Post-Christmas Cold Pattern is Here: I didn't bite two weeks ago and the cold has still settled in. Today will be one in a number of days here recently where we will stay below normal. The could-cover has been and will be the focus through the afternoon with rain moving in this evening. Highs will range from 44-48 for Upstate towns this afternoon as Western NC towns range from upper 30s to low 40s. These temperatures are slightly cooler than I expected this morning based on the intervals of sun or thin clouds that were possible. Expect more clouds than sun the next seven days with below normal temperatures as we roll towards January.
Off to a Much Different Start This Winter Compared to Last: I guess I can understand to how a person could come to the conclusion that warm air could ultimately win the battle this winter. It may just work out that way since we live a good ways from the north pole. However, the fact is, we have already had a much different winter than last year based on the recent heavy rains from two weeks of a very active sub-tropical flow of energy. It's a stark contrast compared to the drought-like conditions of last winter. That's not even taking into account that last winter was basically warm from start to finish with very few cold spells and none of them lasting.
The odds are less than slim that a drought or very dry pattern will take back over after the two weeks of drenching rain we have endured.. Also, the odds are slim that we end up warmer than last winter from this point forward. The snow-cover to our north backs up that thinking since it will be much easier for cold air masses to move south and east without modification. There will no doubt be warm stretches though and there always are since we live closer to the equator than the north pole.
Some Snow & Sleet for Western NC - This Evening & Tonight: There is an interesting situation developing tonight for a period (maybe long period in some places) of sleet or snow for a good portion (rain for others) of Western NC. And, we're not just focusing on the high elevations... we're talking valleys as well. This mixed bag of wintry precip. will happen before some warming overwhelms the column from the top-down as the warm layer (above 5,000ft) is pulled to the ground due to the heavy precip rates within the warmer, moisture-filled layer over the top.
The areas that should be on guard are towns west of Asheville (even in the valleys), especially near the Balsam Mtns southwest of Waynesville and Asheville.
It looks like a front-end thump (probably 3-9 hour window and possibly longer in a few places) of sleet/snow and possibly freezing rain is going to happen IN SOME SCATTERED NC AREAS, especially along the Balsam Mountain area in and around the counties of Macon (Franklin), southern Jackson (Highlands, Glenville Mtns, Cashiers), Haywood (Clyde, Waynesville, Cataloochee Mtn, Canton areas) and even possibly in portions of Buncombe County this evening/overnight between the hours of 6pm and 3am. Importantly though, a change of one degree is all it will take to change the precipitation-type. This is a messy forecast and very challenging because there will some of everything going on.
I checked forecast soundings and there is a decent cold layer sufficient for frozen for a time (probably 3-6 hour window). Also, some evaporation. cooling will cause temperatures to cool and hover between 31 & 33 in the low-levels for the areas mentioned above. But, a the warm layer above 5,000ft could keep most places liquid or at least inconsistent frozen, especially later in the night. Both NAM and GFS thermal profiles are similar on the early morning runs and both are marginal at 5000ft with 0.5C, 0C to -0.5C (0.5C at the lowest). 0z model runs were only slightly warmer, but they were close enough in the mid-levels to mention this possibility as well, especially once some evaporative cooling is realized. **The newest 12z runs have trended colder and more widespread with the mid-level freezing layer supportive of a mixed bag.** In these situations, precip. falling in areas where mid-level to low-level cold air gets trapped (could be around the Balsams) may be the wildcard for more sleet or snow and potentially worse road conditions than is expected in other forecasts. On the flip side of that, heavy precip rates will eventually lead to a dynamic warming situation (in some towns) where the warm layer is eventually pulled down to the surface bullying the cold layer and using the moderate to heavy precipitation to make that happen.
The interesting part is that, due to southwest flow where the moisture is coming from, this could create sizable snowflakes for a time and dangerous road conditions for a time as well. This will be especially if the mid-level to low-level cold gets trapped and doesn't get over-powered very quickly. ^ I've seen this exact thing happen in past storm setups for the areas/towns mentioned in Jackson, Transylvania, Haywood and Buncombe counties.
Since the layer of cold won't be all that established or widespread, there will be patchy areas of all rain as well. Then, slightly warmer will likely win the battle by late night or very early Saturday in most Western NC towns menlting away the bad road conditions (aside from the high elevations where NW flow snow will take over).
The bottom line is: Watch out traveling on some of the highways in Western NC this evening and overnight. Rain will most likely melt whatever falls early evening and tonight.