Coldest Morning Of Fall Here

Coldest morning of year so far this Fall here on north side of Tucson along the Rillito Wash. Low temperature here at house fell to 21 F, making the morning 4 F colder than the lows on the 17th and 18th. There is a light touch of frost on roofs, cars, and trash bins, even though dewpoints are very low. Quick look at early WRF indicates that the model forecasts this to be the coldest morning, with temperatures up a bit tomorrow because of easterly winds. That will probably be tough to call, since some low spots may go calm, with colder temperatures than model forecast. The two plots are from MesoWest and show plots of surface conditions at about 7:30 am MST. Above is broad view and below is zoomed on Tucson metro. Many temperatures around in the 20s, with some teens over toward Benson. One station was reporting 10 F, but that looks suspicious.