Rain could be plentiful or scant as systems approach Tucson area

Tucson could have very heavy rain this weekend, or not much at all.

It all depends on the way a trough over the Pacific Ocean, sliding down the coast from the Alaska area, ends up interacting with moisture from two tropical systems off Mexico’s coast.

At this stage, the more “dire” models with high-end forecasts show 3-5 inches of rain falling in the Tucson area this weekend, said Gary Zell, meteorologist with the National Weather Service in Tucson. The low-end models show less than a half-inch.

“It really all comes down to where the moisture will be, and how much will get sucked up ahead of the trough moving into the western United States,” Zell said.

If the trough moves more slowly, heavy rain could result in the Tucson area. If the trough moves fast, the rain totals will probably be much lower.

What’s pretty certain is that plenty of moisture will be in place across the region thanks to Hurricane Priscilla, which was off the tip of Baja California Thursday morning and forecast to eventually cross the Baja peninsula. As it breaks up, its remnants could slide over Southern Arizona.

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“The moisture is looking pretty good for Tucson for Saturday, Sunday and Monday,” Zell said.

In fact, there are low chances of rain Thursday and Friday, before they increase over the weekend.

Zell noted that the October 1983 storm that caused torrential rain and widespread flooding in the Tucson area was the result of a similar setup — tropical storm remnants interacting with a trough coming off the Pacific. But it’s too soon to know how this setup will play out, he said.

“Hopefully each day we’ll be getting more clarity on that,” Zell said.