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Svr Wx threat April 1-April 2 2024

KevinH

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I almost hate to do this BUT here we are. While it is too early to say how this potential event will perform, we can still have fun discussing it :)
The SPC isn’t QUITE ready to pull the trigger on highlighting an area, but I would not be surprised if they did for the time frame indicated. The wide area of warm DPs gets my attention.


Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Wed Mar 27 2024

Valid 301200Z - 041200Z

...DISCUSSION...
An upper trough/low should continue to move south-southeastward over the western states on Day 4/Saturday. Over much of the central CONUS, upper ridging should generally prevail, with a gradual northward advance of low-level moisture across the southern Plains. Although a plume of elevated instability should accompany this moisture return, a cap is expected to suppress robust convective development Saturday.

On Day 5/Sunday, the upper trough/low over the western CONUS should slowly advance eastward across the Southwest. But, there are still some differences in various guidance with the evolution of this trough/low. Some GEFS ensemble members show a slower ejection, with a closed 500-mb isohypse remaining over the West. Other members align more with the deterministic ECMWF is showing a more open wave, but with a positive tilt into the northern/central Plains. Another potentially complicating factor is a northern-stream upper trough, which may phase with the lower-latitude trough and help induce stronger cyclogenesis across the mid MS Valley/Midwest around Day 6/Monday.

Even with these continued differences, it appears that severe potential should gradually increase from Sunday into Monday across parts of the southern/central Plains, mid MO into mid MS Valleys, and perhaps also into the OH Valley/Midwest.

For Sunday, some severe potential may be focused across parts of MO into IL along and near a sharpening surface warm front. Mid-level height tendencies look to remain neutral through Sunday evening across this area, with nebulous large-scale ascent. Even so, low-level warm advection may help initially elevated convection to develop across MO in a moderate instability and strong deep-layer shear environment. If this occurs, then some severe threat may continue eastward into IL through Sunday evening. At this point, too much uncertainty exists regarding thunderstorm initiation and coverage to include a focused 15% severe area for Sunday.

A larger area of severe potential may be realized on Monday from parts of the southern/central Plains into the mid MS and OH Valleys. This will be largely dependent on the timing of ejection of the upper trough over the Southwest, and whether it can phase any with a northern-stream trough moving southeastward out of central Canada. Regardless, a broad warm sector, with 60s surface dewpoints, should be in place from TX/OK east of a dryline and northward to a warm front located somewhere in the vicinity of the OH Valley. The exact placement of these surface features remains rather uncertain Monday, as does the potential strength and northeastward track of a surface low across the mid MS and OH Valleys. Deep-layer shear appears strong enough to support organized severe thunderstorms, a consideration was given to adding a broad 15% severe area for Monday. But, there still seems to be too much spread in possible solutions with the upper trough to introduce an area yet.

Finally, some severe threat may continue on Day 7/Tuesday along and ahead of a cold front moving across parts of the Southeast and eastern states. But, predictability remains very low at this extended time frame.
 

KevinH

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Not seeing a lot that jumps out at me in recent model runs as being highly favorable for widespread/significant severe (unlike, say, around this time last year). All the troughs, at least as portrayed by the GFS, either eject in a flattened-out, highly positively-tilted fashion wherein the stronger height falls and colder air aloft remain on the cool side of the main surface boundary; or those that don't have antecedent moisture issues similar to the one we just had.

The one exception might be in the Plains on April 1, where the exit region of the trough starts to overspread the warm sector before it becomes totally positively tilted and strung out SW-NE. Parts of eastern KS/OK to western-central MO/AR look to have some potential in this scenario. As a Midwest chaser, would sure like to see that trough become more neutral to negatively tilted with time going into the next day, but at this point that's not what looks likely to happen.
 
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Clancy

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Not seeing a lot that jumps out at me in recent model runs as being highly favorable for widespread/significant severe (unlike, say, around this time last year). All the troughs, at least as portrayed by the GFS, either eject in a flattened-out, highly positively-tilted fashion wherein the stronger height falls and colder air aloft remain on the cool side of the main surface boundary; or those that don't have antecedent moisture issues similar to the one we just had.

The one exception might be in the Plains on April 1, where the exit region of the trough starts to overspread the warm sector before it becomes totally positively tilted and strung out SW-NE. Parts of eastern KS/OK to western-central MO/AR look to have some potential in this scenario. As a Midwest chaser, would sure like to see that trough become more neutral to negatively tilted with time going into the next day, but at this point that's not what looks likely to happen.
Will mention there has been significant run-to-run change of the presentation of the troughing, and I would bet on that continuing to change throughout most of the medium range. The troughing coming in from Canada seems to play a significant role in the shape and trajectory of our main trough, though I'm not nearly well-versed enough in that kind of jazz to make any real conclusions about it.
trend-gfs-2024032718-f156.500wh.conus.gif
 

KevinH

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aaaaaaand SPC highlight areas for April 1-2

1711623099752.png
1711623194558.png

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Thu Mar 28 2024

Valid 311200Z - 051200Z

...DISCUSSION...
...Day 4/Sunday: Mid Mississippi Valley into the Central/Southern
Plains...
The upper trough/low over the western states should slowly advance
eastward towards the Southwest and southern/central High Plains on
Sunday. Upper ridging is forecast to remain over the central/
southern Plains through Sunday night, which in tandem with a
low-level temperature inversion should tend to suppress most
convection. One possible exception may be along a sharpening warm
front across MO/IL, where some guidance suggests elevated convection
may form either Sunday morning, and/or Sunday night with strong
low-level warm advection/lift occurring. Steepening mid-level lapse
rates are forecast to overspread the mid MS Valley from the
southwest through the period. These lapse rates, along with
increasing moisture/instability in the presence of strong deep-layer
shear, may support a risk for isolated supercells with associated
threat for large hail. Regardless, confidence remains too low in
this mainly elevated convection occurring, given upper ridging
persisting, to add a 15% severe area for Sunday along/near the warm
front in MO/IL at this time.

...Day 5/Monday: Southern/Central Plains into the Mid Mississippi
and Ohio Valleys...
Even though some differences remain in medium-range guidance
regarding the ejection of an upper trough over the central CONUS on
Monday, confidence has increased in the general location of relevant
surface features, including the primary low, position of a
southward-extending dryline, and northward extent of the warm front
into the OH Valley. Even though the overall upper trough orientation
may remain somewhat positively tilted, most deterministic guidance
shows that a mid-level speed max and associated shortwave trough
will eject northeastward over the southern/central Plains through
Monday evening. Low-level mass response should encourage the
eastward development of a surface low to the OK/KS vicinity in a
similar time frame. Favorable low-level trajectories emanating from
the Gulf will act to increase low-level moisture in tandem with
steepening mid-level lapse rates and daytime heating across a broad
warm sector extending from the southern/central Plains into the
lower/mid MS Valley and OH Valley.

A favorable thermodynamic and kinematic environment for organized
severe convection will exist across much of these regions, with
supercells capable of producing large hail and tornadoes possible
initially. With time Monday evening/night, some upscale growth seems
probable across the mid MS and OH Valleys, as mid-level flow should
become increasingly parallel to a surface cold front. Therefore, a
15% severe area has been introduced for Monday where confidence is
greatest that robust convection will develop in a parameter space
characterized by weak/moderate instability and strong deep-layer
shear. A nocturnal minimum in severe convective potential may be
realized Monday night into early Tuesday morning across parts of the
lower MS Valley into Mid-South, given the positively tilted nature
of the upper trough.

...Day 6/Tuesday: Ohio/Tennessee Valleys into the Appalachians...
Some severe threat should continue Tuesday over parts of the OH/TN
Valleys into the Appalachians as the upper trough continues
eastward. Even though there is still some uncertainty with the exact
placement of the primary surface low and evolution of the upper
trough, enough confidence exists in a fairly narrow corridor across
these regions to add a 15% severe area for Tuesday. Rich low-level
moisture should be in place ahead of an eastward-moving cold front.
Redevelopment and/or re-intensification of convection seems probable
by Tuesday afternoon. Strong deep-layer shear and weak instability
should be sufficient for organized severe convection posing some
threat for damaging winds, and perhaps tornadoes given the forecast
strength of a low-level jet focused over parts of the OH/TN Valleys.
The northward extent of the severe risk across OH and vicinity
remains uncertain, as the placement of the warm front varies in
model guidance. Similarly, convection should eventually encounter a
less unstable airmass across the Appalachians. But, an isolated
severe risk may continue Tuesday evening into early Wednesday
morning across the southern/central Appalachians into portions of
the Southeast.

...Day 7/Wednesday and Day 8/Thursday...
Predictability remains too low to include a 15% severe delineation
for Wednesday across the Mid-Atlantic/Southeast along/ahead of a
cold front. By this extended time frame, there are significant
differences in model guidance regarding the evolution of the upper
trough, including its possible interaction/merging with a
northern-stream trough, and placement of relevant surface features.
Still, at least an isolated severe risk may persist Wednesday
along/ahead of the eastward-sweeping cold front. Once this front
clears the East Coast, severe potential appears minimal across the
CONUS next Thursday.

..Gleason.. 03/28/2024
 

JPWX

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Meanwhile at MEG

We have the corresponding severe weather 15% "Slight Risk" from SPC over Northeast MS

Yet we have this quote from their (MEG) morning discussion:

"At this point, severe weather is not anticipated for the region during this time."
 

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UK_EF4

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I do think we have to keep a very close eye on this upcoming threat. These positive tilt longer wave troughs can often end up being quite menacing in my opinion... before Dec 10th 2021 I would have been much more dismissive at this point in the forecast, but what I've learnt from that is with those positive troughs they can easily uptrend - particularly when you get a negative tilted shortwave moving into the threat area as the latest couple GFS runs have had.

I'm not trying to insinuate that we would see anything close to the Dec 2021 event by making that comparison either - half the models barely agree on the trough shape let alone show anything similar to the GFS solution - but with the potential for a big warm sector, models underestimating moisture, and the increasing kinematics we are seeing on the latest GFS - the ceiling is quite high in my opinion. The flipside of that coin is that the floor is also very low (for tornadoes)... going to be an interesting few days of model watching regardless!
 

Clancy

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I do think we have to keep a very close eye on this upcoming threat. These positive tilt longer wave troughs can often end up being quite menacing in my opinion... before Dec 10th 2021 I would have been much more dismissive at this point in the forecast, but what I've learnt from that is with those positive troughs they can easily uptrend - particularly when you get a negative tilted shortwave moving into the threat area as the latest couple GFS runs have had.

I'm not trying to insinuate that we would see anything close to the Dec 2021 event by making that comparison either - half the models barely agree on the trough shape let alone show anything similar to the GFS solution - but with the potential for a big warm sector, models underestimating moisture, and the increasing kinematics we are seeing on the latest GFS - the ceiling is quite high in my opinion. The flipside of that coin is that the floor is also very low (for tornadoes)... going to be an interesting few days of model watching regardless!
We've definitely had a fair share of significant events from positive tilted systems. Though they may underperform more often compared to negatively tilted configurations, and the balance of ingredients may be more delicate, it's definitely not worth writing off outright. Still 100+ hours away though, so things could change-a-plenty between now and then.
 
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I do think we have to keep a very close eye on this upcoming threat. These positive tilt longer wave troughs can often end up being quite menacing in my opinion... before Dec 10th 2021 I would have been much more dismissive at this point in the forecast, but what I've learnt from that is with those positive troughs they can easily uptrend - particularly when you get a negative tilted shortwave moving into the threat area as the latest couple GFS runs have had.

I'm not trying to insinuate that we would see anything close to the Dec 2021 event by making that comparison either - half the models barely agree on the trough shape let alone show anything similar to the GFS solution - but with the potential for a big warm sector, models underestimating moisture, and the increasing kinematics we are seeing on the latest GFS - the ceiling is quite high in my opinion. The flipside of that coin is that the floor is also very low (for tornadoes)... going to be an interesting few days of model watching regardless!
Well said , agree … seen some bad outbreaks positive tilted trough
 
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