5/5/07 FCST: NE/KS/OK/TX

[Jim Bishop]

With the GFS & European showing both good agreement and consistency, I thought it's about time to make a forecast thread for Saturday, May 5th.

Getting straight to the point this looks like a big severe event over Western Nebraska, Western Kansas extending as far south as the Texas & Oklahoma Panhandles in a more isolated terms. Western Nebraska and Kansas could see numerous supercells capable of tornadoes, some strong.

The GFS ejects the first in a series of shortwave troughs into the Rockies and develops a surface low in Eastern Colorado with a dryline from Western Nebraska down into the Texas Panhandle. With dewpoints generally in the 60s CAPE values are forecast to be in the 2000 - 3000 j/kg range. Shear looks very impressive, supportive of tornadic supercells. In fact with the southeast 850mb flow around 35-40 knots, coupled with moderate to potentially strong instability, I'd imediately be concerned about several tornadic supercells over Western Nebraska & Western Kansas, some producing strong tornadoes.

This all hinges upon the GFS & European solutions verifying, of course. For what it's worth their respective Ensemble means have been supportive of this event for days.

 

[Chris Wilburn]

Of course this all depends on the models like you said, but I really like the nw Kansas/sw Nebraska area at this point. This is where the better 500mb flow is located both from a speed and directional point of view. Moisture will be plenty with low 60 td's likely, CAPE around 2,000 J/kg, and wind fields that look very impressive. The reason I like the area I mentioned is the 500mb flow looks much better up there. Still early but will be interesting to watch as SPC has it on their 4-8 day outlook. Also, Friday looks interesting as well and in just about the same place and with just about the same intagibles as Saturday, but that is for another thread. Will be interesting to see if the models continue to handle bringing the trough in the forecasted area on Friday and Saturday. Moisture and CAPE will be there regardless, but with a nice surface low and low/mid level flow it could be a really interesting day on Saturday.

 

[Joshua Jones]

NW KS will be my target, I will probably be targetting around Colby to kind of base out off, we shall see though, still a few more days of planning.

Josh KI4LZK

 

[Matt Hines]

All of the High Plains is looking interesting on Saturday, and possibly for the next couple of days to follow. The cap will be a little stronger down my way, and that may make it better for chasing since supercells would be more on the scattered side. Wind fields look impressive and moisture should not be a problem (usually never is here in May and June and has not been a problem so far this year). As stated earlier, it could be an extended stay for some folks as Sunday and Monday look to have potential as well. Still a bit far out, but based on the season here so far, it looks like another potential big
day(s)!

 

[Brian Stertz]

Update based on 12z ETA

The biggest severe wx day of all will be Saturday's event during what appears to be a string of possible chases. The 12z ETA was showing a nice focus on the warm front across C/NC Kansas and possibly into SC Nebraska by evening. The parameters all point to some significant severe wx and certainly tornadic supercells. The main question lies with surface inflow. The ETA forecast was showing moderate sfc inflow. However, the actual inflow may be enhanced by the strong storm updrafts, so do not feel this will be a limiting factor. The potential is certainly there for strong tornadoes as Jim has mentioned...and given the good 0-3km SRH and strong CAPE combo, this may have the potential for significant tornadoes EF-3 +. Certainly will be something to monitor closely as the models hone into finer details on later runs. Definitely appears to be a green light go for chasing Saturday.

 

[Jim Bishop]

I don't like the latest GFS solution. It shows a weak cool front sliding south over Western Nebraska and Northwest Kansas early on Saturday. No longer will there be a dryline but a treatreating front/warm front over Northern Kansas/Nebraska Saturday afternoon/evening. Having said that it doesn't appear there will be much movement of the front until early in the evening, and it will be oriented north-northeast/south-southwest. So, convection can still fire along that boundary and, given the likely shear vector being northeast, storms should be able to quickly move away from the boundary.

So I still favor discrete storms over Northwest/North Central Kasnas/South Central Nebraska despite the absense of a dryline. Given the strong shear still forecast by the GFS and likely 2500 - 3500j/kg CAPE, I still say numerous tornadic supercells are likely, some strong tornadoes. This could end up being a huge event for Eastern Nebraska/Northern Kansas.

 

[Brandon Sullivan]

Right now I like the Central Kansas Area.. Just an overall good combination of all parameters.. I will likely leave on Saturday afternoon as I have commitments until then.. Then chase it home on sunday.. Nice 3500 + CAPE with -9 LI and 70 degree dp's.. Shear Values pretty impressive with both speed and directional shear in good supply. Will be interesting to watch how it pans out

 

[Van DeWald]

Definitely north central Kansas will be the target, likely between Salina and Hill City. 30-40kts of 0-1km shear, very favorable LCLs below 1000m 0-1km EHI of 8, CAPE off the charts so much so that you could take a bath in it. Definitely looks like very active day. Am beginning to think the SPC day 3 outlook might be too far west.

 

[Jim Bishop]

Am beginning to think the SPC day 3 outlook might be too far west.

The current SPC day 3 Outlook is for Friday, May 4 not Saturday, May 5. But I wonder why they don't mention Saturday's threat in their 4-8 day outlook. I suppose it's not too important either way, as it will likey be in their 3 day outlook tomorrow.

 

[afischer]

Van, are you referring to Saturday (5/5)? If so, that'd still fall under the SPC Day 4-8 outlook. (I've made the same mistake, especially late in the day when looking 3 days ahead). Regardless, I agree with your thoughts, and am not finding many reasons why a couple of tornadic supercells should not occur on Saturday across portions of northern KS and southern NE. The GFS solution looks a little more believable to me (especially given its track record this far out with similar events of the past 2 months); it's not quite as strong/progressive with the shortwave energy ejecting into the northern high plains on Friday, and thus doesn't sling the associated surface front so far south and east. The GFS triple point and dryline positions on Saturday are thus a tad farther north and west respectively, beneath stronger high-level flow/deep layer shear. Looks good to me. In addition to the general set-up looking darn good for stormchasers, I also agree that we could have the strongest potential instability thus far this spring gathering over the central plains on Saturday due to steepening lapse rates atop rich boundary layer moisture... certainly won't hurt tornado potential any. It must be early May!!

 

[Van DeWald]

Oops, yes, I had my SPC outlook days mixed up. Current day 3 is only through 12Z Saturday.

 

[Mikey Gribble]

I agree that this is looking like the best instability we have had yet this year. Way to early to zoom in on a target, but as things look right now I would focus in on Hays and just SE of there for storm initiation (depending upon where exactly everything sets up). Everything looks good for a couple tornadic supercells across central and northern Kansas. Deep layer shear AOA50kts once you get North of central Kansas and high CAPE has supercells written all over. I am worried about cloud cover over the target area, but there is a mid-level dry slot that punches into northern Kansas in the afternoon.
It seems like one of the easiest forecasts this season as far as picking a target goes. Get just South of where the temperature contours start to cross back over the dry line in North central Kansas and wait for storms to fire. I will be watching for the tail end storm. I think any of the storms that go up in that Hays and just SE of there area and have unimpeded inflow will probably go tornadic as they track NE into the backed low-level flow.
There might be an outflow boundary across south central Kansas to watch too.

 

[BrandonWhittington]

As of right now, and looking at how everything will set up, I do think that I will focus all of my attention on the Dryline in the TX and OK Panhandles. The way this year has been going, models have been having a difficult time placing the dryline. Cloud cover up north is my biggest concern. Clouds should erode along the dryline and allow for Instablity to climb like no other. Some models are even suggesting Dew Points to be approaching 70 degrees, making CAPE values close to 4000 along and just east of the dryline. I think that models are pushing the dryline a bit too far east. I would expect the dryline to evolve along the NM and TX Panhandle Border, due the amount of rain we have gotten down here. This looks to be one of those situations that I will want the cap to be a little strong. Premature ignition looks to be a great possibilty. So overall, I will focus more on the dryline in hopes to catch that one lone moster supercell.........

 

[Jim Tang]

IMO this looks most like a SD/NE threat. Areas further south will be locked in an area of shortwave ridging which will reduce lift in an already pretty capped atmosphere. Further to the north the cap is weaker, the forcing is stronger, and a shortwave trough is moving through the area.

 

[Matthew Crowther]

IMO this looks most like a SD/NE threat. Areas further south will be locked in an area of shortwave ridging which will reduce lift in an already pretty capped atmosphere. Further to the north the cap is weaker, the forcing is stronger, and a shortwave trough is moving through the area.

If you buy the NAM, then yes. However, I do not buy it. The GFS and ECMWF show more of a surface low in extreme eastern CO with sufficient height falls and vort lobes rotating into the Plains to result in CI over KS before 00Z and probably all the way down the dryline. I expect a large area of tornadic supercells on Saturday. Right now the (preliminary) best area looks to be from SC Nebraska near Holdredge to Russell to Medicine Lodge to Gage.