From Near 100 to the Mid-80s: What’s Behind This Weekend’s Big Temperature Drop?

After several days of intense September heat, a significant change is showing up in the forecast for Rowan County and the surrounding region.

Temperatures will remain firmly in summer territory through Friday, with afternoon highs reaching the mid-to-upper 90s. By Sunday, however, many locations are forecast to only reach the mid-80s.

For Rowan County, the forecast goes from a high near 97 degrees Friday to around 85 degrees Sunday.

That is a drop of roughly 12 degrees in just two days.

Davie County has an even larger change in the current forecast, falling from around 97 Friday to 84 Sunday. Davidson County drops from 96 to 84, while Cabarrus County goes from around 98 Friday to 86 Sunday.

So, what is causing such a dramatic change?

First, We Have to Break Down the Heat

The hot weather we've experienced this week is associated with a strong area of high pressure in the upper levels of the atmosphere.

Think of this ridge as a large dome over the region.

Air beneath an upper-level ridge generally sinks. As that air sinks, it warms and dries, which makes it difficult for widespread clouds and thunderstorms to develop.

That has helped produce plenty of sunshine and temperatures well into the 90s across our region.

It has also helped keep meaningful rain chances away from Rowan County and much of the surrounding area through the workweek.

That ridge has been strong enough to produce temperatures more typical of the hottest part of summer than the beginning of September.

But the ridge isn't going to remain this strong forever.

The Ridge Begins to Break Down

The first important change occurs as we head into the weekend.

A series of disturbances moving through the larger weather pattern will begin weakening the ridge that has dominated our weather.

Instead of having strong high pressure firmly controlling conditions, the atmosphere becomes more favorable for a front to move into the Carolinas.

This is important for two reasons.

First, weakening the ridge makes it easier for showers and thunderstorms to develop.

Second, the approaching front will eventually help push the hottest air away from our region.

That is why Saturday essentially becomes our transition day.

Saturday: Still Hot, But Changes Begin

Don't expect immediate relief Saturday morning.

Temperatures are still forecast to climb into the 90s.

Rowan County currently has a forecast high around 93 degrees Saturday, while Cabarrus County could still reach around 95.

But unlike the previous several days, we will also have an increasing opportunity for showers and thunderstorms during the afternoon and evening.

Current forecasts give Rowan, Davie and Cabarrus counties around a 30 percent chance of afternoon showers and thunderstorms.

Davidson County currently has a higher 50 percent chance Saturday afternoon.

The exact coverage and intensity of thunderstorms will become clearer as we get closer.

At this point, it remains too early to determine whether severe thunderstorms will become a significant concern.

What is much more certain is that Saturday marks the beginning of the pattern change.

Then the Front Moves Through

A weak front is expected to move through the region Saturday into Sunday.

Behind it, our wind flow changes and cooler air begins spreading into the Carolinas.

That's when you're really going to notice the difference.

Here is the current Friday-to-Sunday temperature change:

Rowan County: 97 to 85

Davie County: 97 to 84

Davidson County: 96 to 84

Cabarrus County: 98 to 86

Those are substantial temperature drops over a relatively short period.

And after several afternoons with heat index values reaching or exceeding 100 degrees, highs in the mid-80s are going to feel considerably different.

It's Not Just the Afternoon Temperatures

The nighttime temperatures are another important part of this pattern change.

Through the end of the workweek, overnight lows remain warm, generally in the lower-to-middle 70s.

By Sunday night, we're looking at:

Rowan County: Around 64 degrees

Davie County: Around 65 degrees

Davidson County: Around 64 degrees

Cabarrus County: Around 66 degrees

Those temperatures will make Monday morning feel considerably different from the mornings we've experienced this week.

The combination of cooler temperatures and potentially lower humidity will provide the first meaningful break from this extended stretch of September heat.

Is This Fall Arriving?

Not exactly.

The calendar says September, and meteorological fall began September 1, but one cooler front doesn't mean summer weather is finished.

September can still produce plenty of hot days across North Carolina, and temperatures could climb again later in the month.

What this front does show us is that we're reaching the time of year when cooler air masses have an increasingly realistic opportunity to make it into the Carolinas.

During July and much of August, getting a front to push through our region and deliver a meaningful temperature change can be difficult.

As we move deeper into September, those opportunities gradually become more frequent.

So I wouldn't call Sunday's weather the arrival of fall.

I would call it a reminder that fall is getting closer.

What I'll Be Watching

There are two parts of this weekend forecast that I'll be watching closely.

The first is Saturday's thunderstorm potential.

As the upper-level ridge weakens and the front approaches, the atmosphere becomes more supportive of showers and thunderstorms than it has been during the workweek.

We'll need to see how much instability develops and exactly when the front and other boundaries move through the region before determining whether stronger thunderstorms could become an issue.

The second is just how cool and dry the air becomes behind the front.

Right now, the forecast strongly supports a noticeable cooldown Sunday and into the beginning of next week.

Small changes in the position and speed of the front could still affect exactly how quickly that cooler air arrives.

The Bottom Line

We still have several very hot days to get through first.

Wednesday, Thursday and Friday will continue to feel much more like the middle of summer than the beginning of September, with highs in the mid-to-upper 90s and triple-digit heat index values possible in parts of the region.

Saturday becomes the transition day.

Showers and thunderstorms become more likely as the ridge weakens and a front approaches.

Then Sunday brings the payoff.

High temperatures fall into the mid-80s across Rowan County and much of the surrounding region, followed by overnight temperatures in the mid-60s.

After spending much of this week flirting with 100 degrees and dealing with triple-digit heat index values, Sunday is going to feel very different.

It isn't quite fall yet.

But we're finally going to get a taste of what happens when summer begins loosening its grip.