An atmospheric pattern known to send Arctic air rushing southward is looking more likely next week, according to forecasters who have been monitoring the phenomenon.
Around Jan. 21-25, colder-than-average temperatures are looking like a virtual certainty around the Great Lakes and along the Canadian border, and more likely than not for much of the rest of the eastern half of the country. Forecasters at the Climate Prediction Center in College Park call for 60-70 percent odds of below-normal cold across Maryland next week.
The cold will likely persist through early Thursday, with temperatures normalizing after that.
Normal highs this time of year at BWI Marshall Airport are about 41 degrees, with lows of about 24 degrees. We are in the midst of what is the coldest stretch of the year, on average -- those temperatures are the coldest averages you'll see at BWI.
Forecasters have been eyeing such a chill since starting to observe a phenomenon known as sudden stratospheric warming in the Arctic about a week and a half ago. When it occurs, it is known to force cold air to build in the lowest layer of the atmosphere, the troposphere, and send it driving southward.
Below-average temperatures have been relatively rare in the Baltimore area in recent years. In a stretch that started in February 2011, only one month has posted a below-normal monthly average temperature at BWI -- last November.
Of course, they come in fits and starts. Over the past three years, BWI has reached the single digits only twice, reaching 8 degrees both times, Jan. 24, 2011, and Jan. 31, 2010. In the couple of years before that, the cold was more common, with a coldest point of 2 degrees Jan. 17, 2009.