By Thursday afternoon, a front will have nudged far enough south to give us a chance of rain late in the day. It will take its time moving through, so I'll leave a chance of rain in all day Friday and the beginning half of Saturday. The rain won't be terribly widespread or heavy though; as illustrated by this plot of precip from numerous computer models:
In fact, the GFS is the only model spitting out any rain locally, with the 06Z coming in drier than the 00Z run. I do have to say that the NAM doesn't forecast far enough out to capture a potential rain event as it brings the front in a tad later than the GFS. The only thing this front is assured of doing is bringing in MUCH cooler air! Highs are forecast to be in the upper 70s to low 80s by the weekend... Can you say fall is here!?
The cooler air will be aided in what we call Cold Air Damming (CAD). The high pressure moving in behind our frontal system will move from the Great Lakes to the Northeast, which will put it in prime position to develop CAD. Here's the model representation of it:
You see, winds around high pressure flow clock-wise, meaning if you're south of it, you will see easterly winds. These easterly winds around a high situated in the northeast runs into the Appalachian Mountains and isn't allowed to flow up and over. This means the cold air gets dammed up and must go somewhere! That somewhere is usually to the southwest along the spine of the mountain chain and into northern Georgia. If the high is strong enough, it can filter that cold air all the way into our area! We aren't forecasting it be to QUITE that strong, but it is certainly possible. Another result of CAD is a thick stratus deck, low level clouds. You'll certainly be able to see that along the Appalachians this weekend and I'll be sure to grab a satellite image for you! Clouds help keep temperatures down during the day and if the high is strong enough, we could see temperatures even cooler than what I'm forecasting right now... Either way, we are going to see temperatures below average for the duration of your weekend.
Tuesday: A few high clouds but otherwise mostly sunny. Highs near 92.
Tuesday Night: Mostly clear with lows dipping into the mid 60s.
Wednesday: Partly cloudy with highs near 93.
Wednesday Night: More clouds move in, in advance of the front. Lows in the mid to upper 60s.
Thursday: A slight chance of rain later in the day. Otherwise, we'll be partly to mostly cloudy with highs near 90.
Friday: The cooler weather filters in! First, we have to deal with some rain, but as noted earlier; the rain won't be all that widespread nor heavy. Highs in the low to mid 80s.
Saturday: Mostly cloudy with highs near 81. (Subject to change cooler....)
Sunday: Partly to mostly cloudy with highs near 80. (Subject to change cooler....)
Monday: The high pressure in the northeast moves east, out of CAD positioning. This will clear our skies but temperatures will still be near 80.
Looking in the extended range, I notice the GFS (and the Euro to a certain extent) bringing a longwave trough into the eastern half of the country next Wednesday/Thursday. I'll watch the models closely to see if they continue this trend, which could bring some cooler air (and maybe rain!) our way next Thursday and Friday.
Thank you,
David Reese
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