5/1/08 FCST: KS/MO/OK/AR/TX/NE/IA

[Van DeWald]

4/28 00z GFS still looks pretty good for potential development along the dryline...most likely across western Iowa. Noted dryline pushes to about the Missouri River by 00z 5/2, with a pronounced bulge into west central Iowa. While there appears to be a healthy cap in place at 18z with said dryline across eastern Nebraska, looks like best show may be late afternoon/early evening. 0-1km shear is progged to increase to around 30kts by this time as a 100kt upper level jet streak places the area in the left exit region. Will probably see convection fire down the front into western Missouri, eastern Kansas, and Oklahoma, but am liking the tornado setup in my own back yard for this one.

 

[John Hudson]

I know it's really still to early to call the ball, but I was curious about the SPC Day 4 outlook. They've covered a significantly wide area for this outlook, including TX/OK/AR.

Looking at this morning's 00Z GFS run, it really looks like it's going to be well capped down there, and the best Td's look to be in the NE KS/SW IA area. Unless the cap splits open all along the dryline, I wouldn't expect much to happen in the OK/AR region until the LLJ gets going late evening.


John

 

[John Peters]

Eta draggs 65 deg Tds into SE KS by 00Z on Friday, yielding more imressive cape values (3000-3500 j/kg) along the dryline. It's also projecting 500 mb sheer just shy of 50kts over most of the higher instability, with a 30-40kt LLJ. It seems like, once again GFS is more aggressive with the mid level sheer (is this a regular tendency?).

If the system were to advect the higher Tds into the area in question earlier in the day (in coincidence with the stronger projected LLJ, higher SRH), i could see a pretty significant afternoon event occuring. As of now, initiation would likely occur later in the evening along the dryline with less inhibition and more instability.

Also, if something were to somehow initiates east of the front under the cap, it will be subject to better upper level sheer profiles, and will be more likely to remain isolated.

 

[Mikey Gribble]

In response to John Hudson... The GFS has been very consistent in eroding the cap with convection breaking out along the OK-KS border by 00Z. The NAM fell in line with that too on the 12Z run. In addition to that the GFS has convection breaking out all the way down to the Red River after dark as the cold front over takes the dryline. I'm sure that is why they included that area. I wouldn't be surprised to see a squall line develop along the cold front after dark in Oklahoma.

 

[Kevin Crawmer]

Interesting setup in the works for Thursday. There are still a few questions that have been addressed earlier. The dynamics are definitely in place for at least a localized tornado outbreak. Eastern KS and the adjacent MO counties look to be in the most favorable location for this activity. A quick look at the sounding for Parsons, KS in SE KS reveals a SW of 474, BRN of 14.8, and EHI of 6.3. LCLs in the 900s appear to be in place as well. The nice, curved hodograph looks good compared to some I have looked at this year.


All in all looks to have the potential to be one of the more impressive setups this year so far. As far as chasing is concerned....terrain shouldn't be a problem until the storms get into MO, but initiation may be later than one would like (approx 00Z). It looks as if once they do get going that they could become severe quickly.

 

[Scott Lincoln]

A quick look at the sounding for Parsons, KS in SE KS reveals a SW of 474, BRN of 14.8, and EHI of 6.3. LCLs in the 900s appear to be in place as well. The nice, curved hodograph looks good compared to some I have looked at this year.

All in all looks to have the potential to be one of the more impressive setups this year so far. As far as chasing is concerned....terrain shouldn't be a problem until the storms get into MO, but initiation may be later than one would like (approx 00Z). It looks as if once they do get going that they could become severe quickly.

A quick look at BUFKIT profiles (GFS 12z run) for western Iowa shows a strong cap at 1pm that quickly erodes through the afternoon and breakable by 4pm and is virtually gone by 7pm. Looks like the culprit is some strong large-scale vertical ascent. I also dont think that I'm seeing a dryline making it into Iowa - looks like the triple point is down in Kansas on the GFS. I'd say its possible that storms could form earlier than 6pm ahead of the low. Just have to keep in mind that the system will probably slow down as often happens and end up in Nebraska/Kansas instead of Iowa/Missouri.

 

[Ben Prusia]

If The NAM/WRF is right......then everybody and their mother will be in northern Oklahoma/southern Kansas along I-35 on Thursday afternoon. The 12Z model data which now goes out to the aforementioned storm shows the frontal boundary and dryline intersect about halfway from the Oklahoma/Kansas border to Oklahoma City along I-35. Northeast of this feature, the model breaks out some precipitation, along with the model showing SSE surface winds and a not as powerful LLJ that the GFS model from last night was forecasting. The model veers H85 winds a tad to the SSW, but leaves 925mb winds due to the south which should be an alright ideal. The model could be overdoing the dewpoints as just about 70 degree Td's may be hard to reach, but should that verify, watch out! Showing a moist layer at H7 and at H85, should not think that the cap is an issue in this area, but further south along the dryline, the layers are drier and the cap becomes more of a hinder for thunderstorm development in that area. According to Earl's model site, the severe parameters including the STP are maximized in this area so if this model verifies, watch out again!

It still appears that the 12Z GFS model is a little more quicker on the situation on Thursday and a little more northerly as it puts the dryline/frontal intercept in SE Kansas. With the NAM/WRF showing less 0-1km SRH due to the weaker LLJ, the GFS still maintains its stronger wind speeds in the crucial level.

But, for now, still feel that there are still some considerable model differences including the position of the dryline/frontal boundary intercept and the strength of the LLJ which will then dictate where the storms will develop, what mode of development will happen, and how strong. NAM/WRF favors an area in north central Oklahoma into extreme southern Kansas, while the GFS still prefers an area in east central Kansas southward to northeast Oklahoma. Further model runs will hopefully hose in an agreement on the location of the best severe features. Both models do break out precipitation in the location of the progged frontal boundary/dryline intercept. Either way, both areas depicted by the models are decent chasing areas and the storms should be moving at chasable speeds. Still looks like a decent severe weather setup on tap for the 1st of May.

 

[Mike Hollingshead]

I think if the NAM were to be right, I'd rather be in northern IA somewhere than anywhere else. The cold front and very veered 850 winds to the south just aren't enticing. I just can't think of seeing anything cool in 850 winds like that. If I could, I may be more apt to consider them. I think staying home might be the best option if the NAM were to be right. The play in IA would probably be enough to get me to go chase it though.

That said, there's obviously other model options! Give me the GFS and I'll take an area near home in eastern NE. If I had to bet, I'd bet it comes out as a cross between the 12z GFS and 0z ECMWF. I hope it winds up like the 0z ECMWF, then several locations from I80 in NE to the OK border would work.

 

[Michael O'Keeffe]

I am hoping the 12z GFS verifies as it has been consistant the last few runs putting insane EHI values of 6 to 7 over SE KS and 0-1km SHR at over 360!!! In addition the slightly higher CAPE values that I was hoping to see have increase to around 3000j/kg in SE KS/NE OK. As for the LLJ I don't see how it could be a problem with the SLIGHT veering in it. So all in all if the GFS verifies I will be setting up in SE Kansas.

As for the WRF it still looks good, but I like the NC Oklahoma area better for obvious reasons that I don't feel like getting into right now.

 

[Mikey Gribble]

I still like the KS-OK the border area after looking over the 12Z runs. The NAM has the best area for tornadoes further South (NE of OKC) where the LLJ backs up to the dryline (and strongest 850mb winds are down here), but I think the GFS seems a bit more believable in its placement of the stronger low-level winds. Regardless, the best area for tornadoes should be ahead of the dryline some where between the OKC to Wichita area.
There are a few things that are keeping this area from being supportive of violent tornadoes(EF4-5), but given the strong 0-1km winds, good CAPE, and respectable LCL heights I think there could be some strong tornadoes(EF2-3). The NAM is weaker with wind speeds at all levels when compared to the GFS and it veers 850mb winds more. If the GFS can verify (or even a compromise of the two leaning more towards the GFS) then I think we may see some long track tornadoes as well. Right now my biggest concerns are moisture quality/depth and veering 850mb winds. If 850mb winds veer slightly to SSW then I don't think it's a terrible thing given the weak directional shear in the lowest 1km, but if they veer more than that I think it could be trouble. Rarely do you get good tornado days when 850mb winds veer badly. With closed lows you always have to watch your directional shear and this setup is no exception. We really need to maintain or improve on the directional shear that the GFS is showing if we want a good tornado threat. On the moisture question the main thing that concerns me is the the veering 850mb winds (again). There will be favorable trajectories in the 925mb layer for a good moisture fetch in the 48 hours leading up to Thursday afternoon, but I am a little afraid that the moisture may be shallow and that the veering 850mb winds could advect in some drier air and mix down our dewpoints. I really haven't looked at this much yet though so I am shooting from the hip. I am definitely going to spend some time on it tomorrow though.
All in all the tornado threat is conditional, but it is also quite high (with strong tornadoes possible). As others have mentioned the higher threat will be over a small area and I don't expect more than one or two storms (during daylight hours) coming off the dryline in the North-South area from OKC to Wichita along the dryline, but those few storms could be cyclic tornadic supercells if the models verify. The GFS and the NAM (GFS especially) are showing some pretty potent composite indices in this area. The fragile/shakey nature of this setup has me thinking it could go either way, so I'm still not terribly excited, but everything looks OK so far. I posted a full forecast on my blog if you're interested http://loadedgunchasing.com/blog.html

 

[Mike Hollingshead]

The banana shape to the sfc low on the nam and gfs both just concern me. They make things look great in that area down there with sfc winds trying to be a little backed, but does that usually happen with these? I don't know, doesn't seem they turn out well.

(I must say I'm horribly sorry for saying anything at all negative about the runs. I know how horrible that can be for some. At least it gives you something to blab about after it's all turned out ok. "Damn naysayers" *rant done* lol)

I just got a look at the 12z ECMWF on COD and that orientation of things still looks wonderful. Nice consolidated surface low, and deep. Hopefully the 0z runs tonight will agree more with the ECMWF on that aspect.

 

[John Peters]

If the GFS can verify (or even a compromise of the two leaning more towards the GFS) then I think we may see some long track tornadoes as well.

Last system it seemed like GFS was much more aggressive in terms of mid level winds than NAM (and even projected a slightly more intense LLJ). NAM ultimately verified, and I'm more liable to trust it's predictions this time around. I do agree that if the GFS does pan out, we'll be seeing a much more significant event than the former situation.

 

[Mikey Gribble]

John said...
"Last system it seemed like GFS was much more aggressive in terms of mid level winds than NAM (and even projected a slightly more intense LLJ). NAM ultimately verified, and I'm more liable to trust it's predictions this time around. I do agree that if the GFS does pan out, we'll be seeing a much more significant event than the former situation."

I didn't pay a whole lot of attention to the details on what verified over the last several weeks, but I actually think the NAM was a little too conservative on low-level winds on the last chase (Pratt target). The chase before that when the cell went up at dark South of Norman the NAM was totally out to lunch on the low-level wind fields. The GFS was a lot closer on that one, but it was way off on the position of the triple point. I don't think you can trust either model right now because they've both been taking dives lately. Neither one IMO has performed better than the other in the last month. They both have sucked equally lol. I only glanced over the ECMWF, but it is worth mentioning it is leaning towards the GFS with the strength of the mid-level jet streak.

 

[Mike Hollingshead]

http://www.rap.ucar.edu/weather/model/eta72hr_sfc_mslp.gif

http://www.rap.ucar.edu/weather/model/eta78hr_sfc_mslp.gif

Interesting what it does between 0z and 6z, crashing the southern area. Actually it's crashing it through the day from 18z on.

Based on just that I'd lean towards the north option. Problem is looking upstairs. Not a lot upstairs says north, lol.

http://www.wxcaster2.com/CENTRAL_ETA_250M-6KM_SHEAR-VECTOR_72HR.gif

Enough shear along the warm front in IA still though. Still that stupid banana low. If it wasn't crashing things so fast to the south, and it wasn't eastern OK, I'd be leaning that direction, but as it stands I'm still leaning to NE/IA.

Edit: This is a bad sign...the mask from Scream.
http://beta.wxcaster.com/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_72HR.gif

 

[Mikey Gribble]

What's crashing? The cold front dryline intersection is in southern Kansas at 00Z and by 06Z it's overtaking the dryline in Oklahoma. Unless you are planning on chasing until 3AM I don't see what the issue is. The models have been showing the cold front overtaking the dryline Thursday night for several runs now. It's nothing new. Hence my post earlier in this thread when somebody asked why SPC highlighted the area all the way down to southern Oklahoma and I said because a squall line would probably form along the cold front after dark.
I just think it's funny how people favor their backyard and then get pissed when somebody disagrees with it. I don't care what anybody else says in their forecast so I don't know why they'd care about what I say in mine.
Then I get some ignorant comment on here asking if I had a model that "predicted the strength of tornadoes". Really??? Obviously you don't know how to forecast and haven't chased very long because with a little experience and forecast knowledge it's really not that hard to recognize a setup that supports strong tornadoes. How do you think any forecast office makes a distinction between a low end tornado threat and a setup that can support strong tornadoes??? Do they have a model that "predicts tornado strenght"? No. It's called forecasting. You should try it some time. BTW this comment is just directed to the person who made that comment earlier.
I'm not saying that we'll get strong tornadoes, but I am saying that if the GFS verifies we will certainly have the potential for strong tornadoes. If you don't want to believe me on that then look at the forecast composite indices for Thursday. Those formulas are written by SPC forecasters among others. They must not know what they're doing either.
Everybody chase north and I'll chase south. That's just fine with me. I would rather not have the traffic down here anyways.