I have had my eye on this system for the past week, and models are finally beginning to come towards a consensus. It appears that a strong area of overrunning precipitation will push into WNC sometime on Tuesday, and that will meet a cold wedge of air that will be funneled in from the Northeast. What does appear certain over the next week is heavy precipitation. Over 5” of rain will be possible later next week, but my current focus is on resolving the details of when the precipitation begins on Tuesday.
What Details Need To Be Worked Out?
Precipitation Timing
When will the system move in from the South, and how strong will the wedge be? If the wedge is allowed to build into the night on Tuesday before precipitation moves in, I think we stand a better chance of seeing accumulating snowfall around WNC. If it comes in during the day on Tuesday, I think the chance of us switching to snow will dramatically decrease.
Strength of Cold Wedge
As high pressure builds to our NE during the day on Tuesday, cold air will infiltrate the surface layer around WNC. Some models show this near frozen layer much deeper compared to others. Depending on the exact positing of when the high pressure sets up and its orientation, will determine just how much cold air is available.
Rate of Precipitation
Heavy precipitation will cause the column of air above WNC to go isothermal(frozen) sometime Tuesday evening. Depending on how heavy this precipitation is will determine how long we will see mixing (if any). Some models bring as much as 1” of rain in a six hour period Tuesday evening. Wetbulbing could occur where dry air allows precipitation to stay frozen as it falls through near frozen air. This is the natural atmospheric process that I believe could produce snowfall at the onset of precipitation Tuesday evening.
Model Data:
Below you can see a sounding from the 12z GFS that shows the column of air around Asheville. I have circled the crucial area where the temperature barely rises above freezing. This is what I am watching regarding the possibility for heavy snow/sleet Tuesday night.
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Below is the 12Z GFS precipitation depiction and it shows the transition just northeast of Asheville. Temperatures are so borderline, that we will need to wait until short range models get into range to have a better idea as to if accumulation around Asheville will be possible.
12z GFS Precipitation Depiction Courtesy of Weathermodels.com
Elevation Above 3500’ Look To Get Hammered With Heavy Snow Tuesday Night
I am more confident that higher elevation locations in WNC above 3500’ will see heavy snow Tuesday night. Accumulation will certainly be possible as well, with some models showing an astonishing 12”+ around Boone before a switchover to rain. There is great volatility with models currently, and very small details within these models can change over the next few days. Thats why I am watching the front of this moisture stream very closely.
Extreme Flash Flooding Possible Late Next Week/Next Weekend
I am becoming increasingly concerned about the flash flooding potential later next week as this stream of moisture brings over 5” of precipitation to the area. Already soggy soil will not handle the excessive moisture that the atmosphere will bring next week, and that will cause problems all across the SE. Some locations in NGA and SWNC could see over 10” of rainfall in the next 7-8 days. That will push streams and rivers out of their banks, so if you live in these areas next to a creek.. please be prepared to move to higher ground. Below you can see the most recent GFS total precipitation model for the next 7 days.
12z GFS Total Precipitation Courtesy of Weathermodels.com
Recap:
Some higher elevation sleet/freezing rain could be possible tomorrow night above 3500’
Rain likely for others below 3500’, a few sleet pellets cant be ruled out
Next system moves in Tuesday afternoon, heavy precipitation Tuesday night could turn to snow
Higher elevations above 3500’ in WNC will switch to snow and 3”-6” of snow could be possible
Accumulating snowfall cannot be ruled out below 3500’, short range models will be needed
Next system moves in next weekend, and could push weekly precipitation totals above 5”
Dangerous flash flooding will be possible to end the week, especially SW of Asheville
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