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andyhb

May 15th-16th Severe Events

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both the 12Z GFS/NAM show a pretty negligible cap across Oklahoma at 7pm on Friday... But neither show any convective development across the area either..

 

Because convergence along the dryline is rather weak and there isn't much of a trigger elsewhere. That's a different story up in NE though.

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both the 12Z GFS/NAM show a pretty negligible cap across Oklahoma at 7pm on Friday... But neither show any convective development across the area either..

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both the 12Z GFS/NAM show a pretty negligible cap across Oklahoma at 7pm on Friday... But neither show any convective development across the area either..

I just glanced at it. I'll be in cell hell in western OK on a rig so trying to get all the info I can. They don't usually allow cell phones on location

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Because convergence along the dryline is rather weak and there isn't much of a trigger elsewhere. That's a different story up in NE though.

 

NE definitely looks like the hot spot for Fri.  NAM and GFS show considerable differences in the instability in OK on Fri afternoon.  Any chance a rogue cell pops up in OK if the NAM verifies with the CAPE in C OK?  Forcing was certainly an issue last Wed when the supercell popped in SW OK and moved northeast into OKC.  But, there may have been just enough forcing last week compared to this coming Fri.

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Friday has multiple things working in its favor, at least in terms of forcing and boundaries to work with. The warm front lifting north is a given, particularly near the triple point. Assuming the current model depiction is close to being right, we will have to watch closely the cell or two closest to the surface low along the warm front/occlusion. Then there's the dryline, which the 4km NAM has been insistent on firing discrete cells on, to about as far south as I-70 in Kansas. Some previous runs had also hinted at just a touch of residual convection in the morning. 18z NAM actually backs off a bit on that idea, which in turn allows for fairly broad area of strong instability (much of Nebraska) of 3000-4000+ J/kg SBCAPE. If there were any leftover outflow boundaries, those would be obvious focal points as well.

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This was perfect.  Every other explanation I tried to read on it was hard to understand what they were trying to say.  I'm a much more visual learner... the stirring the coffee explanation made it click.

 

Thanks. 

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Still not all that concerned yet about the possible VBV issue we will probably have on Saturday since low-level shear is progged across the board to be impressive. I think we will get mixed storm modes probably, some tornadic supercells, some severe clusters... The main thing that leads me to not totally discount the higher-end tornado potential at this point would be that tornadoes/mesocyclones rely largely on the lowest 0-3KM Shear (rather than deep-layer shear), which on Saturday will be very impressive and conducive to tornadogenesis with 30-40kts and veering with height to at least 700mb... A much bigger concern really is the degree of lower-level instability with most models showing modest instability really (SBCAPE 1000-2000J/KG). MUCAPE likely won't be much of a problem imo for Saturday with widespread 2000-3000J/KG values over the warm sector and near the dryline. Models also indicate widespread convective development from Nebraska to central OK. But, the main question (given at least modest warm sector destabilization) will be the convective mode which will largely be affected by how much of an impact the wind profile has on updraft development and maintenance. There are several examples where VBV wasn't that big of an issue, but there even more examples where it probably ruined a potential high-end event.

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Still not all that concerned yet about the possible VBV issue we will probably have on Saturday since low-level shear is progged across the board to be impressive. I think we will get mixed storm modes probably, some tornadic supercells, some severe clusters... The main thing that leads me

to not totally discount the higher-end tornado potential at this point would be that tornadoes/mesocyclones rely largely on the lowest 0-3KM Shear (rather than deep-layer shear), which on Saturday will be very impressive and conducive to tornadogenesis with 30-40kts and veering with height to at least 700mb... A much bigger concern really is the degree of lower-level instability with most models showing modest instability really (SBCAPE 1000-2000J/KG). MUCAPE likely won't be much of a problem imo for Saturday with widespread 2000-3000J/KG values over the warm sector and near the dryline. Models also indicate widespread convective development from Nebraska to central OK. But, the main question (given at least modest warm sector destabilization) will be the convective mode which will largely be affected by how much of an impact the wind profile has on updraft development and maintenance. There are several examples where VBV wasn't that big of an issue, but there even more examples where it probably ruined a potential high-end event.

Yet another issue Saturday is with an MCS blasting through Saturday morning and killing the larger-scale environment too. I tend to favor a solution similar to last Saturday and frankly, maybe even more localized. I remain skeptical, but we'll see. There will likely be pockets of stronger instability and locally enhanced tornado potential, but the VBV concerns combined with many other red flags place a lot of doubt in the severity and aerial extent of the threat.

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VBV isn't that high on my list of concerns for Saturday. The orientation/geometry of the trough is definitely less desirable than last Saturday, though. Either way, if you eliminated the concerns over prior convection and destabilization, it would be a fairly impressive setup with a near-certainty of several or more tornadoes. Just not as impressive as last Saturday, which could've been historic without those issues.

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I just glanced at it. I'll be in cell hell in western OK on a rig so trying to get all the info I can. They don't usually allow cell phones on location

I think you're gonna have a bad time if you're gonna be out there on Friday and Saturday. Lol

I live in Eastern Oklahoma..

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I think you're gonna have a bad time if you're gonna be out there on Friday and Saturday. Lol

I live in Eastern Oklahoma..

 

Read more and post less please.

 

These "you're gonna get it posts" add nothing to the discussion.

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Just my gut feeling but setups like this seem to always have something in central KS... profiles certainly support something significant there on both GFS/NAM as well. Just my gut feeling. I could be wrong though. Time shall tell!

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VBV isn't that high on my list of concerns for Saturday. The orientation/geometry of the trough is definitely less desirable than last Saturday, though. Either way, if you eliminated the concerns over prior convection and destabilization, it would be a fairly impressive setup with a near-certainty of several or more tornadoes. Just not as impressive as last Saturday, which could've been historic without those issues.

You can still get big, even almost historic outbreaks with highly meridional flow.  3/28/07 and 5/5/07 come to mind.  But I don't think you'll have enough of an EML to limit upscale growth.

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Just my gut feeling but setups like this seem to always have something in central KS... profiles certainly support something significant there on both GFS/NAM as well. Just my gut feeling. I could be wrong though. Time shall tell!

Tornadoes in mid-may in KS is usually a good bet.

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Tornadoes in mid-may in KS is usually a good bet.

Wednesday of last week was a big day for them. Saturday even had quite a few reports in the northwestern portion of the state.

 

They'll probably see several tornadoes between Friday and Saturday, I'm fairly certain.

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I could chase on Friday. North Platte isn't too far for me. I don't know if I will. Storms may move towards the Sand Hills of Nebraska, which has few roads.

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Wednesday of last week was a big day for them. Saturday even had quite a few reports in the northwestern portion of the state.

 

They'll probably see several tornadoes between Friday and Saturday, I'm fairly certain.

I think KS was above normal going into May.. it has been a hotspot in general this year. Then again it has to make up for last year. ;)

 

I've never quite liked this trough as much as the last one just from a 500mb standpoint, but I'd be surprised if it didn't drop a few dozen tornadoes as it goes about its business.

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Western and central OK look pretty nice for Saturday on the 00Z NAM. Good turning in the lowest few thousand feet (as is anticipated), good instability with MUCAPE of 1500-3000J/KG... decent southerly LLJ at 850mb of 30-40kts, winds at 925mb of 30kts, and backed sfc flow... SCP of 10-20... STP of 3-7... Even west central KS looks okay, but VBV and thermodynamic issues come up the further north you go.. One issue I do have with it is how far west it shows the dryline.. Think it'll mix further east. Another problem is the vast amount of precip it shows past 00Z Sunday in the area... And develops a large cluster/bow at around 03Z.

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By the way, wanted to give a shoutout to Brett for straightening out some of those people on ST (in the 5/16 thread).

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0z 4km NAM very impressive near I-80 corridor near Kearney, NE popping one big time isolated supercell. Really recovers nicely after morning convection

Things clear out real quick Friday morning via NAM. Virtually nothing on simulated radar in the state by 18z. The instability values look more realistic this run too. 2500-3500 J/kg SBCAPE in the threat zone, as opposed to some previous runs popping over 4500 J/kg. Still nothing to shy at. I would not be surprised at all if SPC goes with MDT for the upcoming day 2 outlook.

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For Saturday, my current thoughts would be somewhere in SW OK or NW TX in the general 4/10/79 corridor, where it seems like the greatest combination of favorable upper level winds, backed low level flow, less influence of morning convection, etc. seems to reside. Also seems like more and more guidance has come around to popping a secondary lee cyclone somewhere in E CO, which would make sense given the southern vort max rotating through the base of the trough Saturday afternoon.

 

I think that it needs to be stated that the stronger mid/upper level flow in the morning/early afternoon on Saturday as opposed to the previous event may encourage morning convection to move faster out of the target area, although if it keeps regenerating, that might not matter.

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One plus this Saturday is not two major MCSs in Oklahoma back-to-back days. Remember last Thursday and Friday? This Saturday we only have Saturday morning rain to contend with over target. Friday rain should mostly eject northeast. BTW Friday still looks good for a local target. Last Saturday MCS cool pools were particularly cool for this late in the year. Doubt it is that bad this time. Thoughts borrowed from Brett R on Stormtrack. Anyway Saturday will work out at least for local targets. If not MDT the SPC will put out small 10% TOR.

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So who here is familiar with the MPAS model?  I don't know anything about it or its performance.  On another site someone posted that the MPAS is trending toward a pretty high end event on Saturday.  I thought it was pretty interesting.

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So who here is familiar with the MPAS model? I don't know anything about it or its performance. On another site someone posted that the MPAS is trending toward a pretty high end event on Saturday. I thought it was pretty interesting.

Model for Prediction Across Scales (MPAS) was created by NCAR... Never had heard about it before lol

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Parameter space for tomorrow seems to be dropping off with each run of the NAM/4 km. Growing less enthused with the setup since it seems the initial mid level jet is going to lag.

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I was planning on chasing tomorrow but Nebraska is too much for me to drive on my own.  I'm still planning on headed up to OK/KS from College Station for Saturday though.

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Parameter space for tomorrow seems to be dropping off with each run of the NAM/4 km. Growing less enthused with the setup since it seems the initial mid level jet is going to lag.

Saturday looks very significant on the 4km NAM though... widespread 0-1KM EHI values of 4-5 across KS/OK... Even the NAM to an extent shows a substantial threat especially over western OK.

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Saturday looks very significant on the 4km NAM though... widespread 0-1KM EHI values of 4-5 across KS/OK

 

Yes, the 18z 12 km NAM did show some VBV wind profiles (likely due to the trough being a bit sharper with more backed flow in the mid/upper levels), but it seems like the consensus between the two is a supercellular storm mode for a decent portion of time. It's going to be a case of seeing how organized the morning convection/whether it leaves a deep cold pool and how fast it moves to the northeast of the dryline through late morning/early afternoon, because shear is going to be strong, perhaps very strong.

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