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Chicago Storm

April 24-30th Severe Potential

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Wind profiles in the 00Z NAM are a bit tamer than the 18Z which was tamer than the 12Z...LI's improve along with a few other parameters, 700mb looks pretty solid over the instability but the 500s are off and coming in with a bit too much southerly component...

 

Yeah, the trend isn't our friend here. The trough is looking more occluded with each and every run. That said, we have many more run cycles for this to correct/adjust (though it could just as easily go in the other direction too). These trends would lead me to believe a D3 MDT is not in the cards, however.

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Wind profiles in the 00Z NAM are a bit tamer than the 18Z which was tamer than the 12Z...LI's improve along with a few other parameters, 700mb looks pretty solid over the instability but the 500s are off and coming in with a bit too much southerly component...

 

 

Right. Enough of a VBV signature to really start looking at it. This is for the KS/OK border at 0z. But the VBV goes away at 3z. Weird stuff.

2f06naw.png

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Right. Enough of a VBV signature to really start looking at it. This is for the KS/OK border at 0z. But the VBV goes away at 3z. Weird stuff.

2f06naw.png

might disregard the VBV to an extent for now.

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might disregard the VBV to an extent for now.

Why sir?  It's been somewhat persistent appearing every other run, this time it seems to have stuck around a bit and intensified some...

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might disregard the VBV to an extent for now.

 

This isn't exactly something to disregard with SSW 500 mb flow.

 

This is really shifting away from a more robust threat right now.

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This isn't exactly something to disregard with SSW 500 mb flow.

This is really shifting away from a more robust threat right now.

it is still 4 days out, and it is something that's barely been showing, then it shows up more clearly for one particular hour on the NAM on a few soundings, then not on the next hour, and it suddenly is a big issue? I'd wait for the euro to also start showing it and for the GFS to show a VBV more prevalently before I pay too much attention to it. The idea that this threat isn't that robust isnt exactly warranted YET. Just look at the parameters that are still in place, as well as the thermodynamics. While a VBV could/would potentially temper the tornado threat some, I wouldn't say that the setup is not robust. That's really just my opinion though, I'd wait until we get more high-res guidance involved in this to start with that kind of stuff of "really shifting away."

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it is still 4 days out, and it is something that's barely been showing, then it shows up more clearly for one particular hour on the NAM on a few soundings, then not on the next hour, and it suddenly is a big issue? I'd wait for the euro to also start showing it and for the GFS to show a VBV more prevalently before I pay too much attention to it. The idea that this threat isn't that robust isnt exactly warranted YET. Just look at the perimeters that are still in place, as well as the thermodynamics. While a VBV could/would potnetially temper the tornado threat some, I wouldn't say that the setup is not robust. That's really just my opinion though, I'd wait until we get more high-res guidance involved in this to start with that kind of stuff of "really shifting away."

I couldn't have said that better. We're 3-4 days out. It's a little early to be minimizing the threat...

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And the 00z run of the GFS has breathed new life into this system. Much more favorable wind fields with no VBV profile evident.

very impressive at 03Z in SC KS with 0-1KM Shear of 30+ kts, and 0-1KM SRH of 300+m2/s2. Can't post the sounding because I'm on my phone, but the amount of sig matches from SARS are crazy.http://climate.cod.edu/data/forecast/sndgs/00_GFS_075_37.79,-97.15_severe_ml.png

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This system has people - me included - living and dying with every model run.  We won't get a D3 Moderate, but as long as the overall pattern looks good there's no point in worrying about it until the day before/of.  

 

 

That being said, for as hype the community has been so far, this system is far from a sure thing.  

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And the 00z run of the GFS has breathed new life into this system. Much more favorable wind fields with no VBV profile evident. 

There is some VBV in SC OK, but N OK and SC KS are the primary threat areas with no VBV evident there. Then you have the NAM with it's typical overblown CAPE values approaching or exceeding 5500 J/Kg, and weak VBV in the same general vicinity as the GFS. The only place that I found VBV on the 00z runs of the GFS and NAM was a small area confined to SC OK.

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Ah, VBV, we meet again - one of the most frustrating of all caveats, from a predictability standpoint. It's so hard to discern the impact it will have on the threat's magnitude and spatial distribution. If the trend toward VBV doesn't reverse over the next 24-36 h, then the window for a true top-end event rivaling 4/26/91, 5/3/99, 3/13/90, and that ilk is probably closing. Even so, I wouldn't write this off at all, if it's roughly what the current consensus shows. Three events in 2011 come to mind (4/14, 5/24, 6/20) as illustrations on why dismissing VBV profiles out of hand can be unwise. With 4000-5000 J/kg SBCAPE looking quite likely, this is especially true.

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What's VBV?

Veer-Back-Veer.  It's a vertical shear profile where there is a layer where winds back in the mid-levels, above significant low-level veering with height.  It can often cause messy storm modes and/or supercells to not be as long-lived.  However, as Brett pointed out above, there have been some events with such wind profiles where it hasn't mattered (even though those events probably would've been even worse than they already were had they not had the VBV wind profile).

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What's VBV?

typically where the wind profile veers to the southwest in the low-levels, then backs to the south or slightly southeast even sometimes in the mid-levels (usually in the 700-500mb range), then veers back to more southwesterly in the mid/upper levels. Sometimes if it is bad enough and the instability isn't that great, it can tear apart storms/updrafts or lead to a really messy/mixed storm mode.

Often times it is more of a VB signature when this occurs than a true VBV.

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What's VBV?

 

 

Veer-Back-Veer, it's a wind profile that describes winds that turn counter-clockwise as you continue ascent through the atmosphere. A great analogy I once read was imagine stirring sugar in your coffee in a clockwise direction, and then suddenly violently stirring counter-clockwise; the nice smooth funnel you had becomes a mess. Sorry for not giving credit to whoever first gave that analogy, I'm sure it was someone on this forum.

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Sorry, here's the actual link. http://youtu.be/FpTTPLQ4uTc Greg Johnson on it!

listened just to hear what they had to say and Chris Chittick was on there with Greg Johnson... And the two kids on there seem to know their stuff for the most part and supposedly have good connections with SPC. One of the kids said they talked with Greg Dial, and he said that this likely would be a D3 MDT, if he was issuing it, and according to the message it sounded like he was. Who knows, we'll find out if that is actually the case PDQ. Not like it holds any more value to if Tuesday will be as big of a day as has been hyped.

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SPC issued an ENH risk for NE KS/SE NE for later today for the possibility of very large hail... 5% tornado probs extending from SE NE to NW OK.

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There is some VBV in SC OK, but N OK and SC KS are the primary threat areas with no VBV evident there. Then you have the NAM with it's typical overblown CAPE values approaching or exceeding 5500 J/Kg, and weak VBV in the same general vicinity as the GFS. The only place that I found VBV on the 00z runs of the GFS and NAM was a small area confined to SC OK.

 

The problem is models are extremely bad at predicting VBV because it's a function of wind speeds and directions in the mid AND low levels, so errors in one level can throw the whole thing off. So we have to look at the synoptic pattern in general to assess the chances for VBV. In general, it's less likely around the base of an amplifying trough, and more likely in a high-amplitude or occluded situation, which is what models are trending towards.

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Meanwhile the 00z Euro wants to drag this thing south of the Red River. Has seemed to be a common theme this year that model concensus has decreased closer into events.

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Meanwhile the 00z Euro wants to drag this thing south of the Red River. Has seemed to be a common theme this year that model concensus has decreased closer into events.

may as well just pick your favorite model with this 00Z suite. NAM/GFS are pretty similar for the most part I guess, but the ECWMF is drastically different.

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my look at things, at least from what I saw on the model soundings and looking at the lids via bufkit for DFW, ICT, and OKC, it looks like the NAM was like 3-4 hours later in storm initiation timing than the GFS. but timing being said, once the storms get going, it's not a  question of if, but how bad. any look at the model soundings for the Euro?

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my look at things, at least from what I saw on the model soundings and looking at the lids via bufkit for DFW, ICT, and OKC, it looks like the NAM was like 3-4 hours later in storm initiation timing than the GFS. but timing being said, once the storms get going, it's not a  question of if, but how bad. any look at the model soundings for the Euro?

 

Does anyone have access to Euro soundings?

 

It blows up convection pretty early, so a lot of them might be convectively contaminated. It would also imply foci closer to DFW where surface temperatures and thus LCL's will be higher.

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Forbes must of saw something today.  Tues/Wed went from "tornado outbreak," (From his previous forecast) to more of a "Limited tornado outbreak." (With his current forecast)

No he basically said the same thing today as he did yesterday

 

 

Today:

TUESDAY 4/26

Severe thunderstorm and limited tornado outbreak likely in central OK, north-central TX west of I-35, east half of KS, south and central NE, extreme northwest MO, spreading overnight into northeast OK, central and southwest MO. TORCON - 5 central KS, central OK; 4 south NE; 3 rest of area. A chance of an isolated severe thunderstorm in south-central TX. TORCON - 2

 

 

 

Yesterday:

 

TUESDAY 4/26

Computer models disagree on how far north and east the severe weather threat will extend. But it looks like at least a limited-area

severe thunderstorm and tornado outbreak will occur in late afternoon through late evening in north, south-central and southeast KS, west MO, extreme southeast NE, northeast and central OK, north-central TX near Wichita Falls. TORCON - 5 south-central and southeast KS, central, northeast and southwest OK; 3 rest of area except 2 southeast NE

 

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Does anyone have access to Euro soundings?

 

It blows up convection pretty early, so a lot of them might be convectively contaminated. It would also imply foci closer to DFW where surface temperatures and thus LCL's will be higher.

remember, since last year, the Euro's been increased in resolution from ~20km down to ~9km on a grid scale. and when you reduce the grid boxes, things that didn't show up before except in parameterizations now actually show up in the grid-points. so, can the model really handle things the same as it did before? this is especially true when convection becomes involved.

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Looks like they nearly pulled the trigger on the D3 moderate. But decided not to due to some model variability and capping concerns.

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that actually makes sense. and the enhanced risk area, in combination with the model trends the last 3 days, I'm pretty sure the areas affected are pretty much aware the potential is there. waiting one more day before pulling out the moderate or even high risk is not the worst idea in the world in this situation, imho. if they didn't have the "enhanced" option, I'm sure they would have went moderate. but this gave SPC the right leeway to wait for some better focus.

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TUESDAY IS STILL LOOKING LIKE A HIGH IMPACT SEVERE WEATHER DAY

ACROSS CENTRAL AND EASTERN KANSAS. THE MAIN CHANGE FROM EARLIER

MODEL RUNS SUGGESTS THE WESTERN CONUS UPPER TROF MAY EJECT A BIT

QUICKER ACROSS THE CENTRAL PLAINS TUESDAY EVENING INTO TUESDAY

NIGHT. THIS SCENARIO OF STRONGER WIND FIELDS MAY COMPLIMENT

TIMING OF MORE OPTIMAL THERMODYNAMIC PROFILES NEAR PEAK

HEATING...WHERE A VERY UNSTABLE AIRMASS WILL RESIDE IN THE WARM

SECTOR WHERE EVEN THE MORE CONSERVATIVE GFS SHOWS AROUND 4000

J/KG OF MLCAPE. THE WARM FRONT NOW LOOKS TO MOVE NORTH OF THE I-70

CORRIDOR BEFORE DARK...WITH SURFACE DRY-LINE AND TRIPLE POINT JUST

WEST OF THE FORECAST AREA BY EARLY EVENING. WHILE THERE IS SOME

QUESTION REGARDING BULK SHEAR VECTOR ORIENTATION IN VICINITY OF

THE DRY-LINE...THE OVERALL SHEARING ENVIRONMENT SHOULD STILL

SUPPORT DISCRETE TO SEMI-DISCRETE SUPERCELLS...WHICH MAY

EVENTUALLY EVOLVE INTO SOMETHING MORE QUASI-LINEAR TUESDAY NIGHT.

BOTTOM-LINE...THE EJECTING NEGATIVE TILT UPPER TROF STILL LOOKS

TO SUPPORT ALL MODES OF SEVERE WEATHER WITH POTENTIAL FOR VERY

LARGE/DESTRUCTIVE HAIL AND STRONG/LONG TRACK TORNADOES.

 

Latest AFD from NWS Wichita 

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Here is text from the Hazardous Weather Outlook from NWS Wichita

 

 

 

 
A SIGNIFICANT SEVERE WEATHER OUTBREAK REMAINS POSSIBLE ON
TUESDAY INTO TUESDAY NIGHT ACROSS THE ENTIRE AREA. SUPERCELL
STORMS WITH THE POTENTIAL FOR VERY LARGE DESTRUCTIVE HAIL AND
STRONG LONG TRACK TORNADOES WILL BE POSSIBLE...MAINLY FROM
LATE AFTERNOON THROUGH ABOUT MIDNIGHT. DETAILS WILL BE REFINED
IN THE NEXT COUPLE OF DAYS.

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