This setup is really interesting from a meteorological perspective. Because this is something we are more likely to see in January than October. And, to non-meteorologists, you may simply shurg and go, “okay, cool.” but to a weather nerd like me, it is really cool to see how the change in the atmospheric setup between October and January manifests itself in the model guidance and, perhaps, in what actually happens.
NERD ALERT!
For those who are curious, take a look at this! Here is a look at the 500mb map:
In Jauary, we would be talking about a southeast wind pulling in Gulf of MExico air ahead of a cold front that would likely plow cold Canadian air through the area. The clash between those two airmasses, along the cold front would set up a line of showers and storms, some severe, with the chance for heavy rain, lightning, wind gusts up to 70mph, hail and a few tornadoes.
But in October, the atmosphere isn’t as cold as it would be, naturally, in January. And that shifts some things. First off, it means the amount of natural instability is lower. The amount of shear is also, generally, lower. The push of colder air isn’t as cold.
All of those factors would limit the threat for severe weather.
But! In October, the temperatures at the surface are naturally warmer, because it is still closer to Summer – this increases instability! The waters in the Gulf are also warmer, and that means the air temperature – and dewpoint – are naturally higher at the surface. That can also increase instability. Depending ont he situation, even with less shear, in October, you can still squeeze out tornadoes with more instability.
But! Since the air behind the front isn’t as cold, the difference in dewpoint from one side of the front to the other can become the driver to storms, instead of just temperature.
That means that the storms can, in essence, outrun the forcing a bit easier and become more isolated and discrete, rather than just a big long line of storms. Or, they can become multi-cellular clusters. And what are we seeing this time?
Storms outrunning a front! And they are discrete!
So, a setup that, in January, would be a slam dunk for storms and severe weather along a line instead becomes a much more difficult forecast where the details really, really matter! That is why my post yesterday about the blob of drier air was so important to the forecast.
And it is probably something some (read: most) meteorologists may (read: likely) simply overlook. And then when no severe weather happens just shrug and say, “well, it looks like storms didn’t happen… Mississippi weather is crazy like that!” When, in reality, it was a very known, understandable and explainable situation – if they would just look. (but I’ll get off my soapbox).
What’s the end result, Nick?
A great question! The end result is a situation where watching radar trends and surface observations becomes very important. And knowing that if you have outdoor plans tomorrow afternoon / evening that you should have a backup plan and a way to get alerts from the National Weather Service as storms won’t “look” as scary on radar as they would normally in a similar situation, but may provide just as much punch. It also means that some folks tomorrow may get ‘a lot’ of storminess while other miss out on almost everything. Yup! Another one of those events.
And a great example of this is the estimated rain totals. You’ve got a spread of “zero” to more than 6″ of rain!
So, sure… Weather is crazy! But weather is also explainable.
In English, Nick!
Given the current setup, there is a chance for storms and severe weather. The Storm Prediction Center offered an afternoon update that expanded the risk east, but otherwise held the threat ‘as-is’ with no meaningful changes.
This included expanding the area of 5-percent tornado risk.
That 5-percent risk, given the time of year, means you are 5-times more likely to see a tornado tomorrow than any other day. And, I’m betting, if you read the section above you are probably nodding your head thinking, “well, yeah, that makes sense!”
TIMELINE
It looks like things may be going barely slower than the data was suggesting 24 horus ago. Now it is looking like 11a through 8p.
THREATS
Brief heavy rain, lightning, wind gusts up to 60mph, small hail and the potential for brief and weak tornadoes
