Hottest weather of the year on tap for Vegas, Dallas and OKC
A large dome of hot air, responsible for many days of extreme temperatures, will expand westward from the southern Plains to much of the Western United States later this week, AccuWeather meteorologists say.
As the heat expands, the frequency of thunderstorms will diminish over the Southwest, while some places over the southern Plains that have dodged rain for weeks could have an opportunity for a downpour.
The extreme heat was produced by the persistence of a large northward bulge in the jet stream. When combined with a lack of rain, there have been a substantial number of days and locations with highs of 100 degrees Fahrenheit or greater so far this year.
While the ongoing and upcoming heat from the south-central to the southwestern United States may seem typical for July, temperatures will be 5-10 degrees above average for most locations through next week.
Abilene, Texas, will blow past 40 days of triple-digit heat so far this year as the heat maintains its grip this week. That is well above the annual average of 15 days and a total of eight days from the entirety of 2021.
San Antonio has already accumulated more than two dozen days of 100-degree temperatures so far this year, compared to an average of nine such days, according to AccuWeather Meteorologist Nicole LoBiondo.
Last year, the Alamo City did not hit 100 until Sept. 6. The record for days with century-mark highs or greater for San Antonio is 59 from 2009. It is possible that this year will move into the top five in terms 100-degree highs or better for the city. Number five on the list was set in 1938 with 33 days.
Dallas has had plenty of days with 100-degree highs so far this year with 13 as of July 6. The city averages about 20 days per year and is already ahead of 2021, when there were only eight days with triple-digit heat, according to LoBiondo.
The same heat dome has also been contributing to the lack of rain chances in the region.
Oklahoma City has gone more than two dozen days without more than a few drops of rain. Dallas averages 3.71 inches of rain from June 4 to July 4, while Oklahoma City averages 2.79 inches of rain from June 10 to July 4.
"The last time there was more than a trace amount of rain in Dallas was on June 4," LoBiondo said.
The core of the heat will expand and build over the interior West, but enough of the heat dome will remain over the southern Plains to continue to bring more days with 100-degree highs. In some cases, temperatures will throttle upward and potentially eclipse season-high marks. Dallas could surpass the 103-degree mark for the first time this year over the next seven days.
After Oklahoma City reached 100 on Tuesday for the first time this year, a second day in the triple digits was observed on Wednesday. Multiple, additional days with triple-digit highs are possible. Temperatures will have a chance of reaching the triple digits daily through early next week.
As the core of the high pressure area responsible for the heat dome inches westward, the same jet stream dip that has fueled thunderstorms from the northern Plains to the Southeast states will also inch westward.
It is possible that the jet stream may shift far enough to the west to allow a weak front to drop southward over the southern Plains. While this front is not likely to have enough influence to bring a significant cooldown to states such as Oklahoma, Texas and Louisiana, it could set off spotty thunderstorms this weekend.
Even though beneficial rain from the front appears to be highly unlikely, there is a chance for some locations to receive their first measurable rain in weeks.
Heat to throttle up over the interior West
While the weather is already hot in many areas, daytime highs are likely to increase by several degrees in cities such as Phoenix, Las Vegas and Denver.
Las Vegas, which has not hit the 110-degree mark so far this year, could do so either during the weekend or early next week.
Phoenix is likely to match highs in the 110s from mid-June, which occurred prior to the onset of the North American monsoon and the thunderstorms it helps to deliver. Denver hit 100 F for the first time back on June 11, and the Mile High City could give the triple digits another run this weekend.
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Salt Lake City has hit 100 four times so far this year. Three days occurred during the middle of June before the monsoon got up to speed. Multiple days with highs at or just above 100 are possible starting this weekend through much of next week, forecasters say.
"The westward shift and expansion of the heat dome will lead to a downtrend in the number and coverage of thunderstorms associated with the monsoon in the coming days," AccuWeather Long-Range Meteorologist Brandon Buckingham said.
Some locations likely to experience a drop in the number of showers and thunderstorms include Flagstaff, Arizona, and Albuquerque, New Mexico. Flagstaff has received 1.13 inches of rain since June 15, compared to an average of 0.40 of an inch for that timespan, while Albuquerque has picked up a whopping 2.38 inches of rain compared to a more typical 0.56 of an inch of rain.
The same shift in the weather pattern that will bring an uptick in the heat for the interior West may help to turn off the firehose of rain in much of Montana. Multiple locations in the Big Sky State, including Yellowstone National Park, have been hammered with bouts of torrential rain and flash flooding in recent weeks. Helena, Montana, was hit by flash flooding this past weekend.
"The pattern change will create a drier, more westerly flow of air across much of Montana, instead of a plume of moisture from the south starting this weekend," Buckingham said. "While there can be some gusty thunderstorm activity, the risk of flash floods should be considerably lower."
Some leftover moisture will remain trapped beneath the heat dome and will likely get recycled in the form of spotty gusty and highly localized drenching thunderstorms, AccuWeather forecasters say.
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