Today is a First Alert Weather Day for the potential at strong, possibly severe, thunderstorms.
We have already seen a few rounds of showers and storms this morning and expect to see more off and on throughout the day today. Our confidence is high that we will see several waves of storms this afternoon, some of which could be strong or severe. However, the messy nature of this set up means that there is still uncertainty on if storms will be severe.
Regardless of whether or not storms are severe, we still expect widespread heavy rainfall which could amount to 2 to 4 inches in many spots, with isolated amounts of 4 to 6 inches possible as well. Because of this, there has already been a Flash Flood Watch issued for many communities of North Alabama until 6pm. This watch includes Madison, Marshall, Morgan, Limestone, Cullman, DeKalb, & Jackson counties in Alabama as well as Lincoln, Franklin, & Moore counties in TN.
TIMELINE The greatest threat for stronger storms will occur earlier in the afternoon when we see our warmest temperatures. This is likely to occur after 2 p.m. to 3 p.m. as storms roll in from the southwest. I expect storms to develop to our southwest earlier in the morning and push northeast along with the surface low pressure system. The first wave of storms will have the potential to be supercells, if they stay singular, as they move through the Shoals and Northwest Alabama. As the evening moves along, storms will move more in a cluster, potentially in the form of a line. The line will be near I-65 sometime after 6 p.m. to 7 p.m. and push east from there. The threat will end around midnight as the storms move into northwest Georgia.
IMPACTS The primary threats with today’s storms will be damaging straight-line wind gusts in excess of 50 to 60 mph and tornadoes as well as flash flooding. Heavy rain and small hail of a half inch to an inch may be possible as well. The main biggest threat for tornadoes, hail, and wind will come with the first wave of supercells between 2 p.m. to 7 p.m., and then the threat turns more towards gusty winds and heavy rain. The latest update from the SPC has increased our tornado threat across parts of NW Alabama, including Colbert, Franklin, & Lawrence counties.
Any areas of bowing along the line of storms would signify an area more intense wind. Along this line, especially earlier on in the event, we may also see a few brief tornadoes. The threat for tornadoes through the evening will be small, but still real and something worth watching. Hail is not likely once the sun sets. As the storms roll through there may be periods of intense rainfall which could lead to areas of Flash Flooding in places of elevated rain totals. Many will see rainfall between an inch to two inches, but there will may be several places may see as much as three to five inches of rain. It is in these areas that flooding will be more likely, with northeast Alabama in the cross-hairs of the heaviest rainfall.
WHY? When forecasting severe storms, we look for many atmospheric ingredients. However, there’re 4 main ones that stick out. They go by the acronym, S.L.I.M. Shear, Lift, Instability, & Moisture. By winter severe storm standards, it looks like we will have enough of each ingredient to bring the potential of storms Wednesday evening. We will have plenty of atmospheric shear, or rotation. There are strong southerly winds at the surface and stronger southwest winds around 1 mile up in the atmosphere which promote rotation in these storms. A cold front and resulting storms ahead of the front, moving through will provide the source of lift that we need to form storms. The two ingredients that will be in question are instability or “storm fuel” and moisture. Earlier model runs had a lack of both variables, but the latest High-Resolution model data has shown and increase in these ingredients which would bode well for storm development. Current model runs show that should also have plenty of low-level moisture with forecasted dew points expected to be into the mid-60s across much of Valley.
What Could Spoil Our Threat? As mentioned above, fuel/instability and moisture will be what makes or breaks storms later in the day. We will really have to watch areas along the Gulf Coast and how their storms develop throughout the day. Right now there is an area of storms near New Orleans that is moving northeast towards South Alabama. If storms continue to develop along on the Gulf Coast and into South Alabama, that would limit the low-level moisture flow as well as the amount of energy we can pull in from the south. Temperatures will also be something to watch during the midday hours as well. If we can make the upper 60s, possibly the low 70s, then we would have enough energy for storms to stay severe if there is moisture present. If our late morning and midday showers continue to keep temperatures into the low to mid 60s, that will limit the amount of energy we can build for the afternoon. That energy suppression would reduce the threat of severe storms later in the day.
Tips & Reminders A few reminders on what you need for a First Alert Weather Day. Make sure you have multiple sources to get your weather information. One way is by downloading our 48 First Alert Weather app where you can receive updated videos forecast as well as stream coverage live once the storms move in. Another great tool is a NOAA Weather Radio. You can also get information watching our live storm coverage on-air or online, as we will cut into programming as necessary. Don’t forget to secure outdoor items. Being that it is the holiday season there are more outdoor decorations that may still be up, which you may want to take down or tie down with these strong gusts in the forecast. Lastly, you can always look for updated on our social media pages throughout the day as we will try to post updates as frequently as possible.
As always, the forecast may change as we get more information and the storms begin to form. To make sure you are staying update with the latest forecast, keep back here online and on our 48 First Alert Weather App. Remember to “be prepared, not scared”!