Monsoon promises much-needed rains for the parched west, but prospect of lightning could mean more fires


After enduring heat waves and years of minimal monsoon humidity, the desert southwest appears to be back with an already above-average monsoon season.

The region expects to see below average temperatures throughout the week due to precipitation, providing welcome relief after extreme heat in early summer.

Cooler temperatures and widespread rainfall could help satiate the parched soil, and the WPC expects the drought to improve.

The southwest monsoon rains continue

Monsoon thunderstorms this week are expected to continue to bring vital rains to the region. On Monday and Tuesday, rain showers and heavy thunderstorms will extend from Arizona to the Grand Bassin.

“Isolated to scattered thunderstorms will develop again over the higher terrain around noon before drifting into the valleys later in the afternoon until the evening,” said the National Weather Service (NWS) in Las Vegas.

The main threats associated with the strongest storms will be heavy downpours causing flash floods and strong wind gusts of up to 50 miles per hour that could produce dust.

As the week progresses, monsoon moisture will be centralized over the Four Corners, extending slightly northward into parts of Wyoming by the end of the week.

Rain totals on Thursday and Friday increase, with up to an inch and a half of precipitation per day in some areas. Heavy rain spreads Thursday and Friday, when Utah, western Colorado and western New Mexico will experience slightly higher rainfall totals than at the start of the week.

“The southwest monsoon is expected to remain fairly active for the foreseeable future and bring much-needed rainfall to this part of the country. However, the potential for flash flooding will also continue in isolated places in the southwest and central Grand Pelvis, especially on burn scars. ”WPC said.
The bulk of the precipitation is expected to hit Arizona, an area in desperate need of substantial relief after decades of drought. Up to 5 inches of rain could fall in parts of the state during the week, with locally higher totals where stronger storms pass.
“More scattered or even widespread storms are expected for the second half of the week as a more organized weather system could affect the region. The storms will be able to produce both locally heavy rain, strong winds and dust.” , the NWS said in Phoenix. mentionned.

Flash flood watches have been issued in four southwestern states, including California, Nevada, Utah and Arizona, in effect until Monday afternoon and evening due to potential flooding lightning in areas with localized heavy precipitation.

A flash flood killed a visitor to the Grand Canyon.  Drought in southwest could worsen monsoon flooding

Flash flooding became a major problem in Arizona and Utah last week, resulting in scenes of cars sweeping neighborhood roads at the foot of whitewater and train derailments resulting in injuries.

Burn scars from wildfires in the region are of most concern for flash floods – after a fire incinerates a swath of land, the soil left behind is hydrophobic, acting more like concrete than a sponge. Rainwater then drains easily from the burnt soil, sometimes drastically, causing flash floods.

The rain brought in by the monsoon season is a sigh of relief, but lightning from stronger thunderstorms could cause more harm than good, producing more fires and leaving more scars from burns.

More lightning could mean more forest fires

Statistics from the National Interagency Fire Center show that on average from 2008 to 2012, 12% of forest fires were started by lightning while most were man-made, but fires started by lightning burned nine times. more hectares on average than man-made fires. .

Four large fires are currently burning in Arizona, and dry vegetation due to the drought could be of concern to lightning from monsoon thunderstorms. Fortunately, most storms will contain a lot of rain and humidity, the biggest threat being flash floods.

“Scattered to widespread wet thunderstorms are expected to continue in the southwest, southern Great Basin and southern Colorado,” the National Interagency Fire Center said.

This monsoon season has been more active than the 2019 and 2020 seasons, but the Phoenix NWS points out that there have been a lower than average number of lightning strikes since 1990 – a good thing for extremely active fire season.

A different story could play out this week in the Grand Bassin and the Northwest, where dry thunderstorms are expected to cause forest fires on Monday and Tuesday.

“Although of high base, these storms are expected to produce predominantly wet strikes. Nonetheless, the fuels are extremely dry / record high over much of the northwest. Efficient lightning-induced ignitions are possible with drier strikes at the top. periphery of storm cores, which justifies maintaining a large isolated dry storm peak, “said the Storm Prediction Center.
Monsoon rains bring wet thunderstorms to the southwest while the northwest could see more lightning-ignited forest fires during dry thunderstorms

Northern California and southern Oregon will experience high fire weather conditions Monday due to the potential for dry thunderstorms in an area already devastated by the country’s largest wildfire.

The Bootleg Fire, located near the California-Oregon border, devastated more than 300,000 acres of forest. Firefighters said it might take a significant weather event to put it out.

“We are experiencing extremely dry conditions with record to near record temperatures. Ground conditions due in part to historic drought have accelerated the fire season. Fire spokeswoman Katy O’Hara told CNN.

Ready to evacuate in Oregon as massive Bootleg fire surpasses 300,000 acres

“The extent and magnitude of the Bootleg fire will necessitate a late season weather event, such as a major storm that is either widespread wetting rain or snow, which in southern Oregon is typically produced in late fall, ”O’Hara said.

Conditions this week do not appear favorable to help with the firefighting efforts, and lightning from dry thunderstorms could make matters worse.

“Isolated dry thunderstorms can also form in northern Idaho and western Montana with very hot, dry and unstable conditions in the Pacific Northwest, Rockies and plains from north to north of Minnesota and north of the Great Basin, ”the NIFC said.

The SPC has highlighted a critical fire danger in eastern Montana as winds pick up during an episode of record heat. Montana currently has 14 major wildfires, the most in the country just above Idaho with 13.

“During the afternoon, sustained southeasterly surface winds at 20 mph will likely overlap with 15-20% relative humidity for at least a few hours. Although the winds are somewhat marginal for the critical strengths, a critical zone has been maintained for parts of eastern Montana in far northeastern Wyoming given the presence of critical / record dry fuels, ”the SPC said.

Red flag warnings cover the northwest where dry thunderstorms, gusty winds and warm temperatures increase fire risk

More than 3 million people are included in red flag warnings in the northwest and northern Great Plains on Monday amid high fire danger. Almost all of the states of Idaho and Montana are on a red flag warning, and the excessive heat warnings encompass all of eastern Montana where temperatures climb into triple digits again to start the week.

Overall, the 2021 U.S. wildfire season crushed the record-breaking 2020 season, with more than 2.5 million acres (roughly the area of ​​Connecticut) burned compared to 1.8 million acres in the same time last year.

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