We are approaching that time of the year once again, time for severe weather season. 2017 has started off stormy. We’ve had a couple outbreaks already over the Southeast. Most notably January 20th- 22nd. Numerous tornadoes affected the southeast, including South Carolina.
The threat of severe storms is in the forecast for midweek. The Storm Prediction Center issues outlooks for the possibilities of severe weather. There are Day 1, Day 2, and Day 3 outlooks. Day 1 and Day 2 get updated a few times a day, Day 3 is updated once a day. I attended the National Tornado Summit/Severe Weather Conference where it was mentioned, more updates on these products are forthcoming throughout the day. There is also a Day 4-8 that highlights areas of interest for severe weather.
Once we get within three days, the Storm Prediction Center starts issuing outlooks. There are 6 categories of risk.
General, Marginal, Slight, Enhanced, Moderate, and High.
You are probably wanting to know what those risks mean, let me help break down the risks.
First, what is a severe thunderstorm? The National Weather Service defines it as this, a thunderstorm producing hail one inch or larger in diameter and/or winds equal or exceed 58 miles an hour
General (Level 0 of 5) – A general risk means there is a chance of thunderstorms, none of the storms are expect to be severe. These storms have a small hail threat and winds close to 40 mph.
Marginal Risk (Level 1 of 5) - Isolated severe thunderstorms are possible. These will be fairly limited in coverage, intensity, and duration. Marginal days normally produce hail up to 1”, Winds 40-60 mph, and a low tornado threat.
Slight Risk (Level 2 of 5) – Scattered severe storms are possible. These storms are short lived, isolated intense storms. Reports of strong wind, and wind damage. Hailstones between 1-2” in diameter are possible. A few tornadoes are possible.
Enhanced Risk (Level 3 of 5) – Numerous severe storms possible. Persistent, widespread storms. Few storms are intense. Damaging winds reported. Widespread damaging 1-2” diameter hailstones reported. Few tornadoes are reported.
Moderate Risk (Level 4 of 5) – Widespread severe storms likely. Long-lived widespread intense storms. Widespread wind damage. Destructive hail 2” or higher. Strong tornadoes possible.
High Risk (Level 5 of 5) – Widespread severe storms likely. Long-lived, very widespread and particularly intense. Destructive hail Tornado outbreak. Derecho.
What is a Derecho? is a widespread, long-lived wind storm associated with a band of rapidly moving showers or thunderstorms variously known as a squall line, bow echo, or quasi-linear convective system. Although a derecho can produce destruction like that of a tornado, the damage typically occurs in one direction along a relatively straight swath. Thus, the term "straight-line wind damage" sometimes is used to describe derecho damage.
One last thing, it is always good know the difference between a Watch and a Warning.
A Watch means conditions are possible for the development of Tornado, Severe Thunderstorms, Flash Floods, etc…
A Warning means that a Tornado, Severe Thunderstorm, Flash Flood, etc is occurring. Seek shelter now.
Living in the southeast during spring is difficult. Some years we have numerous severe weather events, and other years’ spring is quiet. Who knows what this spring will hold, but the next time you hear a severe weather is possible, you’ll know what these risks mean.