Just wanted to offer a brief update for everyone tonight. I’ll try to have more details tomorrow morning, if needed.
It looks like the latest model guidance is showing a slightly higher risk for areas south of I-20 tomorrow – particularly in the afternoon and evening. If you are looking for a timeline of events and specific threats… here you go:
It still looks like two rounds. It still looks like mostly rain and lightning. There will be some storms that pack some strong wind and hail. And we can’t rule out the potential for a few tornadoes across the region. And I think a strong tornado will be possible (up to EF3).
The current Moderate Risk area from the SPC may need to be extended farther south given the latest data. Or, at the very least, an extension of the Enhanced Risk to the southeast to encompass more of the Louisiana Parishes and Mississippi counties.
Here is a look at the current risk:
Looking at Round 1 tomorrow afternoon let’s jump to the Updraft Helicity Streaks below, you can see a pretty reasonable trend where there are two clusters of storms – one north and another south. And the southern batch across southeastern Louisiana and southern Mississippi has grown over time while the batch to the north continues to shrink.
Reminder: the Updraft Helicity Streaks are when we let the computer try to pick out where the strongest storms may be. It isn’t a guarantee, but it is a signal.
While the Karrie Meter, from the NAM model, is pretty adamant about a cut-off along I-55 tomorrow afternoon/evening, if any storm is to develop across western Mississippi of Southeastern Louisiana and track tot he northeast into a ‘less favorable’ environment, I don’t think that would ‘stop’ the storm much as the general atmosphere will be plenty primed for severe storms. .
So if you’re looking at that map and thinking, “I’m in Wayne County! No bad weather for me!” I would really caution you against that.
The other, slightly more concerning, trend is the strength of those updraft helicity streaks is growing, too.
I’ll be honest, I forget where I learned this (I’m pretty sure it was at a conference) but when looking at these UH maps where the value is plotted a good threshold to note is “50” and “150”. Again, a bit of COVID-brain maybe, but if memory serves, “50” is when we start to talk about severe weather, wind gusts over 60mph, and hail with the potential for a tornado. When we get to “150” we start to talk about the potential for a strong tornado.
And the maps above are showing (left) 60-percent of members suggesting a tornado is possible and (right) 30-percent suggesting a strong tornado is possible.
And that is outside of the current “Moderate Risk” area.
And looking at the sounding data from the HRRR model, it paints an equally as ‘hey tornadoes are possible’ picture.
Again, that is all for Round 1. We get a lull for a bit in some spots and then Round 2 shows up early Wednesday morning. Deepening on how things shake out with the storms tomorrow afternoon, the storms for Round 2 on Wednesday morning may be less robust, but will still pose a chance for produce heavy rain, lightning, wind gusts up to 60mph and the potential for a brief tornado. But we won’t really have a ‘good look’ at that until tomorrow afternoon/evening.
