Well! The last 24 hours has been quite the ride as the model guidance continues to funnel in. So far we have see a bit of a move south with the colder air, a bit of a subtle shift faster in the model guidance with the system, and perhaps a bit of a strengthening, too.
There is a TON to go over, so please take a look at all of this. If you read through it all and still have questions, feel free to reach out!
We have also seen the model guidance showing the development of a stout deformation zone on the northwest side of the system. This is pretty typical of winter systems. The difference is usually snowy deformation zones are pulling in air off the cold Atlantic Ocean or across the Continental United STates.
Not the Gulf of Mexico. Where the available moisture is, like, a lot higher.
It just means that we may end up with a deformation zone that is one steroids. And some folks may see a lot of snow for our region. A. Lot.
Originally I wanted to do a county-by-county look, but I think I’ll wait to do that until tomorrow when we are a bit closer. Instead, I’ll walk you guys through some details and below offer a regional timeline.
PRECIPITATION DETAILS
Recall my favorite graphic… The “Will it snow” graphic!
Well, we are about the check off just about every step on the chart to get snow across much of the region across much of the timeline.
Let’s start with the Skew-T Chart.
It looks like we will have plenty of moisture in the Dendritic Growth Zone. That is the part of the chart on the left side of the graphic above where the vertical lines turn yellow. When those lines are close together, it is a good indication that the atmosphere is saturated.
So that the is the first step!. Check!
Next on teh list: Do we have Vertical Velocity between 850mb and 500mb? Let’s check the 700mb map (700mb is between 500mb and 850mb). And the map shows plenty of red which means we have a good amount of vertical motion.
What it also shows is a wavy pattern where we have corridors of vertical motion and corridors of less vertical motion. So the precipitation intensity will not be completely uniform.
Alrighty. So, we have some. Check!
The next stop on the list… Omega values. For that we go back to our Skew-T Chart
In this case, we are now looking for the purple-ish / pink-ish lines that are horizontal ont eh left hand side of the graphic.
Anytime those lines are poking out from the left and toward the right, it means that we have forcing in that level of the atmosphere. And when we get that in the Dendritic Growth Zone in particular, it means we are pushing more moisture into a zone that is making snowflakes than that region can hold. So we are really cranking out creating a bunch of snowflakes!
And that is what we see in the above chart.
So that is a big ole Check-o-roni.
On the same graphic, we now need to look and see if we have moisture in the same region. And to do that, we look at the vertical red and green lines If those are close together, we have plenty of moisture.
And bam, that is what we see! So we get another check!
Then we look to make sure the red line is below 32F the show way across that plot. And it isn’t. At least not until we get aallll the way down to the surface. So, another check mark for us!
Following the “will it snow” chart that puts us into the category of “SNOW!!!”
…. however. This is far from set in stone. And I think there is enough uncertainty and wishy-washiness within the model data to not go slam dunk all snow quite yet.
In fact, my forecast call for everyone near and south of the HWY 98 corridor to switch to a Wintry mix for a few hours on Tuesday. And that Wintry mix will likely be a rain/snow mix. But we may see some rain/sleet closer to the coast and there is a decent shot that Coastal Mississippi and SE Louisiana to switch to all sleet for a brief period in the afternoon. same with coastal sections of SW Alabama.
The reason?
As areas of low pressure swing through, they often pull warmer air northward higher off the ground than at the surface because the colder air is more dense and it is harder to move. And warm air rises! So the warmer air out int he Gulf rises over the colder, denser air and streams northward. This may warm parts of the sky above us to above freezing and it will melt the snowflakes.
But then down at the surface, it will be near or below freezing again, so the now-melted snowflakes re-freeze! And then they are called sleet. Just like in the graphic from the NWS shown above.
And we do see a little bit of that in some of our shorter-range higher-resolution model guidance. The NAM model – which is biased to usually be a bit too warm and a bit too humid – is showing some warm air advection off the Gulf. This would be an influx of warmer air up around 3000ft.
So far, it shows the warmest it would get for folks north of HWY 98 is about 30F, so everything stays as snow. But south of there, some warmer air may mix in at times and allow for a changeover to a wintry mix.
REGIONAL PRECIP TIMELINE
SNOWFALL TOTAL ESTIMATES
Against my better judgement, I am going to share a casual map on what I think snowfall totals will look like. I want to emphasize that I think it is too early for super specifics. But I do think we can start to glean some range from the guidance that came in today.
First I want to say that there is a decent chance we see a “good” snowfall in the area that is a Top 10 all-time snowfall. And there is about a 10% chance we see an all-time snowfall in some spots. And it may not even be close.
But it will depend on where the deformation zone sets up.
This is as specific as a map as I can make today. A Yellow-Orange-Red map. This is the areas that I think have the best chances to see “some”, “a lot”, and “potentially record-setting” snowfall. With “Some” and “a lot” being purposefully vague. Same with record-setting. Though, given that most records in the area are between 3″ and 7″ of snow, that should give you an idea of how high the top-end may be. And “Some” simply means “Some” without really an accumulation attached to it on purpose as I think those areas are still in a bit of limbo about if snow actually accumulates. And if so, how much.
Please – PLEASE! – take this map as a “moving target” as I think the band of higher snowfall totals will move either north or south a bit and perhaps even east or west. It is Saturday night and the snow doesn’t really start until Tuesday morning. A lot can change.
Heck, the area could grow in size and even more people could see crazy amounts of snow!
It is still a bit too far out to know for certain.
THE COLD
Regional average temperatures are looking pretty chilly. The chart below says it all. There are some spots that will fall below freezing Monday morning and may not pop above freezing again until Friday!
And regionally, the average low by Wednesday morning will be 17 degrees. That is the average regional temperature. It means some folks will be down around 10F to 15F while others are still closer to 20F or 25F.
Brrr.
The biggest dictator of just how cold we will get is the snowfall totals. The higher the snowfall totals the colder the temperatures on Wednesday morning. We will also still have a bit of a breeze at that point. Not a “bad” wind, but enough for it to be really, really cold.
Here are a look at temperatures from NQLBOT, our AI Weather Helper. Lows in the teens. Experienced Temperatures (which consider wind, sun, humidity and other factors) in the single digits.
This is dangerous cold. Pipe-bursting cold. Really bad for plants cold.
But we should climb out of this by Thursday and into Friday in many spots.
THE BOTTOM LINE
It is going to turn much colder by Monday morning. Then cold again Tuesday (all day) and Wednesday (all day) before warming up on Thursday and Friday. The cold Wednesday morning will be pretty dramatic. We are talking some of the coldest air we have seen since January of 2018 perhaps.
While all of this is happening, we will have a little system swing by in the Gulf that will produce some snow across the region on Tuesday. Some folks will see all snow, others will see it mix with rain at ties or sleet at other times.
That means accumulating snow on Tuesday. That snow sticks around Tuesday night and into and through Wednesday and into Thursday morning. It will start to melt Thursday afternoon, but may refreeze again Thursday night and into Friday morning (depending on your location).
That means some folks may head home Monday night and be stuck at home until Thursday afternoon. In the cold. Others may not be able to leave again on Friday morning because the roads are frozen over. And those should melt reasonably well by Friday afternoon. Meaning Saturday is the first, real, chance for some folks (not everyone) to get out of the house easily.
And, look, I’m not a Road’ologist. So I can’t know what every road will look like the entire time. But I can make estimates based on precip and temperatures.
This chart is a general chart for the area. It won’t be applicable to everyone all the time, but it will hopefully give you some general idea about how the roads may look between Monday night and Friday afternoon.
So please take the time this weekend to prepare. Get the food you need, check on your heater, make sure you have ways to keep warm.
And please check on folks who don’t have easy access to heat. That could be older folks, people who live in uninsulated houses, or even friends and family in mobile homes that have exposed floors underneath the house.
Make sure your pipes are wrapped up. Make sure any exposed pipe is insulated. And get read yto drip your faucets on Tuesday night and perhaps again on Wednesday night.
This will be a burst of some pretty cold air. Some precip. And some unusual conditions for the region. Prepare accordingly.
Thank you;I hope there will be no quiz involved!I. I trust your technology even though I don’t understand it all.Again,thank you.