Monsoonal Moisture Fueling Southwest Flood Threat Through Late Week

August 3,2016
Following a relatively dry July, monsoonal moisture has returned to the Southwest for the start of August. The moisture will fuel the development of numerous showers and thunderstorms across the region through late week.
Impacts from those storms are what you would expect during the Southwest monsoon, including:

• Heavy rain and flash flooding.
• Strong wind gusts that may cause damage or contribute to blowing dust.
• Dangerous lightning.

Radar, Watches, and Warnings

Heavy downpours led to flash flooding in the Phoenix area late Tuesday afternoon. Several roadways in the area were closed due to the flooding, including Interstate 17, which caused a major traffic nightmare during the evening commute.
(MORE: Interstate 17 Closed in Both Directions As Heavy Rains Slam Phoenix Metro Area)

The area with the best chance to see thunderstorms the next couple of days includes much of Arizona, southern Utah, southern Colorado, New Mexico, southeast California and southern Nevada.
(FORECAST: Phoenix | Tucson, Arizona | Las Vegas | Needles, California)
The National Weather Service has issued flash flood watches for parts of New Mexico, Arizona, southwest Colorado, southern Utah, southern Nevada and a small part of southeast California.

Southwest rainfall forecast through Wednesday

Rainfall totals across parts of the Southwest, especially in Arizona, could range from 1 to 3 inches (with locally higher amounts possible). Be careful out there, and remember to not drive into flooded roadways.
The National Weather Service Forecast Office in Phoenix, Arizona, has issued a checklist for residents and visitors to the area.

• Make sure that your vehicle wiper blades are in good shape (no cracks or blades hanging off their holders).
• Have a fully charged cell phone handy.
• Allow extra time to get to your destination.
• Have patience on the road.
• Keep your attention focused and respect other motorists.

Monsoonal Storm Recap Since Last Week

The moisture began to return to the Southwest late last week.
Thunderstorms late Friday and Friday evening across the Southwest produced dust storms, wind damage and locally heavy rain, especially in Arizona.

• Dust storms, with visibilities near zero occurred in the Arizona counties of La Paz, Pinal, Yuma, Yavapai and in Riverside County, California.
• A wind gust of 89 mph was reported at Gila Bend, Arizona.
• Wind gusts to 70 mph in Phoenix, Arizona, knocked down power lines and over 25, 000 customers were without power for a time, according to Arizona Public Service.
• There was a report of 1.02 inches of rain just north of Scottsdale, Arizona.

Thunderstorms developed Sunday evening in Arizona, Utah and Nevada, and some flash flooding was reported in southeast Arizona and southeast Nevada, due to storms sitting over the same areas for multiple hours at a time.
Showers and storms developed again Monday across the same areas, with flash flooding reported in southern Utah due to slow-moving downpours.

Setup for Southwest Rain and Thunderstorms

Monsoonal moisture has been spotty across the Southwest over the past month, due to an expansive ridge of high pressure that has blocked moisture from flowing into the region. Some changes have occurred as the high shrinks and slides eastward.
This has allowed moisture, coming up from the south and southeast, to surge up into the Southwest U.S.

Moisture has pushed into the Southwest resulting in increased t-storm activity.

As we move through late week, monsoonal moisture will remain in place, and a few more disturbances will move from east to west across the region.