Warm air is expected to escape the tropics into next week.
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.
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 rise into the 40s and even 50s into early week. Even Utqiaġvik, on the northern brim of Alaska, is predicted to warm above freezing in the early part of the week ahead. 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 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.
This setup will also bring abundant moisture from the tropics northward on the Pineapple Express, a conveyor belt of moisture that begins in the Hawaiian region and that typically brings heavy rains and flood potential to the West Coast in the winter and spring.
This flow will bring plenty of precipitation to southern Alaska through Tuesday, especially on the southward-facing slopes. How much rain and/or snow will fall depends on how quickly the belt of moisture treks eastward.
Extended Outlook
According to NOAA's Climate Prediction Center, this warmth could last well into November.
The NOAA forecast for above-average temperatures is nearly a lock for much of Alaska around Halloween, and is one of the most unusual forecasts issued for the state, according to Alaskan climatologist Dr. Brian Brettschneider.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.
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