Thursday, September 22, 2016
Trough Over Great Basin Impacts Arizona Through The Weekend
There were isolated showers over southeastern Arizona yesterday afternoon - as per radar/gauge rainfall estimates above from Maricopa County FCD. Two ALERT stations in Oro Valley area had light rain amounts yesterday afternoon and Ron Holle reported 0.37" at his house up there. The view to the north from campus at 3:00 pm MST yesterday (below) shows the developing shower near Oro valley at far left of image.
The forecasts from the 06 UTC WRF runs at Atmo again forecast very slight chances for isolated showers over southeast Arizona this afternoon and tonight.
I show two 500 mb forecasts here from the 06 UTC WRF-NAM forecasts. This morning 500 mb temperatures over Arizona (above) are warm with temperatures of -2C observed at a couple of spots. However, as near as central California temperatures within the cold, short-wave trough are as cold as -25C. As this short wave moves eastward into the northern Plains during the next several days an interesting evolution is forecast by the model. A region of very strong cold advection develops to the rear of the trough axis and digs southward toward our area. By midday Sunday a separate closed cyclone has developed nearly overhead with temperatures colder than -15C; quite a change. The ECMWF model forecasts are quite similar, so it will be interesting to watch how the pattern actually evolves this weekend.
Posted by Bob Maddox at 8:11 AM