{"id":5117,"date":"2026-09-05T17:38:52","date_gmt":"2026-09-05T17:38:52","guid":{"rendered":"https:\/\/discussions.weather.arizona.edu\/?p=5117"},"modified":"2026-09-05T17:43:02","modified_gmt":"2026-09-05T17:43:02","slug":"september-4th-2026-generally-fair-weather-today-with-only-isolated-storms-in-the-eastern-arizona-mountains-the-moisture-axis-shifts-west-into-southeast-arizona-sun-mon-bringing-some-scattered-even","status":"publish","type":"post","link":"https:\/\/discussions.weather.arizona.edu\/?p=5117","title":{"rendered":"September 4th, 2026: Fair weather today with only isolated storms in the mountains of eastern Arizona. The moisture axis shifts west into southeast Arizona Sun\/Mon, bringing some scattered evening and overnight thunderstorms.\u00a0"},"content":{"rendered":"\n

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

Hurricanes Karina and Marie continue to move west across the Pacific, while Hurricane Lowell is expected to move north near the western Hawaiian Islands. Satellite water vapor imagery shows moisture transport from Baja California into southeastern Arizona and New Mexico around the subtropical high-pressure system. The subtropical jet will bring moisture sheared off from Marie into the region tomorrow. Satellite imagery and weather station data indicate reduced surface moisture in Arizona, lessening the potential for severe rainfall. New Mexico has more surface moisture, but warm mid-level 500 mb temperatures will limit the vertical extent of storms that develop. <\/p>\n\n\n\n

Forecasts show limited thunderstorm activity today, mostly in New Mexico’s mountains, with very few storms in Arizona. Tomorrow, monsoon moisture will shift west, bringing thunderstorms to eastern Arizona and west-central New Mexico, but rainfall is expected to be light, especially in western Arizona and southern Nevada due to dry surface conditions. Most precipitation will fall on Monday, primarily in New Mexico and south of the international border in SE Arizona. After Monday, no activity is currently being forecast through to next weekend.<\/p>\n\n\n\n

Yesterday’s Weather<\/h2>\n\n\n\n

Visible satellite\u00a0imagery overlaid with lightning and radar from\u00a04 pm\u00a0yesterday\u00a0shows showers and thunderstorms from southeast Arizona northeast into New Mexico. The strongest storms were near Sierra Vista and in west-central New Mexico. The western portion of Arizona had very low surface dewpoint temperatures.<\/p>\n\n\n

\n
\"\"
GOES-19 visible satellite imagery overlaid with radar reflectivity and GLM lightning from September 4th, 4 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.\u00a0The forecast precipitation looks about right, except for the southern part of Santa Cruz and the southern half of Cochise counties extending southward into Mexico.\u00a0<\/p>\n\n\n

\n
\"\"
HRRR-UA WRF 12Z 24-hour accumulated precipitation forecast (left) and corresponding observed precipitation from MRMS (right) for September 4th.<\/figcaption><\/figure>\n<\/div>\n\n\n

Precipitation reports from the Rainlog network are below. The heaviest rain was in Santa Cruz and Cochise counties in Arizona and in the mountains east of Alamogordo in New Mexico. Most valley locations had very little rainfall.\u00a0<\/p>\n\n\n

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

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

Hurricanes Karina and Marie are still moving westward across the Pacific Ocean while major Hurricane Lowell will begin moving northward and skirt the far western Hawaiian Islands.<\/p>\n\n\n

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

The polar low and jet stream (black\u00a0arrow)\u00a0are\u00a0maintaining\u00a0their\u00a0position in the Pacific Northwest. From tomorrow onward, Marie will begin to interact with the subtropical jet (red arrow), and mid- and high-level moisture will be pulled across western Arizona and southern California, bringing a few light showers. The monsoon moisture flow (green arrow)\u00a0is from northern Mexico into far southeast Arizona and New Mexico. An upper-level low covers the northern Gulf of Mexico.<\/p>\n\n\n

\n
\"\"
GOES-19 upper-level water vapor image September 5th at 8 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

The\u00a0visible satellite picture from 7 am\u00a0shows two flows:\u00a0the first is the monsoon flow from Mexico into southwest New Mexico, then bending to the northeast into southwest Kansas\u00a0(green arrow). The other flow is mid- and high-level clouds coming from Hurricane Marie into southwest Arizona\u00a0(red arrow).<\/p>\n\n\n

\n
\"\"
GOES-19 visible satellite imagery from September 5th at 7 am, College of DuPage.<\/figcaption><\/figure>\n<\/div>\n\n\n

Overall surface moisture has decreased in Arizona and slightly increased in New Mexico, as shown by 2-meter dew point temperatures from 7 am this morning.<\/p>\n\n\n

\n
\"\"
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. The observation shows a warm layer aloft between 530 and 490 mb, which will slow the rise of cumulus clouds this afternoon.\u00a0<\/p>\n\n\n

\n
\"\"
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 250 mb, the polar jet is across northern California into southwest Idaho. The subtropical jet is from northern Baja to northeast Arizona. The ridge has two centers; one in northern Mexico and the other in north Texas. The western part\u00a0of the low in the\u00a0Gulf of Mexico\u00a0is near Brownsville.\u00a0<\/p>\n\n\n

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

The polar jet extends\u00a0from central California into southeast Idaho at 500 mb. The ridge is\u00a0over west Texas and northern Mexico with a broad flow from the tropics into southeast California. An upper-level flow is\u00a0in southeast Texas.<\/p>\n\n\n

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

At\u00a0700mb, there is a fair amount of moisture south of the ridge, and some is moving northward into Arizona, but there is no strong flow.\u00a0<\/p>\n\n\n

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

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

Looking through most of the forecast soundings for Arizona and New Mexico, only a few soundings have a temperature and moisture profile that will support thunderstorm development. The mountains in New Mexico should have the best thunderstorm activity, though Flagstaff at 3 pm (left) shows that storm development is possible. Note that the High\u00a0Lonesome site (right) is southeast of Albuquerque, near Vaughn.<\/p>\n\n\n

\n
\"\"
HRRR-UA WRF 12Z forecast soundings for Flagstaff at 3 pm (left) and High Lonesome Ranch, NM at 3:30 pm (right).<\/figcaption><\/figure>\n<\/div>\n\n\n

Very few storms are in Arizona today, as shown by the forecast radar reflectivity animation. The strongest activity is in New Mexico, in the southern half of the state.\u00a0<\/p>\n\n\n\n