Tuesday, September 9, 2014

Cool, wet weekend; then maybe taste of fall next week

Those of you who have been griping about hot weather can celebrate.  It looks as if a real change to cool conditions is on the way, although it might make the weekend rather unpleasant.

The first real shot of chilly air is expected to push out of Canada and into the northern edge of the United States over the next few days. There will even be a bit of snow in the northern Rockies, and scattered frost over parts of Montana and the Dakotas.

That autumn-like air mass will push eastward, bringing much cooler air to the Great Lakes over the weekend and then the Northeast early next week.

The edge of that cool air will move through the Carolinas on Friday, but there are some real questions over whether the cold front will have enough of a push to reach the Deep South.  That means the front could stall over Georgia and South Carolina, setting the stage for a cool, cloudy, wet weekend.

In September and October, it's not uncommon for these late-summer and early-autumn cool air masses to get hung up near or just south of the Charlotte area. When that happens, small low pressure systems develop on the stalled front and move eastward, bringing a mix of drizzle, light rain and even moderate rain showers.

It's a version of the cold air wedge, and it could be in our future this weekend.

By early next week, computer models indicate that the front finally will push south, allowing skies to clear in the Charlotte region. If that happens, we could be in for a real taste of autumn, with daytime highs in the mid 70s and morning lows in the low and mid 50s.

A sure bet: Speaking of cold air wedges ... Tuesday was another example of how you could make a lot of money betting against the computer models when it comes to wedge patterns in the Carolinas.

The models almost always are too optimistic in predicting when the wedge will weaken and allow the clouds to break and sunshine to return. On Tuesday, the models showed sunshine returning by midday Tuesday to Charlotte, with temperatures climbing into the mid 80s.  Naturally, the clouds hung tough all day.

That happens nearly every time in these wedge patterns.

Assuming the wedge breaks down Wednesday, we'll see a brief return to summer-like weather, with highs reaching the mid 80s.  Temperatures could hit the upper 80s Thursday, but then the cold front will arrive Friday and bring it all to an end.

5 comments:

James Edgar said...

The computer models are also always far too optimistic (in the eyes of us cool-weather fans) about when the final break from 90-degree days will come. "Cool weather is upon us," some forecaster says every year on Labor Day. I just hope it never gets as bad as it was in '07, when our last 90-degree day was in mid-October.

And I think we all know that as soon as you think, "If it rains one more drop, I'm going to scream bloody murder," just go seed your lawn. As soon as you do that, it won't rain a drop for 6 weeks, or at least not until the wind blows all the seed into your neighbor's yard...

Alannc44 said...

It does seem like the models could be updated to take into account the mountains and their effect on these wedges. (assuming the mountains play a part in them)

BH said...

Alan, The mountains play a key role in banking the cold air to form the wedge. Just hope we can avoid too many of those patterns this winter, as they often mean freezing rain here.

Clay Jackson said...

What a coincidence my wife gave me the same cool & wet forecast for our bedroom this weekend.

Anonymous said...

Why this obsession with sunshine? It's the main cause of it being too hot. The only things that needs bright sunshine are crops. Go live in Florida for a year. I guarantee you'll never pray for a cloudless day again. Is 85 and sunny really that much more preferable to 70 and cloudy?

Bring on the cool...