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Severe Weather Threat 1/5-1/6/2025

CheeselandSkies said:
Found the monster hodograph (southeast AR):

View attachment 32497

Yes folks, that's over 820 m2/s2 0-3 KM SRH. CAPE profile is rather skinny and lapse rates are marginal, but there's fairly substantial 0-3km CAPE. Even a QLCS would be capable of producing strong tornadoes in that scenario.
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If that's the case, then watch for that Level 2 Slight to be expanded into western AL with Level 3 Enhanced from Central/Northern Louisiana, Southwest AR, and much of Central into North MS.
 
CheeselandSkies said:
Found the monster hodograph (southeast AR):


Yes folks, that's over 820 m2/s2 0-3 KM SRH. CAPE profile is rather skinny and lapse rates are marginal, but there's fairly substantial 0-3km CAPE. Even a QLCS would be capable of producing strong tornadoes in that scenario.
Click to expand...
Maybe a bit of convective feedback?
 
If those surface winds were backed a bit more inte the ark/la/miss region... Yikes! Maybe a saving grace for a bigger tornado threat. I think your biggest risk is going to be damaging winds unless those winds get backed a bit more. I'm guessing it's more veered because the low pressure occludes?
 
From NWS Jackson: (grab yourself a snack and be amazed)

Bottom Line Up Front:

IMPACTS: Strong to severe storms capable of producing damaging winds to 60 mph , tornadoes, and hail up to 1" will be possible Sunday afternoon and evening, with the primary risks likely associated with and in close proximity to an approaching line of storms.

TIMING: Storms will approach areas generally west of the Mississippi River by early afternoon, nearing the I-55 corridor by late afternoon into early evening, and finally exiting eastern Mississippi late Sunday night.

.. Meteorological Discussion ..

Sunday will feature strong to severe storms bookended by a roller coaster of temperature swings.

The forecast is complex with a lot of confounding variables at play. A robust and strengthening closed upper low will form as a shortwave trough occludes and moves west to east across the Southern Plains, into the Lower and Middle Mississippi Valley, and then towards the East Coast. This trough is aggressively moving into the area on the coat tails of a slow-to-depart upper longwave trough leaving little time for deep layer ridging to establish in our vicinity. This suggests the airmass residing over the area, as well as the boundary layer advection trajectories, will be only partially modified by the western Atlantic and Gulf of Mexico and will retain some characteristics of their recent continental origins.
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Part 2:
Despite the poor window of opportunity for robust boundary layer thermodynamic recovery, substantial height falls aloft (E.g. 12Z GFS suggests 500 mb height falls of around 8-12 dam through the afternoon/evening Sunday) with a trend from a positively tilted trough orientation to one of more neutral orientation should foster at least a narrow corridor ahead of the approaching cold front as a surface/850mb low pressure/height area begins to deepen. This will strengthen boundary layer flow while at the same time result in that flow becoming more veered to southerly as opposed to east- southeasterly, allowing a but better orientation for moisture/thermal advection. With the front rapidly approaching by Sunday afternoon, the window of time for this more improved advection structure will be narrow and likely confined to the vicinity of the front itself where dewpoints will surge from the 50s into the lower and possibly middle 60s F and temperatures in the low/mid 70s to upper 60s F within a few hours time directly preceding the expected squall line. For this reason, indeed as supported by early CAM guidance, the primary storm mode is likely to be linear in nature with the greatest risks for severe weather in proximity to the rapidly eastward moving convective line. While this scenario is substantially less concerning currently than our last weekend event and the net parameter space will be considerably less robust, some similarities do exist. Namely in that the best thermodynamic support will likely be west of our area. Similarly as well, wind shear however will be increasing through the evening with 0-3 km SRH increasing from an already-adequate 200-300 M^2/S^2 to above 400 M^2/S^2. Coinciding with 40-50 kt effective deep layer shear and the aforementioned substantial height falls aloft, robust and deep convection will be supported despite the lack of robust thermodynamic support. This "high shear - low CAPE" type of environment is one of the most common cool season modes for severe weather and past experience suggests that predicting the scope of impact can be challenging. As an example, forecast point soundings as sampled from the current 12Z GFS model show little if any severe risk based purely on algorithmic comparison to past events. Again, this is common in these types of cool season severe weather risks and it is inadvisable to look too closely at traditional severe weather composite indices for that reason as the apparent lack of conditional instability can result in those algorithms underestimating hazard risk. These factors should support a risk for damaging wind and perhaps a few tornadoes. With little instability, not the least contributed to by poor lapse rates both near the surface and aloft, the risk for hail larger than around an inch appears low and the best chances for severe (1") hail appears to be generally west of I-55 where at least some thermodynamic instability may be realized prior to sunset.

Putting it altogether, we have

1. Robust lifting both aloft (height falls/increasing upper divergence due to trough orientation), and near the surface (approaching cold front, increasing prefrontal confluence).

2. Strong deep layer flow with enlarging, curved hodographs (850 velocities increasing from 40 kt to 50-60 kt out of the south with 500 mb velocities increasing from 50-60 kt to 75-90 kt out of the west-southwest)

3. Boundary layer moisture supportive of deep moist convection with little convective inhibition though, admittedly, limited thermodynamic instability overall.
4. Narrow warm sector characterized by only partially modified airmass advection.

The forecast above, "Strong to severe storms capable of producing damaging winds to 60 mph, tornadoes, and hail to 1" will be possible Sunday afternoon and evening, with the primary risks likely associated with and in close proximity to an approaching line of storms." is therefore one of moderate confidence and is reflected in forecast products as a "Slight" Risk (2/5) for severe weather for much of the area and a "Marginal" risk for severe weather in eastern Mississippi.
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JBishopwx said:
Oh, that's just for Sunday. Another two long paragraphs for Monday-next week
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Continue Season 9 GIF by The Office
 
00z hrrr is robust on parameters for the ArkLaMiss area. Not so robust on the updraft strengths though (but as a side note I don't think higher shear low cape setups and simulated low top supercells do well with updraft strengths on models in general so take that as a grain of salt with updraft strengths not looking that great.) Still stand by my prediction of an decent sized enhanced mainly wind threat with a side of tornadoes.
 
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Austin Dawg said:
I don't know if it's for certain, but I heard the Tupelo tornado back in the 1930s was followed by snow flurries in the area.
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You are correct. Tupelo had a trace of snow on April 5th, 1936.
 
My prediction was correct; there she blows, wind driven enchached but a very large 5% tornado risk. That's almost definitely gunna be a small 10% by the event is go time. (Id place my bets on the 10% being right on top of the 30% wind risk.)

Hrrr is rather bullish on low top spinners ahead of the line, still would like to see more backing near the surface for any substantial tornado threat day2probotlk_0700_wind.gifday2probotlk_0700_torn.gifScreenshot_2025-01-04-05-59-29-05_40deb401b9ffe8e1df2f1cc5ba480b12.jpg
 
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I see that Enhanced Risk being expanded across all of Central MS and into at least southern North MS counties due to both damaging wind potential and potential for supercells out ahead of the main line. The 12z HRRR did show that potential. I don't see a 10% SIG hatch unless modeling increases the supercell potential out ahead of the main line.
 
And once again kudos to NWS Jackson MS for having a great detailed discussion.

This right here caught my eye: "In contrast, wind shear
will be increasing through the evening with 0-3 km SRH increasing
from an already-adequate 250-350 m^2/s^2 to above 400 m^2/s^2.
Coinciding with 40-50 kt effective deep layer shear and the
aforementioned substantial height falls aloft, robust and deep
convection will be supported despite the lack of robust CAPE levels
seen on the 00Z GFS."
 
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