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Severe Weather 2024

slenker said:
If I remember correctly, December 10 2021 was the result of a very positively tilted trough. It makes me wonder how the moisture return was so strong for that system - was it already in place before the event unfolded?
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Can't remember trough tilt for that event but, especially in the South, we can indeed have quite serious severe weather events with positive tilt troughs.
 
slenker said:
If I remember correctly, December 10 2021 was the result of a very positively tilted trough. It makes me wonder how the moisture return was so strong for that system - was it already in place before the event unfolded?
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Pretty much - Take a look at the first few pages of the December 10th thread on here. It’s Fred giving a meteorology masterclass on positive tilt troughs and how you shouldn’t dismiss a threat based on just that, especially outside of the plains as @Clancy alluded to.

Through my time on here and the other boards, I’ve seen Fred throw a laundry list of really nasty Dixie/Southeast Days that started out as a positive tilted trough.
 
slenker said:
If I remember correctly, December 10 2021 was the result of a very positively tilted trough. It makes me wonder how the moisture return was so strong for that system - was it already in place before the event unfolded?
Click to expand...

The trough associated with that event was rather positively tilted initially, but became less so with time, and nearly neutral-tilt by the time the outbreak began in earnest shortly after 0Z 12/11.

Here are the 500mb maps from 12Z 12/10/21 and 00Z 12/11/21. In any case you can see it had quite a broad wavelength with a large area of strong southwesterly flow aloft spreading out over the warm sector, as opposed to being confined to right along/behind the initiating frontal boundary as is often seen with sharply positively tilted troughs that may be highly amplified N-S but have a "squashed" or narrow E-W wavelength.

500_211210_12.gif

500_211211_00.gif
 
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CheeselandSkies said:
Here's the 500 mb map for 0Z 12/11/2021, shortly before the Quad-State supercell produced its first few, weak tornadoes.

View attachment 31836

Source:

SPC Severe Weather Event Review for Friday December 10, 2021

www.spc.noaa.gov

I wouldn't call that "very" positively tilted. Just modestly so, and with a quite broad wavelength. This development compared to earlier model solutions was one of the reasons this event's ceiling uptrended so dramatically in the last 24-48 hours beforehand.

In addition to that, the Quad-State supercell and a couple of the other major players (and support for this was one of the reasons Fred suspected this event had a few more things going for it tornado-threat wise than most positive-tilt setups) initiated in the open warm sector, instead of right along the cold front.

Your classic positively-tilted setup that is less favorable for severe weather in general, and supercell tornadoes in particular, has a squashed, narrow E-W wavelength with the base of the trough leaning sharply to the southwest while the exit region shears out to the northeast, away from the warm/moist sector, and the mid-upper level flow is parallel to and tends to lag behind the cold front. This makes it difficult to get cells that can initiate and move off the boundary while remaining discrete, and if they do they move out into weak deep-layer shear. As you can see with the 2021 setup, in contrast there was strong southwesterly flow across a broad area across the warm sector.
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Excellent post. I’ve personally always paid more attention to the amplitude of the trough vs the tilt, as well, as you note, it’s location relative to some of the other important severe wx features (warm sector, LLJ axis, surface low etc).

As a Kentucky native that watched the lead up and tracked the 12/10 event live, it’s still kind of mind boggling how historical it was. Kentucky was hit hard on 4/3/74, but since then, there hadn't been anything like 12/10.

Mayfield was the tornado of the day by far, but you also had the other EF4 produced by the quad state cell. Then you had an additional 122 mile tornado that hit Tennessee and Kentucky. Then with two significant tornados striking Bowling Green (which is not a small town by any means), it really was an upper echelon outbreak for the state.
 
Tempestas Tonitrua said:
Excellent post. I’ve personally always paid more attention to the amplitude of the trough vs the tilt, as well, as you note, it’s location relative to some of the other important severe wx features (warm sector, LLJ axis, surface low etc).

As a Kentucky native that watched the lead up and tracked the 12/10 event live, it’s still kind of mind boggling how historical it was. Kentucky was hit hard on 4/3/74, but since then, there hadn't been anything like 12/10.

Mayfield was the tornado of the day by far, but you also had the other EF4 produced by the quad state cell. Then you had an additional 122 mile tornado that hit Tennessee and Kentucky. Then with two significant tornados striking Bowling Green (which is not a small town by any means), it really was an upper echelon outbreak for the state.
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Watching the quad-state cell all the way through felt like a once-in-a-lifetime experience in the worst way possible. I remember looking at it as it started to form near Little Rock, having absolutely no clue how horrible and historic it would become.
 
Clancy said:
Watching the quad-state cell all the way through felt like a once-in-a-lifetime experience in the worst way possible. I remember looking at it as it started to form near Little Rock, having absolutely no clue how horrible and historic it would become.
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I doubt very many of us expected it to go nuts the way that it did until it played out like that.

As for forecasting, here's the latest CPC forecasts for the next 6-14 days:

6-10 days, temperature:

610temp.new.gif

6-10 days, precipitation:

610prcp.new.gif

8-14 days, temperature:

814temp.new.gif

8-14 days, precipitation:

814prcp.new.gif

As can be gleaned, things look to be getting warmer and wetter after Christmas. Now, whether that would translate into severe potential depends on whether the primary ingredients for severe weather could come together in just the right place at just the right time. At least the warmth and moisture would likely be present...
 
GEFS & CIPS definitely sniffing out some late December severe potential. 12Z GFS shows a potent system, but questions about the northward extent of instability. Definitely the time period to watch.
1734630716872.png1734630749124.png1734630858404.png
 
Scott81 said:
Is that 987 mb low to far north for severe weather?? Or does it need to be closer?
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It wouldn't be as significant a threat as if the main low was in Oklahoma. It would still imply a strong squall line with embedded tornadoes at best. However, the threat would increase if a secondary low developed and that will need to be watched for.
 
JPWX said:
It wouldn't be as significant a threat as if the main low was in Oklahoma. It would still imply a strong squall line with embedded tornadoes at best. However, the threat would increase if a secondary low developed and that will need to be watched for.
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There seems to a trailing secondary that forms but almost certainly too late to make a difference for the main threat area. Of course, if that changes, could be a different story.
1734634090501.png
 
Clancy said:
There seems to a trailing secondary that forms but almost certainly too late to make a difference for the main threat area. Of course, if that changes, could be a different story.
View attachment 31847
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Yeah, a lot going on there...and after days like 12/15/21 and 2/8/24, I wouldn't discount the possibility of that northern surface low pulling up just enough moisture and 3CAPE for at least a few low-topped spinners into the Midwest/Great Lakes if that surface/upper air pattern were to verify verbatim.

The bolded date was the last time I'm gonna not chase simply because it's winter in the upper Midwest. I mean it this time...
 
CheeselandSkies said:
Yeah, a lot going on there...and after days like 12/15/21 and 2/8/24, I wouldn't discount the possibility of that northern surface low pulling up just enough moisture and 3CAPE for at least a few low-topped spinners into the Midwest/Great Lakes if that surface/upper air pattern were to verify verbatim.

The bolded date was the last time I'm gonna not chase simply because it's winter in the upper Midwest. I mean it this time...
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The wildest of weather almost never fails to wait for the silliest of setups to present itself.
 
One thing to keep an eye on, with the setup for the 28th as depicted on the GFS, is that the moisture is remarkably deep for the time of year...so deep, in fact, that many of the forecast soundings across much of the warm sector of the system have nearly saturated profiles throughout the column, resulting in poor lapse rates and weak/nonexistent instability despite the rich moisture. Still quite far out, but something to note.
 
CheeselandSkies said:
One thing to keep an eye on, with the setup for the 28th as depicted on the GFS, is that the moisture is remarkably deep for the time of year...so deep, in fact, that many of the forecast soundings across much of the warm sector of the system have nearly saturated profiles throughout the column, resulting in poor lapse rates and weak/nonexistent instability despite the rich moisture. Still quite far out, but something to note.
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We might be looking at more of a heavy rain/flash flood threat if that verifies. I distinctly remember Christmas Day 2015 because I received 8.75 inches of rain that day and we had numerous flash flooding throughout Monroe County. That remains my highest 24 hour rainfall total that I've measured since moving into my new house post 2011.
 
Taylor Campbell said:
The point soundings I’ve pulled off the GFS the last several days in the warm sector have demonstrated a healthy instability profile with steep mid level and low level lapse rates.
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SPC needs to catch up...

An additional focus for increasing deep convective potential will be
into the Thursday/Day 6, Friday/Day 7, and Saturday/Day 8 time
frame. This will be as a secondary upper trough emerges from the
Southwest deserts and moves toward the Deep South. This could lead
to a severe risk in a corridor from east/southeast Texas and the
ArkLaTex to Lower Mississippi Valley. While some severe storms will
be possible, perhaps especially Thursday/Day 6, there is lingering
risk magnitude uncertainty related to moisture/destabilization given
the potential influences of the preceding shortwave trough and cold
front. Forecast uncertainties at this time frame precludes any 15%
outlook areas.
 
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