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Excessive Heat Warning

Wildfire risk to persist even as West Coast throttles back from unusual June heat wave

By Alex Sosnowski, AccuWeather senior meteorologist
June 16, 2019, 10:20:02 AM EDT

While Pacific coastal areas settle back into a cooler, more typical June pattern, the recent heat wave has increased the risk of wildfires and flooding at the same time across the interior.

The recent heat wave sent temperatures soaring up to 30 degrees Fahrenheit above average into the 90s and over 100 in some coastal areas from California to Washington, shattering record highs. Meanwhile, highs climbed well above normal into the 60s, 70s and 80s over the mountains.

"A more typical weather pattern that favors a persistent sea or bay breeze with areas of morning low clouds has settled in along the coast," according to AccuWeather Senior Meteorologist Brett Anderson.

Sat SW heat June 14

The pattern is known to locals as "June gloom."

Temperatures will hover within a few degrees of average along much of the California coast this weekend.

"Farther north, temperatures will be between 5 and 10 degrees above average in many areas west of the Cascade Mountains in Washington and Oregon through this weekend," Anderson said.

Highs will generally range from the 60s to the lower 70s along the California coast this weekend. Along the Interstate-5 corridor in the Northwest, temperatures will range from near 90 in Medford, Oregon, to around 80 in Portland, Oregon, and middle to upper 70s in Seattle.

NW heat June 14

Rain and mountain snow from this past winter and early spring has resulted in a prolific amount of vegetative growth in the region.

The recent hot weather has accelerated the drying of grassy areas and brush. Very warm to hot days are forecast to continue across much of the interior.

Highs across much of the interior will range from the 80s and lower 90s in Washington, east of the Cascades, to the low 100s across the California and Arizona deserts this weekend.

As a result, conditions will remain favorable for the ignition and spread of wildfires over the coming weeks with no big rainstorms in sight. Most of the region typically receives little or no rainfall during June, July and August.

Multiple fires have ignited in recent days in the West, including a small wildfire that briefly erupted near Six Flags Magic Mountain in Southern California.

Sand Fire Air Drop

A plane drops fire retardant on a hillside in an attempt to box in flames from a wildfire during the Sand Fire in Rumsey, Calif., Sunday, June 9, 2019. (AP Photo/Josh Edelson)

Several large fires continue to burn in Arizona and New Mexico. The Coldwater Fire in the Arizona mountains has consumed nearly 17,000 acres and was only 30% contained as of Friday, according to the Incident Information System.

Sporadic thunderstorm activity and the associated lightning strikes are likely over mountains and hillsides from the Sierra Nevada to the Cascades and other ranges farther inland through this weekend.

While human activities are the leading cause of wildfires, lightning also poses a significant threat.

Towering Cu

Towering cumulus clouds, such as this, are often the sign of a developing thunderstorm.

Earlier in June, several lightning strikes caused a cluster of small wildfires in the Shasta National Forest in Northern California.

Hikers, mountain bikers and climbers in the region should keep an eye out for rapidly changing weather conditions and seek shelter at the first sign of a storm.

If hiking in the mountains, be sure to stay within the tree line to reduce the chance of being a target for lightning.

Another side effect of the weather pattern this time of the year is the melting of snow over the high country in the region.

The recent heat wave has raised the temperature of the heavy snowpack from this past winter to the point where melting is accelerating at progressively higher elevations.

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The runoff will lead to fast flows and high water levels along the small streams and short-run rivers that emerge from the mountains. Dangerous conditions and flooding along the banks of these waterways is likely.

In a few cases, thunderstorm downpours over the mountains can enhance the runoff and make flooding worse.

During the recent heat wave, record highs were set three days in a row in San Francisco from Sunday to Tuesday. Highs were 92, 100 and 98, respectively.

When San Francisco hit 100 on Monday, it was the first time since Sept. 2, 2017, that triple digits were recorded.

Tuesday was the third consecutive day above 90 in downtown San Francisco, a streak that's previously happened only 13 times on record and only the third time it's occurred outside of September or October.

This past Monday, Oakland, California, shattered its old record of 90 set in 2002 with a high of 97.

During the middle of the week, the heat swelled into the Northwest, where both Seattle and Portland, Oregon, set back-to-back record highs on Tuesday and Wednesday.

On Wednesday, Portland reached 98 degrees and shattered the old daily of 93 set in 2002.

Records dating back to the 1920s and 1930s were broken in the Northwest on Wednesday, including at McMinnville and Hillsboro, Oregon, with highs of 96 and 97, respectively.

Download the free AccuWeather app to see how temperatures will trend in your community. Keep checking back for updates on and stay tuned to the AccuWeather Network on DirecTV, Frontier and Verizon Fios.

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