4/21/07 FCST: OK / KS / TX / NE

[David Drummond]

Personally I have had enough "outbreak scenarios". The best chases I have ever had were not outbreak days at all except for one, but rather "normal" chase days such as what appears to be setting up for Saturday, or even plain ol slight risk days.

There are definitely some signs setting up for some classic panhandle severe weather and the devil will be in the details when we start coming in the T -3 day range, but I recognize this pattern as one that is VERY condusive to some excellent chasing in good chasable terrain.

And that's really what you should be concentrating on more than 3 or so days out...pattern recognition. As it looks now, I have seen setups like this produce what we used to call the "chain of pearls".....supercells scattered up and down the dryline....take you pick of one.

 

[Jim Bishop]

The 12z WRF sure shows some interesting changes. I like the area from Southwest Kansas down into the Texas Panhandle. Nice vort max and strong 250mb jet max moving right into that area. Surface and 850mb flow is more backed and the mid level flow is more veered.

The one really bad thing is how it mixes out the low level moisture across the high plains. I'm not buying into that yet, but it sure doesn't make me feel great about surface dewpoints. The one good thing is the -16C to -18C 500mb temps, which still support half decent CAPE values. We shall see. I never like the WRF solution beyond 60 hours anyways...it always seems to have some strange issue. I'd take the GFS over the WRF beyond 60 hours any day.

 

[Brett Roberts]

Just took a peek at the 12 NAM (84hrs out) and lets hope the NAM does not verify as it only has low 50s at best along the dryline... That is really pushing it for me. THe sfc low is all the way up into SW SD and NW NE... With SFC temps progged to be in the upper 70s pushing 80, that creates a nearly 30 F TD depression....Yikes!!!!!!

Will be interesting to see what the 12z GFS has to say...

Not sure if we're looking at the same thing, but overall, the 12z NAM looks good for the TX Panhandle target, IMO. Moisture could certainly be better, but this run does show mid 50s DP's over that area (granted, more like low 50s farther north into KS) - hopefully that will improve as we approach the event. Aside from moisture, things look great with a 997 mb sfc low in W NE at 00z, temps in the low-mid 70s (not sure where you're seeing 80 anywhere along the dryline setup), and backed sfc winds with great directional and speed shear. Still looks like a nearly-ideal chase day is in store, with some good potential for tornadic supercells if moisture return is a bit better than progged.

 

[Jay McCoy]

I didn't know the elevation increased as you moved West. Thanks for filling me in Jay. I'm really not trying to screw with you Jay lol. I just had to throw that in. I have chased the caprock, western Kansas, and Colorado plenty of times and I am aware of the effect elevation has on convection. I'm just not banking on geography to make up for the lack of better moisture. I'm not sold on the idea of the dryline not mixing East due to saturated soil conditions either. Evapotranspiration can only do so much. I do agree that the GFS has been a little off on the dryline location on some earlier setups this season, so that is obviously something that will need to be considered.

The GFS is starting to pull the dryline further back west as I expected. The dryline hasnt mixed east yet this season and I dont expect it to this time. Even SPC has pulled the day4 outlook back west. I expect the dryline to be close to Amarillo on Saturday. I would love for it to mix east a bit and set up close to hwy 70 (pampa to clarendon). Some of our best events come when the dryline is close to the edge of the caprock.

I am not worried about you messing with me Michael. Its all good. I take it in stride that people look at models and think differently. Since you have chased this area you know it doesnt take monster DP's to get incredible storms. I am not expecting a 60+ tornado event. I never said it would be but I do expect a number of tornados in the east panhandle and west oklahoma. No moster HP's just some beautiful classic motherships dropping a few cones

The more pessimists we have the less chasers we will have which is great. Shane and I both hate traffic jams. But I bet even the naysayers will be out in full force this weekend with their tripods in the road . And Like Shane and Jason I like the smaller events just as much. 1 good rotating supercell is enough to keep me happy

 

[Mike Hollingshead]

The GFS is starting to pull the dryline further back west as I expected.

Is the new GFS run out somewhere? I don't see it yet(just coming in on ncep). It seems a lot of folks post mere minutes before new data is out and I never understand that. But looking at the 0z gfs it doesn't seem like it's moved all that far from past runs.

12z nam looks like A$$ for dews. I wonder if that is mostly "dew"(sorry lol) to those soundings right along the coast, just having the front pass over them. I wonder if it then doesn't account for how deep the moisture is just south of that(as it was pretty deep in the western gulf yesterday). That's all that gives me some(very little) hope for Saturday...hoping the model puts too much weight into the crap air now on those soundings in far south TX...and that it's not as bad as the NAM makes it appear. But I really have no idea how it handles all that. It seems there'd still be some good moisture down there in the western gulf, off shore.

 

[Donald Giuliano]

A quick glance at the 12Z NAM shows that the moisture concerns voiced by a number of other posters appear to be well-founded. The main problem with the moisture is, I think, related to a vort max rotating through the SE US coast Thursday night/Friday. Although the surface dewpoints in the Gulf don't show a huge effect from this, at 925mb dry air is advected into the northern Gulf, rounds the base of the ridge, and then advects (above the surface) up from the south into the Plains on Saturday and mixes out the modest moisture already present. In other words, we're not even getting neutral advection from the Gulf, we're getting dry air advection. Not what I want to see, and not what I was expecting, but perhaps should have. Further, I see no reason to doubt this solution, as it looks perfectly realistic, no matter how undesirable.

That said, even with the crappy moisture forecast by the NAM, there is still a large area of decent CAPE with no CIN, especially over NE/SD. The main problem is that because of the low dewpoints the LCLs over much of this area are also very high, and the best shear is forecast from southwest NE down through the TX panhandle, where the corridor of instability is narrower, as one would expect given the situation. Obviously this would limit the threat in both space and time.

In summary, things still look interesting as everything else remains in place, and I love the terrain out there; but it does indeed appear that moisture will be a limiting factor. Even though a wedgefest is looking doubtful, the lean moisture could lead to awesome LP/classic storm structure with high-contrast tubes, I think I can deal with that.

 

[Mikey Gribble]

I hate to make a frivolous post in here, but the "dewpoints look like A$$" comment was pretty funny and it does an excellent job of summing up the 12Z NAM. If the NAM holds true and moisture return is that bad, I would definitely be sitting this one out. As much as I love chasing, I'm just not going to drive 5 plus hours without a reasonable chance of tornadoes.
I haven't seen an update of the GFS on Rap, so I don't think it's updated.

 

[Donald Giuliano]

Is the new GFS run out somewhere? I don't see it yet(just coming in on ncep). It seems a lot of folks post mere minutes before new data is out and I never understand that. But looking at the 0z gfs it doesn't seem like it's moved all that far from past runs.

The status of all real-time NCEP model runs can be found here:

http://www.nco.ncep.noaa.gov/pmb/nwprod/prodstat/

 

[Karen Politte]

I hate to make a frivolous post in here, but the "dewpoints look like A$$" comment was pretty funny and it does an excellent job of summing up the 12Z NAM. If the NAM holds true and moisture return is that bad, I would definitely be sitting this one out. As much as I love chasing, I'm just not going to drive 5 plus hours without a reasonable chance of tornadoes.
I haven't seen an update of the GFS on Rap, so I don't think it's updated.

I've been biding my time watching most of the discussion evolve along with the models for this event, largely because I'm burned out on a lot of the discussion. At least I'm not burned out on forecasting LOL. But I'll keep plodding along I suppose. I like Michael's take on things, and I too was tickled enough by MikeH's funny on the A$$-points that I had to join in again.

The 12Z ETA is out today and I guess I'll play with it like it was actually a useful tool, although most of us know that the NAM went to lunch sometime a couple of years back and hasn't been seen since.

In pinpointing what's ailing with this upcoming system for Saturday 4/21, I think one has to look no further than the current surface map and put 2&2 together. A cold froPA took place across the south-cntrl/southeast US overnight and has dagged a front off the Gulf shore again - as has been progged by the models since the outset. Surface winds are northerly and have swept some modified wintry (alright - early springtime) air out into our moisture supply.

The associated ridge with the backside of this departing system causes Saturday's hopes some real grevious issues, the large HI having it's foot planted firmly in the Gulf all the way through the weekend assuring us not one ounce of true moisture to play with. I appreciate that many are hoping this event will unfold on higher terrain and compensate for the lack of instability and I also appreciate the respectable shear setup. As for evapotranspiration......yes a lot of the ground may be wet out there but I don't think that the atmosphere will be able to actually harness that to it's fullest potential. In my experience, I think that the time to really sit up and take note of evapotranspirational enhancement of the available mositure is in the humid, green months of late May, June and July when the cornfields are in overdrive. In mid-April in the high Plains I don't know how much we can rely on that.

It is feasible to expect T-Td depressions in the range of 20 degrees or so. This may provide some classic supercells and possibly some aesthetically pleasing LPs - which is all one should expect when chasing with limited moisture. As the sun sets, the atmosphere cools and LCLs lower I would imagine that any chaser's tornado potential would rise, assuming that you have a supercell ongoing and the convective mode has not been destroyed for the event by a cluster of multicells or an MCS/squall.

I can totally understand why those who can chase this event will chase - it is, after all, all about hope. This naysayer, however, will not be chasing due to many much more important engagements and the fact that a 10+ hr drive from central AR is simply not worth it. So my tripod is one you won't encounter out there this weekend. I will wait until May and am completely happy to do so. In the meantime I will be interested to watch this system develop from a comfortable armchair somewhere on Beale St. in downtown Memphis.

KL

 

[Skip Talbot]

I find it interesting that both GFS and WRF are plotting 60 degree dewpoints in South Dakota. Boths models are comparable in the strength of the surface low pressure at 997-998 mb over central Nebraska (but vary in placement). I guess this is contributing to good moisture convergence in these northern areas. SPC's day 4 has areas all the way to the North Dakota border highlighted, so they certainly think this event isn't limited to the southern plains. Winds will be better backed closer to the low's center and there will be better veering through the 850-500 levels in these areas as well. Areas south through the panhandles still look good for supercells despite the blow WRF dealt us with its moisture forecast, but I think those of us who aren't already in the southern plains should be considering Nebraska and even South Dakota for chase options on Saturday.

 

[Stan Rose]

. I will wait until May and am completely happy to do so. In the meantime I will be interested to watch this system develop from a comfortable armchair somewhere on Beale St. in downtown Memphis.
KL

yeah, that's what i said last year! Not this time. Don't know what will happen in May. Do know that Sat has a lot of potential, even if it's not a major tor outbreak. I'll be happy with the 60 dews or 58 dews or even 55 dews. Just another detail. I won't be surprised if the lousy moisture doesn't show, but a ridge over the gulf doesn't cause me any undue concern. 24 hours of limited return on friday looks fine to me. As Karen said, gotta be hopeful.

 

[Brian Emfinger]

Dewpoints may only be around 55 degrees but that will work for me. And we are so far out we could still end up having 60+ degree dewpoints. I think dewpoints around 55 degs will be sufficient however to at least have some nice structure (which is extremely sufficient for me at this point) and if the T-Td spreads come down a bit then we could be set for another NW Texas Outbreak. I imagine there will still be a ton of people out there Sat.. anyone going further north JUST because of the March 28th crowds?

 

[Jeff Snyder]

Just as a note, let's try to keep all posts about the 4/21/07 forecast. If you have commens, thoughts, or ideas about forecasts or chase ideologies in general, please use an appropriate Weather and Chasing thread.

 

[Matt Hines]

Looks to be a pretty good set-up here in the Texas Panhandle region on Saturday. Models continue to pull the upper level dynamics back further west with each run. Euro. has been the most consistant the past few days and now GFS seems to be trending that way as well. We will not have deep gulf flow, but dewpoints in the 50s seem like a good bet. That is definatly all we need in April up here at 3,600 ft. If this were late-May or June...I would not be too excited. Case in point, all the tornado events here in my area this year have been with dewpoints less than 60F. Looks like sheer will be very nice...(500mb) 210 at 50-55 kts....(700mb) 190 at 45-50 kts...(850mb) 170 at 35 kts. Again, still a few days out...but looking better with each run!

 

[matt patterson]

If you look at the OK mesonet there are widespread 50+ tds all over Ok with some upper 50s in southern OK... WIth a couple good days with southerly winds we should start to see the moisture increase. I think that if there was a problem it would be concerning the depth of the moisture as the 850mb is very dry, relatively speaking, and that seems to be what is causing the models to mix down that dry air... If it were anywhere else, i would be worried but its the caprock, its saturday in Mid April, and i want to see some storms, so thats my reasoning....
The next 48 hours will be interesting.