10:20 PM UPDATE: Tornado watch has been cancelled for all of our area as the squall line has moved east and the severe threat has ended. The tornado watch has been extended into Coastal MS, AL, and FL. Only a few lingering showers remain over the area.

Severe and tornado threat has cleared for areas east of I-55 down towards Assumption parish.

The high wind warning over northwestern portions of the area has been cancelled as well. Wind speeds will begin to decrease behind the front.

Timing: The line will move to the east and begin to clear in the early overnight hours around 10pm-12am. Some lingering showers are possible behind the front in the early morning hours before clearing by daybreak.

Discussion

A strong upper-level low will be becoming negatively tilted moving to the east-northeast over the Southern Plains towards the Great Lakes by Thursday. With this feature, a surface low will track over Northern Louisiana with an associated cold front draped into the Gulf. Ahead of this front will be scattered showers and storms with the potential for severe storms.

In the low-levels, a strong jet streak will be over the area with a core around 60-80kts. Winds at the surface will be from the south and southeast with good veering (clockwise turning) with height as upper-level winds are from the southwest. This leads to high levels of shear with 0-6km bulk shear around 70-90kts. Helicity values (a measure of spin) are elevated as well with values north of 400 m2/s2. Looking at the upper-levels, on the downstream side of the upper-level low shortwave, is good diffluence (divergence) to allow for good forcing for storms. This is a very good kinematic environment for storms to take advantage of and possibly produce tornadoes.

The synoptic and kinematic environments are rather favorable for severe weather; however, there are a few caveats to the forecast. This is a high ceiling, low confidence type of forecast.

The main fail mode is going to be the thermodynamics. The cold front that passed through the region late Saturday night has moved south of Florida and will stall out. As the upper-level shortwave begins to move closer, the cold front will lift to the north as a warm front ahead of the low. As it lifts north, moisture will begin to return across the region. The big questions are how much moisture (how high do the dewpoints get) and how far inland does the warm front move.

Current model guidance is showing an area of upper 50s for dewpoints ahead of the front and a small window of dewpoints in the mid 60s. The same can be said for temperatures reaching into the mid-to-upper 60s just ahead of the front. This implies a small window in the warm sector before the cold front for a period of around 5 hours for severe weather to take advantage. Values of CAPE (instability) are not too impressive with surface based values only around 500-700 J/kg with the highest values no more then 1000 J/kg near the coast.

All of this over the area can change based on how far the warm front lifts to the north. If the front struggles to clear the coast, the severe threat drops significantly. On the other hand, if the warm front makes its way to, or north of the 10 and 12 corridor, then there is a better chance for severe weather while the warm sector resides over the area before the cold front arrives in that short time window.

Another caveat is if rain showers or storms develop out ahead of the main line. If a large area of rain occurs in the afternoon, that could work to stabilize the afternoon and in essence “steal” some of the atmospheric energy from the main line of thunderstorms. This would work to decrease the risk.

In summary, there is a lot to watch in terms of the exact placement of the surface low and how far north the warm front lifts to determine how much of a severe risk exists. Strong gradient winds around 20-30mph with gusts up to 50+mph during the afternoon into the nighttime hours have a strongest confidence regardless of severe storms. As the main line of thunderstorms moves through during the late evening, damaging wind gusts are most likely with the possibility of a few tornadoes spinning up. Flash flooding could be an issue as heavy rainfall moves through, especially in low lying areas. Rain totals around 1-3″ are likely.

Make sure you are prepared for the potential of strong to severe storms as we head into Tuesday and have multiple ways to receive warning and alerts.

How to Prepare

Be sure to multiple ways to receive weather alerts and stay tuned to updated forecasts during the day. Severe storms are possible during the night, so make sure your phone is unmuted, charged, and turned on for WEA notifications.

Have a plan and a safe place to go to if a warning is issued for your location. Find a lower-level, interior room away from windows. Secure outdoor furniture and decor beforehand.

You can always check out the Interactive Radar here.

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