A two-part, two-pronged weather event threatens the area with severe storms and heavy rain today. Be safe, review your severe weather plans.
Today and Tonight: Any early sunshine will help a high temperature approach 80 degrees. Clouds will quickly build with showers and thunderstorms developing around midday. Through early evening, some of the storms could be severe with tornadoes and gusty wind. Overnight, a squall line will then approach the area and could bring damaging wind gusts and heavy rain—on the order of 2-3 inches. Winds will shift northwest as rain wraps up before dawn Thursday.
The National Weather Service Storm Prediction Center (SPC) has issued an “enhanced risk” for severe weather on Wednesday. This means numerous severe storms are possible within the forecast area. A few intense thunderstorms are possible. On a scale of 1 (lowest) to 5 (highest) severe weather threat, this event is a 3.
1) Tornadoes – plenty of low level wind shear will give storms ability to rotate
2) Gusty Wind – in storms that turn severe, wind gusts could exceed 58mph.
3) Downpours – particularly heavy storms could produce a lot of rain in a short time.
Precipitation: A FLASH FLOOD WATCH has been issued as heavy rain could cause rising water in areas of poor drainage and water covered roads. At this time, it is expected that rivers will be able to handle the forecast rain amounts. 2-3 inches of rain is expected across the 13 Parish, 3 County Forecast Area though a locally higher amount is possible —especially where the heaviest storms occur. Since 2-4 inches fell across the area on Sunday and the ground is saturated, spots prone to flooding can expect ponding water.
Estimated Timeline: There will be two separate windows for the different severe weather threats. First, isolated to scattered showers and thunderstorms are expected from late morning to late afternoon. This window will bring the greatest chance for tornadoes. Second, a squall line with widespread rain and thunderstorms is expected between 8pm - midnight. This window will bring the greatest chance for damaging wind gusts and possibly some hail followed by a period of heavy rain. While a few showers may linger, impact weather will conclude before dawn Thursday.
Impacts and Actions:With many busy at work and school, know the severe weather safety plan of the building you will be in ahead of time. Make sure there is a way to get warnings if they are issued such as a NOAA Weather Radio, the WBRZ Weather Team on Facebook and Twitter or the *free* WBRZ WX App. which sends push notifications to mobile devices if a watch or warning is issued for your location. Double-check the forecast before hitting to road home and consider adjusting your commute to avoid driving into severe weather. Verify that outdoor events such as after school practices are safe before attending. If you will driving tonight and encounter a water covered road, please turn around. Especially at night, there is no telling how deep the water is or if the road is in tact below. Remember, a watch means “conditions are favorable, and a particular threat could develop” and a warning means that “threat is happening and you should take action immediately.” In a tornado warning, seek shelter in a low-level interior room and avoid mobile homes is possible. In a severe thunderstorm warning, get inside of any sturdy structure.
Up Next: Clouds may linger on Thursday though some sun is expected as well. Northwesterly winds will usher in much cooler air with highs struggling for the low 70s! Overnight will be almost chilly with lows in the low 50s. Friday through Sunday will bring abundant sunshine, no humidity and light breezes. High temperatures will get progressively warmer from the mid 70s to the mid 80s. Low temperatures will be in the mid 50s.
THE SCIENCE: In response to a deepening longwave trough moving southeastward from the Upper Midwest to Southeast, a surface low pressure system will move from north Texas to northeastern Arkansas between now and Thursday Morning. A warm front will lift from the Gulf of Mexico, northward into Mississippi during the afternoon. As this occurs, a southerly 30-50 knot low-level jet stream will develop in the region with a mid-level jet out of the southwest. This will provide considerable “spin” to the atmosphere with storm relative helicity between 300-400m2/s2. Instability will be a limiting factor and much of it will be confined to areas south and west of Baton Rouge and such those locations face the greatest risk for a tornado. The northeastward extent of the instability means the greatest chance for a tornado is expected southwest of a Natchez to Houma line. During the evening hours, the strongest directional shear will depart and the tornado threat will lessen. Then, as the 500mb trough approaches overnight a squall line will eject southeastward ahead of an advancing cold front. Precipitable water will increase to approximately 2 inches. This will allow for thunderstorms to produce heavy rain and 2-3 inches could occur in a short time. While directional shear will be lower, strong speed shear aloft will mean that damaging winds could still mix down to the surface. Once the front blows through, showers will end with just some lingering cloudiness into Thursday morning. Northwesterly winds from surface to upper levels will promote maintenance of an unseasonable cool air mass through the first part of the weekend. Thursday and Friday nights will be the coolest periods as a surface high just south and west of the area continues light northwesterly breezes and clear skies maximize radiational cooling. Lows could briefly dip into the upper 40s in Southwest Mississippi. As the high pressure system shifts east of the area, thermometers will gradually moderate through the weekend but dew points will remain below 60 degrees and comfortable through Sunday.