The equinox on Wednesday may herald the arrival of fall, but summer is very much going to be in effect for most of the U.S. through the end of this month.

Consistent warmth has baked much of the U.S. in a month that usually heralds a transition to pumpkin spice lattes. Instead, iced coffee or perhaps a nice, cold sweet tea have been in order to deal with relentless warmth that has a number of cities from the Southwest to the Northeast primed to have their hottest September on record.

Temperature anomalies on Tuesday, September 22

Temperature anomalies on Tuesday, September 22.

If the month ended today, at least 26 cities across the country would have their warmest September on record. They range from El Paso, Texas to Denver to Cheyenne, Wyo. to Boston. Also among the record setters is New York, which could set a new record by a wide margin. This September is outpacing the current record — set in 1961 — by 3.1°F.

A host of other cities including Cleveland and Chicago would also see this September among their top five warmest.

Summer’s temperature grip should stay firmly in place for the rest of the month just about everywhere across the U.S., save the Pacific Northwest which is in a bubble of average temperatures. These hot temperatures are in line with fall climate trends. Fall has warmed by as much as 3.5°F in the Northern Rockies, 3.2°F in the Northeast and 3°F in the Southern Plains since 1970.

U.S. falls are warming
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The reason for this September’s heat is a stubborn jet stream that’s taking the fast track across the U.S. from west to east. The jet stream is a fast-moving river of air that usually zig-zags its way across the U.S. To its north, cooler temperatures usually prevail while on the south side, warmer temperatures are the norm.

For the past few years, there’s been a major zig and zag that’s left a ridge on the West Coast and trough on the East Coast. That pattern is a big reason why record heat has been the story out West while folks on the East Coast have been chattering their teeth all winter.

The jet stream has stayed in a more straight-line pattern this September, keeping warm air trapped across the entire U.S. except for a little dip over Washington and Oregon that has helped cool that region and snuff out wildfires that exploded across the region in July and August.

However, heat is expected in California through the end of the month, which could help wildfires continue to rage there. The state has already experienced some if its most destructive wildfires in history this year as drought and hot temperatures have kept the state primed to burn.