The main concern for the mountains is how far inland will the remnants of Florence get + how fast will they move. The National Hurricane Center has been going with the European Model which has been, by far, the most consistent with the track.
Main jet stream cores are far to the north, and while there is some SW flow over the area now that is likely to weaken with large-scale subsidence in advance of Florence by later this week.
GOES-16 Water Vapor Image – Evening of September 10, 2018
While I think it will be Wednesday into Thursday before confidence on the inland track and speed increases by a significant amount, it is possible to discuss some of the possibilities ( for planning ).
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 1-5
The 51-Member European Ensemble Mean ( above ) shows Florence moving beneath a 500 MB upper air ridge axis during the next 5 days, which has been responsible for recent intensification.
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 4-8
The 4-8 day period, during September 14-18 above, keeps the main jet stream cores far to the north and a large, elongated upper ridge over the eastern USA.
The break or weakness in the ridge ( above ) shows where the remnants of Florence are likely to be.
Worst And Best Case Scenarios For The Cumberland Mountain Range
It appears nearly certain that Florence will turn into a disaster, perhaps a Mega-Disaster, for portions of the middle Atlantic. Historical odds would favor locations along and east of the Blue Ridge for worst conditions.
With the above noted, at this point in time, major flooding can not yet be ruled out for the Cumberland Mountains and surrounding Mountain Empire.
*While the European Model has been most consistent, individual runs and ensemble members have been widely varied on MAX rainfall amounts with up to 48.00″ ( 4 Feet ) in the worst case scenario being predicted for portions of Virginia and North Carolina along and east of the Blue Ridge. Anything remotely close to that would generate historic, deadly flooding ( of course, anyone knows that ).
Individual runs of the operational European, as well as its ensemble members, can be expected to continue to vary on rainfall amounts during the next couple of days despite a rather consistent trend of bringing a major hurricane into the Atlantic coast. A problem is with weak winds aloft the remnants will begin to slow down once it loses forward momentum and begins to feel frictional drag of the land.
Here I will briefly outline what would be the best and worst case scenarios for the Cumberland Mountains, where this website is mainly focused upon.
Best Case Scenario
The best case scenario to watch for would be that the remnants turn north following landfall and remain far to the east, keeping the Cumberland Mountains and Mountain Empire amid the subsidence zone of sinking air around the periphery of the core.
With a system like this one must begin to talk about orographic forcing, such that the best case setting for the Cumberland Mountains with the remnants moving far inland would be for them to move toward northern Georgia, southwestern North Carolina to maintain a southeasterly flow into southwestern Virginia and eastern Tennessee. This scenario, of course, would be the worst case for western North Carolina.
Worst Case Scenario
The worst case scenario to watch for would be for the remnant core to move toward northern North Carolina and southwestern Virginia, east of the Cumberlands, with a wrap-around northerly upslope flow generated into the local mountans with a stalling system. The orographics would then favor excessive rainfall over the local mountains and near the core of the remnant low ( especially on enhanced nocturnal convergence ).
There are many other possible scenarios, of course, but these are just ones mainly focused upon the Cumberland Mountains ( and based upon past climatology ).
