Waiting on a 'January Thaw'? You may be in luck this week
Monday, January 8, 2018, 16:10 - The intense cold weather that most of the east experienced between Christmas and New Year's is on its way out - at least temporarily.
A significant pattern change will bring milder temperatures to the east, and cooler, stormier weather to the west this week, as the jet stream shifts position over the continent. This will be a welcome change for millions, after the end of December 2017 and the early days of January 2018 brought an Arctic-like environment to much of the country, with temperatures well below average. In some cases, strong winds made the intense cold even more extreme as wind chill values dove well into the minus teens, and occasionally into the minus 20s.
The map above shows temperatures relative to normal values around the beginning of 2018, where most of the eastern half of the U.S. experienced negative anomalies. Some areas of the north were 20 to 30 F below average, while negative values extended as the far as the Deep South, reaching a large swath from Texas to Florida.
At the same time in the Southwest and over California, drier and warmer-than-usual weather reigned as high pressure kept Pacific storms at bay. Parts of the region are showing the early stages of drought, after a remarkably dry fall and early winter.
One of the features of our winter forecast was an extended mid-winter break from the cold pattern and that still looks to be on track. We expect a pattern reversal to begin to develop this week going into mid-January, with a northerly displaced jet stream allowing milder air to spread across much of the country.
This change comes with a more active storm track in the east, where the brutal cold was marked by largely dry weather across the region - away from lake-effect snow areas - until the powerful nor'easter that tore up the Eastern Seaboard last week marked the beginning of a change. This week, we'll be watching a strong low pressure system out of Colorado and one developing over the Gulf of Mexico to pull milder, moist air over much of the eastern third of the country, bringing rebounding temperatures across the region.
The west will also be stormier, with Pacific systems bringing much-needed moisture to California, the Sierra Nevada, and the Great Basin, where, thus far, winter precipitation has been well below average. As mountain snowpack is critical to the water supply for the rest of the year, this will be welcome news for the region. It comes at a cost, however; after the record-breaking fire season across California, mudslides and debris flow in burn areas is likely, along with flash flooding.
Even as we expect warmer weather for most, it is important to keep in mind that 'normal' temperatures during late January and early February are at their coldest levels of the year. Therefore, it is quite possible for many places to still see snow and ice despite the milder pattern. Above-average temperatures are expected overall through the remainder of the winter across much of the southern half of the country, however, some areas in the north - from the Pacific Northwest to the Great Lakes - could see below-average temperatures during the coming months.
With files from The Weather Network meteorologist Mario Picazo.
Thumbnail: Marian H Jenkins, Toronto, ON