May 4, 2020

Baking West, Shivering East: U.S. Temperature Contrasts to Amp Up This Week

United States
by
Bob Henson
,
Weather Underground
Climate change may be impacting jet stream patterns
Forecast from the 12Z on Monday, May 4, for Sunday, May 10, 2019. Credit: tropicaltidbits.com

Climate Signals Summary: The heat wave engulfing the western US and the frigid weather forecast in the East are connected by the jet stream, and climate change may be affecting the frequency, intensity, and timing of these kinds of East-West weather divides.


Article Excerpt: A startlingly cold air mass for May will invade the eastern United States later this week, just in time for Mother’s Day weekend. Meanwhile, the latest in a surge of record warmth over the Southwest will push northward through the Pacific states.

The hot-west-chilly-east pattern is being driven by a familiar pattern, one where the jet stream buckles poleward in western North America and then dives toward lower latitudes across the eastern half of the continent. The eastern cold push will be reinforced by a lobe of the polar vortex that normally stays much further north by mid-spring. (This lobe is in the tropospheric polar vortex, the lower-altitude version that is more prone to dip into midlatitudes than the stratospheric polar vortex.)

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This week’s strongest push of cold air may arrive so quickly that it’ll take a day or two for the relatively warm ground and strong May sun of lower latitudes to defang it. Monthly low temperatures would be difficult to achieve, given the timing within the month and the landmark cold events of the 19th and 20th centuries, but daily record lows are quite possible, and perhaps an even larger number of record-cold daily maximums. Spring leaf-out is running a week or more ahead of schedule across large parts of the southern and eastern U.S., which suggests that any frost or freeze could produce more damage to tender vegetation than usual for this time of year.

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A resurgence of record early-season heat is on tap this week, starting in southern California and Arizona and pushing northward by week’s end. Last week, all-time April record highs were set in Pueblo, Colorado (94°F); Elko, Nevada (88°F); Santa Fe and Las Vegas, New Mexico (86°F and 85°F), and Alamosa, Colorado (82°F), among others. On Thursday, both Las Vegas and Death Valley, California, set their all-time April records for hottest daily low with 79°F and 90°F, respectively.

This week's heat is likely to bring the highest readings of the year so far to Arizona, with daily-record highs of 105°F or higher possible by Wednesday in Phoenix, Yuma, and Tucson. The heat will push off the southern California coast by Thursday, when Los Angeles may soar well into the 90s Fahrenheit. By Saturday, highs could be threatening records in the mid-80s as far north as Portland, Oregon.