Kevin Myatt is The Roanoke Times' weather columnist.

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@roanoke.com
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Weather with Kevin Myatt

Recent columns

• We got graupel, but not on official record
• Moisture could get caught up in cold blast
• Forecast for Weather Journal: Partly print, with frequent Internet
• Column archive

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• Sprinkles or flurries possible Tuesday, but maybe something bigger for the weekend?
• For now, it looks like a quiet, mostly mild week ahead for SW Virginia
• Coldest morning of winter so far likely across much of Southwest Virginia; Tuesday precipitation looking doubtful
• Weather Journal blog

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So, how low will it go?

There's no doubting the strength of the Arctic air mass that is about to envelop most of the United States east of the Rockies -- it's the biggest and deepest in at least six years. But it's the nitty-gritty details that will determine just how cold it gets in Southwest Virginia.

You may have noticed that various TV and Internet sources have been bouncing around with our projected lows for Friday and Saturday morning.

The weather map on the back of the Virginia section of The Roanoke Times, prepared by Weather Central in Madison, Wis., forecast a low of minus 1 in Sunday's editions, but had backed all the way off to 12 degrees for Saturday morning in Tuesday's paper. Take a look for yourself what it shows today.

The exact position of the surface high pressure system pushing the cold air down is critical. If it sets up right over us, it will be colder.

Whether we get that one perfectly clear night with calm wind is also important. Any amount of wind and cloud cover limits radiational cooling, or heat from the surface escaping into the atmosphere.

Any amount of snow cover could make a huge difference. No big winter storms are in the offing, but even a quarter-inch out of a rogue snow shower tonight or Thursday could aid in reflecting heat away from the surface.

My best guess: a low of 7 in Roanoke and 2 in Blacksburg by Saturday morning -- very cold, but not historically so.