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

[SteveCarter]

How about waiting until Thursday night to worry about DP's and moisture? This is STILL way to early to plan, or NOT plan to chase this weekend. This is what happens when these threads are started this early. MODS...why not limit a FCST to a MAXIMUM of 4 days out? You can always post in the weather and chasing forum further out when there is not a difinitive time OR area, such as this was when the thread was started. And for the record.....because of the distance, I'll probably wait until the second event occurs next week. I can't chase for 7 straight days, even tho I'd like to! I guess there will be an immense fine-tuning process taking place Thursday and Friday. having said all this...I think the moisture WILL be ok, but...to far away to really know.

 

[Kenny Drake]

There's also some question about climatological bias toward the moister eastern areas where a larger % of tornadoes are rated F2+.

Rich T.

Good find, however could the higher population density in the eastern areas versus the western areas have something to do with the ratings?

Okay back to topic. I think this far out the best thing to look at is model consistency. Doing some quick comparisons vs the previous run (this website isn't tell me what the initialization time is, so I'm going to guess 00Z vs 18Z) the GFS has stayed almost exact in location of the 500mb wave at 00Z Sunday. Amplitude is also very similar however the new run is hinting at a slightly farther north (maybe about 50-80 mile difference in isobaric locations). Now to compare against the ECMWF I picked the 12Z Sat timeframe. This is where the major difference comes in, however as said these models are probably at different initialization times. The ECMWF still has the 500mb trough axis over the CA/Nevada/Arizona region while the GFS has the 500mb trough already ejected into the plains with the axis over the TX/OK panhandle. It appears the ECMWF kicks the trough out fairly rapidly and catches up with the GFS by 12Z Sunday. This of course has major implications, therefore its quite obvious why the SPC has not been able to pinpoint a closer local. This seems quite similar to the March 28th event, in which case we could possibily see a mirror event in terms of location. However, with the timing differences I'm merily just pondering the possibilities.

 

[Jim Tang]

This is really not a March 28 event. March 28 was associated with a deep closed 500mb low with extremely steep lapse rates and was neutral-positively tilted. This open trough is negatively tilted and will zip on out of here. Overall I'm not very enthusiastic; boundary layer moisture doesn't look too good. Now if the dryline does not mix east as quickly, which could happen if one goes by the pattern of this year, and the fact that the ground is fairly wet, the dewpoint depressions probably won't be as big as a problem. But if we look at Mar 28, we notice that that system was in the process of cutting off. This is not; many times models will prog deep systems too fast, but I've also noticed they can also prog mobile shortwaves too slowly. Another concern is how strongly the winds back. On Mar 28 they were extremely backed, but not in this case, especially if the sfc low is too far north/east. Given southerly 500mb winds, we'll need backing winds to keep those hodographs curved like they were on Mar 28. Finally, with the trough negatively tilted, the strong forcing will be right over the warm sector, and there is a chance that everything could line up very quickly. On Mar 28, the best forcing was lagging behind the warm sector which helped things remain discrete for a while.

 

[Gerard Jebaily]

When the wave first started showing up on the 180hr frame of the GFS, its looked much more impressive than it does now. I think that we may have a decent setup given the current model outputs. But the overall strength of this system is forecast to be much weaker than what was first anticipated. I do agree that moisture wont be a problem. But attm, I'm not betting this will be something significant. However, alot can change in the next 5 days.

 

[Jason Boggs]

I think some of us (including myself) try to get too technical this far out, and fail to look at the big picture. Let's look at right now. Moisture in deep south TX is in the mid 60's right now so the gulf is wide open for Saturday. Right now, no cold fronts are forecasted to scour out the moisture, so higher Td should keep making their way northward, especially as the trough gets closer. Td in the upper 50's will be adequate in the warm sector on Saturday. Speed and directional shear appear to be good enough to produce rotating updrafts. Obviously this far out, many things can change, but it does look like a rather interesting day on Saturday.

NOW JUST FOR FUN:
TARGET AREA IS PAMPA,TX

 

[Wesley Luginbyhl]

After some shifting in the models again, I am beginning to lean towards Saturday to having the best potential out of the up coming system. It will take a major change in the models to get me not to chase this day. There are just too many ingredients looking to show up for this storm not to atleast go for a little Saturday drive to the panhandles. The forecast soundings have been looking pretty good over the past few days. Storm motions seem to be slowing down a little from where they were a few days ago. Maybe in a few more days the models will start to give a clearer idea about what will happen. One thing I like however is that the GFS has been pretty consistant with almost SE winds ahead of the dryline for a few days now. I am prolly more curious than anything else just to see how my Alltel service is through the eastern panhandles and western OK region.

 

[Ray Walker]

I really dont know why anyone would not like this setup. It is going to produce tornadoes, an outbreak? well probably not but who knows. I think dewpoints will average 62 to possibly 65 degrees. I think instability will be in the 2000 +jkg range and wind profiles will be pretty darn good. I think we are looking at a good chase day, not a massive tornado outbreak day.

 

[Jim Bishop]

Every year the moisture argument comes up on this forum. For this particular setup the moisture should be fine. We are looking at mid to possibly upper 50s dewpoints in the high plains of Nebraska, Kansas and Texas. With 500mb temperatures forecast to be between -16C to -18C (possibly as cold as -20C), a 55F dewpoint should be adequate. Although I agree the quality of moisture could be better since we'll be mixing from the Southeast U.S.

To be honest I'm a little concerned the 500mb flow will be too backed and the storm motion will end up being nearly parallel to the dryline (north-northeast). This would promote linear storms of course. This concern is based on the 00z 4/18 GFS. But, this event is still 4 days away, so I'm sure the tilt of the trough will change a bit. In any case the shear supports supercells.

 

[Shane Adams]

Sorry to post slightly off-topic, but the subject has ben brought up. Regarding the moisture thing, it's important to realize it doesn't have to be an outbreak to be chaseable....in fact most of the best days aren't "huge" days at all. I think a lot of the anxiety comes from the fact it's a mental letdown when the scenario goes from Armageddon to just "average".

But average is gooood I think Sat will be just fine.

 

[Mikey Gribble]

It's not that I don't like this setup. It is a synoptically evident severe weather event, but unless dewpoints are >60 then I really don't think this going to be a major tornado event. On 3/28, dewpoints were well into the 60's. You had a 64 degree dewpoint in DDC at 00Z. I would be very suprised if this event ended up being comparable (tornado wise) to 3/28, unless you get dewpoints in the 60's.
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.
Don't get me wrong about this setup. I do think it has a lot going for it and I do believe it is a solid bet that this will be a major severe weather event, it is just the tornado potential that I am skeptical about. I haven't looked at anything closely yet, but I am planning on starting up my forecasting for this event today once the NAM picks it up.

 

[Billy Griffin]

Yesterday's rain event certainly won't hurt, albiet this is very shallow moisture near the surface. But with trajectories good the next couple of days, including today, evapotranspiration will aid in good return flow. Frankly, I don't see what the problem is regarding moisture. Most of Oklahoma is seeing ~ 50TDs and with 100% ground saturation. I can honestly see ~65 TDs near the OK/TX panhandle border by Saturday afternoon/evening.

To reinforce some positive thought, just take a look at WV imagery over the western US and especially the Gulf of Alaska. When I started this thread, I was excited in what I was seeing evolve up here in the Pacific NW. Last night, we had a good convective event for even here in Seattle. The trough continues to dig and looks like a solid pattern is setting in for the next series of systems, starting with this one progged for Saturday!

I guess, for once, I'm just being overly-optimistic. I see this being a very good day. No, not likely to have tornadic cells lined up from Texas to South Dakota, but I find this one more of classic dryline day.

Heck, at least one thing, we're not debating over how far east into the hills / trees we'll be chasing this one! (KOW)

 

[Brian Stertz]

Absolutely...Shane's right on the money...it's a dryline event and in a great viz chase area on a weekend. How much better can you get?? The morning DDC forecast discussion was some great reading...and Amarillo forecast discussion is also pretty charged up.

 

[Billy Griffin]

"Virtual" forecast as of now... MDT risk for much of SW Kansas, TX and OK panhandles and far western OK. By mid-afternoon Saturday, surface low intiates convection over the high plains of E Colorado, NW Kansas and parts of SW Nebraska. Potential will exist for low-topped cells and cold-core tornadoes along the WF in this area. Cold rain / snow over much of Wyoming and the Dakotas.

Farther south, along the dryline, initiation will hold off until late afternoon (3-5pm). As the jet interacts with the dryline, several isolated sups will erupt along the dryline corridor from near Liberal, KS south to near Claude, TX. 3-4 isolated supercells form up for a classic dryline chase! These storms will all have the potential to become long-lived supercells, capable of very large hail and a few tornadoes. The tornado threat will continue after dark, before the mess all congeals into a MCS over central KS & OK.

My target as of now = get an EARLY start on the day and arrive by 12 noon at good ol' McLean, TX. Wait for initiation along dryline, then adjust from there.

 

[Mark Farnik]

Depending on how busy I am and how I feel, I may chase the potential cold core event over eastern CO/southwestern NE/northwest KS. Unfortunately I'm going to have to sit out the southern target this time. I wouldn't be able to get down there in time, anyway, even if I really wanted to chase, as I'll be in Co. Springs tonight, Thursday and most of Friday. Our Fort Morgan HS Knowledge Bowl A Team (which I'm a member of) qualified for the CHSAA State Knowledge Bowl Tournament which they're holding at Colorado College. I won't be back from the tournament until late Friday evening.
So I'll take a look at the models then and again Saturday morning, as well as see what the SPC forecast and BOU/LBX/GLD's take on the setup are before I make up my mind. My preliminary target would be Holyoke, CO, which is only an hour and a half drive east of me, so it would be a relatively backyard chase. I'm in definite 'wait and see' mode on this one. But if it looks like anything less than surefire cold core 'naders, I won't chase it and save my gas money to chase the better setups once we get into May, which I just realized is only a week and a half away!
My college semester ends May 8th, and after that I won't have ANYTHING going till the very last week of May, so I'll pretty much be able to chase whenever I want from May 8th to May 26th... I'm sooo excited!

 

[matt patterson]

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...