Our forecast continues to trend toward a higher risk of widespread showers and thunderstorms beginning Wednesday afternoon and lasting into Thursday. The biggest change isn’t necessarily that we’ll see more storms—it’s how they move. A cold front is expected to slow down and eventually stall across the Carolinas, providing a nearly stationary focus for repeated thunderstorm development. Instead of storms quickly moving through, some areas could see multiple rounds of heavy rain as storms repeatedly track over the same locations. That has increased our concern for localized flash flooding, especially from Wednesday night through Thursday when tropical moisture surges into the region.
Right now, our area remains under a Slight Risk (Level 2 of 4) for excessive rainfall. While the highest flood threat is forecast farther east across eastern North Carolina and southeast Virginia, confidence has increased enough for the excessive rainfall outlook to be expanded westward into the western Carolinas. That tells us the ingredients for heavy rain are becoming more favorable across our area as well.
The atmosphere has remained fairly quiet this evening, with only isolated and generally weak showers developing. There simply hasn’t been enough support in the upper atmosphere to organize thunderstorms. A few weakening showers or storms may drift into the mountains overnight from Tennessee, but they should continue to lose strength as they move east. Overall, tonight is expected to remain relatively uneventful.
Wednesday marks the beginning of a much more active weather pattern.
As the cold front approaches from the northwest, showers and thunderstorms will become more widespread during the afternoon and evening, especially across the mountains and foothills before expanding farther east. Unlike the isolated storms we’ve seen recently, tomorrow’s storms will have a well-defined boundary to develop along, allowing for much better coverage.
The atmosphere will also become a little more favorable for stronger storms. Winds higher in the atmosphere will increase enough to help organize a few thunderstorms, meaning an isolated severe storm will be possible during the afternoon and evening. The main concern with any stronger storm will be damaging wind gusts, although widespread severe weather is not expected.
The period from Wednesday night through Thursday has our full attention.
As the cold front slows down and eventually stalls somewhere across western North Carolina and the foothills, it will become the focus for repeated rounds of thunderstorms. At the same time, deep tropical moisture associated with Tropical Storm Bertha will surge northward into the Carolinas.
When those two ingredients come together, the concern shifts away from severe weather and toward flooding.
The atmosphere will be holding an incredible amount of moisture, allowing thunderstorms to produce very heavy rainfall in a short amount of time. Rainfall rates could exceed 1.5 to 2 inches per hour, and some communities could receive 2 to 4 inches of rain, especially if multiple storms move over the same location.
One of the biggest concerns is something we refer to as training thunderstorms.
Imagine a freight train rolling down the same set of tracks. Each train car passes over the exact same crossing. That’s essentially what could happen with thunderstorms. Individual storms may move along at a decent pace, but they’ll continue developing and following the same path along the stalled front. If your community ends up underneath one of those “tracks,” rainfall can add up very quickly.
The exact location where this happens is still uncertain because it depends on where the front ultimately stalls. A shift of only 25 to 50 miles could dramatically change who sees the heaviest rain. That’s why it’s too early to pinpoint exactly which counties will receive the highest totals.
However, confidence continues to increase that someone in our foothill counties will experience localized flash flooding.
Generally speaking 1-3 inches looks likely. We do anticipate some localized areas of 2-4 inches, and is possible that someone receives 3-6 inches. It’s tough to nail down exact totals right now though
Because of that increasing confidence, don’t be surprised if Flood Watches are eventually issued as we get closer to the event.
Unfortunately, Thursday doesn’t look much different.
The stalled front is expected to remain nearby, allowing additional showers and thunderstorms to develop throughout the day. While temperatures will actually be cooler thanks to increased cloud cover and easterly winds, the heavy rain threat will continue.
If the ground becomes saturated Wednesday night, it won’t take nearly as much rain on Thursday to produce flash flooding. Creeks, streams, poor drainage areas, and roads that typically flood during heavy rain will need to be monitored closely.
The good news is that this pattern should gradually improve late Thursday into Friday as the front slowly begins drifting south of the area.
By the second half of the weekend, we’ll finally begin transitioning back toward a more typical late July weather pattern.
Rain chances will decrease, sunshine will become more common, temperatures will return to near seasonal levels, and we’ll go back to the familiar pattern of scattered afternoon and evening thunderstorms instead of widespread heavy rain.
Summarizing:
Wednesday afternoon will bring increasing coverage of showers and thunderstorms, with an isolated strong to severe storm capable of producing damaging wind gusts.
The bigger story, however, begins Wednesday night and continues through Thursday as a stalled cold front combines with deep tropical moisture from Tropical Storm Bertha. That setup creates an environment favorable for repeated rounds of heavy rain, and some storms could produce rainfall rates of 1.5 to 2 inches per hour.
Our area is currently under a Slight Risk (Level 2 of 4) for excessive rainfall, and confidence continues to increase that parts of western North Carolina could experience localized flash flooding. While we can’t yet say exactly where the heaviest rain will fall, now is the time to review your plans if you live in a flood-prone area. Never drive across a flooded roadway, and make sure you have multiple ways to receive weather warnings over the next couple of days.
We’ll continue refining the forecast as confidence increases on where the stalled front sets up, because that will ultimately determine who sees the highest rainfall totals and the greatest flooding threat.
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