Showers On Thursday?

First, a quick look at some low temperatures, which have been bouncing all over the place inside the City of Tucson. Yesterday morning it was very cold here at the house, with a moderately heavy frost. Low temperature hit 21 F (versus 32 F at TUS and 33 F DM AFB). Winds here went calm again last night and the low dropped to 23 F, but east to southeast winds during the night kept south portions of the city considerably warmer. Low at airport was about 39 F, while DM remained even warmer at 45 F.

The models forecast a chopped up 500 mb pattern over the Pacific to evolve into a strengthening short wave over the Southwest by Thursday this week. However, there remains considerable variance among the various models, even at the relatively short-term, 72-hour forecast time. The GFS ensemble forecasts at 500 mb (from 00 UTC last evening) are shown above valid at 12 UTC on Friday, January 10th. The uncertainty in the ensemble forecasts is small, except over Arizona and the Southwest.

The new NAM forecasts this morning forecast little in the way of precipitation over Arizona through 12 UTC on Friday (above). The operational GFS from last evening, however, forecast a fairly large area of precipitation accumulating over much of Arizona through the same period. So some chance of the first precipitation of the New Year later this week, but considerable uncertainty still in the cards.