Hot And Dry In Southern Arizona

Conditions have been hot and dry over much of southern Arizona for the past 5 to 7 days. Here in Tucson the high temperatures the last two days were 102 and then 104F. Phoenix has been over 100F each day during past week, with hottest day coming yesterday at 111F (even hotter out at Yuma where it was 113F yesterday). Thunderstorm activity has been pushed far to the south over much of Mexico by the dry air. The plot of CG flashes above is for the 12-hours ending at 06 UTC today (August 31st). Most storm activity was down near the southern third of the GoC or along the Continental Divide - Sonora was almost thunderstorm-free yesterday.

Here in Tucson the GPS estimated PW has fallen steadily during the past 5 days and is currently well below an inch. The time series above shows GPS PW on campus, along with the 12-hourly PW from the TWC soundings, also taken on campus from the NWS Office.

The 12 UTC analysis of blended PW (from CIRA at Colorado State, above) indicates values of 1.5 inches are confined mostly to the south of about 30 degrees N. The 11 UTC analysis from CIMSS (University of Wisconsin) below indicates about the same. There is still a strong intrusion of very high PW from the tropics into the southern end of the GoC, and it will probably take a tropical disturbance to push the mT air back into the Southwest. The ECMWF does forecast the development of a weak, tropical low near the south end of Baja out at days 6 and 7, so this will be something to watch during the coming week. 

I used the ERSL interactive web page to take a look at GPS PW for the entire 2014 summer period, since June 20th through this morning. That time-series is shown below. After the jump to high values at the end of June, PW stayed mostly at and above 30 mm during July. The trace for August is more roller-coasterish with numerous ups and downs. The general trend during the last half of August has been down, except for the tropical increase associated with Hurricane Marie last week.