A lot of buzz about the first shot of legitimately cooler air for the area that is set to arrive next week. So I wanted to take some time to explain some of the difference between the model guidance and where I think things will land.
Her eis a look at the operational model guidance. This is the deterministic guidance that starts with one set of initial conditions and we “let ‘er rip” to see what it says will happen.
That is a pretty wide spread between the two models. The ECMWF says 32F to 42F depending on your location. The GFS says 48F to 53F depending on your location. But that is to be expected, in a sense, because both of these models use different methods to predict the future. And they also start with different initial conditions.
Then there is ensemble model guidance. This is when we take a bunch of different initial conditions and run the same model about 30 to 50 different ways and then average the results. It is a great way to get a good feel for the most likely potential outcome because you have so many options to choose from.
You can think of it like the spaghetti models for hurricanes. We look at a ton of options to get a better feel for the most likely direction for a certain parameter. In this case, temperatures!
In this situation, the EPS shows 35F to 45F and the GEFS shows 39F to 50F as the spread between north and south. So, as a ballpark forecast, we could say, there is enough evidence in the model guidance today to support the potential for temperatures around 37F near I-20 and temperatures around 47F near the coast.
That is a pretty sharp gradient! 10 degrees over about 125 miles!
WHICH ONE IS RIGHT? NONE.
I hate to be “that guy” but I am about to be him. None of those models are specifically correct. Sure, maybe the temperature at your house is the same as one of the temperatures shown on one of those maps, but that would be more coincidence than accuracy.
Instead, think of model guidance as — well — guidance! It isn’t supposed to be accurate. It is supposed to be helpful!
So lets start with the GEFS first. This one shows the big blob of cold, behind the cold front, shooting south toward the Gulf Coast by Sunday. But it splits in half by Tuesday of next week. One blob heads toward Texas and the other zooms toward the northeast.
This is due to the subtropical ridge nearby doing a good job at deflecting any “big” cold away from our area. We still get chilly. And maybe even “cold” but it wouldn’t be “big cold” by any means.
Now let’s look at the EPS model.
It is pretty similar, but juuuuust different enough to allow some cooler air to ooze into our area.
In fact, the first map on the left is nearly identical to the map from the GEFS model. And honestly, that’s a big win! That gives us more confidence in the short-term forecast.
But where these two differ is the GEFS takes the cooler air to the northeast and the EPS lets it sag a big into the Ohio River valley. That slight detour is what allows some of the cooler air to sink southward.
But because the EPS is just an averaged ensemble, it can’t “see” individual – and more precise – things.
For instance, the ECMWF can “see” a second shot of cooler air that plows toward theGulf early next week from Canada.
The first shot moves east the other blob of the first shot pushes into Texas and it allows the second shot of cooler air – a bit like a running back running behind a pulling guard and a full back – to fly between the two and hammer the Gulf Coast.
That air is currently sitting in Siberia, for what its worth. It’s real deal cold. It would modify quite a bit before it got here, but it has girth, for certain.
The GFS model sees the same air and also moves it into Canada.
But pushes the air eastward and given the strength of the ridge in the Gulf.
YOU’RE NEVER GOING TO BELIEVE WHY…
You may have heard about Hurricane Tammy out in the open Atlantic.
Well, there is only one way I know how to explain this… And that is Morpheus from The Matrix:
Yes. A hurricane. The thing that thrives on warm water, lives under a dome of upper-level high pressure, and can’t stand dry or land is the thing that is going to decide just how cold it gets along the central Gulf Coast.
And that hurricane is currently about 1,900 miles away.
Well, buckle up! Because this is crazy….
According to the ECMWF model, the ridge across the Southeast gets squashed between the incoming cold from the north and a piece of Tammy that curly-cues around the ridge from the south. Yup! A piece of Tammy calves off and drifts to the southwest and then back around to the north and across Florida as we move into early next week.
That movement, squashes the ridge of high pressure near us and allows the cold to come barreling southward.
You know what isn’t on the GFS model?
If you said “Tammy going through mitosis” you are correct – sort of. Tammy does split, but both chunks slide northeastward, leaving the ridge strong enough to thwart the incoming cold air.
COMING BACK FULL CIRCLE
Pun intended here.
I will say that the ‘splitting Tammy’ phenomenon is shown on the GEFS and the EPS ensemble models which is why those two models are closer in temperature than the operational model guidance, GFS and ECMWF.
So I think a splitting Tammy situation is possible. And that is why there is a legitimate risk for a shot of some pretty chilly air to make it down to the central Gulf Coast.
But given the strange nature of the pattern that would have to unfold in order for that to happen, I am hesitant to call for any freezing temperatures. And I am also hesitant to call for any widespread frost.
But I will say that keeping an eye on the tropics the next few days will tell you more about the chance for a frost next Thursday than monitoring any cold front will. And if that isn’t the most “2023” sentence I’ve ever written, I don’t know what is.
As usual, a VERY detailed analysis. Just wish the date and time on each image was visible. I ‘will’ be watching the tropics. In fact, this morning, Tidbits was showing a tropical system in the Caribbean around the 8th or 9th.