Thermometer whiplash jolts region once again

Many locations in Southwest Virginia had frost on Tuesday morning. The mercury may scrape 90 at a few spots by Wednesday afternoon.

Thermometer whiplash has become a rather common malady for our region during the past year.

We’re barely a month past what appears to be the only instance in Roanoke’s recorded weather history (dating to 1912) when we went from accumulating snow (1 inch on April 4) to 90 degrees (April 10) in less than a week.

Within that week, the temperature jumped from 34 to 87 between April 6 and 8 at Roanoke, and from 27 to 79 between April 6 and 9 at Blacksburg, which melted off more than 5 inches of snow that fell there on April 4.

With a record-breaking low of 35 at Roanoke and record-tying low of 31 at Blacksburg on Tuesday morning, we could make similarly large jumps in just two days this time around.

The way this cool-to-warmth turnaround is happening is remarkably similar to what happened on June 27 to 29 last year.

In that three-day period, Roanoke vaulted from 54 to 104 and Blacksburg from 47 to 95. On the middle day of that thermometer flip, June 28, Roanoke started at 59 and warmed to 97, while Blacksburg started at 52 and hit 90.

As with this thermometer flip, unseasonably hot air built into the Upper Midwest as unusually cold air dipped into the East, and then the hot air expanded east and southeast, with westerly downslope winds over the Appalachians contributing to the sudden warming.

Temperatures took a sharp downward turn at the end of October, in connection with Superstorm Sandy and the Arctic front that combined with a hurricane to create it.

From Oct. 25 to 28, it dipped from 80 to 46 at Roanoke and 77 to 38 at Blacksburg. Stretch that time frame out from Oct. 24 to 30, and temperatures went from 83 to 37 at Roanoke, and from 78 to 30 at Blacksburg with six-tenths of an inch of snow.

But neither this week nor any of the others mentioned can match the double-flip of late January and early February.

Jan. 27 lows were 20 at Roanoke and 11 at Blacksburg. Two days later, highs were 74 and 68, respectively. Then, by Feb. 1, it was back to 20 and 12. There was ice, flooding rain, severe storms and light snow accumulation during that week in Southwest Virginia.

In the past several months, we’ve had a series of blocking patterns in which the jet stream makes large curves north and south as large domes of high pressure in the north have blocked its typical west to east flow.

As these “ridges” and “troughs” in the jet flow move eastward, often begrudgingly, our temperatures flip quickly from hot to cold or cold to hot.

While we are likely done with near-freezing temperatures after a spring with frequent and late cold intrusions, some more up-and-down temperature rolling is likely in the weeks ahead.

Storm chase season begins

The first group of Virginia Tech storm chasers bundled up and headed out to the Plains states on Tuesday. Despite departing in record cold temperatures, it appears they will be headed toward significant severe weather chances later this week in the central U.S.

As I wait to take the driver’s seat in a chase van for the second trip scheduled near Memorial Day, I will be following the progress of the chasers on the Weather Journal blog and on Twitter. You can follow them directly through the Twitter handle @hokiestorm.

Weather Journal runs on Wednesdays.

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