The Southwest monsoon season kicked off June 15 and has wasted no time getting underway, as early-season monsoonal moisture continues to surge into the region and trigger the development of daily thunderstorms capable of producing flash flooding.
Deep tropical moisture from the Eastern Pacific, courtesy of Tropical Storm Celia, is being pulled northward by the upper-level winds over the southwestern U.S. and northern Mexico. This increase in moisture has provided plenty of fuel for thunderstorms to develop each day.
The first batch of monsoonal moisture arrived over Father's Day weekend. Albuquerque, New Mexico, exceeded its average June rainfall (0.57 inches) in just three days when 0.83 inches was recorded between Friday and Sunday.
This latest influx of monsoonal moisture will continue to produce scattered showers and thunderstorms across the Southwest and the southern Rockies through late week. The storms will contain locally heavy rainfall and pose the risk of flash flooding, especially across portions of southwestern Colorado and northwestern New Mexico.
NOAA's Weather Prediction Center has highlighted portions of the Four Corners region as having a risk of excessive rainfall each day through at least Thursday.
An additional half-inch to an inch of rain is possible in areas that see showers and storms on Wednesday, followed by another one-quarter inch to half-inch on Thursday. Many places have already received 1 to 3 inches of rain over the past few days, so soils are already overly saturated in these areas.
Flood Watches have been issued for parts of New Mexico through Wednesday evening.
Areas near recent burn scars will be most at risk for rapid runoff and debris flows, as well as areas where heavy rainfall occurs on successive days.
The radar loop below shows where showers and thunderstorms have been ongoing over the past three hours.
Any active Severe Thunderstorm Warnings are indicated in yellow, while any active Tornado Warnings are indicated in red. Additionally, any lightning strikes are depicted by the white lightning-bolt icons.
Monsoon season in the Southwest
The Southwest monsoon season begins June 15 and lasts through Sept. 30 each year.
Monsoon is a term given when winds blow tropical air toward typically desert locations, and Arizona and the Desert Southwest certainly qualify.
According to the National Weather Service, a ridge of high pressure in Mexico blocks any moisture from reaching the Desert Southwest in early June, allowing for days of hot, dry weather. Later in June and into July, the ridge drifts north into the Four Corners region of the U.S., allowing some tropical moisture to be carried northward from the Gulf of California and the Pacific Ocean.
Combine the desert heat with the copious amounts of tropical moisture, and you have a setup ripe for strong thunderstorms with torrential rain. What's more, northern Arizona is home to the Mogollon Rim, an area of high elevation that can provide the additional lift needed to trigger the development of thunderstorms that will often drift into the Phoenix area.
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