Published: August 14,2015
When the National Weather Service issues "excessive heat warnings" for the hottest region of the country, you know it's hot.
Those warnings are in place for more than 14 million Americans in three states as the bubble of high pressure responsible for the recent heat wave in Texas and Louisiana shifts westward to Arizona, putting the Desert Southwest in the hot seat.
And it's not just the Southwest that's feeling the heat. The Northwest and northern Rockies have also been baking lately. But while relief is starting to move in, that relief is creating problems of its own in the form of strong winds and the threat of lightning strikes – and those raise the danger of wildfires, both new and existing.
Southwest: August Records in Jeopardy
Southwest Heat Setup
In a way, to call this a "pressure cooker" could be considered more than just a metaphor. The high-pressure zone will literally exert a downward influence on the air over the Southwest. Since clouds and rainfall require rising air motions (not to mention adequate moisture), large-scale sinking air tends to prevent or inhibit precipitation from developing.
That means more sunshine, which in turn, means more heat. In addition, the air mass itself is warmer in the first place, so the sun is heating up air that's already toasty to start with.
Relative to historical norms, the epicenter of the heat will be over central and southern Arizona through the weekend. As of this writing, both Phoenix and Tucson are forecast to come within two degrees of their respective all-time highs for the month of August.
Three-Day Forecast
The National Weather Service has issued excessive heat warnings for most of Arizona's lower elevations, along with the lower elevations of the Las Vegas area, the low deserts of southern California, and even into the mountains and inland valleys around Los Angeles and San Diego. If you are in any of these areas, take precautions against the heat. Drink plenty of water, stay in the shade as much as possible, and take a break now and then in an air-conditioned building.
In Los Angeles, highs are likely to soar well into the 100s in the San Fernando Valley, even as the city's westside beaches enjoy comparatively mild temperatures stopping in the lower 80s. The Weather Channel smartphone app and weather.com give you forecasts down to neighborhood and zip-code level, so make sure you check the forecast for your specific area of interest to get the forecast most relevant to your plans.
Northwest: Cooling Winds Whip Up Fire Danger
Current Fire Weather Alerts
A cold front is arriving in the Northwest and has begun to knock down the heat west of the Cascades already.
Unfortunately, this friendly front brought along some bad company – a punch of strong winds in the middle and upper levels of the atmosphere. Some of that wind momentum will be pulled to ground level as the cold front crosses the Northwest Friday, bringing an unwelcome spike in winds over an area already dealing with wildfires. Existing wildfires will be difficult to control during the windy conditions Friday into Friday evening over areas east of the Cascades.
On top of that, the front will have enough punch to set off some thunderstorms over the northern Rockies – and lightning strikes from those storms could set new fires, particularly where lightning bolts land outside the rain footprint of their parent thunderclouds.
Current Fire Weather Conditions
While the wildfire danger is unwelcome, the cold front will sweep the broiling heat out of the region for a little while. Highs will be back to near-normal levels in eastern Washington and eastern Oregon Friday, and the more seasonable conditions will sweep east into Idaho, Montana and Wyoming for Saturday.
MORE: Western Wildfires, July 31 - Aug. 11, 2015
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