No rain in September or October

  Rain sucks!!! I love this weather! First time in 35 years that we didn't have any rain in October or September. Let's hope we don't have any in November or December!!!


November 3, 2008 - 6:05PM

Parched fall follows wild, wet monsoon in Valley

Mike Branom, Tribune

From deluge to drought practically overnight. In the aftermath of a violently wet monsoon, the Valley's weather went to the other extreme during September and October.

No measurable rain fell during those two months for the first time in 35 years, and only the fifth time in the recorded weather history of Phoenix, the National Weather Service said.

Previous years with no rain are 1906, 1938, 1953 and 1973.

On average, with climate data collection beginning in 1895, Phoenix receives about 1.3 inches of rain during September and October. September is typically the wetter of the two months.

But this year only trace amounts fell, on Sept. 8-10 and Oct. 4.

This drought is all the more notable for how it came after the 10th-wettest monsoon in Valley history. Between June 15 and Sept. 30, the official rain gauge of Phoenix took in 5.7 inches; the usual amount is less than half that.

The monsoon ended with a bang - a night of bangs, actually.

On Aug. 28, a series of thunderstorms pummeled the Valley, dropping 0.94 inches of precipitation in an evening.

But after that, just 0.04 inches fell over the next two days before nature's faucet completely shut off.

And what's a dry spell without heat? Both September and October were warmer than normal, ranking ninth and 16th, respectively, in terms of average temperature, weather service records show.

If there is any silver lining to the Valley's lack of clouds, it is that no statistically significant connection between fall and winter precipitation has been found.

However, the federal Climate Prediction Center is forecasting an increased likelihood of below-normal precipitation in Arizona this winter.

For Phoenix, there is approximately a 45 percent chance for below-normal rainfall (less than 1.5 inches), a 34 percent chance of near-normal precipitation (1.5 to 4 inches), and a 21 percent chance of above-normal precipitation (more than 4 inches).


Monsoon season ends, ranks as 10th-wettest

Mike Branom, Tribune

Measuring a summer's worth of rainfall in a bucket is easy. But try putting a number on the excitement generated by the just-concluded monsoon season.

One July afternoon, U.S. 60 flooded. Another evening in August, there was so much lightning from what a weather expert labeled a "gorilla thunderstorm" it seemed the Valley's skies had shorted out. Add to this the tree-toppling, roof-ruining wind, and no wonder the plentiful precipitation seems an afterthought.

"From a meteorologist's point of view, it was a very exciting, very eventful and very challenging season, because we had some very hairy storms," said Tony Haffer, who is responsible for the local National Weather Service.

Very wet storms, as well.

The monsoon that concluded Tuesday dumped 5.70 inches of rain in the Valley's official rain gauge, making this the wettest summer since 1984 and the 10th-wettest in the Valley's recorded meteorological history, according to the National Weather Service.

In an average monsoon, the rainfall total at Phoenix Sky Harbor International Airport is 2.77 inches. But that mark was passed in early August.

"It was a matter of all the ingredients coming together," Haffer said. In this case, tropical moisture was plentiful and ready to react with the summer's heat.

Consider that on July 13, the day when more than 2 inches of rain fell on west Tempe and Guadalupe in an hour, the dew point was 75 degrees - 20 degrees above the former benchmark for monsoon conditions.

Even more, in 2008 the roulette wheel of weather chose the area near the airport as the storms' preferred destination. This quirk of fate, which Haffer chalked up to the monsoon's hit-or-miss temperament, ensured high rainfall totals would be not just noted but forever recorded.

A check of the rain gauges monitored by the Maricopa County Flood Control District reveals a pattern to the near-nightly flashes of lightning and crashes of thunder.

This summer, seven rain buckets took in at least 6 inches of rain, and these are located in a rough circle with the airport at the center.

"Mother Nature, in the summertime, is that of showery weather; one place can get deluged where a place close by might just have some light rain," Haffer said.

Haffer himself was responsible for one of the monsoon's biggest developments: specific start and end dates.

Tired of people stumbling over the traditional definition of the monsoon's arrival - three straight days of at least 55 degrees dew point - Haffer decided the season now will run from June 15 through Sept. 30.

One benefit is standardization in year-to-year rainfall comparisons. But Haffer said he'd like to hear from the public whether it made a difference to them.

Also ending Tuesday was the "water year" of Salt River Project. The water and power company measures precipitation in a span from October through September, as this doesn't arbitrarily cut winters in half.

During the most recent water year, Phoenix received 10.5 inches of rain, more than 27 percent above average. And in the high country, runoff from bountiful snowfall filled SRP's reservoir system to the brim.

"Our three rivers - the Salt River; Tonto Creek, which feeds into Roosevelt (Lake); and the Verde River - typically see about a million acre-feet of runoff in a given year," SRP hydrologist Mark Hubble said. "This water year, it was closer to 1.8 million."

The total amount of rain and snowmelt ranked as the 19th-best in Salt River Project's 105-year history

All this in a water year forecast to be drier than average.

Hubble noted the winter began with La Niņa conditions, when the waters of the tropical Pacific Ocean are cooler than usual. During these times, Arizona's winters are usually dry and warm.

"Turns out, we ended up getting a lot of precipitation, but it came pretty fast and produced a lot of runoff," Hubble said.


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