... Dry high pressure builds in across the Great Lakes through Thursday, continuing a slow cooling trend over the region. Meanwhile, Hurricane Ian will track north across Florida and approach our area over the weekend, bringing widespread rainfall and gusty winds.
NEAR TERM /THROUGH TONIGHT/... As of 1100 AM EDT Wednesday: No significant updates this morning as grids look good for now. Cirrus shield is moving in a little earlier so this may impact afternoon highs, so have tweaked temperatures slightly. Otherwise, pressure gradient increases across the area between high pressure building in from the north and Ian to the south. Expect wind speeds to pick up across the area as mixing begins this morning. Low end gusts possible all areas with slightly higher gusts across the mountains. Varying amounts and thicknesses of cirrus will spread over the area through the day. With the cooler air mass and lower thickness values, highs will be around 10 degrees below normal. Even though the dry air mass remains, the cooler temps will keep RH values above critical levels for fire weather concerns. That said, RH and wind could be close enough to criteria that coordination with land managers may be needed.
Cirrus increases overnight across the area. The tight pressure gradient remains with a low level jet developing. This will keep wind speeds elevated with gusts possible all areas. Can't rule out mountain valley fog even with the winds, especially the sheltered Little TN basin. Lows will be around 10 degrees below normal. Patchy frost will be possible across the mountains even with the winds and dry air mass, especially sheltered locations.
SHORT TERM /THURSDAY THROUGH FRIDAY/... As of 300 AM Wednesday: Ian is forecast to be crossing central FL at 12z Thu, with guidance shifting its track east of previous runs. This takes Ian into the Atlantic just east of Jacksonville, FL, by 12z Fri. Meanwhile, an ~1030 mb high will be settle over the eastern Great Lakes. The tightening pressure gradient between these systems will result in breezy conditions, with gusts of 25 to 35 mph possible. There will be an increase in cloud cover Thursday aftn, as cirrus expands north from Ian, then some deeper moisture will arrive by daybreak Friday. PoPs increase from SE to NW across the forecast are during the day Friday, as rain shield/outer rainbands from Ian spread in. Highs will be 5-8 deg below normal Thursday, and 10-15 deg below normal Friday, as hybrid CAD develops. Lows will be near normal. Based on the latest forecast track and timing of Ian, not expecting any excessive rain/flood threat until Friday evening.
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 320 AM Wednesday: With Ian's forecast track now spending some time in the Atlantic east of the GA coast Friday, Ian may strengthen slightly before making landfall somewhere along the GA or SC coast Friday night. This track shift also results in heavier QPF potential due to a slow-moving deformation zone crossing the forecast area Friday night thru Saturday. There is still uncertainty on getting the really heavy rain rates you'd expect with a tropical system. A CAD wedge will remain in place, limiting instability. Also the low-level flow may be more out of the NE longer than previous forecasts, which may cut down on the upslope rain totals along the Blue Ridge escarpment. With that said, the overall consensus is an uptick in QPF totals, especially Friday night thru Saturday. If these totals verify, we could see 3-5 inches in a 24-hour period near the escarpment, which could result in an elevated landslide threat. But there is still a lot of uncertainty on the QPF. The other concern Friday night thru Saturday will be gusty winds, which combined with saturated soils, may cause some power outages due to downed trees. Ian will be undergoing extratropical transition, and tropical-storm-force winds are still not expected this far inland. Lows will continue to be near to slightly above normal, while highs will be about 10 deg below normal Saturday.
Ian still is forecast to stall out over the region, and keep unsettled weather across the forecast area Sunday into Monday. But the system will be dissipating, and additional rainfall should be light to modest at best. In any case, conditions should steadily dry out through the remainder of the period, but some degree of moisture (and PoP) lingers into early next week. Temps should remain below normal throughout.