An Uptick

Low-level moisture has slowly increased over southeast Arizona (see plot of GPS PW trend at TWC) since mid-day yesterday, essentially south of line from Douglas to Oro Valley to Sells and out through Why. Morning dewpoints today are 10 to 20F higher than yesterday morning and surface pressures are up 2 to 3 mb – so some good and some bad in the obs. There has been weak southerly to easterly flow aided by outflows from storms along and south of the border. There does appear to be a weak surge signal in low-levels of the Guaymas sounding this morning. But overall it’s a pretty chopped up synoptic pattern, with mostly westerly flow over the southwest U.S. at 500 mb. Definitely more CAPE along the borderlands today. If Tucson were to mix out to 8 or 9 g/kg this evening there would be a silver of CAPE here at lower elevations.

The NAM indicates that today will be a day of adjustment at 500 mb with the small anticyclone center that’s over northwest Sonora this morning trying to consolidate over New Mexico. The main center remains over the far southeast U.S. A weak inverted trough extends from southern end of Gulf of California to the bootheel of New Mexico. The NAM continues to strengthen this trough some and move it slowly up into southeast Arizona. If this indeed occurs, it will help push moisture and outflows northward and that could lead to considerably more storm activity this evening and especially tomorrow. The NAM appears to have a convective feedback effect going between noon and midnight in the area between Nogales and Green Valley, where the model forecasts a rain bulls-eye of around 3 inches. So, we should keep careful watch to the south today to observe whether the model has latched onto something other than an internal convective runaway.

The NAM forecasts a substantial increase in moisture and precipitation on Wednesday and Thursday, as it apparently shifts the subtropical air northward for a couple of days. So, it looks like a week of much increased possibilities for rainfall than what we’ve experienced in past several days. In the longer term, the ECMWF is again very aggressive with the next Pacific trough and brings it inland across all of the west, putting the Fall-like pattern back into play.