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March 17-18 Severe Weather Event


DanLarsen34
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The three cells near Meridian, MS are going to be big trouble. I think we're heading into the potential long-tracker phase of this event.

One of them is already warned.

Almost pinpoint to the 45 hatched area on the High Outlook from SPC, too.

It's kind of interesting how much tornadic activity that has already occurred - it's like the HRRR nailed the storms but lowballed UH swaths by 50%+.

We could be heading for a nightmare scenario in Dixie. Heroes at NWS/SPC are going to save many lives tonight as well. Super thankful for those that chase into nightfall and the lives they may help save, too.

Sent from my Pixel 3 XL using Tapatalk

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5 minutes ago, janetjanet998 said:

8-10 active TOR warnings but nothing insane right now or TDS

Ngl definitely some 5/20/19 vibes with a lot of warnings, lot of wall clouds, but relatively (key word) few tornadoes. The night is young though. Plenty of time for the high risk to verify 

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Just now, cheese007 said:

Ngl definitely some 5/20/19 vibes with a lot of warnings, lot of wall clouds, but relatively (key word) few tornadoes. The night is young though. Plenty of time for the high risk to verify 

 

Yup. Spann just mentioned that the system is in phase 1 out of 3.  Long evening/night ahead.

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Just now, cheese007 said:

Ngl definitely some 5/20/19 vibes with a lot of warnings, lot of wall clouds, but relatively (key word) few tornadoes. The night is young though. Plenty of time for the high risk to verify 

Definitely nothing big so far or crazy, but a lot of activity for sure. Hoping we continue this trend.

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1 minute ago, Wmsptwx said:

Definitely nothing big so far or crazy, but a lot of activity for sure. Hoping we continue this trend.

Would be somewhat ironic for two high risks to fall short in similar manner. What was the cause for the 5/20/19 fizzle anyways? I know folks were vexed at the time 

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3 minutes ago, cheese007 said:

Ngl definitely some 5/20/19 vibes with a lot of warnings, lot of wall clouds, but relatively (key word) few tornadoes. The night is young though. Plenty of time for the high risk to verify 

I think there have been a decent number of tornadoes so far today, just nothing violent or long track. 

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3 minutes ago, cheese007 said:

Would be somewhat ironic for two high risks to fall short in similar manner. What was the cause for the 5/20/19 fizzle anyways? I know folks were vexed at the time 

Calling this as "falling short" is pretty ridiculous, frankly.  We haven't even had damage surveys out.  I understand the desire to see an EF4/EF5 maxi wedge OTG with a clear video/chase sequence on a high risk day, but that does not need to happen to satisfy the justification for high risk criteria, particularly when we're still relatively early in the event.

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Just now, CryHavoc said:

Calling this as "falling short" is pretty ridiculous, frankly.  We haven't even had all the damage surveys out.  I understand the desire to see an EF4/EF5 maxi wedge OTG on a high risk day, but that does not need to happen to satisfy the justification for high risk criteria, particularly when we're still relatively early in the event.

I acknowledged in other posts that we are early. Just seems similar so far. Not at all ruling out things changing! 

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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.

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2 minutes ago, cheese007 said:

I acknowledged in other posts that we are early. Just seems similar so far. Not at all ruling out things changing! 

Ah, I see those now.  Just been a long day of refreshing twitter, this page, discord, and watching streams.  Haha.

I feel like we only need one big cell to wind up and drop a monster and it takes the event from "very solid outbreak" to "a historic day".

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4 minutes ago, jojo762 said:

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.

Agreed, certainly big tornado threat with qlcs, but as for big time discrete stuff, may have seen window for that passing by.

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Ah, I see those now.  Just been a long day of refreshing twitter, this page, discord, and watching streams.  Haha.

 

I feel like we only need one big cell to wind up and drop a monster and it takes the event from "very solid outbreak" to "a historic day".

Well yeah, but 1 violent tornado won’t verify a high risk.

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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.

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1 minute ago, Calderon said:


Well yeah, but 1 violent tornado won’t verify a high risk.


.

It doesn't require any EF4/EF5s to verify high risk, if the NWS wording for high risk is to be followed.  High risk specifically indicates a strong (60%?) chance for EF2+ tornadoes.  What do you use as a definition for high risk?  Has that changed in recent years?  I was just looking over that criteria last night, but it was from 2008.

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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.

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4 minutes ago, CryHavoc said:

It doesn't require any EF4/EF5s to verify high risk, if the NWS wording for high risk is to be followed.  High risk specifically indicates a strong (60%?) chance for EF2+ tornadoes.  What do you use as a definition for high risk?  Has that changed in recent years?

I think that was the original poster's point.  A single violent tornado doesn't verify a High risk - many tornadoes do.  We've had many tornadoes today, hence high risk verified.

I think what a lot of us (myself included) forget is that tornado probabilities in SPC outlooks reflect confidence in a tornado outbreak.  They are not direct forecasts of violent tornadoes.  A smaller outbreak that verifies a high risk, and that will confidently occur, warrants a 45% tornado threat.  Another larger outbreak, but with greater uncertainty from the forecasting perspective, might warrant 15% or 30%.  Just because the second outbreak was bigger than the first doesn't mean the forecast was wrong - it just means that there was more uncertainty leading up to the big outbreak, compared to the smaller outbreak.   We've likely had a several long tracked strong tornadoes today which fits well well with the forecast.


In other words, tornado % (i.e, 15%, 30%, 45%, 60%) in the forecast doesn't necessarily correlate with outbreak size.  It correlates with confidence leading up to the outbreak.

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The bust talk is a bit extreme, although I’m shocked Mississippi didn’t get a little more as the main show today has definitely been Alabama. Atmosphere is too worked over at the moment across the Mid South for this to really take off tonight in my opinion. 

Still it’s been one hell of an afternoon. And truthfully I think tomorrow in the Carolina’s offers a potentially bigger threat than today to be honest 

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Just now, CryHavoc said:

It doesn't require any EF4/EF5s to verify high risk, if the NWS wording for high risk is to be followed.  High risk specifically indicates a strong (60%?) chance for EF2+ tornadoes.  What do you use as a definition for high risk?  Has that changed in recent years?

I have gathered there are several people here that basically think any event that doesn't include several EF-5s going through large metro areas to be a bust.  It's insane.  Like the guy earlier saying this should be an enhanced risk at the most.  We've seen numerous tornados today, certainly some of them strong and the event isn't over.  We definitely may be seeing the end of the discrete storm mode but the threat will continue well into the night.  

 

I mean heck we are going on about 7 hours straight of tornado warnings right now and this is a bust? 

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