{"id":4477,"date":"2026-08-10T18:14:35","date_gmt":"2026-08-10T18:14:35","guid":{"rendered":"https:\/\/discussions.weather.arizona.edu\/?p=4477"},"modified":"2026-08-10T18:14:35","modified_gmt":"2026-08-10T18:14:35","slug":"august-10th-2026-thunderstorms-will-start-in-the-afternoon-in-the-tucson-area-with-a-second-batch-of-more-organized-thunderstorms-in-the-evening-from-graham-county-with-heavy-rain-and-strong-winds","status":"publish","type":"post","link":"https:\/\/discussions.weather.arizona.edu\/?p=4477","title":{"rendered":"August 10th, 2026: Thunderstorms will start in the afternoon in the Tucson area, with a second batch of more organized thunderstorms in the evening from Graham County, with heavy rain and strong winds associated"},"content":{"rendered":"\n

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

The subtropical high-pressure monsoon ridge at 500 mb is centered over northwest New Mexico, and temperatures at this level over western New Mexico and southeastern Arizona are cool enough to support thunderstorms. Surface dewpoints remain high, and despite boundary layer cooling from last night’s activity, convective temperatures are expected to be reached today in SE Arizona. Visible satellite imagery shows that while northwest Arizona has lingering clouds from recent storms, most of the region remains clear, and dry air persists in New Mexico. The National Weather Service has issued a flash flood watch for parts of southern Arizona. <\/p>\n\n\n\n

Forecasts indicate that thunderstorms will develop in eastern Pima and Santa Cruz counties this afternoon and move northwest, though they look relatively unorganized in the simulated radar reflectivity forecast. Another round of stronger, more organized storms moves into the Tucson area by 9 pm and continues northwest toward Phoenix. The greatest precipitation totals are expected in the mountains west of Tucson in central Pima County. Tomorrow’s activity is predicted to be extremely similar in its pattern and movement, though with more intense rainfall and greater 24-hour accumulations. <\/p>\n\n\n\n

By midweek, a trough from the polar jet will shift wind patterns and reduce monsoon moisture, with longer-range forecasts suggesting a return of the monsoon ridge after August 20th.<\/p>\n\n\n\n

Yesterday’s Weather<\/h2>\n\n\n\n

Yesterday evening, severe storms developed in central and western Pima County and then moved north into Maricopa County.\u00a0Below is the HRRR-UA WRF forecast at 12Z (left) and corresponding radar observations at 8\u00a0pm last night. \u00a0\u00a0<\/p>\n\n\n

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HRRR-UA WRF 12Z simulated radar reflectivity forecast for 8 pm (left) and corresponding MRMS mosaic composite radar reflectivity observations (right). <\/figcaption><\/figure>\n<\/div>\n\n\n

The 15Z forecast appears to have a better handle on the situation, though the forecast was certainly not perfect. The precipitation forecast for western Pinal County developed further west, and then the Phoenix and Gila Bend storms merged as the outflow boundaries collided.\u00a0<\/p>\n\n\n

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HRRR-UA WRF 15Z simulated radar reflectivity forecast for 8 pm (left) and corresponding MRMS mosaic composite radar reflectivity observations (right).<\/figcaption><\/figure>\n<\/div>\n\n\n

The infrared satellite image from 9 pm shows the huge storm near Gila Bend and the much smaller one in Phoenix.\u00a0<\/p>\n\n\n

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GOES-19 infrared satellite imagery from August 9th at 9 pm, College of DuPage.<\/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. The area in the green box was missed by the 12Z forecast, as well as isolated storms along the Colorado River.\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 August 9th.<\/figcaption><\/figure>\n<\/div>\n\n\n

The HRRR-UA WRF 15Z\u00a0accumulated precipitation, for the same time period, was better than 12Z.\u00a0<\/p>\n\n\n

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HRRR-UA WRF 15Z 21-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) for August 9th.<\/figcaption><\/figure>\n<\/div>\n\n\n

The Maricopa and Pima County\u00a0Flood Control Alert rain gauge data is below.\u00a0A storm\u00a0formed in northeast Phoenix and moved southwest to Buckeye.\u00a0Not all areas of Phoenix enjoyed the rain, and the heaviest rain did not fall until the storm passed Loop 303.\u00a0<\/p>\n\n\n

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

The Tucson area missed out on any significant heavy precipitation.\u00a0\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

The location of the strongest storm points to the reason why the forecasts had trouble with the additional storm development: the Gulf Surge moisture. No weather balloon was launched in Yuma at 5 am,\u00a0but the Yuma Doppler Radar\u00a0Velocity Azimuth Display Wind Profile did show the surge yesterday morning.\u00a0<\/p>\n\n\n\n

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

The Tropical Upper Tropospheric Trough (TUTT) over the Gulf of California may have aided the storms in Arizona, although it appears to be weakening as it moves slowly north now off the coast of San Diego. Another TUTT\u00a0is moving northwest from the southern tip of the Baja Peninsula.\u00a0<\/p>\n\n\n

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

The\u00a0visible satellite image from 8:20\u00a0am shows clouds\u00a0from last night\u2019s storm in northwest Arizona. Otherwise,\u00a0mostly\u00a0clear skies are over the rest of the region.\u00a0<\/p>\n\n\n

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

There is not much change from yesterday, with dry air in New Mexico and moisture in the southern half of Arizona. The NWS has a flash flood watch for Pima, Santa Cruz, and southeast Pinal\u00a0counties.<\/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 12Z HRRR-UA WRF forecast initialization (left) and the observed sounding\u00a0from Phoenix at 5 am (right)\u00a0are similar today.\u00a0Both have boundary layer cooling from\u00a0last night’s\u00a0storms,\u00a0though the heating needed to overcome this cool air is possible given today’s surface temperature forecasts.<\/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,\u00a0the TUTT near southern California\u00a0isn\u2019t visible on this analysis. Although there are two lows in Mexico annotated, only the TUTT over the Baja Peninsula is shown on the upper-level water vapor image shown earlier. The low over Chihuahua is a messy feature in the trough axis, not in the observational analysis. The TUTT\u00a0over Baja is also located further south than what appears on\u00a0the forecast initialization below.<\/p>\n\n\n

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At 500mb, the monsoon high-pressure has moved a little to the south and is more elongated across northern Arizona and New Mexico. Temperatures aloft remain around \u20136\u00b0C, which is cool enough to support thunderstorms in Arizona again.<\/p>\n\n\n

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At 700 mb, the monsoon high has moved a little further north than yesterday, but the general circulation remains the same.\u00a0<\/p>\n\n\n

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

The forecast\u00a0sounding for Phoenix (left) has thunderstorm development\u00a0around 7 pm this evening,\u00a0while the Tucson sounding (right) shows thunderstorm development at 3 pm.<\/p>\n\n\n

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HRRR-UA WRF 12Z forecast soundings for Phoenix at 7:30 pm (left) and Tucson at 3 pm (right).<\/figcaption><\/figure>\n<\/div>\n\n\n

Thunderstorms will form this afternoon in eastern Pima and Santa Cruz\u00a0counties\u00a0and move west into central Pima County\u00a0in the evening hours. Additional thunderstorms\u00a0will be dropping southwest from Graham and northwest Cochise\u00a0counties into Tucson around 8 pm this evening. These storms will then move northwest to the Casa Grande area by 10 pm and weaken as they move into Phoenix after midnight.<\/p>\n\n\n\n