By Alex Sosnowski, AccuWeather senior meteorologist
June 13, 2019, 12:11:28 PM 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 is in store along the coast,” according to AccuWeather Senior Meteorologist Brett Anderson.
The pattern, known to locals as “June gloom” will ramp up and spread northward into this weekend.
Temperatures will hover within a few degrees of average along much of the California coast into this weekend.
“Farther north, temperatures will throttle back to between 5 and 10 degrees above average along much of the Oregon and Washington coasts on Friday and during this weekend,” Anderson said.
Highs will generally range from the middle 60s to the lower 70s along the California and southern Oregon coasts and the 70s along the northern Oregon and Washington coasts.
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 upper 70s and 80s in Washington, east of the Cascades, to the low 100s across the California and Arizona deserts.
As a result, conditions will remain favorable in general 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.
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 Thursday morning, according to the Incident Information System.
While lower temperatures forecast in the coming days may lower the risk slightly, a couple of weak storms from the Pacific Ocean are forecast to move inland into this weekend.
These storms are unlikely to bring rain to coastal and desert areas but 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.
While human activities are the leading cause of wildfires, lightning also poses a significant threat.
Towering cumulus clouds, such as this, are often the sign of a developing thunderstorm.
Earlier in June, several lightning strikes cause 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 record for the date 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.
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