico.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"852\" height=\"855\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-100223.png\" alt=\"\" class=\"wp-image-4929\" style=\"aspect-ratio:0.9965003711201006;width:630px;height:auto\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-100223.png 852w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-100223-300x300.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-100223-150x150.png 150w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-100223-768x771.png 768w\" sizes=\"auto, (max-width: 852px) 100vw, 852px\" \/><\/figure>\n<\/div>\n\n\n<h2 class=\"wp-block-heading\">Today<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The&nbsp;forecast&nbsp;sounding for Phoenix&nbsp;at 5:00 pm (below, left) shows a&nbsp;good profile for thunderstorm development because of increased low-level&nbsp;moisture. The Convective Available Potential Energy (CAPE)&nbsp;is around 600 [J\/kg] with very little&nbsp;Convective Inhibition (CIN).&nbsp;The&nbsp;forecast&nbsp;sounding&nbsp;for&nbsp;Tucson&nbsp;at 3:00 pm (below, right)&nbsp;shows that, despite the&nbsp;low CIN indicated on the sounding, the CAPE is unimpressive. Warming aloft&nbsp;at 500 mb is probably the&nbsp;reason the Tucson sounding indicates less activity than yesterday.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"574\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-101141-1024x574.png\" alt=\"\" class=\"wp-image-4930\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-101141-1024x574.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-101141-300x168.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-101141-768x431.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/Screenshot-2026-08-28-101141.png 1409w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">HRRR-UA WRF 12Z forecast soundings for Phoenix at 5 pm (left) and Tucson at 3:30 pm (right).<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Thunderstorms aren&#8217;t&nbsp;forecast&nbsp;to be&nbsp;as strong in Pima County as they were yesterday, but&nbsp;they&nbsp;are predicted to&nbsp;develop&nbsp;further west into Maricopa County and the Phoenix area by evening. Wind&nbsp;gusts up to 40 mph and blowing dust&nbsp;can be expected&nbsp;with the storms,&nbsp;especially in the Phoenix metro area.&nbsp;<\/p>\n\n\n\n<figure class=\"wp-block-video aligncenter\"><video height=\"560\" style=\"aspect-ratio: 1728 \/ 560;\" width=\"1728\" autoplay controls loop muted src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/20260828-1715-51.9426550.mp4\" playsinline><\/video><figcaption class=\"wp-element-caption\">HRRR-UA WRF 12Z simulated radar reflectivity (left) and 10-meter wind speed (right) forecast from 2 pm to 1:30 am.<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Tomorrow<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Tomorrow, a major increase in precipitation is forecast, with strong to severe storms in Tucson between 3-5 pm and in Phoenix between 6-9 pm. Threats include&nbsp;strong winds, heavy rain, blowing dust&nbsp;and\/or&nbsp;a haboob. It&#8217;s still not cold enough&nbsp;aloft&nbsp;for large hail yet.&nbsp;Additional storms may develop overnight in eastern Pima and Pinal counties.&nbsp;<\/p>\n\n\n\n<figure class=\"wp-block-video aligncenter\"><video height=\"568\" style=\"aspect-ratio: 1730 \/ 568;\" width=\"1730\" autoplay controls loop muted src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/20260828-1720-15.6722776.mp4\" playsinline><\/video><figcaption class=\"wp-element-caption\">HRRR-UA WRF 12Z simulated radar reflectivity (left) and 10-meter wind speed (right) forecast tomorrow from 12 pm to midnight.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Total precipitation forecasts through 24 hours (bottom left) and 48 hours (bottom right) show most precipitation falling tomorrow afternoon and evening.&nbsp;Totals above 0.5&#8243; and up to 2&#8243; are predicted for central Pima and southern Pinal County.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"332\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-208-1024x332.png\" alt=\"\" class=\"wp-image-4934\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-208-1024x332.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-208-300x97.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-208-768x249.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-208-1536x498.png 1536w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-208.png 1732w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">HRRR-UA WRF 12Z total precipitation 24-hour (left) and 48-hour (right).<\/figcaption><\/figure>\n<\/div>\n\n\n<h2 class=\"wp-block-heading\">Outlook<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">From Saturday&nbsp;to Sunday&nbsp;night,&nbsp;the polar jet stream will affect the area. Unlike the typical monsoon, synoptic-scale dynamics cause the ascent needed for storm development (positive vorticity advection).&nbsp;This means storms can occur day and night, and many per day as they&#8217;re not reliant on diurnal heating.&nbsp;The radar reflectivity forecast from tomorrow&nbsp;night at midnight to Monday at 5 pm illustrates this point with both day and nocturnal rainfall predicted.&nbsp;&nbsp;<\/p>\n\n\n\n<figure class=\"wp-block-video aligncenter\"><video height=\"746\" style=\"aspect-ratio: 1140 \/ 746;\" width=\"1140\" autoplay controls loop muted src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/20260828-1728-37.9886441.mp4\" playsinline><\/video><figcaption class=\"wp-element-caption\">HRRR-UA WRF 12Z simulated radar reflectivity forecast from tomorrow night at midnight to Monday at 5 pm.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">From Tuesday, we will have a break in precipitation until the following weekend.&nbsp;It looks like there will be no more triple-digit high&nbsp;temperatures from&nbsp;Sunday&nbsp;into next week.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"820\" src=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-209-1024x820.png\" alt=\"\" class=\"wp-image-4936\" srcset=\"https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-209-1024x820.png 1024w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-209-300x240.png 300w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-209-768x615.png 768w, https:\/\/discussions.weather.arizona.edu\/wp-content\/uploads\/2026\/08\/image-209.png 1077w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Global Ensemble Forecast System (GEFS) ensemble forecasts of 2-meter temperature (top) and 3-hour accumulated precipitation (bottom), NCAR.<\/figcaption><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">Discussion written by Pat Holbrook and Patrick Bunn<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Summary Two tropical storms, Lowell and Karina, have recently developed in the Pacific, with Karina potentially affecting the Southwest U.S. if it moves northeast. Moisture is flowing into the region from remnants of tropical storm Iselle and the easterly monsoonal transport around the subtropical high. Surface dewpoint observations indicate a continuing moisture surge, with similar &hellip;<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[8],"class_list":["post-4839","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-8"],"_links":{"self":[{"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=\/wp\/v2\/posts\/4839","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4839"}],"version-history":[{"count":14,"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=\/wp\/v2\/posts\/4839\/revisions"}],"predecessor-version":[{"id":4945,"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=\/wp\/v2\/posts\/4839\/revisions\/4945"}],"wp:attachment":[{"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4839"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4839"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/discussions.weather.arizona.edu\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4839"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}