Late August Desert Monsoon

[azskyman]

Here in south central Arizona, it has become an active time again for the monsoon. Powerful thunderstorms have roamed at will through the valley of the sun the last week or so, and the most potent of all swept through from NE to SW on the evening of the 28th.

Winds were measured at 80 mph at the NWS Phoenix office, and reports of downed trees and damage seemed to be quite widespread. Unlike many monsoon storms, these were on a deliberate trajectory from NE to SW across the city and county, adding to the outward downbursts ahead of the storms.

I have had near 2" of rain this week during this humid spell, with .78" falling from storms with near continuous lightning last evening.

Quite the show for us desert-dwellers, with more on tap through the weekend.

[TMT]

A report on the storms from the Arizona Republic:

Hurricane-force winds, heavy rain hit Valley

Aug. 29, 2008 06:00 AM

Republic staff, wire reports

A series of fast-moving thunderstorms packing hurricane-force winds plowed through the Phoenix area late Thursday night, uprooting trees, knocking down power poles, ripping off roofs and leaving some 100,000 homes and businesses without power.

There were no immediate reports of injuries.

Arizona Public Service Company said it still had 50,000 customers without electricity early Friday, while Salt River Project estimated 11,000 of its customers were without power.
The storm, which dumped up to a 1.5 inches of rain and three-quarter-inch hail in some areas, shut down Sky Harbor International Airport for about an hour during the height of the storm. Flight delays continued early Friday as crews worked to remove debris blown onto the runways.

National Weather Service meteorologist Leslie Wanek said Sky Harbor recorded peak winds of 75 mph , but radar indicated that winds of up to 100 mph in parts of the metro area as the severe storms moved from east to west during about a 3-hour period.

Flash-flood warnings were issued for the central and East Valley, and residents in Phoenix reported flooding and severe winds that bent palm trees.

The storm damage included Arizona State University's $8.4 million indoor practice facility, said Mark Brand, ASU's assistant athletic director for communications.

The 103,500-square-foot facility was just completed this month. It's a bubble of fabric supported by air pressure, the ASU official said.

Russell Schilt, a 22-year-old ASU student, said he walked about the school's practice facility to see the bubble roof in shreds from the storm. Schilt said he was surprised at the damage the new building took.

"If this isn't the biggest event in the monsoon season, it's right up there," said Ken Waters, a meteorologist for the National Weather Service.

On Thursday, the ingredients for a powerful storm had been hovering over the Valley, but it takes special conditions to break the weather cap, he said.

On many days, the weather system passes with few fireworks, Waters said. On other times, like Thursday night, something powerful happens.

"When you get enough heat and certain conditions are just right, it's like breaking though a roof," Waters said.

Hail was reported in Tempe, Mesa and Maricopa, he said.

In Phoenix, a power transformer exploded on Seventh Street near McDowell Road, in the same area where downed poles and trees surrounded stranded vehicles.

Power poles and lines were down on 40th Street in Phoenix at Shea Boulevard and Cactus Road, forcing drivers heading west to the Arizona 51 to travel to Thunderbird or Greenway.

Hundreds of lightning strikes were seen throughout the late evening in the central Scottsdale area; downed trees littered the Shea Boulevard corridor.

Residents of the Monte Vista Apartments stood next to a 40-foot pine tree that was ripped from the ground. The residents talked about the night's storm as the tree's roots shot into the sky.

"It's the worse storm I've ever seen and I've lived here my entire life," said Alec Perkins, 23. "The tree wasn't split in half, it was completely uprooted."

Concertgoers at the Cricket Pavilion said their show was interrupted by the storm's fireworks.

"The show on the stage is nothing compared to the one in the sky," said Lane Baysden, 35, of Phoenix. "It was about as windy as God would want it to be for Judas Priest."

Commuters can expect an overcast sky this morning, the meteorologist said.

Republic reporters Jahna Berry and Scott Wong contributed to this story.

[Aslkahuna]

Reflectivity values displayed on the UofA radar display on their Atmo site exceeded 69 dBz. Yuma Proving Ground had gusts to 62 mph when the storms came through around midnight. In many respects this was like the August 14, 1996 event which had recorded winds of 115 mph at Deer Valley and a tornado in Tucson.

Steve