{"id":5178,"date":"2026-09-10T17:37:57","date_gmt":"2026-09-10T17:37:57","guid":{"rendered":"https:\/\/discussions.weather.arizona.edu\/?p=5178"},"modified":"2026-09-10T17:39:02","modified_gmt":"2026-09-10T17:39:02","slug":"september-10th-2026-santa-cruz-and-southern-cochise-county-may-see-thunderstorms-this-afternoon-as-activity-retreats-south-to-the-international-border-isolated-mountain-storms-w","status":"publish","type":"post","link":"https:\/\/discussions.weather.arizona.edu\/?p=5178","title":{"rendered":"September 10th, 2026: Santa Cruz and southern Cochise County\u00a0may see thunderstorms\u00a0this afternoon\u00a0as activity\u00a0retreats south to the international border. Isolated mountain storms will return over the weekend in southeast Arizona"},"content":{"rendered":"\n

Summary<\/h2>\n\n\n\n

Tropical Storm Norbert is the latest storm to form in the eastern Pacific, but it is not expected to impact the mainland United States as it is forecast to move westward. In Arizona and New Mexico, tropical moisture has been pushed south, and dry air has advanced into the northern parts of both states, reducing storm potential, especially outside mountainous areas. Satellite imagery shows mostly clear skies this morning across AZ and NM, and surface observations show lower dewpoints in the north, while some moisture remains in the south. <\/p>\n\n\n\n

Thunderstorm activity will be limited today, with Tucson and Phoenix likely staying dry; activity will be near Nogales. Moisture is expected to return on Friday, bringing another round of storms to the mountains, with activity weakening after sunset. With no major tropical systems affecting the region, the low-grade pattern will persist into next week. <\/p>\n\n\n\n

Yesterday’s Weather<\/h2>\n\n\n\n

Visible satellite imagery overlaid with radar and lightning data from 5:30 pm yesterday shows showers and thunderstorms with more extensive areal coverage than on Wednesday and much more lightning. The storms tried to push into Tucson, but weakened before dropping rain in the metro area.<\/p>\n\n\n

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GOES-19 visible satellite imagery overlaid with radar reflectivity and GLM lightning from September 9th, 5:30 pm, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

The 7 pm infrared satellite image overlaid with lightning shows the thunderstorms rapidly increasing in intensity up to this time, but with little Convective Available Potential Energy (CAPE) in the Tucson valley, the storms\u00a0weakened\u00a0as they moved into the metro area.\u00a0<\/p>\n\n\n

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GOES-19 infrared satellite imagery overlaid with GLM lightning from September 9th, 7 pm, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

24-hour accumulated precipitation data from the Pima County Flood Control District rain gauge network shows the storms basically stopping in the Catalina and Rincon Mountains, with over an inch falling at a few gauges on the mountains to the east.\u00a0<\/p>\n\n\n

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24-hour precipitation totals from Pima County Regional Flood Control District gauges, Alert Map<\/a>.<\/figcaption><\/figure>\n<\/div>\n\n\n

Similar data from\u00a0Rainlog below shows the heavy rain in the western half of Cochise and southwest Graham counties. Some light rain did fall in the Tucson metro area.\u00a0<\/p>\n\n\n

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24-hour precipitation totals from Rainlog.org<\/a><\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) are shown below.\u00a0The forecast areal coverage was correct, but it underestimated precipitation amounts.\u00a0<\/p>\n\n\n

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HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) for September 9th.<\/figcaption><\/figure>\n<\/div>\n\n\n

Analysis<\/h2>\n\n\n\n

Tropical Storm Norbert is the newest in the succession of tropical systems in the eastern Pacific, and we will likely have a few more into October. Norbert does not pose any threat to the mainland United States, as it’s predicted to move west. <\/p>\n\n\n

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National Hurricane Center outlook<\/a> for the Pacific basin<\/figcaption><\/figure>\n<\/div>\n\n\n

Moisture flow from the tropics has been pushed southward into Arizona and New Mexico. Tropical Storm Norbert is still weak, but will mature into a hurricane in a few days. The Tropical Upper Tropospheric Troughs (TUTTs)\u00a0are in a similar\u00a0location as on Wednesday.\u00a0<\/p>\n\n\n

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GOES-19 upper-level water vapor image September 10th at 8 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

The\u00a0visible satellite image from 8 am shows only scattered clouds in central to northwestern Arizona and parts of eastern New Mexico. <\/p>\n\n\n

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GOES-19 visible satellite imagery from September 10th at 8 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

Very dry air has moved into northern Arizona eastward into northern New Mexico, as shown by the < 40\u00b0F surface dewpoints. The southern part of the region remains\u00a0moist, but the dry air to the north will slowly move south during the day.<\/p>\n\n\n

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Surface weather station observations for Arizona and New Mexico at 7:00 am, NWS<\/a><\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 12Z initialization (left) and observed (right) sounding for Phoenix at 5 am are below.\u00a0The observed sounding shows a subsidence inversion at 450 mb,\u00a0which the initialization smooths out. The initialization\u00a0shows slightly more moisture between the surface and 900 mb, but precipitable water differs by less than 0.2 mm between the two soundings.<\/p>\n\n\n

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HRRR-UA WRF 12Z (left) initialization and observed sounding (right) at Phoenix for 5 am this morning.<\/figcaption><\/figure>\n<\/div>\n\n\n

At 250mb, a\u00a0strong\u00a0short-wave trough extends from Nebraska\u00a0to northern New Mexico. The\u00a0subtropical high is centered over Pima County while a weak low-pressure system is west of Laredo.\u00a0<\/p>\n\n\n

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\"\"<\/figure>\n<\/div>\n\n\n

At 500 mb, the\u00a0short-wave trough in the Great Plains is just a little east of the 250 mb location, with the center of the ridge along the Colorado River south of Las Vegas.\u00a0<\/p>\n\n\n

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\"\"<\/figure>\n<\/div>\n\n\n

Dry air has dropped\u00a0into northern Arizona and New Mexico at 700mb, due to the circulation from the high centered in southwest Nevada and a front dropping southward in the Great Plains. Monsoon moisture into Arizona and New Mexico has been cut off.\u00a0<\/p>\n\n\n

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Today<\/h2>\n\n\n\n

The Nogales forecast for 2:30 pm is the only sounding in the region that has a profile capable of producing thunderstorms today.\u00a0The mixed-layer Convective Available Potential Energy (CAPE) is low at 210 [J\/kg], and the motion of the storms should be to the southwest.<\/p>\n\n\n

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HRRR-UA WRF 12Z forecast soundings for Nogales at 2:30 pm.<\/figcaption><\/figure>\n<\/div>\n\n\n

The 12Z HRRR-UA WRF forecast radar reflectivity shows the strongest storms in and near Santa Cruz County,\u00a0with lighter storms extending eastward into southern New\u00a0Mexico.\u00a0Tucson and Phoenix should remain dry; dewpoints are low today, and strong winds are unlikely.<\/p>\n\n\n\n