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March 17-18 Severe Weather Event


DanLarsen34
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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

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1 minute ago, jojo762 said:

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

Definitely something to watch as HRRR kinda hints at the same idea but is more bullish. I'm pretty curious to learn more about why they are showing what looks like discrete cells but aren't producing these big UH tracks.

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1 minute ago, MattPetrulli said:

Definitely something to watch as HRRR kinda hints at the same idea but is more bullish. I'm pretty curious to learn more about why they are showing what looks like discrete cells but aren't producing these big UH tracks.

Correct me if I’m wrong, but wasn’t this the case with the model ahead of the 4/12 outbreak last year? It showed widespread OWS convection doing this too.

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Not that this will be anything of the caliber of the Easter outbreak last year but I'm getting vibes mostly with the messy evolution and later ejecting trough. Definitely plenty of red flags like a weak cap in warm sector with numerous storms going, better shear holding off till llj goes nuts at 0z, a later in day trough ejection, lapse rates sufficient but not quite as steep as they were days ago, and seeing some VBV in soundings. I could see a scenario where near the warm front and south sees numerous rounds of severe storms with some tornado threat albeit messy and instability really builds in south of this. As that speed max pushes out, may see a few rogue cells fire in northern Louisiana into southern Mississippi and go nuts in a very sheared and moderately unstable atmosphere. 0z hrrr was hinting at this idea. Definitely will be a nowcasting situation. I wouldn't go high risk tonight but if things looked better for an enhanced corridor of significant tornado potential could always add a small high risk area tomorrow. Regardless of whether there will be discrete supercells with significant tornado potential, I do feel confident in a QLCS with significant tornado potential given the shear magnitude after 0z. 

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The Birmingham NWS HWO has increased hail size from quarter to golf ball in the "enhanced" areas & from golf to tennis ball size in "moderate" sections. The winds outside of tornadoes are still 70 & 80 mph respectively. I guess this could increase again should the SPC increase some of Bham CWA from moderate to "high."

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24 minutes ago, Wmsptwx said:

Seems like there’s a ton of things working against this thing, thinking we see them play it smart and go moderate. 

[sarcasm]Since when has SPC 'played it smart' over the last few years? :damage:[/sarcasm]

I do agree with you though. Seems like most of the CAMs are showing a few ways the event could be limited (in the scope of a full-on outbreak). If anything, the last few HRRR runs seem to start the show in Central Alabama by 20Z with discrete storms in a loaded-gun environment. We'll have to see how the late night storms behave (whether its linear garbage or linear mischief). 

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6 minutes ago, David Reimer said:

[sarcasm]Since when has SPC 'played it smart' over the last few years? :damage:[/sarcasm]

I do agree with you though. Seems like most of the CAMs are showing a few ways the event could be limited (in the scope of a full-on outbreak). If anything, the last few HRRR runs seem to start the show in Central Alabama by 20Z with discrete storms in a loaded-gun environment. We'll have to see how the late night storms behave (whether its linear garbage or linear mischief). 

Its interesting that on the other weather forum the consensus is that the SPC WILL go with the High risk next update while on here people think the SPC will keep the risk Moderate. I need to sleep so I can get what I need done before weather gets bad by mid-afternoon. I'll see what happens when I get up mid-to-late morning. Stay safe everyone.

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Quote

This air mass will advance north during the day and
   diurnal heating will allow moderate instability to develop along a
   corridor from southern LA through central MS into western AL where
   SBCAPE should be on the order of 2500 J/kg. 

2500 J/kg CAPE. Incredible

EDIT: roughly 11.4 million people in the sig tor hatched area on top of that. Could be one hell of a day for the southeast

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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.

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4 hours ago, jojo762 said:

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.

I agree also, UH tracks with relatively low-topped supercells can be misleading, Leaving shortly for my target of Meridian, MS to Tuscaloosa.

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Is this fear mongering too this morning?  Memphis NWS office reemphasizes my concern's from yesterday's post  as well. This is the first time in yrs that I have seen them mention this type of tornadic development potential in their  forecast discussions. 

 

National Weather Service Memphis TN
635 AM CDT Wed Mar 17 2021

.UPDATE...Aviation Discussion.

&&

.PREV DISCUSSION... /issued 153 AM CDT Wed Mar 17 2021/

DISCUSSION...
Storms will quickly start to develop over eastern Arkansas and
northwest Mississippi by about 3 AM. Storms are expected to fire
with the warm front, which will lift north. These storms will
likely reach the Memphis metro shortly after sunrise, and head
north with the rapidly lifting shortwave and surface warm front
through the morning. Storms are expected to be more surface based
with large hail expected at first. Lapse rate will be around 7
C/Km. Tornadoes can`t be ruled out this morning due to modest
helicity values but the main threat this morning will be that
large hail.

Our biggest concern will be this afternoon/evening storms. The
warm front should push north later today, in conjunction a cold
front will approach the area from the west allowing for a warm
sector to be set up. After these morning storms pass, short range
models show a lull in convection. This lull is important for
destabilization. During this time our SBCAPE will increase to
1500+ J/Kg in the warm sector. This, in conjunction with high
shear values will promote large hail, damaging winds and the
potential for strong tornadoes (EF2+). In addition to the severe
weather threat, locally heavy rainfall is possible. We`re looking
at widespread 1-2" with localized higher amounts.

The first set of storms should remain discrete but short range
models show a line moving front the west around 22z. This QLCS
will remain in a favorable environment for tornadoes and damaging
wind as the low-level jet begins to intensify, but the large hail
threat will begin to decrease. Short range models continue to show
modest helicity values with large Significant Tornado Parameter
values and our continued 1500+ J/kg CAPE values. These tornadoes
can develop quickly and it can be difficult to provide much lead
time, especially far from the radar. Given the potential for
nocturnal tornadoes, it is important to plan ahead and ensure you
are capable of receiving timely weather alerts. Try and develop a
safety plan this morning so you can get to your safe place fast if
you receive a warning.

 

 

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Again this is only anecdotal, but I will be curious to see if the history and data that I've logged with system set-ups similar to this remain consistent.

The circled areas for my state are where I'm most interested to see if storm impact is higher. This is only based on my own data from the last 10 years (full disclosure, 4/27/2011 is one of my personal analogs that is included - which I am fully aware is extreme and not the same). I'm certainly no scientist.

3 18 2021.jpg

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I'd like to see a stronger low for sure to be in all in but with the ingredients in place, you've gotta go High for today. The LCL is basically on the ground, a strengthening LLJ throughout the day, as much as 3000 j/kg of CAPE, tons of moisture yet great lapse rates, extremely high SRH and ample shear. It's hard to think this evening that everything won't be spinning in the mid South

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