It looks like the potential for widespread significant severe weather is – again – in the cards this Thursday for portions of the Southeast and gulf coast. Model guidance continues to show a large area with the potential for storms to produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls and a few strong tornadoes.
And I know what you are thinking….
Yeah. Again. Not ideal.
From the SPC
The storm Prediction Center has issued an Enhanced risk – a “3” out of “5” on the 1-to-5 scale where “5” is the highest risk for the most significant severe weather – for a good portion of Mississippi as well as parts of Louisiana, Arkansas, Tennessee and Alabama.
This is – roughly – in the same place that went through the severe weather just one week ago.
From the SPC:
…Lower Mississippi Valley and Southeast States… A robust shortwave trough will move from southern TX early Thursday northeast through the lower MS Valley during the day and into the OH Valley overnight.
Thursday morning a cold front will extend from the Great Lakes southwest to a weak surface low in eastern TX, then south into the western Gulf. In response to the ejecting shortwave trough, the cyclone is forecast to undergo significant deepening as it develops northeast during the day. A cold front will accelerate through the lower MS Valley and into the Southeast States, while a warm front initially from northeast TX into northern LA and central MS lifts northward to near the TN border by evening. It is likely that elevated storms will be ongoing in warm advection regime across northern MS, AL and TN.
This activity is expected to continue lifting northward allowing for destabilization from the south with time. Rich low-level moisture with upper 60s to near 70 F dewpoints will advect northward through warm sector contributing to moderate instability with up to 2000 J/kg MLCAPE.
Potential will exist for discrete storms to develop in the warm sector as the boundary layer destabilizes during the afternoon. Vertical wind profiles with very strong shear and large 0-1 km hodographs will support supercells capable of producing strong tornadoes and large hail. Activity will spread northeast through the lower MS valley during the day and into the TN Valley by late afternoon into the evening.
Additional storms may also develop along the cold front with linear structures capable of damaging wind.
Courtesy: SPC.NOAA.GOV
The big question, at this point, within the data is how early in the day does storm initiation begin and how clustered do storms become after initiation.
Model Data
So far, the model data continues to show the potential for severe weather across much of the region highlighted by the SPC. Underneath that, it looks like short-range guidance may be picking up on a – small, but not ignorable – increased potential for a few strong tornadoes.
Here is a look at some data from mid-morning (around 10am) on Thursday.
This sounding was pulled from south Mississippi and shows some pretty subtle stuff worth noting. The “Big 3” that I see include (1) more drier air aloft, (2) downdraft CAPE is nearly twice as high, and (3) a very slight cap of warmer air closer to the surface.
What does that mean? Well… (1) drier air aloft allows for hail to form and allows for rear-flank downdrafts to become more pronounced, (2) higher DCAPE numbers means the downdraft air will have an easier time tilting any rotation at the surface into the vertical, and (3) the cap of warmer air may inhibit storm initiation from clustering storms together quicker meaning supercells would have an easier time developing.
What does all of THAT mean? Subtle increase in the chance for stronger tornadoes. Because in order to get a stronger tornado, the atmosphere needs RFDs, RFD-CAPE and it helps when that happens within a supercell thunderstorm.
Karrie Meter
Looking at the Karrie Meter data across the region, there appears to be a pretty wide coverage area of 4s and 5s for Louisiana, Mississippi, and Alabama.
The above map is pulled from the short-range NAM-3km model, but I think it paints a good picture of the potential threat for severe weather. A healthy chunk of 4s and 5s – with a few splotches of 6s, too – would be a good indicator that a Slight to Enhanced Risk for severe weather would be needed from the SPC.
And the SPC has pegged the entire area with an Enhanced Risk. So both pieces of data line up. And that increases my confidence that severe weather will be possible.
Timeline & Threats for south Mississippi
We are just starting to get into a place where Ic an make approximations for a timeline. These will be a bit more general and are likely to shift around during the next 24-36 hours.
I-20 Corridor
8a-12p – A few showers and storms may develop btu the threat for severe weather should be limited. the main threats at this time will be heavy rain, wind gusts up to 35mph, and pea hail.
12p-4p – Scattered storms will be possible, some supercellular. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and tornadoes – some strong.
4p-8p – A line of showers and storms will push through the area during this time. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of quarters, and brief tornadoes.
Highway 84 Corridor
8a-12p – A few showers and storms may develop btu the threat for severe weather should be limited. the main threats at this time will be heavy rain, wind gusts up to 35mph, and pea hail.
12p-4p – Scattered storms will be possible, some supercellular. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and tornadoes – some strong.
4p-8p – A line of showers and storms will push through the area during this time. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of quarters, and brief tornadoes.
Highway 98 Corridor
8a-12p – A few showers and storms may develop btu the threat for severe weather should be limited. the main threats at this time will be heavy rain, wind gusts up to 35mph, and pea hail.
12p-4p – Scattered storms will be possible, some supercellular. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and tornadoes – some strong.
4p-8p – A line of showers and storms will push through the area during this time. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of quarters, and brief tornadoes.
Highway 26 Corridor
8a-12p – A few showers and storms may develop btu the threat for severe weather should be limited. the main threats at this time will be heavy rain, wind gusts up to 35mph, and pea hail.
12p-4p – Scattered storms will be possible, some supercellular. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 60mph, and tornadoes.
4p-8p – A line of showers and storms will push through the area during this time. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 60mph, and brief tornadoes.
Along the coast
8a-12p – A few showers and storms may develop btu the threat for severe weather should be limited. the main threats at this time will be heavy rain, wind gusts up to 35mph, and pea hail.
12p-4p – Scattered storms will be possible, some supercellular. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 60mph, and tornadoes.
4p-8p – A line of showers and storms will push through the area during this time. The main threats during this time will be heavy rain, frequent lightning, wind gusts up to 60mph.
Bottom Line
We are still trying to nail down specifics, but in general it does look like the potential for severe weather exists for Thursday. And it may be as potent – or even more potent – than last week’s potential. It simply depends on your locations. And knowing the different in impacts for each location involves knowing specifics that we are still trying to nail down.
Prepare now, though! Look through your plans for Thursday. Going to work? Working off site? Working from home? Kids in school? Kids at a friends? Grandma at home? Any doctor appointments? Things like that. And then think about where you would go or what you would do if a Warning was issued for your area. Is there a safe place to take shelter?
The timeline looks to be an all-day event, but that doesn’t mean it will be storming all day. It just means that storms will be possible all day. And the main concerns are for heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and tornadoes. There may even be a few strong tornadoes.
We will keep hammering through the data to provide the most up to date forecast. In the meantime, hang in there. And review your plans. Know what you would do in the event of a Warning! These types of things can make navigating the next 48 hours that much easier.
