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5:14 AM Tue, Nov. 20th

First measurable rain expected this week

Warmest, driest fall/winter ever for Prescott area

Pam Shannon and son-in-law Brent Bergman watch the kids play on the west steps of the courthouse during the rain in this 2010 image. (Courier, file photo)

Pam Shannon and son-in-law Brent Bergman watch the kids play on the west steps of the courthouse during the rain in this 2010 image. (Courier, file photo)

It’s been a long time coming for the Southwest, but the cold season’s first precipitation event is on tap for early this week.

“Models are in decent agreement and have been for the last three days, so our confidence is getting a little better with every new model run,” said Tony Merriman, warning coordination meteorologist with the National Weather Service (NWS) office in Bellemont, Arizona, mid-day Friday, Jan. 5.

Exactly when the event will occur is still a little up in the air.

“The only issue is timing,” Merriman said. “It could slow down and make it a Wednesday event, or it could speed up to make it a Monday event, but right now it looks like Tuesday afternoon and night looks to be the best chance.”

An update mid-day Saturday, Jan. 6, indicated that the forecast was still on track with Merriman’s statement.

Something that will likely accompany the precipitation is some moderate to high wind, he said. There may also be some snow at about 8,000 feet or higher.

“It’ll get to about 6,000 feet, but by that time, most of the precipitation will be east of here,” Merriman said.

There is a slight chance Prescott will get a dusting of snow early Wednesday morning, said Dave Byers, meteorologist with the NWS office in Bellemont, but there’s only a 20 percent chance of precipitation when that occurs.

Overall, the Prescott area should receive about a half inch of rain, Byers said.

Warm & Dry streak

If this forecast pans out, it will end an unprecedented weather streak in the Prescott area.

Between September and January, it has been both the driest and warmest in recorded weather history in Prescott.

In that time frame there has been 0.53 inches of precipitation, according to NWS records. The next lowest amount in that time frame happened in 2005 with 1.3 inches. The third lowest was in 1903 with 2.81 inches.

Looking at the average of the average temperatures between September and January, 2017 was the hottest with 53.9 degrees. The second hottest was in 1918 with 52.6 degrees. The third hottest was in 1997 with an average of 51.8 degrees for that period.

Contributing factors to this phenomenon are two weather patterns occurring this season. One is La Niña.

“We’re in a weak La Niña pattern, and that’s typically a drier and warmer than normal winter pattern,” Merriman said.

At the same time, there is another natural climate driver called the arctic oscillation.

“Basically it allows a lot of cold air to come in off the eastern United States,” Merriman said. “When you have low pressure to the east, you also have high pressure to the west. The combination of those two have been helping in keeping us dry and warm.”

While this has been the case so far, it’s not necessarily an indication of what’s to come later in the season.

For instance, in 1989, Flagstaff’s first snow of the season didn’t come until Dec. 28. By the time the season was over, 113.4 inches had fallen. Conversely, in 1935, the city’s first snow came on Dec. 27 and the season saw only a total of 16 inches.

“It’s really hard to tell what’s going to come,” Merriman said.