5/10/10 FCST: TX / OK / KS / CO/ MO

I would we wary of those who are simply jumping on board with the NAM based on one run. I'm not sure how the NAM can have a "better handle than the GFS" when you've literally only seen one run from that specific model. Meanwhile the GFS and ECMWF have been pretty darned consistent with their placement of surface features and the upper level system. I'd still tend to lean towards the slightly quicker positioning of the GFS and euro, and am pretty convinced that we will be seeing a sweet spot right in south central Kansas. While the GFS is known to have a fast bias, the NAM lately has had a slow bias in my opinion. This has been shown with the Wednesday - Friday timing of this current system in the midwest. Had the NAM verified we would have been looking at several days of tornadoes in Iowa and Illinois, but in turn had a much quicker streak and are now left with racers in Ohio on Friday only which the GFS nailed well in advance.

On that note, the 18z NAM is already faster than the 12z NAM, and while not completely in agreement, is trending towards the GFS.

Not a lot to add detail wise as most have already hashed out through the obvious issues which is all one can really nail down at this point, but I wanted to add my two cents in on being very wary of believing the NAM immediately before even seeing two runs to see if it has any idea at all of what to do with the system, which it already appears to not be capable of.

At this point I'll take a compromise, but leaning towards the GFS. As H said, the cold air usually plays in in some form of another. That cold air is like molasses, and will really try and keep a lid on northward movement, but I'd think getting north to around Pratt is not unreasonable. That continues to be my area to watch or 84 hour out target city. Think we'll be seeing the dryline set up about 75 miles west of the I-35 corridor from Pratt, Kansas south with a hot zone for a couple tornadoes in south central Kansas and even into Oklahoma should the cap be breached. Seems there is always a beast down there near the Red River.
 
Hmmmm! Do you think we will all be anticipating each new run of models for this system with baited breath?;)

Chuck...already in that boat with everyone else!

FIM (thanks for the info Jeff), GFS and ECMWF all fairly similar with the 500mb wave on their 12Z runs. Agree with Mike H., the 18Z NAM is a little more progressive/flatter than its 12Z counterpart. Subsequent model runs will be very interesting indeed as the potential event draws closer.
 
I would we wary of those who are simply jumping on board with the NAM based on one run. I'm not sure how the NAM can have a "better handle than the GFS" when you've literally only seen one run from that specific model. Meanwhile the GFS and ECMWF have been pretty darned consistent with their placement of surface features and the upper level system.QUOTE]



The GFS and ECMWF have been anything but consistent with their placement of the upper level system. I don't know what would make you think that.
Here is a picture of the 500mb chart with the GFS from day 7
Day7 500GFS.jpg

now here is a picture of the ECMWF from the same time
Day7 500mb.jpg

The GFS has the trough way out east in Missouri and Iowa. The ECMWF in the same run has it a state and a half west of there in the Texas panhandle. Obviously those two solutions are drastically different.

Here is a picture of the GFS from 4.5 days out.
108hr 500mb.jpg
This run of the GFS keeps the jet streak back over the western part of Oklahoma. That is one state west of where the GFS showed the same thing two days earlier.

Then here is the 500mb chart from this mornings GFS.
3.5day GFS 500mb.jpg
It's got the jet streak nosing into Illinois. That is a state and a half east of where it showed it yesterday at this same time.

I fail to see how the GFS has been consistent with its placement of the upper level trough and the surface features.

The ECMWF has been more steady than the GFS and it's favored a slower solution over the last few days. The GFS has been all over the place with it's placement of the trough and surface features with this setup. Then the NAM comes out this morning with a slower solution which is much more similiar to past runs of the ECMWF than the 12Z GFS solution is. So if you asked me which model is more stable and accurate I'm going with the NAM and ECMWF.
I think the surface features will end up being a compromise of the Texas panhandle NAM solution and the ECMWF central Kansas solution. I'm really hoping for that. I don't want to tangle with a fast GFS solution where low level winds start to veer. There are few things I hate more in this world than veering 850mb winds.
 
18Z GFS is out, and one thing is for sure, and that is that the 12Z GFS and 18Z GFS are basically spitting images of each other. Carbon copies.
 
The ECMWF has been more steady than the GFS and it's favored a slower solution over the last few days. The GFS has been all over the place with it's placement of the trough and surface features with this setup. Then the NAM comes out this morning with a slower solution which is much more similiar to past runs of the ECMWF than the 12Z GFS solution is. So if you asked me which model is more stable and accurate I'm going with the NAM and ECMWF.

Good points, and thanks for the examples. It's true the GFS has been all over the place, and only recently that the EC has put the wave on a fast track. But I just checked the 18Z GFS, it seems as progressive as the 12Z GFS (both of course still faster than the 18Z NAM).

A silver lining is that only in the past couple runs of the GFS have the following days (May 11, 12, ...) begun to look pretty good, IMHO. But that's a topic for another thread - sorry Mods! :)
 
GFS has consistently trended further east with this one it seems... last two/three days of runs or so.

I've seen scenarios in which the GFS ends up correct with this sort of trend. Of course it can be too fast at times... as anyone will fondly remind me.

Wasn't March 30 (or there about) of 09 a good example of the fast GFS solution winning out?

There's probably more. Easy to tell what chasers want; but this has no bearing on reality, of course. Can only wait and watch.
 
18Z GFS is out, and one thing is for sure, and that is that the 12Z GFS and 18Z GFS are basically spitting images of each other. Carbon copies.

I'm waiting for the 00z GFS, we should have the info in what about 3 or so hours?

Can anyone confirm that off hour runs (ie 6z and 18z) are not generally as accurate? A friend of mine in OKC told me a couple weeks ago that they use different parameters for the GFS in the "off hours" as he called it.
 
The last several runs of the GFS and the Euro have sped the system up a lot. All we can hope for is a compromise between them and the NAM I guess.

I knew it was stupid to get excited about model runs 3 days ago...
 
I'm waiting for the 00z GFS, we should have the info in what about 3 or so hours?

Can anyone confirm that off hour runs (ie 6z and 18z) are not generally as accurate? A friend of mine in OKC told me a couple weeks ago that they use different parameters for the GFS in the "off hours" as he called it.

I have been told that on the 06z and 18z runs that they use some old data with some new data as well as some different paramaters. They also tell me that 0z and 12z use all new data. I can not find something on NCEP's website that confirms that but I have been told that many times.

Sometimes the 18z and 06z can be used to see what the 0z or 12z models can be trending towards (slower or faster).
 
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Well, the 00z NAM is out and the hodographs for SW OK are downright scary. The NAM is insistent, so far, on setting up the dryline on the OK/TX border. The positives of this setup are still very much there, so I'll focus on the negatives. The cap is still fairly strong and the NAM doesn't fire any convection off the dryline. But with a shortwave moving through the area around 00z and a nice dryline bulge, I would expect stuff to fire.

Another drawback is the veering 850s. They don't back until 00z. This shows up as lower dews (lack of widespread 15C Tds) in the 850mb level. Overall, still a significant setup. I curious as to how the other models handle the setup.
 
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It's a relief to see the 00Z NAM hasn't really moved the dryline since the 12Z run. But it has de-amplified the wave considerably, consistent with GFS trends, and consistent with faster movement. Also a slight (insigificant) reduction in CAPE. Still, the EHI's are amazing: 0-3km is > 12 in SW OK, ie off the charts!
 
Well, the 00z NAM is out and the hodographs for SW OK are downright scary. The NAM is insistent, so far, on setting up the dryline on the OK/TX border. The positives of this setup are still very much there, so I'll focus on the negatives. The cap is still fairly strong and the NAM doesn't fire any convection off the dryline. But with a shortwave moving through the area around 00z and a nice dryline bulge, I would expect stuff to fire.

Another drawback is the veering 850s. They don't back until 00z. This shows up as lower dews (lack of widespread 15C Tds) in the 850mb level. Overall, still a significant setup. I curious as to how the other models handle the setup.

The 00z NAM is very impressive indeed. Upper 60 dews with close to 4,000 CAPE and 0-1 and 0-3 SRH/EHI values off the charts along the dryline in western OK. The winds do slightly veer at the 850mb level before 00z, but are due south by 00z with 15-17C dews at the 850mb level. There is still a bit of CINH to be burned off east of the dryline as you mentioned Andrew. SW OK looks very nice with the dryline right along the TX/OK border. 10-12C 700mb temps are forecasted along and east of the dryline. I guess the negatives as of now would be the cap and which model will ultimately win out. Hopefully it's the NAM because it looks insane on the 00z run. I can't imagine the cap not breaking with the parameters that are in place. The GFS should be out shortly so I guess wait and see what it says. If this current run of the NAM is correct I would say KS is basically taken out of the equation for a good chase. I guess the exception may be a very small area in SW KS. I just noticed the shortwave at 00z on the 700mb chart so hopefully that along with a dryline bulge in the SW/Western OK vicinity should break that cap.
 
It's a relief to see the 00Z NAM hasn't really moved the dryline since the 12Z run. But it has de-amplified the wave considerably, consistent with GFS trends, and consistent with faster movement. Also a slight (insigificant) reduction in CAPE. Still, the EHI's are amazing: 0-3km is > 12 in SW OK, ie off the charts!
I agree, it's nice to see the NAM sticking to its guns on the western placement of the dryline. The last thing we need on a day with 500+ chasers is for storms to end up E of I-35 in terrain where you have to be right next to a tornado to see it!

The instability and shear both look close to ideal, though I am more concerned about the cap if our shortwave verifies so low-amplitude. The 500 mb height field doesn't really show much of a kink S of the OK/KS border this run, and I think we'll want some good synoptic-scale rising motion to compensate for the substantial CINH. Fortunately, the 700 mb omega chart still shows significant rising motion near the dryline by 00z all the way down to the Red River or so, but I'd prefer the more pronounced wave on this morning's run.

Another trend I noticed on this run vs. this morning's is that the cold/dry air hangs a little tougher over OK/KS into Sunday night and even early Monday morning. If you believe this run, it's of little consequence in the end, as the WF still makes it up into S KS by late afternoon with good, deep moisture overspreading OK and the TX PH. But it's something I'll be watching on future runs. I'm thinking this may be related to the downstream trough off the east coast digging a bit more this run, which seems to have caused problems for us repeatedly this year.

Given how subtle the shortwave responsible for this event is with an upstream kicker, I'm sure the model roller coaster ride will be a rough one over the next few days.
 
The 00z NAM is very impressive indeed. Upper 60 dews with close to 4,000 CAPE and 0-1 and 0-3 SRH/EHI values off the charts along the dryline in western OK. The winds do slightly veer at the 850mb level before 00z, but are due south by 00z with 15-17C dews at the 850mb level. There is still a bit of CINH to be burned off east of the dryline as you mentioned Andrew. SW OK looks very nice with the dryline right along the TX/OK border. 10-12C 700mb temps are forecasted along and east of the dryline. I guess the negatives as of now would be the cap and which model will ultimately win out. Hopefully it's the NAM because it looks insane on the 00z run. I can't imagine the cap not breaking with the parameters that are in place. The GFS should be out shortly so I guess wait and see what it says. If this current run of the NAM is correct I would say KS is basically taken out of the equation for a good chase. I guess the exception may be a very small area in SW KS. I just noticed the shortwave at 00z on the 700mb chart so hopefully that along with a dryline bulge in the SW/Western OK vicinity should break that cap.

On the 12z run and past runs of the NAM I was fairly optimistic about the cap breaking... But the 00z run leads me to be more worrisome.. In all honestly, looking over some past case studies, including the study by Jon Davies about 700mb temps and storm potential, and just general experiences, the 700mb temps are not that undoable! But when you look at SKEW T you can easily tell that the cap is centered around H85-H8...

NAM_218_2010050800_F69_35.0000N_99.5000W.png


My best suggestion right now, if we continue to look at such a strong EML, would be to play the dryline bulge, which is well aligned with the left exit region of UA Jet, and hope for a well timed shortwave as currently evident to spark things off in the afternoon hours.

That being said, should the cap be broken and storm initiation occur, it goes without saying from past posts that the kinematic/thermodynamic environment favor a severe weather outbreak.. Which is why I would likely gamble the opportunity anyways..
 
I totally agree with you Brandon. The cap is definitely becoming one of my top concerns. I hate seeing 850mb winds veering ever so slightly with the 00Z NAM, but that will have no impact on tornado potential unless it gets worse (850mb winds veered slightly on May 4th, 2003 and that worked out pretty well).
I am not good at all on anticipating whether or not the cap will break. I'm sure the SPC guys know a lot more given their experience and range of forecasting tools so I'll pretty much stick with their guidance on the capping question. My god what a waste that would be if we got the NAM's setup and the cap didn't break lol. You would have some seriously pissed off chasers driving back home across Oklahoma.
 
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