Seriously. I’m doing my best to stay on top of the specifics, but we are just starting to get into the window of time where specifics are something we can estimate. And the data coming in isn’t much better than the data that is already here.
Another GIF showing the model's suggested placement of the system by Sunday evening. pic.twitter.com/MN7nrsrp1O
— Nick Lilja (@NickLilja) January 7, 2021
So while I wish I could jump in and say, “here is how it will look! Take it to the bank! Write it in pen! Etch it in stone!”
I have to, instead, say, “Well, here is the best estimation of the potential for the general area.”
Doesn’t have quite the same ring to it, I know.
To the data!
Where’s the cold?
As you can see from the tweet above, the data has been a bit more consistent the last ew days. But consistent data can still be inaccurate. Instead, I want to zoom out a bit and try to get a handle on the big picture, set the stage, and then try to make some estimations.
The super cold stuff is currently stuck in Canada. In the 500mb map below, I’ve drawn in the general storm track – northern and southern.
The northern track is trapping all of the really cold stuff in Canada. And that is highlighted by the temperature anomalies. The map below is how far the temperature is expected to be – above or below – away from the average temperature.
A lot of -1s, -2s, and -3s but not many -5s, -8s, and -10s on the map. So cooler, yes. Much colder? No.
And this will play into the confidence level for the chance for wintry precipitation. Since we are toeing the line, it is much more difficult to put a flag in the ground and proclaim anything with any certainty.
What’s up? … Like in the atmosphere
Taking a closer look at the 500mb map from above, you can see that the area of low pressure – up at 500mb – isn’t really in a good position for southern snowfall, either.
In fact, that is a good place for the area of low pressure to be to bring the region severe weather. The main difference this time is that the air aloft will be markedly cooler.
The purple dashed line is the temperaure normally seen during a severe weather event. The red line is the temperature estimated by the model. The green line is the dewpoint temperature estimated by the model. The blue line is the wet-bulb temperature as estimated by the model.
All of these will play a pivotal role in determining the precipitation type.
If, in the yellow circled area, there is an injection of moisture and precipitation – without excess heat – it can evaporatively cool the atmosphere enough to allow any frozen precipitation to fall to the surface because the process of evaporative cooling will drop the temperature to the Wet-Bulb Temperature, which in this graph is hovering around the freezing point.
For more information on reading a Skew-T chart, check this out
But the potential for that to occur will be decided by a host of factors – one being a timeline of events. The longer this system takes to show up and the slower it goes at it moves through, the less likely it is that any wintry precip will fall. The other issue will be with the system’s track through the region. The further south, the better the chance for wintry precip. The further north? Not so much.
Where’s that system going?
And the trend is for the system to be moving slower and the be further north.
On the animation above, it is showing the relative change over time of the area of low pressure. The deeper blues shifting north suggest a trend to the north. And the reds over the region and to the east, suggest the system is slowing down within the model guidance.
Turning data to information
Using what we have learned above, it would seem that the specifics we can try to pull out is that the rain/snow line is shifting north, the timeline is slowing down, and the potential for higher totals of precipitation – however it falls – is increasing.
The purple line would’ve been the rain/snow line 72 hours ago and now it is most likely the blue line.
I really want to drive a point home, for a second. The rain/snow line is not a fixed spot. it moves, flexes and wiggles. So if you are north of the line, you may still see some rain, and if you are south of the line you may still see some snow.
Could this change? Yes. Will this change? Yes. Is this the final forecast and you can lock it up and expect this to be exactly how things play out? No. not at all.
This is the best estimation we can make, right now, with the latest available data. The goal here is to help you prepare for the possibilities, not to give you the final answer about what will happen. Final answers about the future is not what weather forecasting is about. Never has been. It is about preparing you for potential outcomes.
The Bottom Line
It looks like the chance for widespread snow in the region is unlikely, but there will be spots that do see snow. And some places that see accumulations. Those places are likely north of I-20. South of I-20 snow is possible, but accumulating snow is unlikely given the latest data. And closer to the Gulf Coast, snow is unlikely to be seen.
That is about all we can know at this point.
Be prepared for life-altering changes on Sunday and Monday, though.
It is likely that the potential for wintry weather will cause businesses, governments, and groups to make changes to plans and schedules – whether your immediate area sees any wintry precipitation or not.
