North Georgia Winter Storm Threat 2/15-2/18

Good afternoon everyone.

It’s been so long since I got to write one of these in such short range, so I’m not entirely sure where to start. However… things are certainly shaping up to bring an end to the shut-out of a winter we have had. There are still, many, many uncertainties with this system(s), most of which I’ll illustrate here. I have the system broken down into four parts below: timing, precip types, precip amounts, and my early call maps.

TIMING: This is an interesting question due to the differences in the modeling. The fastest model is by far the NAM, which moves precip, in the form of snow, in as early as 6-7AM Monday. The map below is valid 7AM Monday, with that furthest south blue line being roughly the snow line.

namonset2

The GFS also moves some light precip in early Monday, but it is gone by the next frame.

gsonset

It keys in on a “second wave” of sorts 24 hours later early Tuesday morning. It’s also a tick warmer at the upper levels but I’ll get to that in a minute.

gfs2

The Euro, which I can’t technically share here legally, falls down the middle with the main precip arriving mid afternoon into overnight Monday, and has temps much more in line with the NAM.

The Storm Prediction Center’s SREF is more in line with the NAM on timing, though they do use many of the same components so that makes sense, and the Canadian, shown below,  also agrees with the NAM on the early precip, but moves the bulk in on a more Euro-like timeframe late Monday.

7AM Monday

7PM Monday

So, taking a middle ground approach and assuming the GFS is a bit slow outlier at this juncture (it’s ensemble mean is more in line with the Euro, I might add), I would anticipate precipitation starting sometime between 10AM and 5PM Monday. This is subject to change, obviously, as we are still 3 days away but this is a decent first estimate IMO.

PRECIP AMOUNTS: Precip totals are fairly well agreed upon from the NAM/Euro/GEFS/CMC at this juncture, with around 1/2-3/4″ of precip, which would translate into 5-7″ of snow if it all falls as such.The latest GFS mean is shown below and it is on the upper end of that range, but at this point conservatism is best.

This from the overnight CMC (Canadian model) ensemble also shows the upper end (and above) on that spectrum, with up to 1″ of precip.

The current SREF mean is fairly low at around .2″, but the NAM/Euro both show around 1/2″.

PRECIP TYPE: This is the one everyone is wanting to know about: precip type. Snow? Sleet? Ice? Well, latest guidance suggests a mix of all 3 for different parts of the region. This is the only Euro map I’m going to post here, but it gives a decent representation of my current thinking on precip type, though I do think it is a tick too warm so shift these lines south 10-20 miles or so.    

getimg

AS OF RIGHT NOW: I areas like Cornelia, Cleveland, Dahlonega, Dawsonville and north to stay snow for the duration of the event, with areas around Gainesville/Cumming starting as snow then transitioning to sleet and possibly some light freezing rain near the end of the event. This is HIGHLY SUBJECT TO CHANGE, however, especially being 3 days out still.

MY FIRST CALL: I hate to say this is a “call” because it’s simply my thoughts as of the latest guidance, but IF this occurs as I currently think, the areas that stay snow could get into the 3-5+” range, with areas that change seeing a 2-4″ followed by another inch or so of sleet and a coating of ice. I can’t stress enough how incredibly uncertain this forecast is, so don’t treat it as anymore than a forewarning of what *could* happen on Monday. Forecasting snow anywhere is difficult, but it’s even more difficult in the south where one small adjustment can completely mess up everything and leave you with a cold rain.

As we get closer I’ll move this discussion over to the FB page (where it is more easily shared),  but right now continue to check me out on Twitter @negawxman and I’ll stick another update out on here either late tonight (following the 0z runs) or tomorrow morning.

Everyone have an excellent Friday and stay warm this weekend!~TW

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