Saturday’s Cold Front Could Bring More Than Cooler Air — Strong Storms Are Also Possible

After several days of oppressive September heat, a cold front is set to bring a major change to the Carolinas this weekend. But before the cooler air arrives, the front could trigger a round of thunderstorms Saturday afternoon and evening, and some of those storms may become strong.

For Rowan County and the surrounding region, Saturday is becoming the day to watch.

Heat and Humidity Will Be in Place Ahead of the Front

Temperatures will remain well above normal through Saturday. Highs across Rowan, Davie, Davidson and Cabarrus counties are expected to reach the mid-90s Saturday afternoon after another couple of very hot days Thursday and Friday.

That lingering heat and humidity will be important to Saturday's storm potential.

As the cold front approaches, the atmosphere ahead of it should become increasingly unstable. Forecast guidance indicates roughly 1,000 to 2,000 J/kg of CAPE could develop across portions of the region Saturday afternoon. CAPE is one measure meteorologists use to determine how much energy is available for thunderstorms.

There should also be more wind shear available than we've seen during many of the isolated summertime thunderstorms recently.

Across central North Carolina, forecast guidance indicates approximately 25 to 35 knots of wind shear could be present Saturday. That could help thunderstorms maintain themselves longer and potentially organize into clusters rather than simply developing and quickly collapsing.

Damaging Winds Could Be the Primary Concern

If stronger thunderstorms develop Saturday, damaging straight-line winds currently appear to be the main concern.

The combination of strong instability, increasing wind shear and substantial moisture in the atmosphere could support clusters of thunderstorms capable of producing strong wind gusts.

Water-loaded downbursts will also be something to watch.

These occur when a thunderstorm containing a large amount of water produces a powerful downdraft. When that descending air reaches the ground, it spreads outward and can produce locally damaging winds.

The environment Saturday could support exactly that type of storm.

Locally heavy rainfall will also be possible. Atmospheric moisture will remain high ahead of the front, meaning thunderstorms could produce very heavy rain over short periods of time.

Timing Will Be Important

There is still uncertainty regarding exactly when the cold front reaches our area, and that will have a major influence on Saturday's storm coverage and intensity.

Current county forecasts show storm chances beginning at different times across the region:

Davie County: Storm chances mainly after 3 PM.

Davidson County: Storm chances after 2 PM.

Rowan County: Storm chances mainly after 5 PM.

Cabarrus County: Storm chances mainly after 5 PM.

Those times will likely be adjusted as higher-resolution forecast guidance gets a better handle on the speed of the front.

An earlier arrival could increase afternoon storm coverage, while a slower front could push the greatest storm opportunity later into Saturday evening.

This is one reason I don't want to get overly specific about storm timing or severity yet.

This Is a Potential — Not a Guarantee

There are ingredients showing up that could support strong thunderstorms Saturday, but that doesn't mean everyone will experience severe weather.

Exactly how much instability develops, when the front arrives, where individual boundaries set up and how thunderstorms organize will all matter.

Those details will become much clearer as we get into Friday and especially Saturday morning.

For now, the takeaway is that Saturday has a better setup for organized thunderstorms than we've seen during much of this week's hot and relatively quiet weather.

Anyone with outdoor plans Saturday afternoon or evening should continue checking the forecast as we get closer.

Then Comes the Cooler Air

The thunderstorms aren't the only story with this front.

Once it passes, a dramatically different air mass moves into the region.

Rowan County is forecast to go from a high near 95 degrees Saturday to around 85 Sunday and 84 on Labor Day.

Davie County drops from around 94 Saturday to 84 Sunday and just 82 on Labor Day.

Davidson County falls from around 95 Saturday to 85 Sunday and 84 on Labor Day.

Cabarrus County goes from around 96 Saturday to 87 Sunday and 85 on Labor Day.

Overnight temperatures will also become much more comfortable, with lows reaching the lower to mid-60s across the region by Sunday and Monday nights.

After several afternoons with heat index values around or above 100 degrees, it will be a noticeable change.

What I'll Be Watching

Between now and Saturday, I'll be watching several things closely: the timing of the cold front, how much instability develops ahead of it, the amount of wind shear available, and whether forecast guidance becomes more consistent in showing organized thunderstorms across our area.

The overall message for the holiday weekend is becoming clearer.

Saturday will be the transition day.

It starts hot, with temperatures well into the 90s. Thunderstorm chances increase during the afternoon and evening as the front approaches, with at least some potential for stronger storms.

Then, behind the front, temperatures tumble into the 80s for Sunday and Labor Day.

I'll continue to update the Saturday storm potential as new forecast information becomes available.