The severe weather probabilities have been taken up a notch for Friday's event.
The main tornado threat is expected to be over much of Mississippi back into Louisiana and Arkansas, where supercell thunderstorms will initially form and perhaps produce tornadoes with a fairly long track that are capable of significant damage. That's where you see the hatched area. Even around here though, that 5% tornado risk is the basic risk for isolated tornadoes within the Tennessee Valley region. Still worth respecting, even though the higher probabilities, especially of a longer-lived and more intense storm (that could produce a strong tornado, E/F-2 strength or greater), are to our West.
I don't have a link to the article at hand, but hats off to Jim Stefkovich, who used to be MIC in Birmingham, for picking up on this sooner than anyone else I saw, the upgrade and eastward expansion of the risk being so likely. He wrote that for Alabama EMA yesterday morning.
The threat for large hail is looking marginal around here, but our threat for damaging thunderstorm winds is a little enhanced over Northwest Alabama. Of course the really widespread wind damage is again expected to be focused mainly to our West. Our probabilities here are still well worth respecting. All it takes is one damaging storm, and we've got problems if there is not awareness and a good solid safety plan.
What we expect is for supercell thunderstorms to fire up within mainly that red area, the Level 4 out of 5 Moderate Risk. These have the highest threat for producing tornado damage, could be significant damage in some places. And then later in the evening and night, the storms will try to form at least one line, we call a squall line. Sometimes more than one line forms. Sometimes it even gets messy where you still have a supercell or two along with one or more lines of storms. But for the most part, by the time the storms get into Alabama and Southern Middle Tennessee, they are expected to be more in a line, which means the primary threat will shift to a risk for damaging thunderstorm winds, with the threat.
You can now get to my #tornado shelter map MUCH more easily and quickly. I now have it at https://t.co/KrCpli3ltz so that you have an easy to remember address. That will make it a lot easier. I have about 1,600 shelters mapped and I'm constantly adding more.— Craig Ceecee (@CC_StormWatch) March 22, 2023
If you have any questions, leave me a comment on here before the event gets going. Or ask your local National Weather Service office (or favorite broadcast meteorologist) on social media. This is a deal where if people know what's going on and have preparations, I think we'll be all right around here. But the timing of it is unfortunate. Especially on a Friday night, well, I guess more people will be awake, but they sure won't be wanting to think about the weather. So it is important to have a way to get the warning if one comes out for your location. And to have a clear safety plan that you can put into action right away, get to a safe place in less than five minutes of hearing the warning.
And I think that's true even if we mainly see damaging thunderstorm winds around here instead of a tornado or two in the mix. It's dangerous for people to sleep through those without taking any shelter. Remember we did have some deaths early this month from damaging straight-line winds. The tornadoes that day actually did not kill anyone. And I think there were three in North Alabama. So as a better-safe-than-sorry approach, I would take a severe thunderstorm warning seriously tomorrow night. Sometimes a tornado can form quickly from a severe thunderstorm anyway, without additional warning. And the winds are dangerous either way. If you take the trouble to read my ramblings, you deserve some safety and peace of mind for your time.
If you want to try to understand all the scientific jargon, it is below.
SPC AC 230600
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Thu Mar 23 2023
Valid 241200Z - 251200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST
LOUISIANA...SOUTHEAST ARKANSAS...AND WESTERN MISSISSIPPI...
Supercell thunderstorms capable of all severe hazards, including
strong tornadoes, are possible across the Lower Mississippi Valley
Upper troughing is expected to be in place over the western CONUS
early Friday morning. Strong mid-level flow will extend throughout
the periphery of this trough into the more confluent flow north of
the subtropical ridging across the eastern CONUS. A shortwave trough
is forecast to move through this enhanced mid-level flow, tracking
quickly eastward across the southern Plains during the day, and more
northeastward into the Mid MS Valley overnight. Mid-level flow is
expected to strengthen as the shortwave moves eastward, with 100+ kt
at 500 mb spreading across TX into the Mid-South.
At the surface, a low initially over north TX is forecast to move
northeastward ahead of the approaching shortwave, moving into
northern AR by Friday evening and through the Lower OH Valley
overnight. This low is expected to deepen throughout the day, and
this cyclogenesis will result in a broad area of moderate southerly
flow across the Lower MS Valley/Mid-South into the Southeast and TN
Valley. Environmental conditions appear favorable for numerous
severe thunderstorms from the Lower MS Valley through the Mid-South
and into the Mid MS and Lower OH Valleys.
...Lower MS Valley into the Southeast...
A broad warm sector, characterized by dewpoints in the upper 60s, is
forecast to be in place from east TX across much of the Lower MS
Valley and Mid-South early Friday morning. Thunderstorms may be
ongoing early Friday morning along a cold front moving eastward
across east TX. This cold front is expected to make gradual eastward
progress, as its parent surface low deepens while moving from
eastern OK into AR. This overall evolution will contribute to a
continued mass response across the warm sector, with low-level
moisture increasing throughout the day amid strengthen southerly
flow. This increase in low-level moisture coupled with modest
heating is expected to result in airmass destabilization during the
late afternoon. This destabilization coupled with large-scale ascent
attendant to the approaching shortwave (perhaps augmented by
low-level confluence) will likely result in discrete thunderstorm
development within the warm sector ahead of the front.
Current thinking is that this initial development is most likely to
occur in the TX/LA border vicinity. The downstream air mass will be
moderately buoyant, with guidance suggesting MLCAPE around 1000-1500
J/kg and max 2-6 km AGL lapse rates around 8 deg C per km. Robust
vertical shear is also expected, with a strong low-level jet (i.e.
50-60 kt at 850 mb) developing during the evening beneath
strengthening mid-level flow. Forecast hodographs depict
substantial low-level speeds and veering, with 0-1 km storm-relative
helicity from 200 to 300 m2/s2. A discrete supercell mode is
anticipated initially, with all severe hazards possible, including
strong tornadoes. With storms expected to develop in the LA/TX
border vicinity, discrete storm maturation is anticipated across
northeast LA, southeast AR, and western MS.
Upscale growth into a convective line is anticipated after this
initially discrete mode, with the line pushing eastward across MS
and AL overnight. Robust kinematic fields are expected to persist,
support a continued threat for strong gusts and line-embedded
...Mid-South into the TN and Lower OH Valleys...
A more convoluted convective evolution is anticipated from
central/northern AR northeastward into the Lower OH Valley on
Friday. Storms will likely be ongoing along and north of stationary
boundary extending from east-central OK northeastward into northern
KY. A low-probability threat for hail is expected throughout the
morning and into the early afternoon as warm-air advection promotes
continued thunderstorm development along this boundary.
A gradual increase in storm intensity is then expected during the
afternoon as the surface low begins to deepen across AR and
large-scale forcing for ascent attendant to the shortwave increases.
Buoyancy will be more modest than areas farther south, but the
strong ascent and increasing shear is still expected to support
intense updrafts. Given the presence of the stationary front and
stronger forcing, a linear mode is anticipated, with this line then
progressing quickly east-northeastward across the Mid-South during
the evening and into more of the Lower OH and TN Valleys overnight.
Strong wind gusts will be primary hazard within this line, but
line-embedded tornadoes will be possible as well.