Monday, February 1, 2016

Monday afternoon update on Groundhog Day storm potential

I've dissected this storm and possible scenarios daily since late last week and, in fact, started raising the awareness flag last Wednesday on social media. So hopefully by now, the fact that we could get severe weather tomorrow isn't a surprise. From that perspective, nothing has changed.

The scenarios mentioned yesterday are, in fact, still plausible. After studying the overnight and morning data and considering the analogs (past events with a similar setup to this one) and how they turned out, I think we'll see a mix of discrete (individual) storms and mini-lines of storms, primarily during the afternoon hours. As mentioned yesterday, these discrete cells are the most worrisome, as they won't compete with other nearby cells for atmospheric fuel like a line of storms does.

Wind fields from the surface to the jet stream level favor severe weather, including possible tornadoes.

Low level and mid-level moisture fields favor severe weather, including possible tornadoes.

Instability - the rising air, or fuel, that causes growing storms to get bigger - will be sufficient for strong to severe storms. The amount of instability, which may end up determining just how severe storms get, is still TBD. There are definitely indications that it could be sufficient to produce large, rotating storms. There are other solutions that favor a more tempered approach.

The lid on the atmosphere that we call a "cap" will, in all likelihood, erode by mid-day, meaning storms won't be stopped by a layer of warm air aloft.

In other words, all ingredients appear to be in place for severe weather, especially east of the Mississippi River. The pot is sweetened the further east you go from the river, but there's enough "atmospheric juice" in the metro to warrant preparation. Thus the latest update from the Storm Prediction Center (below) has shifted the Enhanced (category 3 of 5) risk to the far eastern metro and lowered the risk to Slight (category 2 of 5) for most of us. However, it doesn't matter if the line between the higher and lower risk areas is 30 miles west or 30 miles east of you! The threat is not gone, it's just being refined. And it could be raised again tomorrow morning if the parent storm slows just a tiny bit...

The bottom line, as of 1:30pm: 

  • Scattered morning showers will gradually strengthen into thunderstorms as the cold front and attendant severe weather ingredients draw closer by lunchtime and as temps head towards 70°. 
  • Some of these storms are likely to form into supercell storms capable of damaging wind and possibly tornadoes sometime after noon, mainly in west TN and MS where the airmass will be most favorable for severe weather. 
  • By mid-afternoon (say 3pm), the radar will likely be seeing scattered supercells, some of which may "cluster" into lines or mini-line segments. Any of these will be capable of severe weather. By rush hour, the storms should be east of the metro. 
  • There is a chance that we could see one last line of storms along the cold front around rush hour/early evening. Most models think the energy along the front will be waning and focused well ahead of it, but a line of storms with some strong wind gusts is possible along the front. 
  • By evening, it's all to our east and the threat is over.

Below you'll find safety tips that you should be reading and  putting into action. Not only do individuals need to review their safety plans, but if you are in charge of an office, retail establishment, school, or other large facility, know what you will do with those who rely on you for guidance if a warning is issued.

It's possible that some places may get no rain, while others nearby get a strong thunderstorm! That is the nature of this type of system. The forecast isn't a bust if you don't get a storm - just be grateful.

Finally, a word on warnings. I expect there will be severe thunderstorm and probably tornado warnings somewhere in the region, maybe nearby. You need multiple ways to get warnings. Please don't rely on sirens to know when to take shelter! If you're inside, you may not hear them. (In fact, you're not supposed to.) Think about where you'll be during the threat hours and how you'll get info.

We highly recommend adding StormWatch+ to our mobile app as one way of getting that warning alert. You can set it for your office, home, kid's school, or even have it follow you as you travel, and get the warnings that apply to your specific location. It is more precise than sirens and weather radios from a location perspective and will alert you well before the media source you are watching or listening to will mention your town or area. Set the types of warnings you want and you'll only get bothered if you want to be. Download links are at the bottom of this blog.

Plan ahead, stay safe, keep up with the latest information, and be prepared, not scared.

Erik Proseus
MWN Meteorologist

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1 comment:

DanTheCigarMan said...

As always. Thanks Erik. Stay safe!