Juneau, Alaska (KINY) - As cold air spills into the Lower 48, a spell of warmer air will sweep through Alaska early this week, with temperatures expected to climb up to 30 degrees above average in some areas.
According to The Weather Station, the rise in temperatures will come as a strong low-pressure system digs in over the Bering Sea, driving the jet stream eastward and southward over the northern Pacific.
As the low-pressure system amplifies, a ridge of high pressure will also strengthen along the western coasts of the United States and Canada.
Between the two systems, winds out of the south will strengthen, bringing tropical air northward from near Hawaii.
This tropical air will modify somewhat as it gains latitude, but high temperatures will top out in the 40s and the 50s across much of central and southern Alaska, and still well into the 30s in northern Alaska on Monday. Even Utqiaġvik, on the northern brim of Alaska, is predicted to warm above freezing in the early part of the week. On average, Utqiaġvik, formerly known as Barrow, sees its last day of above-freezing weather on Sept. 27.
This year, Alaska had its third-warmest September on record, according to NOAA. Two locations – Utqiaġvik and Cold Bay – had their warmest September on record. Alaska also had its second-warmest January-through-September on record.
Based on the current forecast, Utqiaġvik will likely have its second warmest October on record.
While Alaska warms up, rounds of cooler air will spill into the western and central U.S., with some spots seeing highs 30-40 degrees cooler than average, or more.
The continental pattern that features these big waves in the jet stream is known as "amplified," meaning that the waves extend further north and/or south than usual. This can lead to especially large temperature departures, as warmer air streams north and colder air plunges south.
Over the Lower 48, such a pattern often results in one coast having warmer temperatures for a week or so, while the other coast cools off.
In this case, however, more than two-thirds of the contiguous U.S. will experience cooler air while Alaska and western Canada warm up.