Slightly cooler temps for Labor Day in the Valley

PHOENIX -- For the first time in days, the Valley is out from under an excessive heat warning as the Labor Day weekend arrives.

The warning was cancelled by the National Weather Service early Friday as clouds and outflow winds from distant thunderstorms over northern Mexico moved over the Valley, with a few sprinkles of rain. The Weather Service said the extreme 110-degree-plus temperatures of the past couple of weeks are not expected to return during the weekend.

However, temperatures still will be hot, with the average high over the three-day weekend forecast to be 108.5 degrees which, if it happens, would make this the eighth hottest Labor Day weekend ever in the Valley.

The hottest Labor Day weekend on record was in 1945, when the average high temperature was 110.8 degrees. The second-hottest was in 2009, with an average high of 109.5 degrees. The coolest Labor Day weekend was in 1909 when the average temperature was 88 degrees; the second-coolest in 1967 with an average of 92 degrees.

Although cooler, temperatures will still be above normal into the middle of next week. The chances for rain will be confined mostly to the eastern Arizona mountains through Sunday, spreading to most areas Monday through Thursday.

Thursday's high at Phoenix Sky Harbor Airport was 112, eight degrees above normal for Sept. 1.

Almost every heat record was shattered in August, with 117 on Aug. 26 the hottest ever for the month. The average daytime temperature was 109, also the highest ever.

August this year was the fourth hottest month on record in the Valley. The hottest ever was July of 1989, when the average daytime reading was 109.8 degrees.

The average overnight temperature in August was 87.4, the hottest ever.

Jessica Nolte with the National Weather Service said the lack of activity from the summer monsoon is responsible for the hot weather.

"We are not getting near the normals we like to see this time of year because we haven't seen the monsoon," said Nolte. "We haven't had a chance to really start our mornings off a little cooler due to precipitation."

State climatologist Nancy Selover said Arizona appears in for a warm winter.

"Predictions are definitely for warmer and drier conditions this winter" because of La Nina, she said.

"La Nina has a circulation pattern where we have high pressure that tends to block the storms coming down the southern California coast and then moving across into Arizona. Most of the storms tend to stay to the north of us."

A weak La Nina pattern right now is expected to strengthen and keep the fall and winter warm, she said.

"It's predicted to be above normal temperatures for September, October, November and then a little bit weaker, but still warmer than normal for the November, December, January period."