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April 24-30th Severe Potential


Chicago Storm

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Edit: including outlook text

...SUMMARY...

SIGNIFICANT SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS PARTS OF

THE SOUTHERN AND CENTRAL GREAT PLAINS TUESDAY AFTERNOON INTO THE

NIGHTTIME HOURS. TORNADOES...SOME STRONG...WILL BE POSSIBLE...IN

ADDITION TO VERY LARGE HAIL AND DAMAGING WINDS. ADDITIONAL ISOLATED

STRONG STORMS ARE POSSIBLE ACROSS PARTS OF THE OHIO VALLEY TO THE

MIDDLE ATLANTIC COAST REGION.

...CENTRAL AND SOUTHERN PLAINS...

...FORECAST PARAMETERS CONTINUE CONSISTENT SIGNAL FOR POTENTIAL

SEVERE WEATHER OUTBREAK ACROSS PORTIONS OF THE CENTRAL/SOUTHERN

PLAINS ON TUESDAY AFTERNOON/EVENING...

DETERMINISTIC AND ENSEMBLE GUIDANCE CONTINUES TO BE CONSISTENT WITH

BRINGING A NEGATIVELY TILTED TROUGH INTO THE PLAINS DURING THE

AFTERNOON/EVENING ON TUESDAY. A 60+ KT SOUTHWESTERLY MIDLEVEL JET

WILL OVERSPREAD TX INTO OK/KS BY EARLY AFTERNOON WITH STRONG DCVA.

THIS WILL BE ALIGNED WITH A SURFACE DRYLINE STRETCHING S/SW FROM

ROUGHLY CNTRL KS...WRN OK AND W-CNTRL TX BY 00Z/WED. THERE IS STILL

SOME VARIABILITY IN GUIDANCE WITH REGARDS TO THE SURFACE LOW

POSITION...BUT EXPECT THIS TO BE SOMEWHERE NEAR THE KS/NEB BORDER

WITH THE ATTENDANT WARM FRONT STRETCHING W-E NEAR/JUST NORTH OF THE

KS BORDER AT 00Z. RICH BOUNDARY LAYER MOISTURE WILL RESIDE ACROSS

THE WARM SECTOR WITH DEWPOINTS IN THE MID 60S TO NEAR 70 AS FAR

NORTH AS S-CNTRL/SE NEB. STRONG INSTABILITY AND VERY STEEP MIDLEVEL

LAPSE RATES WILL BE IN PLACE BY AFTERNOON...AND STRONG HEATING NEAR

THE DRYLINE SHOULD RESULT IN CONVECTIVE INITIATION BY LATE

AFTERNOON.

CONCERNING CONVECTIVE COVERAGE...UNCERTAINTY INCREASES WITH

SOUTHWARD EXTENT ACROSS OK INTO N TX. DEPENDING ON YOUR FAVORED

MODEL DEPICTION...A BI-MODAL COVERAGE PATTERN IS POSSIBLE WITH THE

INITIAL VORT MAX EJECTING NORTHEAST ACROSS N-CNTRL OK INTO KS AND

S-CNTRL NEB. ANOTHER VORT MAX WILL EJECT FURTHER SOUTH ACROSS

CNTRL/NRN TX LATER IN THE EVENING. THIS COULD LEAD TO A RELATIVE MIN

SOMEWHERE...BUT WHERE THIS IS REMAINS UNCLEAR AT THIS TIME.

REGARDLESS...AT LEAST ISOLATED TO WIDELY SCATTERED INTENSE

SUPERCELLS ARE EXPECTED ALONG THE DRYLINE...WITH GREATER COVERAGE IN

THE VICINITY OF THE TRIPLE POINT WHERE FORCING AND SHEAR WILL BE

MAXIMIZED. STRONG /POTENTIALLY LONG-TRACK/ TORNADOES...VERY LARGE

/PERHAPS GIANT/ HAIL AND DAMAGING WIND GUSTS WILL BE POSSIBLE WITH

ANY STORM THAT DEVELOPS ACROSS THE WARM SECTOR. AFOREMENTIONED

COVERAGE CONCERNS WILL PRECLUDE A HIGH RISK AT THIS TIME.

DURING THE EVENING INTO THE OVERNIGHT...STORMS MAY GROW UPSCALE INTO

AN MCS OR BOWING SEGMENTS ACROSS ERN KS INTO MO. WHILE A TORNADO

THREAT WILL LINGER NEAR THE WARM FRONT...A TRANSITION TOWARD MAINLY

A LARGE-HAIL AND DAMAGING-WIND THREAT IS EXPECTED WITH EASTWARD

EXTENT OVERNIGHT. ACROSS NRN/CNTRL TX...STRONGER FORCING WILL ARRIVE

DURING THE EVENING INTO THE OVERNIGHT HOURS AND SUPERCELLS MAY

DEVELOP LATER THAN FURTHER NORTH. THIS COULD LEAD TO A NIGHTTIME

TORNADO RISK BEFORE STORMS POTENTIALLY GROW UPSCALE AS THEY APPROACH

NORTHEAST TX. ADDITIONALLY...VERY LARGE HAIL AND DAMAGING WINDS WILL

BE POSSIBLE.

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SPC just told you guys to shove your pessimism.

 

But why?  I was very surprised to see them mention a possible high risk and still calling for possible long track tornadoes.  I can get the risk for hail because of the incredible amounts of CAPE but no mention of the less than ideal hodographs.  They may very well be right, but I'd like to know their reasoning.  

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There's been an excellent discussion on the caveats/concerns with this setup. I'd say I'm surprised with the D2 MDT, but in some defense of it, from a coverage perspective I think somewhere in the MDT corridor there's good agreement on fairly widespread coverage and even with the caveats that could/should modulate the tornado threat and magnitude, could still be talking high coverage of large hail instances with the large fat CAPE profiles and very steep midlevel lapse rates.

Edit: the high end tornado language is more questionable nonetheless due to all the concerns that have been previously mentioned and would like to have seen some reference to the less than ideal hodographs in the discussion as was alluded to in the post above mine.

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You know there are some pretty obvious caveats to this whole thing (that don't seem to be getting looked at in that outlook), don't get all high and mighty on the rest of us now.

anom systems produce anom results... Sound familiar? Obviously there are reasons that they have elected to disregard those concerns for now-- it is silly to think the forecaster (and really the whole office, since days like Tuesday are pretty cooperative) is totally missing multiple things that could make/break a SVR/Tornado outbreak. If she/they did actually think that helicity would be that unimpressive and that VBV would be that prominent, they would not be mentioning anything about a High risk, let alone be putting a MDT risk across a large portion of the plains.
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I thought the same thing. It actually looks like multiple rounds are possible when looking at the Euro.

I might just say screw it and sleep in the closet.. LOL

I saw something saying Wednesday it's going to be bad here but local and weather.com are saying nothing at all on Wednesday.

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anom systems produce anom results... Sound familiar? Obviously there are reasons that they have elected to disregard those concerns for now-- it is silly to think the forecaster (and really the whole office, since days like Tuesday are pretty cooperative) is totally missing multiple things that could make/break a SVR/Tornado outbreak. If she/they did actually think that helicity would be that unimpressive and that VBV would be that prominent, they would not be mentioning anything about a High risk, let alone be putting a MDT risk across a large portion of the plains.

 

Its a mistake to take anyone's view on this at face value without reasoning; especially when other forecasters and meteorologists who are just as qualified have raised valid issues.  "Cause the SPC says so" doesn't change that there are issues with the setup.  

 

The reality is that they may have meant to only confine the higher end tornado risk to near the triple point and are simply issuing a moderate area for hail at this time.  We'll know more about that thinking when we see the day one outlook.  I'm more inclined to believe that is the case.  Its also important that its not the SPC's job to give chase forecasts, but public safety forecasts.  Messy storms may very well pose a strong danger to the public even if they aren't ideal for storm chasing.

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anom systems produce anom results... Sound familiar? Obviously there are reasons that they have elected to disregard those concerns for now-- it is silly to think the forecaster (and really the whole office, since days like Tuesday are pretty cooperative) is totally missing multiple things that could make/break a SVR/Tornado outbreak. If she/they did actually think that helicity would be that unimpressive and that VBV would be that prominent, they would not be mentioning anything about a High risk, let alone be putting a MDT risk across a large portion of the plains.

 

There was an outlook back before the 2/23 event where exactly this happened with this same forecaster. Not that I'm saying she's not capable (because you certainly have to be to work there), but if I'm going to take it as gospel, that would mean I don't trust my own forecasting abilities (which isn't the case).

 

Also, as it sits now, this system isn't exactly the most anomalous thing.

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In a way, I'm sort of glad I haven't had the time to completely pick apart Tuesday. From what I've seen, there are some glaring red flags. At the same time, I think the kinematic/thermodynamic environments will favor at least a few strong, long-track tornadoes. I am very skeptical about southward extent and the aerial coverage of the "bigger" threat.

I took a look at the RGEM that's now into range and while it looks slightly more veered at h5 than the NAM, that's still a VBV look that's far from ideal from h6-h3. (For OKC since sounding choices are very limited from MeteoCentre.

post-533-0-00839000-1461566805_thumb.png

post-533-0-34819300-1461566881_thumb.png

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You all forget the Jarell, TX tornado outbreak day eh? That was a day where you had extreme CAPE with low shear and still had multiple violent tornadoes.

When CAPE is extreme once parcels reach the LFC it doesn't matter because storm inflow increases in a proportional manner. So instead of needing strong vertical shear to get horizontal vorticity which gets tilted and stretched the storm creates its own wind field

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You all forget the Jarell, TX tornado outbreak day eh? That was a day where you had extreme CAPE with low shear and still had multiple violent tornadoes.

When CAPE is extreme once parcels reach the LFC it doesn't matter because storm inflow increases in a proportional manner. So instead of needing strong vertical shear to get horizontal vorticity which gets tilted and stretched the storm creates its own wind field

You are using an extreme case though, that day had over 6500 J/kg of SB CAPE if I remember correctly.

 

Conversely though, everyone is focusing on the VBV which would preclude a larger outbreak but that isn't an immediate deal breaker for tornadoes to form and furthermore there will be more than ample bulk shear for severe hail and winds. Also not to mention the wind profiles near the triple point aren't that bad with less VBV.

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Also just comparing run to run on the GFS/NAM, there has been a subtle uptick and backing in low level flow ahead of the dryline. If this were to slowly improve that would greatly help with the low-level wind shear.

I think a combination of this and if 4000+ J/Kg of CAPE is realized would be able to overcome the VBV in Oklahoma. What I think we really need is the 850mb winds to be southerly, which would help massively with the veer back as a whole.

Edit: the low level clouds are absolutely flying north this morning. It has gotten much more moist than it was last night.

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I think a combination of this and if 4000+ J/Kg of CAPE is realized would be able to overcome the VBV in Oklahoma. What I think we really need is the 850mb winds to be southerly, which would help massively with the veer back as a whole.

Edit: the low level clouds are absolutely flying north this morning. It has gotten much more moist than it was last night.

I don't know if it would be enough to overcome the VBV if the worst case of VBV verifies.

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SPC just told you guys to shove your pessimism.

 

Posts like this are simply not needed. The issues brought up by very knowledgeable forecasters here are legit concerns. This would be an awful forum if all we did was focus on the positive aspects of a setup. No one would learn a thing. Hyping every single setup doesn't do anyone any good. They are not being pessimistic, they are being realistic... looking at the data we have available, focusing on trends... its called science. 

 

Another thing you have to remember, most of these guys are looking from a chase perspective... not from an event ceiling. Chase wise, there are most certainly significant issues. Further, we also have to remember that the SPC outlooks are not geared towards chasers, they are geared towards public safety. Therefore, I'm okay with the moderate because I think the threat is significant enough even just looking at hail potential.  I also think the triple point still has strong tornado potential depending on how things work out. Will those be photogenic or chaseable? That remains to be seen... could be messy.

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The SPC didn't make any mention of VBV at all. Strange, I doubt they are dismissing it all together. And if it verifies there's no chance of a high risk, and issuing one would be a mistake on their part, at least in my eyes.

 

With all the focus on VBV here, I can't seem to find any peer reviewed articles that demonstrate its effect on supercell dynamics.  Can someone point me to an article that addresses VBV?

From what I gather from rather "hand-wavy" arguments, VBV implies that a supercell ingests the opposite sign of vorticity from its ambient environment at mid levels, which is detrimental to mesocyclone.  The problem I have with this argument is that the primary "fuel source," or the effective inflow layer to a supercell is usually well below the layer where the back-veer portion of the profile is.  So I'm not entirely convinced that the storm is ingesting the opposite-signed ambient horizontal vorticity at mid levels.

I could be convinced that the changes to the storm-relative wind profile implied by VBV results in more precip falling within the storm's inflow region, and thus evaporative cooling contaminating the storms inflow and leading to outflow dominated storm modes.

Any thoughts?  I spend most of my time reading MCS papers, so I could have missed some recent articles that address this.

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With all the focus on VBV here, I can't seem to find any peer reviewed articles that demonstrate its effect on supercell dynamics.  Can someone point me to an article that addresses VBV?

From what I gather from rather "hand-wavy" arguments, VBV implies that a supercell ingests the opposite sign of vorticity from its ambient environment at mid levels, which is detrimental to mesocyclone.  The problem I have with this argument is that the primary "fuel source," or the effective inflow layer to a supercell is usually well below the layer where the back-veer portion of the profile is.  So I'm not entirely convinced that the storm is ingesting the opposite-signed ambient horizontal vorticity at mid levels.

I could be convinced that the changes to the storm-relative wind profile implied by VBV results in more precip falling within the storm's inflow region, and thus evaporative cooling contaminating the storms inflow and leading to outflow dominated storm modes.

Any thoughts?  I spend most of my time reading MCS papers, so I could have missed some recent articles that address this.

 

It isn't peer-reviewed, but this is an interesting look at the subject from an AMS presentation by Mulholland and Frame: https://ams.confex.com/ams/16Meso/webprogram/Paper274591.html 

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12Z 4KM NAM has a few cells initiating around 5-6pm right along I35 from Orlando OK to just SW of Wichita.  One of them appears to become dominant and move over the Ponca city area.  Would be worth keeping an eye on and it's not something I can ignore.  Having said that, the 4KM NAM has not been performing particularly well.  Any thoughts in particular on this latest 12Z run?

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Weather stations in the area are saying 40% chance and weather.com is saying 40% highest I've seen is channel 6 saying 70%.

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TSA has a 30% for showers/thunderstorms (some severe) after 1PM, increasing to 70% showers/thunderstorms (some severe) after 7PM to about 1AM Wednesday, then decreasing to 30% showers/thunderstorms to about 6AM Wednesday morning.

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12Z 4KM NAM has a few cells initiating around 5-6pm right along I35 from Orlando OK to just SW of Wichita.  One of them appears to become dominant and move over the Ponca city area.  Would be worth keeping an eye on and it's not something I can ignore.  Having said that, the 4KM NAM has not been performing particularly well.  Any thoughts in particular on this latest 12Z run?

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TSA has a 30% for showers/thunderstorms (some severe) after 1PM, increasing to 70% showers/thunderstorms (some severe) after 7PM to about 1AM Wednesday, then decreasing to 30% showers/thunderstorms to about 6AM Wednesday morning.

If I had to guess, from living here for around 12 years of my life I bet it'll be bad for around 7-10 o clock then die down like it has almost every single time.

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Yes I agree with discussing the limiting and positive aspects of a setup b/c it is seldom we see a setup with no flaws. However the tone of some people in the forum is rather condescending to people focusing more on what is good about the setup. But I don't want to start a war so I digress. I'm still feeling good for the triple point tornado potential and more skeptical about the dryline with the issues described above. I think the excellent thermodynamics will certainly help but not mitigate all the other limiting factors. This is not a slam dunk outbreak from a chasing standpoint but the threat is def there for a few significant tornadoes and obviously massive hail.

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