Significant warmth across the US next week, but will it last?

The hemispheric pattern evolution over the next 7-10 days will be quite intricate, to say the least, and could potentially include both a significant — possibly record breaking — warmup, and a large scale cooldown directly behind it. The pattern changes and evolution are being largely driven by changes that are ongoing in the Pacific Ocean, as a large low pressure system and mid level trough form in the Gulf of Alaska. This forces dramatic changes to the pattern across the Continental United States.

Late this week, a large trough centered near the Aleutian Islands of Alaska will begin a dramatic shift. This trough — overall — has been centered near the Aleutians for quite some time now. But a changing pattern, wavelengths, and an extra boost from a recurving typhoon will help to bring forth the change. The Aleutians trough shifts southeast by hundreds of miles this weekend, resulting in a significant storm system pushing into the Pacific Northwest.

On a larger scale, this troughing pushing into the Gulf of Alaska means a southwesterly fetch will develop from the Southwest US into the Central US by the early part of next week. Without any blocking high pressure over Canada to resist it, the development of a large ridge over the Central and eventually Eastern US is likely. This will result in temperatures much above average for this time of year, being aided by the aforementioned warm flow in the atmosphere.

The resulting synoptic and sensible weather will be quite anomalous, especially for a period this late in the Autumn season. Forecast models suggest temperatures could rise more than 10 degrees above average on more than one day, especially from the Plains into the Corn Belt, including the Ohio Valley. This warm weather will also spread to the East Coast during this middle part of the week. 5-Day average temperatures may reach 7 to 10 degrees above seasonal average for this time of year.

This is great and all, but how long will it last? 

The most interesting thing about the upcoming pattern, despite it’s anomalous nature in regards to temperature, will be its progressive nature! Despite temperatures averaging much above average for a few days during the middle part of next week, forecast models are all in good agreement that the pattern will continue to evolve in a progressive nature. The storm system crashing into the West Coast will eventually traverse into the Northern 1/3 of the United States, as a much weaker version of its prior self.

But most notably, the deep trough in the Gulf of Alaska will retreat back toward the Aleutian Islands, opening the door for more ridging to return to those areas in 10-14 days time. This also suggests the development of a cooler, more troughy pattern over the Eastern United States, particularly from the Mississippi River eastward through the Ohio Valley and toward the East Coast, for a period of time around Days 10-14.

This trough could result in a period of below-normal temperatures, directly on the heels of the above-normal temperatures during  the middle to latter half of next week. A roller-coaster type pattern for sure.

But the key word? Progressive. Without any true blocking or large scale storm features to slow the pattern down, the overall weather pattern and mid/upper level jet stream remains progressive throughout the hemisphere. With the Arctic Oscillation trending negative and likely to remain there, there will be some changes to this overall pattern soon. But not quite yet.