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Is western US heat so far this season a sign of what's to come for the rest of summer?


Brutal heat waves during June and July have led to record temperatures and raging wildfires across the western United States.

Does the searing heat signal what's in store for the region for the balance of the summer of 2017, or is relief on the way?

"The short answer is yes and no, and it depends on location," according to AccuWeather Lead Long-Range Meteorologist Paul Pastelok.

Static AP Image Thermometer June 2017

A local thermometer sign reads 120 F as temperatures climb to near-record highs Tuesday, June 20, 2017, in Phoenix. (AP Photo/Ross D. Franklin)


There is usually a surge of heat ahead of the North American monsoon.

The monsoon begins as a southerly flow of air develops over Mexico and expands over the western U.S. as the summer progresses.

The southerly flow pumps tropical moisture northward. The tropical moisture, in turn, pushes humidity levels higher. The higher humidity levels then lead to afternoon clouds and thunderstorms.

Static July West US


This moisture helps to regulate the heat. While brief spikes in heat can still occur, excessive heat generally does not last very long once the monsoon has begun.

Every year there is some variance to the monsoon in the start time, coverage and persistence.

The first weekend in July brought the first storms associated with the monsoon over parts of the Southwest. Early July is about the average time for the beginning of the monsoon.

"This year we believe that ample moisture will bring a generous supply of showers and thunderstorms from eastern Arizona and New Mexico to the central Rockies, but a lack of moisture may greatly limit the amount of thunderstorms in much of California, Nevada and western Arizona," Pastelok said.

Waters off the coast of California and northwestern Mexico are cooler than average.

"The cooler water may suppress thunderstorm activity in the western part of the southwestern U.S. this summer," Pastelok said.

Only on occasion will a few storms erupt in the afternoon over the Sierra Nevada and Cascades.

With less thunderstorm activity and drier air present, excessive heat may be a regular visitor to California, Nevada and part of Arizona.

Static AP Image Salvation Army

Salvation Army volunteer tried to keep cool while working at a special Salvation Army hydration station set up to help people try to keep hydrated as temperatures climbed to near-record highs, Monday, June 19, 2017, in Phoenix. (AP Photo/Ross D. Franklin)


The Northwest is also likely to experience sieges of hot weather through July and early August.

"However, storms from the Pacific Ocean may come calling a bit earlier than average later in August," Pastelok said. "The cloud cover and showers from the storms should trim temperatures later in the summer."

Static August West US


Excess snowfall from this past winter should ensure an ample water supply for much of the West into autumn. However, it is possible the setup could trigger a new drought for California as the year progresses.

The lack of rain, heat and dry air will result in an elevated risk of wildfires into the autumn.

How often does June weather help to predict the pattern for the rest of the summer?

The extent and degree of hot weather during July and August, following a hot June in the West, depends on a number of factors.

Probably the two biggest factors for the western U.S. are the monsoon and persistence. In absence of the monsoon coming to the rescue, as it will in some areas this summer, the cycle of drought and heat often takes center stage.

Heat and drought go hand-in-hand. The two often help each other to gradually build and expand into new areas.

As the soil dries out, more of the sun's energy is available to heat the ground. As the ground temperature increases, more moisture evaporates from the soil and so on.

For example, portions of the northern Plains were already struggling with abnormally dry to drought conditions from this spring to the start of the summer.

"An expanding void of rainfall may set the stage for a broadening area of heat and drought as the summer progresses in part of the North Central states," Pastelok said.

It usually takes a strong storm to break a prolonged pattern of drought and heat. In the summer and early autumn this could be from a tropical system. However, impacts from a tropical system are very rare in the Southwest, especially in California.

The late summer to early autumn is generally not the time of the year to expect relief from oppressive heat and building drought in the Southwest, away from the effects of the monsoon or a tropical system.

So while portions of the Rockies and Northwest experience some relief from summer heat by way of thunderstorms, portions of the Southwest are likely to swelter away much of the remainder of the summer.