jojo762

2 hours ago, jojo762 said:

Pending 00z CAM output, it seems quite possible that a rare D2 high risk is going to be in the cards.. Environment will be absolutely primed over a substantial area. Personally i'd probably pull the trigger for parts of Mississippi and Alabama, as long as CAMs do not show a boatload of junk in the warm sector (which is ultimately the main failure mode with this setup given the lack of CINH and large CAPE values).

Just to simmer down the controversy, or perhaps explain myself better, I emphasized important parts of my post that appear to maybe have gotten entirely overlooked in lieu of the High Risk mention.

For everyone that is being bearish, its very hard to ignore when the NAM, NAM NEST, GFS, EURO, UKMET, Canadian, etc. (literally all guidance available) shows a top tier parameter space in place. 18z NAM NEST (typically runs toward linear/messy solutions, as we all know too well) featured what would likely be a tornado outbreak with a variety of semi-discrete to discrete convection across the warm sector throughout the day. Guess we'll see what the other CAMs have to say soon, but to see the NAM NEST doing that is quite concerning. I see a similar convective evolution to what we had last Wednesday, albeit with likely more intense supercells than we had then due to a more substantial forecast parameter space (both with kinematics and thermodynamics). Cautious pessimism is almost always good, especially when it comes to concerns about lack of a cap in the south, but guidance just does not indicate that is all that much to worry about right now wrt tornado potential.

Pending 00z CAM output, it seems quite possible that a rare D2 high risk is going to be in the cards.. Environment will be absolutely primed over a substantial area. Personally i'd probably pull the trigger for parts of Mississippi and Alabama, as long as CAMs do not show a boatload of junk in the warm sector (which is ultimately the main failure mode with this setup given the lack of CINH and large CAPE values).

00z GFS unsurprisingly is more progressive and faster with Thursday's system than all other guidance -- however it does not appear to matter as all 00Z guidance that is in depicts what would likely be a significant severe weather and tornado outbreak across several southeastern states.

A substantial plume of low-level moisture and >7C/KM lapse rates will combine to generate a large area of 1000-2500J/KG of CAPE south of the warm front. Meanwhile an intense 80-95kt 500mb jet should overspread the warm sector throughout the afternoon and evening while a 50-70kt low-level jet is cranking through much of the day. Do not need STP, EHI, or Supercell composite to tell you that this is not an ideal scenario for folks living in these areas.

My main caveats are potentially early initiation, widespread junkvection, etc... All the usual caveats for this area -- really...

12z NAM depicts a high-end environment (much more volatile than what we had on 3/17 with the verified high risk) across much of Louisiana and Mississippi on Thursday. Given good agreement amongst models on this, fully anticipate at least an ENH risk from SPC with the D3 outlook. 

FWIW, in spite of what I just said regarding the QLCS threat, the line in southern/southeastern Mississippi appears to have numerous kinks in the line with at least weak rotation currently -- as mentioned above the QLCS tornado threat *could* be quite substantial as the LLJ picks up and additional high theta-e air is advected into the area, especially if the line can remain well organized and not get too junky.

2 minutes ago, LauderdaleHurricane said:

Thank goodness this was mostly a bust. I was expecting so much worse the way NWS and SPC was talking. 

This was not a bust. By EOD there will have been perhaps two dozen or more tornadoes, several of which appear to have been strong.

Observational trends lead me to believe that this event is starting to wind down.

Ongoing discrete/semi-discrete supercells in Alabama, while still tornado warned, have exhibited mostly transient and weak rotation for quite some time now. Upstream, in Mississippi, things are significantly more messy and it appears much of the thermodynamic environment has been overturned to an extent that will greatly mitigate a robust risk of significant tornadoes. Obviously as the LLJ starts cranking some more, things could change.

It remains to be seen how substantial any QLCS tornado threat will be downstream as the current line propagates eastward, but I would lean toward a slightly lesser threat than originally anticipated, at least until roughly a line N/S of BMX, where things could potentially ramp up due to a less overturned air mass. Again, the strengthening of the LLJ and the degree of related theta-e transport could substantially impact the current environment and potentially allow for a more robust QLCS tornado threat overnight.

As for the high risk discussion above, I mostly agree. There has been a TON of tornado warnings, numerous tornadoes, perhaps a few stronger tornadoes, but definitely nothing long-tracking or exceptionally high-end. Post-event discussion/analysis of today will be interesting.

Overall I would say that surface temps in some areas maybe just didn't get to where we "needed" them to be... The 0-1km SRH also being weaker on various area VWPs  than perhaps we anticipated also needs to be heavily considered into why today maybe didn't go completely insane. Certainly not a bust, imo though.

1 minute ago, Upper Level LOL said:

Exhibit A in why chasing in Dixie is so hard 

That is some pretty sweet motion AGL though... Likewise, you really cannot get much worse chase terrain than parts of Mississippi and Alabama have.

While things have been fairly active early, its worth noting that area VADs are not particularly impressive attm.

KDGX: 123 m2/s2 0-1km SRH

KMOB: 122 m2/s2 0-1km SRH

KLIX: 174 m2/s2 0-1km SRH

KGWX: 157 m2/s2 0-1km SRH

Only KMXX and KBMX along/near the warm front are particularly impressive right now with both exhibiting 300-400 m2/s2 0-1km SRH.

As far as the high risk is concerned, it really comes down to the debate on IF you trust CAM UH track forecasts verbatim or if you have to extrapolate from the fact that they show convection ongoing in a high-end environment... For the most part I lean toward believing that an uncapped, high-end open warm sector environment with storms firing in it would yield several sig tors. Seems SPC agrees.

00z CAMs overall do not seem to like the idea of intense surface-based supercells in the open warm sector tomorrow. Perhaps its some sort of problem that they are not capable of resolving, but it looks awfully junky save for a couple UH-producing supercells

12 minutes ago, hlcater said:

That's not necessarily true. I think capping will probably be sufficient through at least 17-18z to prevent widespread storm development in the warm sector courtesy of a bone dry EML arriving ahead of the trough. The primary difference that tomorrow has and something I think makes OWS convection more likely is that if you look aloft, there are substantial height falls over nearly the entire warm sector along with stout low level moist advection. These should work together to ensure the best possible shot at storms ahead of the primary band. As such, hodographs and strength of the low level jet late tomorrow afternoon will be something that needs to be monitored intensely given the possibility of (numerous?) discrete/semi-discrete rotating updrafts.

I'm referencing capping by mid-afternoon mostly. Good analysis. 

WRT the talking points about 5/20/19 and tomorrow... As has been discussed to great extent, the capping on 5/20/19 turned out to be "just enough" to withhold substantial warm sector convection (so the sub-cloud updraft point mattered in that case), but tomorrow will feature near zero to zero capping... As I believe @hlcarter has referenced already. 

Obviously there is the contrarian argument to be made that that complete lack of capping could lead to a wide array of junkvection in the open warm-sector -- as has been potentially hinted at times by some guidance.

Regardless of nebulous mesoscale details about warm-sector forcing and residual capping, it feels obvious to me that there is inevitably going to be at least a couple sporadically tornadic open warm-sector supercells tomorrow...

To me the main questions comes down to organizational longevity and how intense they're able to become given some concern about potentially sloppy low/mid-level wind profiles. Particularly the 850mb-600mb layer could ultimately hold back storm organization at times, or even most of the event. This goes for both semi-discrete supercells along the main forcing line in Arkansas in the afternoon, and any potential open warm-sector supercells across Mississippi/Alabama as well. Lastly,  what I am most confident in is that a substantial QLCS event will almost certainly occur much of tomorrow night and into the early morning hours on Thursday -- much like we saw several times last year.

Supercell south of Dimmitt, TX is quickly getting its act together...

12z HRRR is about as strong of a signal as you are going to get for a regional tornado outbreak...

It shows multiple discrete, long-tracking supercells traversing the Texas panhandle throughout most of this afternoon and evening. Given the background environment, these supercells will almost certainly be producing significant tornadoes at some point during their life-cycles. Damn shame I couldn’t chase today.

00z CAMs are very aggressive with tomorrow. Basically every single CAM in this suite shows a broken line of discrete supercells along the dryline in the afternoon. Fully expect a MDT risk from SPC for strong, potentially long tracking tornadoes and very large hail. 
 

Forecast soundings depict an especially anomalous setup for mid-March across the Texas Panhandle...

Tomorrow screams multiple tornadic supercells for potentially a couple to a few hours, followed by a lengthy squall line in the evening.

It is not a common occurrence in March in the Texas Panhandle to get 60s/near 60s dewpoints, let alone that moisture/thermo profile coinciding with highly impressive low-level and deep-layer shear profiles.

Ultimately we all know the failure mode tomorrow is an insta-linear type event. Another potential failure mode is storms interacting too much due to the meridional mid/upper flow and resulting storm motions. CAMs do not seem to exactly like the idea of this going insta-linear tomorrow, but we shall see.

Pretty nice semi-discrete tornadic supercell 40 miles ENE of Lubbock right now...

00z CAMs are mildly impressive for Saturday, especially the HRRR (surprise surprise)... and Broyles will be doing the upcoming D2 outlook for Saturday — buckle up. 

11 hours ago, CheeselandSkies said:

Like I said on Stormtrack, could be a good opportunity for some shake-the-rust-off/break in the gear chases for people who live in/near the risk area, especially falling on a weekend and if you didn't get out much last year due to COVID-19 concerns. That's about it.

A lot of folks on twitter have really been hyping up Saturday. I get that its a mega trough with great timing, there are 60-64tds in place, and the LLJ is cranking, but beyond that the thermo profiles *really* leave a lot to be desired. If I lived in OKC I would almost certainly chase on Saturday to "get the rust off," but with me living up in KC, i'm not so sure its worth it -- especially since any target will likely be in W or SW Oklahoma.

Tomorrow has also really fallen off too, so unless 12z models improve, that is looking like a no go.

Broyles issued severe risks for D5 (Friday, 3/12), D6 (Saturday, 3/13), and D7 (Sunday, 3/14)... While none of these days particularly excite me as far as tornado potential goes at the moment, they will also almost certainly feature severe storms. 

At this moment, I actually like the KS/OK border on Wednesday for a shot at isolated supercells. Any storm that develops will have >1000J/KG CAPE to deal with, and ample deep-layer and low-level shear to boot.

Prospects for severe weather seem to ramp up rather significantly by mid-march. Guidance has been keying in on western troughing for several runs now. **BUT it is March, so moisture will almost certainly be an issue to deal with, especially with the FROPA occurring right now in the GOM, as well as the FROPA/low that is forecast to occur this weekend -- these combined FROPAs really deal a blow to LLVL moisture in the GOM prior to any of our potential systems 3/9 to 3/16.

Nevertheless, it is difficult to imagine a scenario with zero impactful severe storms occurring next week across the Central and Southern Plains with the mid/upper-level pattern depicted on the 00Z GFS -- regardless of nebulous details related to moisture return.

After the time period that JoMo mentions, it sure looks like winter could just about be over. Longer-range guidance, as well as CPC indicates that we’re in store for some nice above-average temps in March.

23 minutes ago, JasonOH said:

I am once again asking for a Southwest trend in the snow maps. 

How's the 50 degree apartment treating you, Jason? 

42 minutes ago, MUWX said:

For the second event in a row, I am hoping for a north trend. 

Feels like an appropriate time to dust this off...

Road conditions have declined markedly over the past hour and a half in the KC metro as a moderate band of snow continues to persist... Roads look pretty bad from my 11th floor view.