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Heat eases across the West this week; Thunderstorms increase in the Northwest

August 07, 2019; 12:35 PM

Temperatures have soared across the West over the first part of this week, but some "cooler" days are ahead later this week as there will be a pretty noticeable change in the weather pattern.

On Monday, Palm Springs hit a season-high temperature of 121 degrees, while Phoenix reached 115 and Las Vegas topped out at 113.

The extreme heat in Palm Springs created a huge difference in temperature from the Pacific coast to the Coachella Valley.


There has also been a surge of warmth into the Pacific Northwest, with highs approaching 90 in Seattle and getting into the 90s in Portland. East of the Cascades, it's about as hot as it's been all year with triple-digit heat being recorded in many areas.

The heat has been largely thanks to a ridge that has been in place over the West. There have been a few disturbances moving along the western side of the ridge, which has been touching off some spotty showers and thunderstorms from Arizona back into some of the high terrain and deserts of Southern California.

Things will be changing through the second half of the week, though, as the ridge begins to collapse and slide to the east. This will be in response to pretty large trough digging into the West.

The reversal from Wednesday...

Western ridge to trough 8/7

to Saturday...

Western ridge to trough 2 8/7

is pretty remarkable. This is a pretty sizable trough for this time of year.

The trough coming in will squash the heat and bring down afternoon temperatures by as much as 10 to 20 degrees across the West, with the biggest change across eastern Washington and Oregon.

Northwest Cooldown 8/7

Even as the ridge collapses, there will be enough pieces of energy moving northeastward to help fire up some thunderstorms in portions of Arizona and Southern California on Wednesday afternoon, with much lesser coverage by Thursday.

The incoming trough will contain the monsoonal thunderstorms to the higher terrain of the Four Corners region, generally keeping storms out of the deserts through the weekend.

Meanwhile, in the Northwest where most of the energy with the trough will be passing by, there will be a few waves of showers and thunderstorms moving through.

The storms will bring some much-needed rain to some areas, but also the potential for flash flooding and strong winds with the stronger storms. Looking at the precipitable water values (a measure of how much moisture is in the atmosphere), there are some noticeable surges east of the Cascades from Friday into Saturday.

Precipitable Water Northwest 8/7

Those are some pretty impressive values for this area. The record PWAT value in the Spokane area is around 1.5 inches, and there will be the potential to get pretty close to that value into the weekend.

Any showers or storms in eastern Washington may help clamp down on some of the smoke from the Williams Flats Fire, especially with this added moisture to work with. That fire has been spreading smoke into Spokane and portions of Idaho and Montana this week.

Even though the rain may help, dry thunderstorms will once again be a concern, and the lightning could start new fires across the Northwest through the weekend. With the potential for strong winds, any fires that do start could spread rapidly.

Because of this threat, Red Flag Warnings will be commonplace across the interior Northwest right on through the weekend.

Zonal Flow early next week 8/7

Heading into early next week, the flow will turn very zonal across the entire United States, which will bring drier weather to much of the West. Any systems will move through quickly, and the monsoon will be quieter overall. Temperatures for most places will be pretty close to seasonal averages.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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