Morning fog & afternoon storms: typical August weather

The Weather Authority
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Thick fog covered a large part of North Alabama and Tennessee Monday morning, and that’s to be expected this time of year. August is known for foggy mornings and hot, dry afternoons; that’s because afternoon storms leave behind wet ground and the nights start to cool slightly through the next few weeks.

Morning fog and low clouds over Alabama, Tennessee, Mississippi and Georgia Monday morning. It’s easy to pick out the Tennessee River north of Chattanooga and some of the topography of the Cumberland Plateau around Murfreesboro.

The warmest overnight period of the year runs through mid-July; by mid-August, the average low temperature drops about a degree. That doesn’t sound like much, but cooler is relative. The atmosphere responds to that by producing foggier mornings in general.

There’s some old weather lore that equates foggy August mornings with snowy winter days. It’s fun to think about and try to keep count, but there is no science to it! You can read more about that here on!

Next set of stormy days: When we use the term ‘disturbances’ like we are using this week, we are describing something that is really an abstract concept. It’s not exactly a ‘wave’ like you’d see on water, and it’s not exactly just ‘energy’ in the atmosphere because that’s too broad a definition.

Think of it like this. It’s similar to the waves generated by someone canon-balling into a pool. There were already some waves on the pool surface, but this one is stronger and it’s disrupting the rest of the pool significantly.

Upper air flow this week sends strong waves southeast that disrupt the quiet, hot summer weather and kick off thunderstorms.

We’ll get a few ‘canon balls’ coming south across the Plains into the South from Wednesday into the weekend. At times, the storms they generate will miss us to the north, west or east. At other times, they’ll come rolling right through North Alabama and Southern Tennessee.

That’s why we have a ‘chance’ of rain and not a ‘guarantee’ of rain this week; there is high confidence that there will be storms in the area, but the coverage will be limited. That means low confidence that any one single spot gets hit with a storm.

So what can you expect time-wise on these storms?

  • Wednesday: a limited chance of some leftover showers from the overnight period on Wednesday morning and a good chance of some heavier thunderstorms again between 5 PM Wednesday afternoon and midnight.
  • Thursday: some showers/clouds linger early Thursday, but the best chance comes from around 2 PM to 8 PM.
  • Friday: this chance depends on how storms go Thursday/Thursday night.  There’s a chance they could stabilize the atmosphere enough to give us a breather on Friday, but if they don’t, we’re likely to see quite a few locally-heavy storms Friday afternoon and evening.

Looking for the rest of the forecast? It’s always online at and in the “Daily Forecast” section on Live Alert 19!

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