Bit Of An Uptick Yesterday

Yesterday there were more thundershowers around than on Sunday. This was due to some slight increase in moisture and a bit of cooling in middle-levels (about 1.5C at 500 mb). Each model forecast I looked at during the day had somewhat different answers for eastern Pima County - my subjective feel is that the 12 UTC WRF-GFS had the best forecast, with more activity over the greater Tucson area, but basically all the models were struggling with the weak synoptic setting. The early WRF-GFS had forecast east winds through the day, but the winds became light and variable by noon. At 6 pm last evening 14 of the 93 ALERT network stations had received light, but measurable, showers (i.e., about 15% area coverage). This morning the total is up to 25 sites for rain during past 24-hours. Max amount was 0.83" at Whitetail up in the the Catalinas.

Today starts with an MCS still active over the northern end of the GoC (see 1415 UTC visible image above), and there are some associated showers out in western Pima County along the border. The 500 mb anticyclone has three circulation centers this morning: 1) over extreme northwestern Nevada, 2) along or just south of border south of Tucson, and 3) near Houston, Texas. Models shift the middle center northward over Tucson this afternoon. Certainly not a "dynamic" situation. Winds aloft are light and variable, but moisture is up a bit, and middle-level temperatures remain quite cool. It is unclear as to whether an outflow is moving northward into western Pima County. An outflow passed Puerto Penasco at around 5 am, but it did not appear to be very strong.

The early WRF-GFS again forecasts the most significant storm activity to remain over central and western Pima County - above is total forecast rainfall through midnight. However, the latest NAM (12 UTC run this morning) forecasts most storms and rainfall to occur over Cochise County, well to the east of what's forecast by WRF. The WRF 12 UTC runs may well have slightly different forecasts also. Basically a day to stay inside, in a cool spot, and observe what transpires during the afternoon.

The early WRF-GFS does forecast significant outflows this afternoon (see 10-m wind forecast valid at 8 pm this evening - below), so there remains a threat of strong winds late in the day. The eastern outflow, if it occurs, will bring significantly more moist air into all of Pima County.