Slim severe threat for Tuesday
Posted October 2, 2012
The passage of a warm front northward across our area today, along with a deep upper level trough west of us and modestly unstable air, has lead the Storm Prediction Center to place much of NC in a low-end chance of seeing storm with severe wind gusts, and as shown in the image here, also a slight chance of tornadic storms, with conditions a little more favorable for such cells off to our northwest over parts of OH, KY and WV.
The contours you see on this map indicate our state would have about a 2-4% chance of a tornado occurring within a 25 mile radius of any point during the 24 hours following 8 AM today. It's worth noting that this is quite a different statistic from the chance of precipitation you often see or hear for a location. A 3% probability of precipitation would mean that given the same weather pattern you would expect to receive measurable precipitation at your location 3 times out of 100. On the tornado map, however, that figure corresponds to a tornado touching down somewhere within a 1964 square mile area surrounding your location 3 times out of every 100 similar situations, so the likelihood of a tornado striking a particular point is much lower.
You may wonder, why even be concerned with such a small probability? The reason, of course, is a matter of tornadoes being a very low likelihood, yet high-impact event. The 3% probability shown on this map is very slim indeed when it comes to a particular point, but is much higher than the probability on any given day and so acts to highlight the fact that conditions are at least a little more favorable for them to form. Overall, it boils down to a reason to keep a more watchful eye on weather conditions today, but not to be overly worried about the potential.
As a point of comparison, at the same time on the morning of April 16, 2011, the same product from SPC showed central and eastern NC with a 15-25% chance of a tornado within 25 miles of a point, and that value was increased to over 30% by later in the morning. The weather pattern in place that day, of course, resulted in 30 tornadoes for our state between late morning and early evening.