Winter Storm Expectations

I have been very hesitant to make any kind of forecast regarding this system, because it has been a wretchedly difficult storm to predict. Winter storms in the Deep South usually are. And it really doesn’t help when the computers, supposed objective arbiters of the atmospheric data, can’t make up their “minds” either. (Models are supposed to be guidance for the forecasters, a way of looking at possibilities in a straightforward and easy-to-grasp way. They are NOT supposed to replace thinking about one’s own forecast and understanding meteorology.) Just one model, the GFS, has shown nothing, a rain event, a mega snowstorm (in Deep South terms), a crippling ice storm, and wintry slop. And that’s just over the past week. Fortunately, two of those options seem to have been ruled out. We’re going to get frozen precipitation. That’s a given.

This system is one of those where we humans have had to sort through things ourselves and make a judgment call. That’s good for learning, but I’m quite glad I am not in a position where my forecast (or input for a forecast) will have any discernible effect upon the local economy and opening/closing decisions. The question really is whether we will get a foully unpleasant, persistent, cold mix of slop for a day and a half, which makes things pretty miserable but doesn’t require anything to be shut down, or whether it will be a crippling winter storm. Oh, and if it is a crippling winter storm, what type that will be. Mega snowstorm or destructive ice storm?

Wouldn’t want that judgment call either, would you?

Unfortunately, I began leaning toward a worst-case scenario a couple of days ago, though I was not confident enough in it to post such a forecast on the Internet. That’s good; I was prepared to call for an ice storm for everywhere from I-20 to Highway 78. Things began pointing in a different, snowier direction yesterday.

OK, I’m going to put this up first and then go into a bit of meteorological explanation for it. This is not an official forecast from any weather agency, public or private-sector. This is MY forecast.

The system is going to be formed from the mixing of a cold arctic air mass coming down from the north and a moist tropical-type low in the Gulf of Mexico. This type of system is very good at bringing significant winter weather conditions to the Southeast, because it gets all the ingredients in the right place and all that becomes important is the amount of each type of ingredient, whether warm air, cold air, or moisture. Usually, systems from the north that are cold enough to bear snow are too dry; warm air intrusion often kills the chances of frozen precipitation for those that are not too dry. It’s a balancing act.

The precipitation is going to begin as snow across much of the state. I think an exception will be areas south of the I-20 corridor, who will probably get sleet first. This is because the cold air will have arrived and the system from the Gulf is just getting started. In areas where the precipitation type will not remain snow, I doubt there will be much snow accumulation from this part of the storm, because high temperatures have been in the 40s and 50s ever since the New Year’s Day tornado event.

As the Gulf low cranks up, warm air advection from the south will increase. The surface temperatures will still be around or below freezing, but air aloft will be warmed by this intensification of the Gulf low. This will result in a changeover from all snow to a mix of sleet and snow from Starkville-Columbus down to perhaps De Kalb. Areas south of that will probably see a changeover to freezing rain. I have been very concerned about the possibility of a major ice storm for the I-20 corridor for several days, as I watched round after round of forecast Skew-Ts come in with a freezing rain signature. This has all the hallmarks of being just that. The National Weather Service is saying up to half an inch of freezing rain (this is a solid coating of ice); I would put the maximum at 3/4 of an inch. Meridian and Jackson are both going to be clobbered by this part of the storm.

The precipitation should continue in these forms through Sunday night. I think that in areas where there is a snow/sleet mix, what percentage of each type you will see will depend on your latitude. I am inclined to put the belt of maximum snowfall a bit north of Highway 82.

After balking at it, I have come around to agreeing that somebody will get a major snow accumulation on the order of 8 inches. There may be isolated areas where a foot of snow falls. As disruptive as that can be, and as risky as it indeed is for power, I think the greater threat exists in the ice storm corridor. Please, please, please, if you are in this area, make sure you will be able to stay warm!

Everyone from that area remember the ice storm of February 1996? I don’t blame you if you’ve put it aside, but this may refresh your memories.

Freezing rain occurred over all the above counties causing widespread damage to trees and power lines. Accumulations of one-half to one inch of ice were common over this area. Over one hundred thousand customers were without power during the event. Most roads and bridges were impassable, and some of the roads had to be closed.

Though I do not think ice storm conditions will envelop the exact same area as before, a repeat of this event is very possible on Sunday for the I-20 corridor!

Stay warm, stay safe, and if you are in line for snowfall, enjoy it!

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