Serious Start Of Summer Storm Season Setting Up

A large plume of middle and high cloudiness stretches from the south end of the GoC northward to southern Utah this morning (see visible image above for 6:30 am MST, 1 July 2012). At sunrise there were virga and a few light sprinkles from the southwest to the northwest of Tucson. The northward push of the cloudiness is being helped by a weak short-wave over the lower Colorado River Basin. Conditions were quite suppressed yesterday afternoon, as dry air from the northwest prevailed along with perhaps some subsidence east of the residual MCV that moved from Sonora across far southwest Arizona.

This morning's Tucson upper-air sounding (below) exhibits a severe super-adiabatic layer (more bad RRS data into the archives) just below 400 mb. The sounding basically has no CAPE; warm middle level temperatures; and a very chaotic wind profile that has no speeds of significance - quite pathetic.

However, there is a strong upper-tropospheric cyclone (see NAM 250 analysis for 12 UTC this morning below) that is moving westward across central Mexico. This feature is forecast by the NAM to move over the southern end of the GoC and then move northward into the Southwest. It is this feature, and associated MCS activity that will trigger a push of deeper, low-level moisture north of the border. At 500 mb, the northern part of this cyclone will move into southern Arizona, assuming the model forecasts verify, and trigger increased thunderstorm activity and a serious start of the summer storm season [aka monsoon]. Art Douglas forwarded a five-day forecast from the ECMWF that showed a large band of heavy precipitation amounts of 2 to 5 inches from near Prescott deep into Mexico for the period ending 8 July.

This morning's WRF-GFS forecast of CAPE valid at 3 pm this afternoon is shown below - little CAPE and very little convection forecast. The model forecasts increased storm activity tomorrow, mostly east and south of the Tucson area. Then the model forecasts a significant increase in moisture and much expanded storm activity on Tuesday afternoon the 3rd. Timing will be critical and the models often are slow in forecasting the northward push of moisture as features such as the cyclone at 250 mb (above) approach the GoC. Thus, a careful watch will be required, since features tomorrow could come together better than the current forecasts indicate. With so many features in play, forecasts beyond two days become very difficult, since each days weather events will impact strongly the next day's storm potential.