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

[Craig Maire II]

On 03/28/07 DPs were in the mid to upper 50s in southwest Nebraska and I had an EXCELLENT chase! Saw one large cone tornado and had a large and powerful tornado just miss the town I was in (Grant Nebraska). So I'm not worried about the DPs for Saturday esp. with a strong dryline, plenty of windshear, instability etc. in place. All it takes is ONE good supercell to make for an excellent chase

 

[Joey Ketcham]

I don't think moisture will be a problem at all, I think if things pan out we could see some supercells and tornadoes. I wouldn't mind camping out along the dryline, but have to see how things pan out.

 

[Michael O'Keeffe]

I agree with everyone about the former moisture concerns. If I remember correctly on February 28 the tds were in the mid-upper 50s! I think that we will see at least some nice classic dryline supercells with tornadoes across the High Plains from W NE into the TX pan and W OK with the amount of instability across this area. Though not extreme enough to produce a huge outbreak like we saw on March 28th I still think we may see a handful of decent tornadoes with maybe 1 or 2 that are pretty strong. All I can say is I'm chasing this setup...I'm keeping my fingers crossed!

 

[Robert Edmonds]

I'm going to wait before I start having concerns about moisture with Sat. since it is still a little ways out. Most of the moisture from what I see shouldn't start its way up for atleast a day or two. With that note I do plan on chasing this day unless this day really falls apart. So far though from watching the forecasts from day to day it seems northern OK, KS, and southern NE will atleast be seeing something this day. However, I'm going to wait before I start narrowing my target.

 

[Mikey Gribble]

I am worried about moisture. You have great dynamics with this system, but t-td are around 20 degrees. That is definitely doable for tornadoes, but I like to see a little less of a spread in the Kansas-Oklahoma area where the mid-level jet streak crosses the LLJ (and you get the best 850-500mb crossover). It definitely looks like a good severe weather day, but I wouldn't go as far as to call it a tornado outbreak yet. Dewpoints in the upper 50's are far from ideal.

 

[Jay McCoy]

I am worried about moisture. You have great dynamics with this system, but t-td are around 20 degrees. That is definitely doable for tornadoes, but I like to see a little less of a spread in the Kansas-Oklahoma area where the mid-level jet streak crosses the LLJ (and you get the best 850-500mb crossover). It definitely looks like a good severe weather day, but I wouldn't go as far as to call it a tornado outbreak yet. Dewpoints in the upper 50's are far from ideal.

Temps will be in upper 70's and DP's in the low/mid 60's is 15 degrees or less. Not bad for the panhandle or west oklahoma by any means. If the triplepoint is trully in this area then I dont see many issues to a good event.

 

[Michael P. Morris]

Looks to me like there are two potential regions for this event. The northern target in Nebraska will be closer to the 850 mb/surface low, so the forcing will certainly be strong. Also looks like there may be some ongoing warm advection type precipitation at the start of the period, which could limit destabilization. Shear will be more than adequate if a storm is able to develop, but the moisture and hence the instability appear to me more limited. It's also too far for me to drive, so maybe that explains a little bit of my pessimism.

I think another area of concern lies along the Oklahoma/Kansas border, roughly in a Pratt-Alva-Woodward triangle, perhaps extending as far west as Dodge City. Here the instability looks higher and the presence of the stronger upper level jet will allow storms to sufficiently vent, perhaps favoring more classic-LP structures. Strong low level shear and mid level flow appear more than adequate for strongly rotating storms, and a subtle surface low will only act to further enhance the low level shear. Again, my main concern here is that the instability still may not be great enough to realize the intense shear that is being forecast for the area, but the GFS apparently thinks that storms will develop in the region, as evidenced by the vertical velocity fields.

Hopefully once this event is in the WRF's time window we can get some more details, but for those who worry about the moisture (including myself) just remember that the March 28th event was able to make do with only upper 50's!

 

[Ray Walker]

Well I dont see northern Oklahoma as having the best shot. I dont know if you all are talking about Monday of next week or not but shurly not saturday. This setup screams Western portions of Oklahoma and east Texas panhandle. Maybe I'm just missing something.

 

[Skip Talbot]

Well I dont see northern Oklahoma as having the best shot. I dont know if you all are talking about Monday of next week or not but shurly not saturday. This setup screams Western portions of Oklahoma and east Texas panhandle. Maybe I'm just missing something.

Well, the GFS has favorable shear across most of the dryline. As the jet noses in, storms may fire first up by the KS/NE border as the shear arrives here first, and then areas to the south should quickly follow. Much of the dryline may light up... like March 28. The GFS is still holding consistent at putting 1500 J/Kg from the NE/KS border down to western OK. With all areas in between seeing ample speed shear, and backed surface winds, you probably have a plethora of options to choose from. Earlier initiation up north might be favorable (if the dew make it that far) it terms of observing during daylight hours. Although instability may be hindered in NE from the morning junk. Down south in the panhandles, you'll have the bulk of the 500mb jet at 0z, but you might have a later show and the T/Td spread might be higher.

 

[Mikey Gribble]

I don't know what model you're going off of Jay, but the 12Z run of the GFS has dewpoints in the mid to upper 50's on Saturday.
http://www.rap.ucar.edu/weather/model/gfs108hr_sfc_dewp.gif
20 degree t-td are still doable, but that's pushing the limits for tornadoes.

 

[Shane Adams]

Well no one thought there would be tornadoes today either and low and behold.....nowadays nothing's taboo. My only concern for the next system approaching is will I see the tornadoes or not.

FWIW, my avatar occurred in 77/57

 

[Billy Griffin]

I didn't mean to create a controversy or argument in this or other closely-related threads regarding the forecast for this weekend, all I wanted to do was start the discussion on the "potential" upcoming weekend event.

To be quite honest, I don't put much faith in the models until 24-36 hours out. What I was really impressed with (and still am) is the familiar pattern off the west coast and into the Gulf of Alaska. I've studied these patterns over the past couple of years since moving here (Seattle area), and this pattern has me very impressed with what could happen here (Oklahoma and Plains) for the period of Friday through early next week.

To stay on topic with the forecast for 4/21/07, I still see a very impressive system and the potential for a great chase day! Seeing as it's the weekend, and I'll be back in OKC, I'm looking VERY forward to my first Plains chase in almost 15 months! Pattern looks good, moisture won't be an issue, great dynamics, models supportive... I can't wait 'til this weekend!

 

[Joey Ketcham]

Well no one thought there would be tornadoes today either and low and behold.....nowadays nothing's taboo. My only concern for the next system approaching is will I see the tornadoes or not.

February 23rd comes to mind too, many people said "ohhh nothing will happen", and the few of us that did choose to chase ended up seeing a tornado outside McLean Texas.

 

[Jay McCoy]

I don't know what model you're going off of Jay, but the 12Z run of the GFS has dewpoints in the mid to upper 50's on Saturday.
http://www.rap.ucar.edu/weather/model/gfs108hr_sfc_dewp.gif
20 degree t-td are still doable, but that's pushing the limits for tornadoes.

For 1 the morning run of the GFS is historically bad. Also the GFS has underdone Td's the whole year. Look at the Euopean. It has handled the systems this year much better and seems to be right on with this one including pulling the dryline furher back west. The GFS has been trying to push the dryline east all year but every event from Clovis to 3-28 to last week the dryline was on the Tx/NM border. The ground in this area is almost saturated 8 inches deep. We are well ahead of our average rainfall so mixing wont be much of an issue at all.

And like theses other guys have pointed out. even 50's have produced big days here. This is the High Plains!! elevation and the caprock itself changes the way you have to think. If we were forcasting for I35 or central Kansas then I would worry but not around here. Like Shane said.. We had Td's in the low 40s and we had tornados near LBB. Only landspouts but still had them. Thats why I have loved chasing this area for over 2 decades now.

 

[Rich Thompson]

I'm not trying to hijack this thread, but the dewpoint depression/LCL concern is worth a few comments. It's true that relatively low cloud bases (small T-Td, low LCL) have been associated with significant tornadoes, and there aren't too many serious supercellular tornadoes documented with LCL heights above 1750-2000 m. Still, that doesn't mean that no tornadoes can occur with higher T-Td spreads.

We think the LCL is related to tornadogenesis through it's impact on residual buoyancy in the RFD. How this downdraft with substantial buoyancy comes about has not been completely explained, so I'd be careful getting too literal with the application of this stuff in tornado forecasting. I'm comfortable saying that a major tornado cluster/outbreak is unlikely with large dewpoint depressions, but I don't start trying to rule out mesocyclonic tornadoes until we exceed 25-30 F. There's also some question about climatological bias toward the moister eastern areas where a larger % of tornadoes are rated F2+.

Rich T.