Could we see a Festivus Miracle??

 

Model data mid and late week last week looked promising for  pre-Christmas snow. There was a lot of chatter on social media but because this pattern has been delayed or not developed as modeled, I was hesitant to mention it until it seemed more apparent an event would take place. Long story short, cold air is on the way but the pattern won't allow the energy to dig enough so we will warm up just long enough to rain then some VERY cold air settles in as Christmas weekend will be below freezing. 

Artic fronts like to have a squall line and or strain out all the moisture as the come through but you need a little energy and moisture along and behind the front for this to take place. Some model data suggest this is POSSIBLE.  From 6am-10 am Friday the SUPER cold arctic air pushes through and we go from 35-40 to 20 degrees in a few hours. There is a slight chance rain quickly flips to snow and get a quick coating to an inch. Best chances will be along i81 and then slightly east of Lynchburg due to down sloping off the mountains. My current odds of these regions seeing accumulating snows under an inch-

Blacksburg 50%

Roanoke- 33%

Lynchburg 25%

Danville 10%

The GFS model (American model) is the most aggressive with rain ending as accumulating snow Friday.  Best shot at a coating to an inch will be above the blue line based on historical data. 

Brief guess...

Ice is inevitable..

Timing of onset vs timing of change to ice will dictate how much snow vs ice we get. What started as a Saturday into Sunday event is now a Sunday event. Some data even has an afternoon start of the storm. 

We will have crazy cold air in place. Temps could be in the teens with snow then ice falling.  This will be snow in the south in places like NE Georgia, TN, upstate SC and into NC that changes to ice. The concern is that as the low moves our direction the BITTER cold is leaving and allows the storm to take an inland path that always leads to some ice in our region. The other odd factor is that because the air is so cold, the precipitation holds off because of the dry air and then starts as the cold air is leaving. Double whammy. 

To get the most snow we need it to start early Sunday AM. Completely possible, but just may not happen. If not, we will get a GOOD snowstorm but it will go down as another mixed bag in much of our region that "could have been".

The mid range euro and NAM, short term model has snow over most the region by 1pm, temps in upper teens and lower 20s.  General rule of thumb is snow tends to change over faster than modeled. This could be the exception but I'd not bet against it.

At 7pm here is an image of temps at 5k feet. Simple put, blue shades are below freezing.  Ice is well into SML and Lynchburg  and likely even farther west with a warm layer being above this one layer.

Southside- highest risk of serious ice after some snow.  Snow range 3-8 inches then ice. 

SML to LYH area- moderate risk of ice after a significant snow.  Snow range 5-10 inches

Places west of the Blue Ridge, I 81 region including Roanoke, Blacksburg and Lexington. Mostly snow, may have some mixing. 

8-14 inches, maybe more. 

Places that remain mostly snow should see double digits. 

Woah, that was fast! 3 to 8 inches of snow likely region wide.

We have a storm on the way. High risk, high reward type event where the margin for error will be very small. 

1. The storm isn't a shock but the magnitude and intensity of the pending event could be shocking. It was on the models off and on all week. We needed the upper air energy to close out and space out and it did EXACTLY what was needed. Adding, if we had any cold air in place this would be a historic snow for much of VA. Instead it's 61 as I type this. 

2. Timing is key. It will snow but a few degrees warm, precipitation moving to fast, etc could be the difference between a slushy inch or two and 7-8 inches. Cold air being a little to slow or storm moving a little to will really change the outcome of the event. 

Timeline- 

Rain develops late evening and overnight. Rain should be hard. Between 4 am and 7 am, the rain should mix with and change to snow. Whatever is falling will be heavy. Snow should between 9 am west and maybe closer to noon eastern areas. Snowfall rates may be among the best we've seen here. Some "hour" data shows several hours of 1-2 inches an hour of snow falling. 

Snow totals- In general, 3-8 region wide is a good guess with a strong understanding this is not a "locked" forecast at all. One thing goes wrong, we end as flurries- conversely a deepening low could flip it to snow sooner and someone gets over 10 inches. Both options are viable at this point.