Spring can sometimes bring wild temperature swings. These can happen anywhere in the U.S. Over the last week, the West has seen a huge shift in temperatures. It became very warm to hot, even in the Northwest, for a time. Record temperatures fell. For two consecutive days, the hottest weather in the nation was along the south-central coast in California. The high heat, along with unseasonably strong Santa Ana winds and dry air, combined to make for a fast-moving brush fire that threatened homes around Rancho Cucamonga, California. Portland, Oregon, area was near 90 one day, and there are some areas along the Gulf Coast who have not been that warm yet this year.
However, over the weekend, a rather strong upper-level trough began to approach from the west and started a cooldown that accelerated through the weekend into Monday. This trough will move through all the far Western states Monday night and Tuesday. Temperatures in some areas will be as much as 30 degrees lower than they were just a few days ago. In the Sierra, I expect there will be snow showers later Monday night into Tuesday down to 6,000 feet or so. The coolest day will be Tuesday in California, Wednesday farther east in Utah and Arizona. The Northwest will be about as cool Tuesday as it was Monday.
Here are some temperature graphs showing the changes over the last seven day. The temperature today is an estimated high temperature for all cities.
LOS ANGELES, CALIFORNIA
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As of the end of June there had been no named storms in the Eastern Pacific basin.
This is some serious and dangerous heat. Outdoor activity is just not at all recommended during the daytime.
Any shower and thunderstorm can contain heavy downpours, heavy enough to cause temporary, low-lying ponding.