Taking a Crack at the Weekend Storm

I've held off and held off posting my forecast regarding this weekend's storm...simply because until now, I had no clue, nor apparently did many other forecasters. Models have thrown several curve balls, and still may not have this pinned down right.

Early along, this looked like a potential major winter storm...with the low traveling south enough to allow plenty of cold air to filter in. Now, it looks like a moderate rain event, with a couple of possible dry-slot "screwzones," and a decent wrap-around/upslope event to end it.

The latest GFS run looks pretty crappy for QPF...with both showing significant dry-slotting/precipitation breakdown, likely due to early downsloping (KTRI is reporting wind from the SE). The NAM gives the entire area a 1" dousing, with totals up to 2" in W NC. I'm going for more of an areawide total of .5"-1", with isolated totals over an inch...especially across W NC (subject to change...18Z run may paint an entirely different picture).

Right now, it appears as if the precipitation will come in three main waves. The first arrives this afternoon in the form of light to moderate rain showers that have developed over AL and GA...and are currently moving north. The second wave arrives later tonight as the main area of rain currently situated over Western TN, MS, and LA. This is moving east. This is where the majority of the rain should come from. The third, and likely final wave, will come as a wraparound and upslope blend of generally light to moderate rain and snow showers. This should begin late tonight/early Sunday morning, and could last through the day Sunday...depending on how well the flow sets up.

A minor CAD event is occurring over parts of SW VA and W NC. Temperatures are in the middle 30s across the area...and will remain that way today. Tonight they may drop below freezing, especially before the onset of the main wave of rain. With temperatures above the surface above freezing...the potential exists for freezing rain today and tonight...mainly across the higher elevations. Right now, it looks as if ice accumulation will be sketchy...and will likely remain below ice storm criteria (.25"). As the rain moves in and becomes heavier, temperatures will begin to rise, as the rain falling is warmer than the temperature at the surface. This should end any threat of ice with this storm.

As the low pulls north early tomorrow morning, it will rapidly intensify (possibly bombogenesis). This, and the passing of a cold front, will help to pull cold air south. As this occurs, wraparound and upslope precipitation should set up, and create for an interesting day of weather. Rain may change to snow in the morning in the highest elevations, and continue as snow levels drop. All told, much of the area should at least see a bit of snow mixed with rain. Favored upslope spots could see anywhere from 1-5"...with other locations above 2500 feet possibly seeing 1-3".

Wind will be an issue with this system. Gusts in the mountains may reach 60 MPH tomorrow.

This probably sounds quite "rambly," as I have literally just thrown together my thoughts on this system. It's been an irritating one to follow, and will probably do something else abnormal before all is said and done. Bottom line, look for some beneficial rainfall, possibly a bit of snow in the mountains, as well as a bit of ice tonight, and a potentially damaging windstorm tonight and tomorrow.

12/15/07-3:07 PM