We've all grown used to the three categories for severe weather outlooks by the Storm Prediction Center. These outlooks included Slight, Moderate, and High. Of course, we've all joked before that Slight risk doesn't really mean slight. In the weather business, a slight risk usually keeps you fairly busy. On many occasions it is later followed with either a tornado or thunderstorm watch. The Storm Prediction Center in Norman, OK has been studying for years how to better communicate severe weather information to the public.
Back in the early days, the slight, moderate, and high risk information was only communicated to weather service offices, media outlets, and emergency managers. However, in the days of instant communication everyone has access to severe weather outlooks. For the non-weather junkie, the three categories can be a little confusing.
Here's an example of the old way.
This is an example of the same day using the new severe weather outlooks.
You have probably noticed there are two more categories now added. This includes the Marginal and the Enhanced. The Marginal is lower risk of severe weather than Slight and the Enhanced is a higher risk than Slight.
The SPC will use the following criteria when assigning the new outlook categories.
Day 1: a. General Thunderstorms - 10% or greater probability of non-severe or near severe thunderstorms. b. Severe Category 1 - Marginal - 2% or greater tornado probability, or - 5% or greater severe hail or severe wind probability. c. Severe Category 2 - Slight - 5% or greater tornado probability, or - 15% or greater severe hail or severe wind probability. d. Severe Category 3 - Enhanced - 10% or greater tornado probability, or - 30% or greater severe hail or severe wind probability. e. Severe Category 4 - Moderate - 15% or greater tornado probability AND 10% or greater probability of an EF2+ tornado, or - 30% or greater tornado probability, or - 45% or greater severe wind probability AND 10% or greater probability of a wind gusts 75 mph or greater, or - 45% or greater severe hail probability AND 10% or greater probability of hail 2 inches or greater in diameter, or - 60% or greater severe wind probability, or - 60% or greater severe hail probability. f. Severe Category 5 - High - 30% or greater tornado probability AND 10% or greater probability of an EF2+ tornado, or - 45% or greater tornado probability, or - 60% or greater severe wind probability AND a 10% or greater probability of a wind gust 75 mph or greater.
In turn, you will see a lot more marginal severe weather outlooks here in the Southeast replacing what used to be labeled as a Slight Risk. You might wonder what the new outlook would have looked like had the SPC used it on April 27th, 2011.
We're beginning to see development of discrete, widely scattered thunderstorms back over east central Mississippi as the atmosphere grows increasingly unstable. Of particular interest is this intensifying thunderstorm to the southwest of Philadelphia, Mississippi. Lightning has been increasing with this storm, as well as signs that it already has a rotating updraft in the mid-levels.
We will need to monitor storms like this very carefully over the next few hours as they will have the potential to become supercells with the risk of a few tornadoes. A Tornado Watch is already in place for most of Mississippi until 9:00 pm. Interestingly, the text of the tornado watch mentions that a few longer-lived supercells with the potential of a couple of strong/intense/damaging tornadoes will be possible.
J.P. Dice has just stepped into the office, and Wes Wyatt will be in soon for a full staff to watch this situation. We will have updates through the rest of the day both on air and online. Stay with FOX6 for complete severe weather coverage.
FOX6 WBRC Weather
Blog Severe Weather Analyst
We're watching the line of storms off to the west very carefully. Regional radar data this morning shows it already approaching the Mississippi River just before 11:30 am. The latest data from our high-resolution models are also keying in on this and have the line approaching our area a little earlier this evening than maybe the last data set or two has shown.
By 5:00 pm, or possibly a little before, we may see a few individual strong thunderstorms develop over parts of the area. This will especially be the case over portions of western and central Alabama... generally along and west of I-65. A few of these could possibly become severe, and these individual thunderstorms would be what we would have to watch most carefully for the risk of a few tornadoes.
By 8:00 pm, the RPM model has the main line of thunderstorms approaching the Alabama state line from the west. We will still have to watch for a few lone supercell thunderstorms out ahead of it though. With the line itself, the potential for damaging winds... possibly as high as 60 to 75 mph... will increase, but there still may be a couple of spin-up tornadoes with bowing segments and embedded supercell-like structures near breaks in the line.
By 11:00 pm, our high resolution model has the main line moving into places like Double Springs, Jasper, Tuscaloosa, and Eutaw. With this line, we will continue to see the risk of damaging straight-line winds in excess of 60-70 mph and the potential for a few spin-up tornadoes. Out ahead of this, we will still need to monitor the situation carefully for the risk of a few individual storms continuing ahead of the main line, with the risk for a few tornadoes.
We will continue to monitor the situation, and we will have updates on air and online through the day as needed.
Fred Gossage with Mickey Ferguson
FOX6 WBRC Weather
Severe weather will likely impact Alabama this evening. A powerful weather system will move west to east across the state packing damaging winds, flooding rains, and even a threat for isolated tornadoes. The greatest risk for severe weather will remain in Mississippi, Arkansas, and West Tennessee. However, it's very likely we will experience some damage later tonight as storms move into the area.
It's possible we could have two separate severe weather threats. The first threat is isolated tornadoes that could begin as early as 5-6pm in West Alabama. If supercell thunderstorms develop, as a few models suggest, the tornado threat may increase for Alabama This will have to be watched. The greatest risk for tornadoes will include Marion, Lamar, Pickens, Winston, Fayette, Walker, and Tuscaloosa Counties.
Highest tornado potential will remain to our West. Note: West Alabama in the 5% tornado risk. That's not incredibly high, but worth noting.
The primary threat still looks to be damaging straight-line winds associated with a pre-frontal squall line. These storms could bring 60-70mph to the area. The highest wind threat will be for areas west of I-65. This line of storms will enter the area between 8pm and 10pm. Storms will persist across Alabama during the overnight hours. With heavy rain likely, flash flooding will also be an issue. We could easily see 2-3" of rainfall fall in a very small timeframe. The highest risk for flooding will include areas west of I-65. It's likely we'll continue to see rain through tomorrow morning for East Alabama.
It would be a good idea to make sure any loose items around your home are brought in today because of the high wind threat. Since some storms will move through the area during the overnight, make sure you have multiple ways to receive severe weather warnings.
What to expect? It's likely the Storm Prediction Center will place much of Alabama under a tornado watch later today. We'll most likely see down trees, power outages, and other wind damage later today. With the heavy rain be careful when driving tonight, it's likely we will also experience some flash flooding. It is very difficult to judge the depth of water over a road at night. If you live in a mobile home it would be a good idea to make plans to stay in more sturdy structure this evening.
Stay with Fox6 for updates on this developing weather story.
Fox6 Chief Meteorologist
This evening we are tracking strong thunderstorms that will impact some of the high school football games in our area. The latest severe storm was over Walker county but that warning was recently canceled. Even if there are no severe storms, the threat of dangerous cloud to ground lightning will spread into Jefferson, southern Cullman, and Blount Counties within the hour. We are also detecting lightning over northern Tuscaloosa and southeast Fayette County.
We will continue to track this activity for you and scroll any new warnings that pop-up on Fox6. You can also keep up with the storm activity using our Free Fox6 Weather app found HERE.
If you hear thunder near your location be sure to move to enclosed shelter. An automobile can be a safer alternative if it has a solid cab. Roll up the windows and wait for the storm to pass. Avoid crowds and avoid tall objects. The storms that we are tracking are moving east-southeast.
Fox6 Meteorologist Wes Wyatt
Greg Carbin is in Tuscaloosa today. He's the Warning Coordination Meteorologist for the Storm Prediction Center. Fox6 Meteorologist Wes Wyatt caught up with Carbin today on the University of Alabama campus to talk about the changes to the severe weather outlooks.
These changes take effect on Wednesday, October 22. You can read more about how these severe weather outlooks will impact you http://www.spc.noaa.gov/exper/dy1-3example/.
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