Severe weather season is clearly underway and we are facing another threat of severe storms on Sunday. While beautiful weather is in place today, and a cool, dry airmass returns for Monday and much of next week, Mother Nature has other plans for tomorrow.
Overview
Southerly wind and increasing high clouds today is a harbinger of the developing storm system to our west. As upper level energy moves across the southern U.S. the next 36 hours or so, it will tap into a well of deep moisture in the Gulf of Mexico that is pulled north into the southern U.S. ahead of it's arrival. Surface low pressure will also form and strengthen as it takes a track from the southern Plains northeast across AR and into the Ohio Valley on Sunday. With very strong wind energy at all levels of the atmosphere tomorrow, and given the moisture source and unstable air moving into the region, the stage is set for what could be an outbreak of severe storms.Tornadoes appear likely and could be violent and potentially long-track during the afternoon and evening to early overnight hours. Fortunately the highest threat for these, as of Saturday morning, is to our south across MS and AL. However, the track of the low pressure system will dictate how far north the most unstable air reaches. We will be watching carefully for any adjustments to that track that could cause the more unstable air to reach the Memphis metro. The most likely scenario locally is scattered strong to severe storms during the afternoon and a squall line during the evening hours. Let's dive into the details.
Timing the rounds of storms
As of Saturday morning, I expect multiple rounds of thunderstorms on Sunday with increasing severe weather chances as the day goes on. Scattered thunderstorm potential exists between each of these as well. This could change!- Morning hours (~5am-10am) - Mostly "garden variety" lightning and thunder in scattered storms. Some hail is possible in these as well.
- Early afternoon (~11am-3pm) - Showers likely with embedded thunderstorms. Again the threat of severe is pretty low, but a brief wind gust or hail threat exists. Additional scattered storms are possible after this round and before the main event.
- Late afternoon/evening (~6pm-11pm) - This is when our highest threat exists. All modes of severe weather will be possible. The most likely scenario is a broken/solid squall line, or QLCS (quasi-linear convective system), capable of widespread wind damage, hail, and potentially tornadoes. If the squall line is well formed (unknown), the wind damage threat is higher than the tornado threat, though a few could spin up in the line. If the storm cells are maintaining their own identities (supercells not yet formed into a line), then the tornado threat increases.
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| The 7am run of the high-resolution NAM3 model, showing forecast radar from midnight Saturday night through 6am Monday. THIS IS A MODEL REPRESENTATION AND IS LIKELY TO CHANGE. (WxBell) |
Threats
- Damaging wind is my biggest concern. High wind could be widespread with gusts reaching 70+ mph. Power outages are likely somewhere in the metro.
- Tornadoes are possible. While the greatest threat for violent, long-track tornadoes currently exists to our south, some of the key dynamics could be in play over the metro in the evening as well. These could be in the form of spin-ups within the squall line or supercells just ahead of the line in the afternoon. Prepare for the potential!
- Large hail is also possible in the strongest storms. In fact, small hail could occur in the early morning hours when the initial wave of thunderstorms along the warm front lifts north. The greater threat for large hail is in the evening hours.
- Very heavy rain is also likely with ponding of water expected and potential flash flooding in poor drainage and urban areas that are particularly susceptible.
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| *UPDATED* Severe weather probabilities for Sunday's event, within 25 miles of you. The black hatched area in the hail panel indicates a 10% probability of hail 2" or larger occurring. The black hatched area in the tornado panel indicates a 10% probability of EF-2+ tornadoes occurring. (NOAA/SPC) |
Boom/bust potential
While the synoptic setup is favorable for an outbreak of severe weather, the details are still TBD and will depend on very small ("storm-scale") features that cannot be predicted much in advance. If the track of the low pressure system moves by a bit further to our north, the metro is more likely to get into highly unstable air and the threat increases. If it tracks a little further south, the best tornado-making ingredients remain suppressed to our south, but we're still left with a threat of high wind and hail. Those small-scale features, combined with the ultimate track of the low, will define what actually happens. There is no reasonable scenario where this all just "goes away." There ARE reasonable scenarios that include strong but not widespread severe, storms, as well as a more potent airmass capable of dropping strong tornadoes getting as far north as the metro. Prepare for the worst, hope and pray for the best!Preparedness
Know your plan based on the provided timing and where you will be. Where is your safe place and is it ready? The graphic below will help in this regard and applies equally to high wind as well as tornadoes. Also use the severe weather safety tips below to ensure you have the essential items in your safe place with you. And if you do not have sturdy shelter (i.e. if you live in a mobile home or the upper floors in a multi-story dwelling), know where you will go beforehand and make plans to get there when a Tornado Watch is issued, not when the warning comes out and you don't have time to act.
Garage your vehicles if able Sunday afternoon and evening to protect from hail and high wind.
Secure anything outdoors that you wish to keep. Even outside of storms, wind could gust to 30+ mph.
Make sure storm drains are clear to reduce the chances of flash flooding.
Have multiple ways of getting warning information. NOAA Weather Radio is great. Severe weather apps are also great*, including SW+ Alerts in our very own MemphisWeather.net app, available in your app store. Social media is good too, but likely won't be as timely unless you are continuously updating your favorite source's feed (ours are linked at the bottom of this post and our Twitter feed is best for regular, timely updates). And of course keep the TV on for local coverage. Sirens are not good but they won't warn you of large hail or high wind, and they likely can't be hear by most people who are asleep in a well-insulated home.
* Note that most severe weather apps, including MWN, and also Wireless Emergency Alerts require that you have your volume ON and Do Not Disturb OFF to get audio alerts that you can actually hear. Here's more on how to configure your settings for SW+ Alerts, available in the MWN app.
Dealing with stress
Finally, a note to those who suffer from storm anxiety, perhaps moreso due to the other non-related "stressers" factored in these days. I have found it best to combat anxiety with information, facts, and preparation, even in situations we cannot control. If the "hype" posts on social media are bothering you, shut them down. Stick to those who tell it straight without hype and that you trust for factual information. We hope to be one of those, but there are several in our area that are excellent. Follow @NWSMemphis for the source of most of the data we use and fact-based information. In addition, prepare ahead of time so that you know that you'll be ready if you have to act. Follow the steps above!The last thing I will say is, even if there is a "tornado outbreak" (God forbid), the facts are that the vast majority of the area is untouched and the vast majority of tornadoes are survivable if you are properly-sheltered. The odds are in our favor! So take a deep breath, or several, follow accurate and reliable sources, stick to facts, and be prepared should you need to act.
After this passes, much cooler weather again moves in for a good part of next week before the next storm system moves onto our radar next weekend.
Stay safe and be prepared, not scared!
Further updates will most likely be posted straight to our social media feeds. Please check there often, particularly Sunday, for the latest information.
Erik Proseus
MWN Meteorologist
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Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
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