Large Diurnal Temperature Range On December 16th

The low here at the house yesterday morning was 28 F, while the high at TUS (the Tucson airport) reached 78 F. A diurnal range over some parts of the city of about 50 F. Looks like more of the same today.

For the weather event coming at the end of the work week, I'll again concentrate on the 500 mb forecasts from the global models. The ECMWF (above is 500 mb forecast valid at 5 pm MST Friday afternoon the 20th of December) continues to be very progressive with the short wave, moving it to west Texas by that time and also continues with a weaker, trailing short wave. The GFS has become somewhat similar in the model runs last evening. Graphic below shows one of the GFS members (valid times are all the same here) that is similar to, and even a bit faster, than the ECMWF.

Three of the GFS ensemble members continue to be distinctly different, forecasting a deep, closed low holding to the west along and off the coast of northwest Mexico - see above. The GFS 500 mb spaghetti plot valid at this time is shown below. The spread of the forecasts is greatest from west of Baja northeastward across the Central Plains. The height differences between the two GFS members shown here is as great as 250 to 300 m west of Baja.

Regardless, 10 of the 12 GFS members forecast precipitation over southeast Arizona for the 12-hours ending at 5 pm Friday. So the models indicate a decent chance for a second December precipitation event before the year comes to an end.