Finger on the Weather

As severe weather season arrives, a primer on risk categories

The rumbles of thunder and smattering of hail stones in the Wichita metropolitan area Monday night and early Tuesday were a reminder that spring is upon us – and with it the threat of severe weather.

When severe weather threatens portions of the Sunflower State, you may hear meteorologists use unfamiliar terms that are actually Storm Prediction Center categories describing the risk of severe weather.

The SPC added categories to its threat spectrum last year, boosting the total from three to five. The Day 1 outlook includes probability forecasts of tornadoes, damaging winds, and large hail. Day 2 and Day 3 offer a glimpse at the combined severe weather risk.

The risk categories are listed:

▪ TSTM (light green) – General or non-severe thunderstorms. Used when there is at least a 10% probability of thunderstorms forecast during the designated period.

▪ 1-MRGL (dark green) – Marginal risk – An area of severe storms that are not well-organized or long-lasting, or have marginal intensity.

▪ 2-SLGT (yellow) – Slight risk – An area of severe storms that last for several hours, which is usually low in coverage with varying levels of intensity.

▪ 3-ENH (orange) – Enhanced risk – An area of greater severe storm coverage with varying levels of intensity.

▪ 4-MDT (red) – Moderate risk – An area where the potential exists for widespread severe weather with several tornadoes and/or numerous severe thunderstorms, some of which may be intense. This risk is usually reserved for days with several supercells producing intense tornadoes and/or very large hail, or an intense squall line with widespread damaging winds.

▪ 5-HIGH (magenta) – High risk – An area where a severe weather outbreak is expected from either numerous intense and long-tracked tornadoes or a long-lived derecho-producing thunderstorm complex that produces hurricane-force wind gusts and widespread damage. This risk is reserved for when high confidence exists in widespread coverage of severe weather with embedded instances of extreme severe, such as violent tornadoes or very damaging wind events.

You’ll see the color spectrum for the categories in this Day 1 outlook.

Reach Stan Finger at 316-268-6437 or Follow him on Twitter: @StanFinger.