Thursday, January 17, 2013

Thundersnow from a potent little storm

The low pressure system that will be responsible for heavy rain and snow today and tonight across the Charlotte region is not your typical winter storm.

This is an unusual system that has fascinated weather fanatics and meteorologists -- the kind of storm we don't see very often.

It is expected to produce thundersnow, and precipitation falling at extremely heavy rates.

Any other winter system that crossed our region with snow, ground temperatures around 50 degrees, and air temperatures around freezing wouldn't be a threat to drop accumulating snow. It would melt on its way to the ground, or quickly when it touched ground.

But this storm is different.

It is very strong, not very big, and will be moving quickly.  It is strong enough to create its old cold weather, actually.

As I've written before, this column is not aimed at meteorologists, but at people who are fascinated by weather. So I won't go into deep detail. But suffice to say there will be a lot of vertical lift in the clouds.

As WCNC-TV meteorologist Brad Panovich noted earlier today, it takes a difference of about 60 degrees between ground and upper level of clouds for a thunderstorm. That's not hard to get in summer, but it's unusual in winter. Ground temperatures will be near 35 degrees, but the very cold air aloft in this strong system will have readings about 20 to 30 degrees below zero.

When that happens, precipitation falls at very rapid rates.

Heavy rain is likely this afternoon and early this evening across the area. And as the center of the system crosses the area, temperatures will tumble, and the very cold air at the top of the cloud columns will be sent to the ground. That will help saturate the air with cold temperatures, enabling snow to reach the ground.

If the snow falls heavily enough, it will overcome the relatively warm ground temperatures and accumulate. Obviously, the process will be helped in places where ground temperatures are cooler (such as the mountains). But if it snows really hard in the Piedmont, those places could get a quick 2, 3 or even 4 inches of snow.

A similar storm hit the area March 1-2, 2009. Heavy rain fell that Sunday afternoon in Charlotte, and the rain changed to snow about 7 p.m. that day. Between 1 and 2 inches accumulated.

But a deformation zone -- one of those areas of heaviest precipitation -- formed in a corridor from Gaffney, S.C., to west of Gastonia. Strangely, that zone was right along Interstate 85. Snow fell at a rate of 2 to 3 inches an hour, and between 8 and 12 inches accumulated. Cars and trucks were stranded on the interstate highway overnight.

Will that happen again tonight?  Possibly, somewhere.

Either way, this is an interesting storm to watch.

Something I forgot ... There are some absolutely amazing temperature contrasts today in the Carolinas.  While we're talking about a snowstorm in North Carolina, on the other side of a warm front stretched across South Carolina, it's like April.

Can you believe that the 3 p.m. temperature in Columbia, just 90 minutes away, is 78 degrees! And it's 81 degrees in Kingstree, S.C., about halfway between Columbia and the coast. Or try 78 degrees in Florence.


Unknown said...

We had thundersnow occur in central NY nearly every season when lake effect snow falls. I think it was Jim Cantore that was reporting weather one day and lightning slashed during a heavy snowfall.

Unknown said...