October 31: Severe Storm Threat This Evening



We’re tracking the potential for strong to severe thunderstorms in central North Carolina for Halloween evening…obviously, the timing is less than ideal.

Before the storms arrive, most of today will be very warm and breezy — temperatures will warm up to the upper 70s and low 80s despite mostly cloudy skies.

Winds will pick up from the southwest by midday, gusting over 20 mph throughout the afternoon.

There’s just a small chance of rain during the day, so the earlier you can go trick-or-treat, the better. The HRRR model’s radar simulation from 10:00am through 6:00pm shows just a few off-and-on showers…but also shows a line of storms approaching from the west this evening.

A line of heavy rain and storms will move in from the west after sunset, and track eastward across all of central North Carolina through midnight. This is our RPM model’s radar simulation hour-by-hour this evening.

That’s one run of one forecast model — but most of the data agrees on the timing. Keep in mind, Mother Nature sometimes has other ideas, so we’ll be watching for the possibility that the line speeds up or slows down. We’ll keep you updated with the latest timing during our newscasts, and I’ll be posting updates on social media through the day as well. You won’t want to get caught out in that line of storms, so try to get the trick-or-treating accomplished as early as possible.

The Storm Prediction Center has included the northern half of central North Carolina — including the Triangle — in an “Enhanced Risk” of severe weather.

Damaging straight-line winds will be the primary threat, and there will be enough wind energy in the atmosphere to support an isolated tornado threat as well. Large hail is unlikely, and while there will be some heavy downpours, they won’t last long enough to cause flooding.

Meteorologists use various statistics to evaluate the specific severe weather threats, and the numbers are pointing in an ominous direction this evening. One statistic is the “Supercell Composite Parameter,” which measures the combination of instability and wind shear that fuels severe storms. Anything over 3 indicates that the environment will support at least some severe weather, and values over 6 really get our attention. As of this morning, the model data estimates a 70%-90% chance that the SCP will be over 6 at 8:00pm.

Another statistic is the “Significant Tornado Parameter” — a self-explanatory term (kind of rare in the science community!). Values over 1 indicate at least a borderline tornado threat, but we get more concerned when the numbers climb to the 2-4 range. Unfortunately, the model data estimates a 50%-70% chance of STP values over 3 this evening.

As you head out for trick-or-treating, make sure you have a source of weather information in case warnings are issued. You can check the radar on the CBS 17 weather app, and you can also set up the app to alert you to weather warnings in your area. Just follow the red circles I’ve drawn on these screenshots…

Storms will clear out after midnight, and a much cooler air mass will move in. Temperatures will drop to the low 40s by early Friday morning, even a few 30s on the map!

Highs on Friday will only climb to the 50s and low 60s, despite abundant sunshine.

Cool but dry weather will prevail over the weekend and into early next week. We’re just looking at slight rain chances sprinkled throughout the first ten days of November.

Again, you can follow me on Twitter, Instagram and Facebook for more updates throughout the day.

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