The SPC has released the midday update on the risk levels for Thursday. No big changes. But there is still a risk for severe weather across parts of the southeast. This post will highlight some of the data that goes into the forecast for south Mississippi in specifics.
It looks like, despite the SPC not highlighting this potential specifically, there will be a chance for strong tornado across parts of south Mississippi on Thursday. This is not a “big” chance, but it is big enough to warrant being mentioned.
Hopefully, a lot of you guys know my forecasting style well enough to know that I’m not one to just willy-nilly throw around the potential for tornadoes. And I’m not one to just say something without some evidence.
So! Let’s dive into the data!
Model Data (prepare to Science!)
Looking at some of the latest data, I want to give some background to why I think there is a brief window for a strong tornado to develop across parts of the area, despite no ‘hatched’ area from the SPC across south Mississippi.
And I’ll break it down with some Science
I know, I know….
To explain this, we have to learn about something “new” called Convective INhibition. Convective INhibition, sometimes called “CIN” or “CINH” is a layer of air that if lifted (due to, say, some sort of atmospheric forcing) would simply just sink back down again. Here is more of a textbook description from the Haby’s Hints website:
“CINH (Convective Inhibition in units of Joules per kilogram) is anti-CAPE (negative CAPE) in the lower troposphere. This is the region where a parcel of air if raised from the lower PBL would sink back down again. Another term for CINH is a capping layer. The capping layer must be broken before lower PBL based lifting is able to move into the +CAPE region of a sounding and develop into deep convection.”
Courtesy: Haby’s Hints
I don’t often talk about “CIN” on here, because it usually doesn’t play a “big” role in our threat for severe weather. And when it does, it is something that I can work through behind the scenes and don’t really need to reference to help explain a certain outcome or potential.
That is not the case for Thursday. Take a look at the maps of CIN below:
Notice in the early morning that there is a donut hole across southeast Mississippi and ear the coast that fills in (slightly) by mid-morning. Then it is gone by early afternoon. That means that around sunrise There won’t be a capping layer, but once we start to get daytime heating, there will be a slight cap, and then tat cap erodes by later in the morning and into the early afternoon.
That slight capping should help to limit the coverage of storms between sunrise and about 10am. And then as we transition from 10am through 1pm, the cap erodes away and storms are free to form anywhere and everywhere that some sort of forcing is present.
Above is a look at 850mb (low level) temperature advection. This is a fancy way to look at the movement of pockets of air. Advection is just a fancy weather way of saying horizontal movement. It isn’t so much “wind” as a pocket of air moving. Some pockets are warmer and some are cooler. These aren’t “fronts” but rather little areas that are only a few degrees different than the surrounding air.
Comparing these advection maps to the CIN maps above, you can see that they line up in a lot of places. The places with CIN are also places that have the red coloring (warmer) with advection.
You’re right! I’m getting pretty deep into the weeds. Here is the payoff.
That warm air that passes through should put a lid on storms “going up” before 10am. But once it passes through, a few little pockets of cooler air will sneak in behind it. And that will act as suction to give a boost to some daytime heating at the surface after 10am. That may help to get a few – but not many – storms to go up quickly. And these few storms would be the only storms around.
And you guys know that lone storms in severe weather situations tend to be the ones that turn severe more quickly.
And there are two canals where this happens across south Mississippi within the data from a few different models…
Areas of concern
Those two canals are highlighted in red below. Those areas are averaged across a few different models (HRRR, NAM, HRW) and sit within a larger area of orange which is taking into account any flaws within the data.
Keep in mind, these are not the only areas where severe weather is possible. Rather, these are the areas where the first storms of the day may develop and have the chacne to become the strongest storms of the day.
This also why inteh county-by-county breakdown why some counties show a potential for “up to an EF3” tornado while others show just a chance for “up to an EF2” tornado.
And a “chance” for “up to” does not guarantee you see a tornado. It is simply looking at the available data and try to build a fence around potentials.
The SPC Risk area and Discussion
Like. said, no “big” changes to the areas.
The SPC only moved the Moderate Risk farther north. Here is the latest discussion from the SPC:
…SUMMARY…
The potential for an outbreak of severe storms including several long-track strong tornadoes, scattered large to very large hail, and severe/destructive winds, will exist Thursday into Thursday evening across a portion of the lower Mississippi Valley, Tennessee Valley, and Southeast.
…Synopsis…
A shortwave trough with attendant 70-100 kt+ mid-level jet will eject northeastward from the southern Plains across the lower/mid MS Valley on Thursday, and continue over the OH Valley and lower Great Lakes region Thursday night.
At the surface, a weak low over northeast TX at the beginning of the period Thursday morning is expected to likewise develop northeastward to the mid MS Valley through the day while deepening. A warm front attendant to this cyclone will likely lift northward across the lower MS Valley/Mid-South and TN Valley towards the lower OH Valley by Thursday evening.
…Lower Mississippi Valley and Southeast…
Storms will likely be ongoing at the start of the period from northeast TX into southern AR and northern MS/AL and TN. This activity will likely be supported by a southerly low-level jet and related warm advection. These storms should shift northward through the morning, allowing for destabilization via diurnal heating to occur across the lower MS Valley. Rich low-level moisture with at least mid to upper 60s surface dewpoints (perhaps lower 70s), should advect northward across parts of the lower/mid MS Valley, TN Valley, and Southeast by Thursday afternoon.
This increasing moisture, coupled with diurnal heating, will likely support MLCAPE of 1500-2000 J/kg developing over a fairly broad portion of these regions. A pronounced low-level jet (50-60+ kt) will overlie much of this region as well, as large-scale ascent from the ejecting shortwave trough overspreads the lower/mid MS Valley vicinity. Strongly veering and strengthening wind profiles from the surface through mid levels will support supercells. 0-1 km SRH along/south of the surface warm front will likely reach 300-500 m2/s2, and low-level mesocyclones capable of producing strong, long-track tornadoes appear likely with any supercells that can form. S
cattered large hail, some of which may be 2+ inches in diameter, and severe/destructive winds also appear probable, both with supercells and any bowing line segments that can develop. At this time, the best potential for strong tornadoes appears to extend from parts of central/northern MS into western/middle TN and central/northern AL, mainly Thursday afternoon and evening as storms move generally northeastward.
Concern does exist regarding the effect of storms forming during the morning on the development of instability, and potential for destructive interference from too many storms developing across the warm sector at the same time.
Still, given the very favorable environment forecast across this region and the potential for numerous supercells, an upgrade to High Risk for multiple strong to potentially violent, long-track tornadoes may be needed in a later outlook update.
Courtesy: SPC.NOAA.GOV
Karrie Meter
Looking at the 12z HRRR data, here is a grid of the Karie Meter map from that data from mid-morning through mid-evening.
A big thanks to Dr. Kim Wood at Mississippi State University for helping put these maps together and kicking them out so quickly this morning.
One thing to note about the Karrie Meter is that it was designed to use with pretty coarse data. So when you look at higher-resolution dat like the HRRR is can produce some interesting looking maps. Based on what I’ve been able to pull from the data is to find where the model thinks the strongest storm is, find the “Couplet” where the highest numbers are a “dot” next to another area where the lowest numbers are a “dot” and the place inbetween is where the model thinks the strongest storm will be.
South Mississippi Breakdown
This is not going to be a rains-all-day and storms-are-all-over kind of day. In fact, this is looking less, and less, like an event where everyone sees severe weather. Instead, there will be a few storms that turn severe, and everyone else sees some rain, thunder and wind at times. There is even the outside shot that some folks stay dry all day.
Taking a look at your likelihood of seeing any type of storm activity…
EVERYONE:
– Heavy rain at times
– Frequent lightning
– Wind gusts up to 40mph
SOME SPOTS:
– Heavy rain at times
– Frequent lightning
– Wind gusts up to 50mph
– Dime-sized hail
FEW FOLKS:
– Heavy rain at times
– Frequent lightning
– Wind gusts up to 70mph
– Quarter-sized hail
– Tornado (perhaps a strong tornado)
Looking at the counties of southern Mississippi, here is a county-by-county timeline and breakdown of what to expect on Thursday. And while the timeline is broken down into chunks from 8a-12p, 12p-6p, and 6p-10p…. keep in mind that the window of opportunity for the strongest storms to START to develop is around 11am. So there is some overlap.
NORTHERN COUNTIES
Simpson County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado.
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength).
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Smith County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado.
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength).
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Jasper County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado.
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength).
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Clarke County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado.
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength).
6p-10p – A few severe storms may linger in the area through 7p. After that, isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
HIGHWAY 84 CORRIDOR
Lawrence County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Jeff Davis County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Covington County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Jones County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Wayne County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – A few severe storms may linger through 7p. After that point, isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
HIGHWAY 98 CORRIDOR
Walthall County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12a-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Marion County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Lamar County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF3 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Forrest County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF2 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Perry County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF2 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
Greene County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF2 in strength)
6p-10p – Isolated storms coming to an end. Followed by a thin line of storms moving through the area during this time. Storms may be strong with heavy rain, some lightning, and gusty wind.
HIGHWAY 26 CORRIDOR
Pearl River County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF1 in strength)
6p-10p – Storms ending
Stone County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF1 in strength)
6p-10p – Storms ending
George County
8a-12p — Passing clouds with isolated storms developing. Strong to marginally severe storms will be possible during this time with heavy rain, frequent lightning, wind gusts up to 60mph, up to dime-sized hail and the potential for a brief tornado
12p-6p — Isolated strong to severe storms possible. Storms may produce heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and a chance for a tornado (up to EF1 in strength)
6p-10p – Storms ending
The Bottom Line
Severe weather still looks possible for the Gulf Coast region of Louisiana, Mississippi and Alabama. a bulk of the severe weather threat looks to be north of I-20, but that doesn’t mean places south of that region are in the clear.
Have a way to get warnings from the NWS on Thursday. Things like a NOAA Weather Radio or an app on your phone set to ping you when a new warning for your area is issued. Or have both!
The timeline for the severe weather threat will be late morning through early evening. And all types of severe weather will be possible: heavy rain, frequent lightning, wind gusts up to 70mph, hail up to the size of golf balls, and tornadoes.
While the worst-of-the-worst may not be in your area, we can’t know for certain at this time who, specifically, will see the most significant severe weather. So it is important to have a plan, just in case ist happens in your area.
