2013-06-19 FCST: CO, NE, KS, OK

[Marcus Diaz]

We're still a few days away but thought I'd start a thread as I'm licking my chops on this one. I'm sure everyone else has been keeping tabs on it as well. My forecast is based strictly on the GFS, but its been very consistent the past 2 or 3 days on this setup. In response to the upper level low coming on shore in the Pac West, surface cyclogenisis ramps up in the northern frontrange up in MT and WY with a deepening surface low. With the ridge breaking down and shifting to the east coast, that should aid in transporting very good moisture through the central Plains in conjunction with the surface low. Mid 60 to near 70 dews look realistic from Oklahoma up through NE. Winds from the H5 to H2 look acceptable with generally a westerly flow of 25-40 kts. What I really like is how the GFS has been showing a nice impulse in the 700s coming out of southern CO through SW KS/NW OK/eastern panhandles area. If this holds up then wherever that impulse lands should aid in mid level flow for any storms developing. A dryline buldge looks likely in SW KS/OK panhandle (maybe the dryer air from that impulse?) which could provide the focus for some classic dryline supercells. Capping seems to be the main fly in the ointment, especially the further north you go. But if anything can fire on the dryline, it'll have not just the good bulk shear to work with, but also a very unstable 3000-4000 j/kg SBCAPE environment. I might have to play hookie from work for this one!

 

[Chris Wilburn]

I haven't noticed this day, but looked after you pointed it out. It does appear to have some pretty good things going for it. The NAM will pick up on this at 12z so we will have that to compare t the GFS. The SW KS/OK panhandle/NW OK region sticks out to me at this time. Dews in the upper 60s-70 with CAPE well in the 3,000-4,000 range will create a very unstable environment. The deep surface low you mentioned brings a dry line into far western SD down through the OK panhandle. The reason I like the target area I mentioned is the slightly better 850mb winds, but that might be too detailed this far out. Sounding for Medicine Lodge valid 00z 6/20 looks very nice! 0-1 SRH over 200 and 0-3 SRH over 450. Nice looping hodograph as well. 500mb winds in the 30-40kt range is more than enough with excellent directional shear, dews, and instability. Supercell percent 97% and CAPE over 4,000. Also, storm speed only 19kts. I will take that! Anyway, just my thoughts. Hopefully the NAM is on board here in about 6 hours or so, but the GFS sure looks good as of now. 700mb temps. in the 12-15C range may keep just enough CAP in place, but with tons of moisture and instability it can be overcome. Just east of the target area it drops down to the 10-12C range. Could be a nice day with a couple very slow moving tornadic supercells in less populated areas.

 

[Marcus Diaz]

The NAM is agreeing for the most part about this setup (I'm just as surprised as you!) The NAM is even showing some stronger 500s across western KS down into OK. It's also pulling the dryline further west with mid 60 dews reaching the NE/KS/CO border triple point. Ample shear looks to be in place in KS/OK along with 2,500-3,500 j/kg SBCAPE. Even though the dryline is further west, it appears as though a surface boundary will sit from DDC - DFW throughout the day. This appears to be a focal point for initiation as the cap will erode thanks to daytime heating. Forecasted soundings show great turning with height which translates to some large clockwise curved hodographs. Any storm that should fire in the moist sector should be supercellular with LCLs favoring tornadoes east of the boundary.

 

[Adam Adkins]

12 NAM reduces the cap a little more. Thank goodness. But it is still a big if. If something develops it will rotate. I assume there will be one single cell that will be able to develop in far NE Colorado and move east. Maybe 12 GFS will trend with the NAM to reduce CIN.

 

[Skip Talbot]

On the past couple runs of the NAM, the lid strength index plots actually show the cap strengthening as the day progresses. It looks like warmer temps aloft are nosing in from the west, with 15C 700mb temps trying to make it western KS by evening. The cap does look fairly open earlier in the day however, from late morning through early afternoon. With the moisture already in place and some upslope flow you may get early storm initiation anywhere along the higher elevations from NE CO down through the panhandles. Veering wind profiles, decent 3km helicity and 6km shear down the dryline that increases through the afternoon look to support some supercells, before they gust out into messy clusters due to the lack of upper air support and inverted V forecast soundings. Stout, increasing LSI's and lack of low level instability as plotted on recent NAM runs may preclude much of a tornado threat though. Perhaps there is a spout play when storms go up in the early afternoon when lapse rates are super steep and if there is a boundary hiding in there somewhere near the dryline. Might at least be a good structure day if you're already in the area.

 

[Chris Wilburn]

On the past couple runs of the NAM, the lid strength index plots actually show the cap strengthening as the day progresses. It looks like warmer temps aloft are nosing in from the west, with 15C 700mb temps trying to make it western KS by evening. The cap does look fairly open earlier in the day however, from late morning through early afternoon. With the moisture already in place and some upslope flow you may get early storm initiation anywhere along the higher elevations from NE CO down through the panhandles. Veering wind profiles, decent 3km helicity and 6km shear down the dryline that increases through the afternoon look to support some supercells, before they gust out into messy clusters due to the lack of upper air support and inverted V forecast soundings. Stout, increasing LSI's and lack of low level instability as plotted on recent NAM runs may preclude much of a tornado threat though. Perhaps there is a spout play when storms go up in the early afternoon when lapse rates are super steep and if there is a boundary hiding in there somewhere near the dryline. Might at least be a good structure day if you're already in the area.

It looked good for a few runs, but then went south. Dews are mixing out along the dry line as well which is creating higher LCL heights. It was showing a nice setup over SW KS, but kept shifting further west. Of course, upper level support was marginal anyway. Oh well, I was hoping to get one more chase in, but it looks like the year is mostly over, which I figured anyway for the most part after May 31st. I was holding out hope for a couple of those mid to late June days up north, but it looks like high pressure is going to set in pretty stout for the plains later this week. Maybe something will be chaseable in the Dakotas but who knows.