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Old 12-05-2017, 05:33 PM
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Default Winter Weather Threat 12/8 - 12/10

Alright, much has been made about the upcoming winter weather threat that is possible here in Georgia as well as Alabama, South Carolina and North Carolina. There are maps flying all over social media and I wanted to try and bring some focus into what is being shown and what I think is reality or possible.

Let's get the obvious out of the way. The NAM modeling brings the most precip to the most areas, the EURO took a step towards the NAM this afternoon with broader coverage but the precip is light. The GFS is only rain and dry conditions. That's where we are at.

That said, I for one don't think we are going to have moisture issues. The front that comes across is VERY positively titled. As it gets draped across the deep south it allows moisture to come riding "back over" into what is now air that is at the surface and vertically somewhere around 32-34 degrees. The issue will be what kind of moisture will be falling out of the sky. These clown maps show how much snow it thinks is accumulating which is nothing more than what it sees falling out of the sky.

Some years back we had an Upper Level Low that rolled through here. At my house in Dacula it snowed like crazy but there was mixing issues and the rate was on and off. Over in Athens... maybe 25 miles the way the crow flies, they had 8" of heavy wet snow that brought down tree limbs. The rate was faster and the moisture was heavier. That is what it will take to get accumulating snow here this week. A heavy rate of snow.

Right now to me, a line from Columbus to Macon over to Augusta northward to a line about Cedartown to Canton to Helen should see a flakes fly. You may even see a lot of flakes fly but just not accumulate.

I am going to attach some clown maps. This is not a forecast or even anything I am buying into just yet. The spread on models is from 0 anywhere to 3" in Columbus. Pick what you like. Yesterday the NAM had 8" in Columbus.

I will attempt to post another update in 24 hours.

Last, this forecast is a tough one. The time of the year is all wrong, the modeling is all over the place, the long positively tilted front stretched out like it is modeled is tough to predict how the moisture out of the gulf will interact with it.

Just like always, need more time and more model runs. The last NAM run is a dream come true for South GA folks.

More to come later.
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Old 12-06-2017, 04:09 PM
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Alright, so 22 hours later here I sit typing and I am more confident in a Winter Weather event that is inbound.

Just to be clear this weather event still has a lot of twist and turns left and we are roughly 2.5 days out from the onset. There is no guarantee and anyone that tells you they know how this will end up is guessing. Also, you don't have to find a secret facebook group to get your information or maps from.

That said, the NAM has been hounding this event for days. It's been doubted and there is still room for more doubt, BUT the EURO, the GFS (now) and the Canadian models have all started to look a lot like what the NAM has been harping on.

So what are the down sides right now? What will keep this from not happening? There are a few things that concern me. Right off the bat the 2M or surface temps look to be too warm. The NAM and CMC seem to be the coldest and therefore crank more precip. The GFS and EURO have warmer temps at the surface. The 850 temps or temp 5000 feet above the earth is plenty cold. No issue there. Do the surface temps that are forecasted by these models... are they 100% correct? The only way to know is for ground truth during the event. I will say I have seen events where models forecasted too warm and temps came in colder. I have also see temps be warmer than forecasted. That is a big deal and one that will have to be watched in real time.

Another concern is that the system will become to robust and bring plenty of moisture but also bring warm temps.

I feel like the models are seeing plenty of cold air in the column, however the surface temps will be the issue. Also, if you get under a heavy band of precip it can "pull down" colder air and take you below freezing. Also, evaporational cooling also plays in.

Therefore, right now I am thinking a mixture between the EURO and NAM is accurate.

For specifics, models across the board keep hammering an area in and around Newnan / Peachtree City. That cannot be ignored.

If the surface temps were lower, I would be all about going all in on this one. However, those have me a little concerned for actual accumulating snow. Snow amounts falling out of the sky is one thing, snow piling up is another.

EDIT: One other thing to keep in mind. Remember in January of 2017 the warm nose that invaded the East side of the state and turned our snow into rain? Or mixing in places? That is on the table now. You can really see it on the Canadian (CMC) models. That will have to be watched as well.
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Last edited by DDD; 12-06-2017 at 04:21 PM.
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Old 12-06-2017, 04:12 PM
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More model data...
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Old 12-07-2017, 04:45 PM
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