Last week, Marie in Apex asked “Is there any truth to the possibility of snow following 7-10 days after a winter thunderstorm?” There’s a long standing old wives’ tale that says that if you hear thunder in winter, you’ll have snow within 7 – 10 days. Sometimes it holds true, and those are the times that everyone remembers. Often, especially in the south, it doesn’t play out that way, and those are the times very few people remember.
At about 3:30am on Sunday, December 16th, I was awakened in my home in North Raleigh by thunder. Today is the tenth day since that early morning, winter storm. Our forecast for today calls for more storms. So, why don’t we have snow? Thunder in the winter isn’t a sign of coming snowstorms, but it is a sign of an active weather pattern. There are times when it means that we will have the right ingredients for a snow storm, and the farther north you go, the more likely it is – simply because the climate is colder as you go north and you need freezing temperatures in order to have snow. Today we don’t have the ingredients for a snow storm in Raleigh. Instead, we have what is necessary for a severe weather outbreak – also the sign of an active weather pattern.
As witnessed by so many in the Deep South during the last 24 hours, warmer air, an abundance of moisture, and a strong cold front can trigger severe storms any time of the year. With the current system moving into our area today, we have an additional piece in place: a jet streak. A jet streak is an area of stronger than normal winds in the middle to upper atmosphere that affects our weather here at the surface. Saving the details of the workings of a jet streak for my next post, I will say right now that there are two regions of it under which we get low pressure at the ground level. Low pressure means rising air, and with all of the other forces that are in place today, an increased chance for severe weather. One of those regions, the left exit region, will be moving over North Carolina as the day progresses. (I’ll explain the left exit region in my next post, too.)
The biggest threat today will be east of Raleigh, but most of North Carolina could see storms with winds of 58 mph or greater, isolated tornadoes, and hail. If a tornado forms today, it could be a long-track tornado, which roughly means a tornado that spends 40-60 minutes on the ground. Today’s set-up is very similar to that of the tornado outbreak on November 28, 1988. Please, stay alert and take any warning issued by the National Weather Service seriously.