Clemson, SC 29631 Weather

What Has Changed

Aviation discussion updated for the upcoming 12z TAF issuance.

Key Messages

1. Relative humidity will likely drop down to around 25 percent across parts of northeast Georgia again this afternoon, leading to increased fire danger in some locations. 2. Dry high pressure persists through early next week. Temperatures will fall below normal beginning Friday, then steadily return to normal through next week.

Discussion

Key message 1: Relative humidity will likely drop down to around 25 percent across parts of northeast Georgia again this afternoon, leading to increased fire danger in some locations.

The upper pattern will remain blocky and high-amplitude again today and tonight, but fortunately we are in the fair weather part of the block with high pressure ridging down from the Great Lakes and Ontario, giving us clear blue sky and near normal temperatures. Guidance suggests the dewpoint will mix out a bit more than yesterday, so some of the lower dewpoint solutions from the CAMs were mixed into the NBM. Forecast soundings from the western Upstate and northeast Georgia show the mixing potential, so we have undercut the NBM once again. That should put the min RH down to the middle 20s in percent this afternoon. The HREF shows that patches of RH below 25 percent in northeast Georgia will be likely. That would warrant issuing another Fire Danger Statement in spite of yesterday's not meeting with expectations. Fortunately, wind will remain light.

Key message 2: Dry high pressure persists through early next week. Temperatures will fall below normal beginning Friday, then steadily return to normal through next week.

The upper level blocking pattern will persist through the weekend, but will finally break down early next week. In the mean time, a subtle slow eastward shift in the upper ridge axis will move the aforementioned sfc high across Quebec to New England and the northern Mid-Atlantic from Friday into Saturday. This should put the sfc high in the perfect spot for a dry cold air damming wedge to develop late Friday and Friday night, and then persist through the better part of the weekend. A new upper low offshore by Sunday is not expected to affect the western Carolinas. As a result, temps will drop down to about a category below normal for Friday as the wedge starts to form late in the day, and will stay 5-10 degrees below normal for Saturday even with nearly full sun. The coolest night should be Saturday night, with lows down into the mid-30s in the mtn valleys, thus cool enough for some good frost potential, with a small chance for frost extending out over the northern foothills.

The pattern deamplifies and becomes progressive on Monday, but the remnant dry high pressure air mass should linger into the middle of the week with temps gradually moderating back to normal. Could the next system approach next Thursday? The GFS looks over-excited with a compact mid/upper low moving across the mtns late in the day, so it was treated with benign neglect for the time being. Temps should hang around normal through the first half of next week.

Aviation

At KCLT and elsewhere: VFR conditions expected thru the period, except for some patchy mountain valley fog and fog around some of the larger lakes. Could see some fog affect KHKY, but the probability is too low to include any restrictions. Will update if fog does end up wafting over KHKY after the AFD has been sent. Mostly light NW to NE winds are expected thru of the period. KAVL will see a slight uptick in winds this aftn, and could have a few low-end gusts.

Outlook: Dry, VFR conditions persist through the remainder of the week and into the weekend. Mountain valley fog and low stratus will be possible each morning.