Svr Wx Event - April 15-17, 2024

[KevinH]

Welp… SPC highlighted a 30% corridor in central OK, parts of N Cntrl Tx, S Cntrl Kansas, with an even larger area of 15% surrounding.




Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Wed Apr 10 2024

Valid 131200Z - 181200Z

...DISCUSSION...
Primary feature of concern will be an amplified upper low that is initially off the CA coast at 12Z Saturday. This low should dampen as it steadily progresses across the Southwest, before amplifying once again as it emerges onto the central Great Plains sometime on D6, as a separate shortwave trough digs towards the Pacific Northwest. Timing spread within the 00Z deterministic and ensemble guidance appears larger relative to yesterday, with the 00Z ECMWF decidedly trending farther east over the past 24 hours. It appears to be on the eastern envelope compared to its ensemble members. The overall forecast impact is with regard to dryline placement and surface cyclone evolution during the day on Monday and beyond.

The actual severe weather setup appears substantial. Air mass modification will ensue northward from the western Gulf on D3, with multiple days to improve the low-level moisture profile amid well above-normal surface temperatures and a pronounced elevated mixed layer. With the likely flow field amplification through the troposphere, all ingredients appear present for a significant severe weather day on D6/Monday. The areal uncertainty of the synoptic features is the primary limiting factor. For now, have added a confined 30 percent highlight to indicate the higher-end potential and the most probable corridor, while broadening the previous 15 percent area.

A lesser severe threat will probably continue into D7/Tuesday. But even further spatial uncertainty, in conjunction with the impact of the prior day convection and consensus signal for the deep cyclone to occlude northeastward, renders low confidence for highlighting a severe threat area yet. The area-of-interest appears to have shifted more to the east relative to yesterday, in an arc around the eastern Corn Belt to the Ark-La-Tex.

 

[andyhb]

This looks like trouble, that's all I'm going to say for now...

You do not see wording like that in a D6 outlook from SPC very often.

 

[KevinH]

This looks like trouble, that's all I'm going to say for now...

You do not see wording like that in a D6 outlook from SPC very often.

Right

 

[CheeselandSkies]

Can we extend the title of this thread to cover Tuesday 4/16 as well? No area highlighted yet but SPC does add...

A lesser severe threat will probably continue into D7/Tuesday. But even further spatial uncertainty, in conjunction with the impact of the prior day convection and consensus signal for the deep cyclone to occlude northeastward, renders low confidence for highlighting a severe threat area yet. The area-of-interest appears to have shifted more to the east relative to yesterday, in an arc around the eastern Corn Belt to the Ark-La-Tex.

Not sure what to make of Tuesday yet. On the GFS, the low is pretty sharply occluded (as SPC notes) yet is still deepening into Tuesday afternoon as it appears to jog due north over eastern SD. Iowa is squarely in the left exit region at 500mb and the 850mb LLJ is screaming at >50 kt. The 3CAPE on the soundings is certainly eye-opening although the moist layer is a tad shallower than I'd like to see, but it's really still too early to get bogged down in such details.

 

[KevinH]

Can we extend the title of this thread to cover Tuesday 4/16 as well? No area highlighted yet but SPC does add...



Not sure what to make of Tuesday yet. On the GFS, the low is pretty sharply occluded (as SPC notes) yet is still deepening into Tuesday afternoon as it appears to jog due north over eastern SD. Iowa is squarely in the left exit region at 500mb and the 850mb LLJ is screaming at >50 kt. The 3CAPE on the soundings is certainly eye-opening although the moist layer is a tad shallower than I'd like to see, but it's really still too early to get bogged down in such details.

Updated the title for you

 

[andyhb]

Incredible soundings on the 12z Euro in the TX Panhandle, SW KS, and NW OK on 4/15.

 

[andyhb]

I'll just leave this here.

 

[Tanner]

Figures, I’ve been doing some research on 4/14/2012 recently.

 

[andyhb]

By far the biggest caveat I'm seeing is timing currently. Timing more along the lines of the operational GFS would be a lesser threat as the trough does not fully eject into the warm sector on 4/15. Instead, it's a more in between scenario that would probably lessen the threat.

The higher end runs (basically the non-GFS guidance) all eject the trough overtop of the warm sector with appropriately intense response from the low level wind fields and basically have profiles favoring tornadic supercells right off the dryline.

 

[KevinH]

What? No SVR?

 

[cincywx]

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Thu Apr 11 2024

Valid 141200Z - 191200Z

...DISCUSSION...
...Significant severe weather episode possible late afternoon and
evening on Monday...
A mid/upper low over the central CA vicinity at 12Z Sunday should
evolve into an open wave as it ejects across the Southwest and into
the central Great Plains by around Tuesday morning. As it crosses
the Rockies onto the High Plains, the tropospheric flow field will
amplify with substantial lee cyclogenesis in the central High Plains
on Monday afternoon. While a moderate amount of spread persists
across respective ensemble systems, 00Z deterministic runs have
converged towards greater agreement with the aforementioned scenario
through D5, with progressively lower predictability in D6-8.

With about 3 days of persistent low-level moisture modification from
the western Gulf beneath an extensive elevated mixed layer, the
northern extent of mid 60s surface dew points should reach into most
of OK east of the dryline by Monday afternoon. Late afternoon
thunderstorm initiation along the dryline appears probable in the
eastern TX Panhandle/western north TX to western OK vicinity, within
a kinematic and thermodynamic profile favorable for strong
supercells. Convective development will blossom both south and
especially north extent during the evening across the central and
southern Great Plains. For this outlook, have expanded the 30
percent area to highlight the greater spatial confidence in a
substantial severe weather episode.

Despite increasing predictability concerns and the impact of prior
day convection, very strong flow fields should persist into at least
the first half of D6/Tuesday as a deep surface cyclone pivots
northeast towards the Upper MS Valley vicinity. While instability
will be weaker compared to Monday, organized severe potential is
evident within an arc from a portion of the Upper MS Valley to the
Mid-South.

In the wake of this lead system, the shortwave trough digging into
the Pacific Northwest may carve out a broad, positive-tilt trough in
the West by mid-week. Consensus of guidance suggests that rich
low-level moisture over the southern Great Plains will not be
scoured by the lead wave. This may yield daily bouts of severe
thunderstorms across parts of the central and southern Great Plains
late in the period and beyond. Predictability for individual day
highlights is too low to warrant 15 percent probabilities yet. ..Grams.. 04/11/2024

you'd be hard pressed to find the previous instance of a day 4+ disco opening up with this line

 

[CheeselandSkies]

you'd be hard pressed to find the previous instance of a day 4+ disco opening up with this line

View attachment 25331

For comparison, the one issued on 4/24/11 for Day 4 (and we know what that was) made mention of "widespread/substantial severe weather" but only "isolated" tornadoes.

Storm Prediction Center Apr 24, 2011 Day 4-8 Convective Outlook

Severe weather, tornado, thunderstorm, fire weather, storm report, tornado watch, severe thunderstorm watch, mesoscale discussion, convective outlook products from the Storm Prediction Center.

www.spc.noaa.gov

 

[jiharris0220]

It’s still quite a ways out, but lapse rates don’t seem to be a failure mode this time around, which was the thing that dampened the other past 2 tornado threats.
It really all comes down to timing, the further east the dry line, the more time in the warm sector supercells will have,
The only thing that’s lacking is the strength of the low level jet, though that could change for the worst when the cams come in.

 

[JPWX]

And if you read closely at the end, another threat may evolve beyond the Day 8 period. That Day 6 15% area I would imagine gets expanded further east and south.

 

[lake.effect]

The GFS paints a multi-day severe weather risk with areas from DC to South Texas up to Minnesota all having potential for severe weather and tornadoes.

D7/D8 in the Ohio Valley looks volatile on the 12z GFS. If that verifies, we could have a 3 or 4 day severe weather outbreak across a large part of CONUS with all modes possible.

 

[UncleJuJu98]

Nice

 

[Timhsv]

Curious as to the possible Capping element?

 

[Clancy]

A lot of folks drawing comparisons to 4/14/12 (for fair reason); important to note just how intense the parameters were for that day. STPs >10, SCP >50 and bonkers shear.

 

[tennessee storm chaser]

Interested how far east this threat can get …slower trough could make big difference

 

[Tempestas Tonitrua]

Curious as to the possible Capping element?

Good thought, something to keep in mind along with trough timing.

Another possible factor are LCL heights, the Canadian wants to put temps into the low-mid 80s in the warm sector edging right on that 15-20 TD difference. Seems to be the only model doing that right now.