Western NC/SC Mountains: After some rain comes down in Western NC Thursday morning, most towns in Western NC (even some valley areas) across and adjacent to the Blue Ridge will receive between 2" and 10" of snow as this system will be capable of generating very high precipitation rates.
As far as timing in Western NC, a changeover to snow will occur during the afternoon and continue through the evening. The time frame for snow will be sometime between Noon and 5PM and continue until Midnight or so. Due to the heavy snowfall rates, travel could get ugly in places... especially up around Asheville and Waynesville. Interstates and highways will become tough to drive on north of the SC/NC border.
You may wonder why the difference between 2" and 10". There will be some towns which get caught under slightly warmer pockets of air along with less intense & less consistent precipitation rates and this will cause far less snow accumulations. On the other hand, there will be places that sustain very heavy snow rates and colder air in the mid-levels and those towns will quickly get popped with more than a half-a-foot of snow. The National Weather Service has posted a Winter Storm Warning for all of Western NC from 1pm until midnight tomorrow night.
Due to heavy wet snow in Western NC, power outages are likely (in some areas) as tree branches will not be able to support the weight of snow coming down so heavily in a short period of time.
Upstate SC/NE Georgia: The majority of what falls tomorrow in the Upstate will be a cold rain in the upper 30s and low-middle 40s. In fact, things will look like "no big deal" through the morning and even part of the early afternoon. Kendra, Alex and I have seen this type of situation before. The March 1st storm of '09 comes to mind where it rained all day and suddenly changed as a cold pocket of air up high moved overhead and flipped the script.
This will likely not be a repeat of that system or situation in '09 because this storm system doesn't have as strong of an area of lift within it's core, nor is it as cold as that one was. Since it doesn't have the capability or dynamics within it's core, lots of snow or high accumulations aren't likely south of the Mountains. However, tomorrow's system will produce heavy precipitation rates capable of changing the rain over to snow for a short time HERE in the Upstate, especially north of I-85.
There will likely be a window of about 1-4 hours late tomorrow afternoon (we'll say somewhere between 4pm and 10pm) where some snow is possible in places like Seneca, Walhalla, Westminster, Toccoa, Hartwell, Pickens, Clemson, Pumkintown, Travelers Rest, Greenville, Anderson, Easley, Williamston, Piedmont, Lyman, Duncan, Greer, Spartanburg, Woodruff, Inman, Campobello, Union and Gaffney (some other towns also). Still, there's no way around this being a marginal setup (as far as there being enough cold air in the critical levels for snow). Because of that, some places in the Upstate stand a high chance of all rain while others may see some 1-2" type slushy accumulations.
The National Weather Service has posted a Winter Weather Advisory for northern Oconee, northern Pickens and northern Greenville in addition to the counties north and northwest of Toccoa, GA in effect from 1pm until midnight tomorrow night.
I'm also focusing on the likelihood of a slightly warmer pocket of mid-level air becoming trapped west of Greenville around Oconee Co., Toccoa, Hartwell and possibly the Anderson area tomorrow evening which would quickly shut off the snow and change it back to rain. This warm pocket has happened before and happened back on March 1st of '09 when Seneca, Westminster, Toccoa and other places saw mostly rain with less snow.
Forecast Models/Discussion: This system is still barely strong enough or cold enough in the critical temperature levels to be much of a headache outside of Western NC. The trends during the last 24-hours have been for a slightly more dynamic and colder system, but the scenario is still "muddy" instead of clear on precipitation type. The heavy precipitation rates really stand out as the most important factor because the heaviest rates will be the reason some towns transition to a longer duration of snow than many other towns do. However, this upper-level system isn't quite strong enough to make snow a sure bet in many places. Also, the timing of this could get tricky if the changeover to snow happens in the evening.
Various forecast model charts are listed to the right. You can see how everything is coming into line for mostly rain south of the higher elevations of SC and NC with a late snow transition possible across Upstate towns.