Pacific Cutoff Now Near Las Vegas

It is a pleasant, cool morning in Tucson, with buildups and some light showers in the area. Storms and showers were widespread yesterday, but mostly light. The ALERT network is down this morning. The high elevation RAWS stations reported around half an inch of rainfall this morning and Carr (in the Huachuca Mountains) had 1.01" during past 24-hours. Kingman, in northwest Arizona, had 0.95". Here at the house we had light showers after dark last evening, and there was 0.12" in the gauge this morning. This brings the September total over 2" here - so the first two weeks of September have proved wetter than either July or August.

This morning's 500 mb analysis from NCAR (above) shows the Pacific cutoff to be inland and centered just northeast of Las Vegas. Fairly strong southwest winds are present over Arizona, and the flow now has a fetch from the Pacific,with drier air being pulled into the circulation in the upper-troposphere. Note that the anticyclone has been pushed far to the south and is located along the Mexican GoM coast. A key question will be whether or not the anticyclone shifts north over the US again after 7 days. A dry-out seems to be on tap for tomorrow and rest of week - definitely a continuing Fall pattern.

This morning's Tucson sounding (above from SPC) has middle-level CAPE above 700 mb, so it is somewhat irrelevant as to how much surface heating we get today. Max wind speeds reach to near 80 kts aloft and strong southwesterly shear remains present in the troposphere. Bit more moisture and CAPE today, with continued cool temperatures, in middle levels, should bring an increase in storm activity for southeast Arizona. The early WRF-GFS forecast from Atmo forecasts an active day (rainfall through midnight forecast shown below) with heaviest amounts in a streak to our north. Once again, however, the WRF-GFS had early storms in the Tucson area that did not materialize - so caution advised. The latest NAM forecast is similar, but it forecasts heaviest rains along the Borderlands. But, another interesting weather day on tap.