1/29 - 5:45pm - Serious Severe Weather Concerns Tonight

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A severe weather setup that we see normally in the springtime is about to unfold on this late January night across a large expanse of the Southeast. While not "unprecedented" or "once-in-a-lifetime", this outbreak is going to impact quite a few people and it's important that everyone have what they need to be prepared and safe. This post is mainly for folks in North Mississippi and West Tennessee, but you can figure out pretty well how you'll be affected if you're not in these areas by some of the maps and information below. Everyone needs to be aware of what's going on because this will be happening at a very bad time of night when even the night owls are asleep.

Fast Facts

A MODERATE Risk of severe weather has been issued by the Storm Prediction Center for the overnight hours in West Tennessee and most of North Mississippi. Tornadoes, damaging winds, and hail are all on the table for these areas as storms move through. Even though places like the Golden Triangle in Mississippi are just outside of the Moderate Risk area I would treat this as if you were in it because these storms are going to be very, very strong still as they move through this region. Please, please, please have a weather radio or smartphone app that's armed and ready to alert you if a Tornado Warning is issued for your location tonight. This will be hitting when most people are asleep so it's a very dangerous situation.

Timing - North MS and West TN

8pm - Midnight - Small chance for some isolated storms. These would carry a tornado, wind, and hail threat.

Midnight - 2am - Slightly better chance for isolated storms, small line of storms may try to form ahead of main line.

2am - 7am - Main line of severe thunderstorms moves through. This will affect everyone. Tornadoes, severe damaging winds, and hail are a good bet during this time.

Discussion

A line of storms stretches from the Great Lakes to Texas right now and will continue to move eastward through the evening. A few reports of severe weather have come in already from this but the main show will be overnight as this line of storms encounters a more rich environment for severe weather.

The main storm mode for tonight will be a squall line of storms with embedded rotation in portions of it (AKA what's termed a QLCS). Supercell storms will be possible ahead of the main line of storms too and could easily produce tornadoes if they develop. Tornadoes in QLCS lines of storms like the one we'll have tonight are more difficult to identify on radar since they're embedded within the line. While not as strong as supercell tornadoes, QLCS tornadoes can be strong and cause massive damage in the right environment.

While directional shear, which is needed to produce tornadoes, isn't very good for this event, the speed shear or tendency for winds to increase in speed with height will be very good. But, the directional shear may just be enough to cause problems. When you combine helicity (caused by shear) with instability in a formula you get what's called the Energy Helicity Index (EHI). This, in my mind, is a good determinant of tornado ingredients in an environment. The NAM model has increased levels of the EHI throughout West Tennessee and Mississippi tonight as this squall line is moving through so these QLCS tornadoes may have some kick to them if they develop. Not good news at all.


Also, since winds at 850 mb (about 5,000 feet) will be howling it will not take much for any part of this line of storms to pull these winds down to the surface and create straight-line wind damage. I wouldn't be surprised if folks affected by the worst of these winds thought they were hit by a tornado. I'm hearing the word Derecho being thrown around a bit with regard to how this system will develop tonight. That's certainly a possibility with this system but I think it's a relatively small chance.

One more thing to mention, and this is not the least important at all, is the fact that moisture and warm air continues to stream in from the south in advance of this system. When the dry line that's triggering these storms hits this richer air tonight you'll know. The whole line of storms should really begin to light up by then. Having air this warm and moist in January is never a good thing because Mother Nature intends to correct it in a violent way.

Follow me on Twitter and my Facebook page for the latest updates tonight!

5/24 - 11:30am CDT - A Repositioning Day

Yep, there's a Moderate Risk for severe storms in parts of Wisconsin, Minnesota, and Iowa today according to the Storm Prediction Center. It's too bad because we simply can't chase there due to the amount of trees and vegetation along with a considerable distance from Oklahoma City where we need to be tomorrow night. Here's the plan then: We're going to drive south from Des Moines to Kansas City and then cut west in Kansas for this evening when we could see some overnight storms with lightning in that region.

Tomorrow still looks interesting to say the least. Right out front I need to say that this setup has a very high bust potential because of all the capping that will be in place. Warm temperatures of 10 degrees Celsius and higher at 10,000 feet (700 mb) will act as this capping mechanism because it will inhibit warm air from rising buoyantly into the layers above for thunderstorm formation. With that said, this cap may weaken just enough for a couple of storms to fire up in Kansas tomorrow. They would likely be very isolated due to the capped environment, so that's definitely a plus here.

We all know by now that the models have not been handling moisture very well lately and tomorrow probably won't be any different. The NAM model has dew points of 65 degrees Fahrenheit and higher in Central Kansas at 4pm CDT. If this is overdone and we see dew points between 60 and 65 degrees it still wouldn't be too bad. An area of low pressure smack dab over the middle of Kansas should help bring some of this moisture in and also create a considerable amount of wind shear for rotating storms, especially near the warm front just south of the Nebraska border. Again, this is all if the cap actually breaks tomorrow. If it doesn't we'll be sweating it out in the sun as we watch cumulus cloud towers fail to rise high enough for storms. Tomorrow morning I'll post again with an update on this potential.

Follow me on Twitter and Facebook for updates!

3/2 - 12:30am - Severe Weather Outbreak Likely

A potent severe weather setup looks likely this afternoon and evening for Tennessee, Kentucky, Alabama, Mississippi, and even parts of Indiana and Ohio. All the ingredients are coming together for what could be a sizable tornado outbreak in these areas, especially around Middle Tennessee and Central Kentucky, maybe extending into Indiana too. We've had severe weather in some of these places just earlier this week, but this setup looks to be even more potent than that. Cities like Louisville, Lexington, Cincinnati, Nashville, Bowling Green, KY, Huntsville, Jackson, TN, Tupelo, MS, Starkville, MS, and Birmingham need to be on the lookout today.

Risks and Timing

The Storm Prediction Center has outlined a Moderate Risk area for severe weather tomorrow in an expansive area of the South. This includes a 15% tornado risk. Storms will likely erupt early this morning as a warm front surges northward and bring a hail risk to West Tennessee while not-as-strong storms will affect the most of the remainder of Kentucky, Tennessee, and Mississippi. These storms shouldn't be a huge deal, but a few might reach severe limits.

A brief break in the action throughout the mid and late morning hours should provide enough recovery time for the atmosphere to recharge and re-fire storms around noon. These storms will try to get going in West Tennessee and Northeast Arkansas, but will gain strength as they hit areas of greater surface heating to the east. These are the storms that could be very bad in a lot of areas. The worst tornado threat throughout the afternoon will be in Central Kentucky and Middle Tennessee, but there's a secondary area that could have tornado problems in Northeast Mississippi into North Alabama if a little more low-level wind shear comes into play. The Storm Prediction Center's latest severe weather outlook seems to pick up on that secondary tornado risk area by extending the Moderate Risk down to East Mississippi and Alabama. Straight-line wind damage and hail will be possible throughout the South tomorrow, so even if you're not in an area where tornadoes will be likely you need to be on the lookout for severe storms. The storms should move out quickly tomorrow evening once the cold front accelerates southeastward through the region.

Details

The reason why Central Kentucky to Middle Tennessee will be the area for maximum tornado potential tomorrow is because of an alignment of a few factors. For one, the fastest upper-level winds will be centered right over this area tomorrow afternoon. When you couple that with almost southerly winds (may be a bit southwesterly at times), you get not only a high difference between wind speed aloft and at the surface, but also a difference in direction. This is called wind shear and it's crucial to sustaining a thunderstorm and allowing it to become strong enough for tornado development. The southerly winds at the surface will help what's called low-level wind shear, and that's usually a pretty big factor in who gets tornadoes.

These southerly winds will also be bringing in moist air from the Gulf, which is the fuel for these storms as they develop. While the best moisture will be over Mississippi, Alabama, and Tennessee tomorrow, it will still be ample for serious severe weather in Kentucky. This moisture will bring some serious atmospheric instability to the region. When you couple this instability with helicity (the tendency for the atmosphere to rotate), you get what's called the Energy Helicity Index (EHI). This is a decent indicator of where the best tornado ingredients will be, and as you can see on the left, the values are particularly high tomorrow across a pretty vast area from Mississippi through Kentucky. Supercells appear likely in Tennessee and Kentucky, but Northeast Mississippi may have more of a mixed supercell/squall line of storms scenario due to less wind shear. This could be an entirely linear squall line event across Northeast Mississippi/North Alabama tomorrow if wind shear under performs. While squall lines don't harbor as many strong tornadoes, it is still a very real threat that needs to be monitored.

Safety

Before severe weather

• Make sure your cell phone is charged in case you lose power
• Have flashlights with fresh batteries ready to go. Your cell phone should NOT be your primary flashlight
• Your NOAA Weather Radio/Cell phone alert app should be ready to alert you
• Make a central meeting location for family members should you lose communications after the severe weather passes

I've said before that I like iMapWeather Radio on the iPhone for weather alerts. This is not any sort of endorsement, but it is an app that I use and it just works.

When a Tornado Warning is issued for your area

• Get to the lowest level of your home, apartment, or office
• Stay away from windows and try to get to the center of the structure you're in
• Evacuate mobile homes and get to a safe, sturdy building immediately
• Make sure you are wearing sturdy shoes
• If you have time (have these ready to go before a warning is issued), put bicycle helmets on the kids and yourself. Quite a few deaths were caused by head trauma in last year's tornadoes.

Please heed ALL warnings. This is a dangerous severe weather setup that needs no playing around with.