2015-06-03 EVENT: CO, KS, NE, WY

[Jeff House]

Wednesday should have more potential than Monday and Tuesday thanks to more upper level forcing and speed shear coming out over the High Plains. I would target the upslope area of northeast Colorado and adjacent areas.

Rather than struggling to get 40 knots of deep layer shear over the target area just in time, on Wednesday 50 to 60 knots of deep shear should be over the upslope target area before initiation. Farther east we are looking at a cold front type advance of the boundary in most of Nebraska, perhaps even into northeast Kansas if reinforced by morning and midday rain. Low level turning is good farther east, but the area may have a lot of ongoing rain and not a lot of upper level severe support. Cells initiating south of the boundary in western Kansas may struggle with warm mid-levels and/or not enough low level backing.

Meanwhile in northeast Colorado, northwest Kansas, southwest Nebraska, and perhaps into far southeast Wyoming upslope flow should establish by late afternoon. The backed surface/850 winds will be under a nice upper jet starting to poke out into the High Plains. The boundary might be a starting place for a target, especially if an OFB can intersect with the synoptic boundary. Cells just north of the boundary or OFB should have enough instability to work with as well. Appears that Tuesday night Nebraska rain will be long gone from the target area by midday Wednesday. Like most of this season it is far from classic, but a few good hoses may be found.

 

[Royce Sheibal]

On a day like today, I'm generally looking at two things: The SPC ensemble and the NAM 4k, with the SPC tending to be more conservative and slower, with the NAM 4k tending to be more progressive and faster.

If you listen to the SPC ensemble, North Platte down to McCook is going to be gravy today. SigTor ingredients are there, you get a little upslope and the SPC 3hr calibrated severe storm contour is at 15% (as high as it goes), which is often how I pick targets.

As for the NAM 4k, college of dupage has their sector target as Ogallala if that tells you anything. I'm expecting three areas of concern today. #1, the intersection of all these goodies around NP. I expect some messy but super-cellular storms possibly quickly forming an MCS in this area. Tornadoes are a good possibility, but expect things to go early. Area #2 is on the upslope in the plains outside of Boulder, CO. This area is pretty obvious, don't need to explain. Area #3 of concern is down the road in SE/SC Neb / NE KS.

In E Neb, we're looking at 3-4k MUcape, dewpoints in the 70 range possible, lots of outflows leftover from this morning, temps should rebound into the 80ish area. Shear is looking good, with 0-1 EHI in the 3 to 6!! range from Lincoln to Lexington, NE. Sadly before things get too far east they will likely go full blown MCS of DOOOOM, but some supercells could maintain on the tail or with a rogue out in front. Nam 4k maintains supercell worthy updraft helicity within the MCS until after dark, even. I feel that further south things will likely end up capped in KS, but you may get one or two chasable cells to pop near the border.

Normal NAM is a bit slower on the progression of shear, and keep the main bulk of the storms on the KS/NE border. GFS keeps things further southwest as well, and even gives W KS a chance for some supercells.

If I didn't have class tonight, I'd be targeting North Platte to GRI. Seems like the consensus until skies clear out. If we can get some decent heating behind the morning MCS, I wouldn't count out SC/SE Neb either.

 

[Ben Holcomb]

After looking at conditions this morning I've noted the following - OFB along I70 in Kansas from last nights convection, a 1008mb low that will be deepening in SW KS/E CO all day, extreme instability building especially along said OFB, mid level lapse rates of 8.5-9 over Kansas and Nebraska.

It seems like we will have upslope play as well, especially in WY. The HRRR seems to support that, and I expect there will easily be a tornado or 3 out there.

What I'm more interested/focused on is this OFB in KS. If it goes, it will go big, and the HRRR seems to support that. Also saw a very tiny picture of the hazwrf depicting a huge supercell near Hays, which seems to be plausible.

Some concerns: Hope things remain discrete on both targets. Especially the upslope one could become quite messy. Dewpoints aren't the greatest there but apparently you never need moisture anyway out there.

Obviously convective initiation is in question along the OFB. Not a lot of forcing, but anything that does develop will be robust and explosive it seems with MLCAPE values approaching 4000J/KG.

 

[Jeff Duda]

Whoooo, that is one strong cap building in across W KS/SE CO.

I see the 15Z RAP erodes the cap by mid afternoon, but I simply don't buy that. The amount of cooling it progs over just a few hours with only a weakly-convergent boundary...yeah I just don't buy it, especially since I noticed the RAP/HRRR doing the same thing last year - PBL mixing is too strong in the PBL scheme those models use (MYNN I believe).

Also it appears the morning convection-allowing models are over-forecasting the return of that OFB, suggesting it will tilt and lift north much more than is currently observed.

Current satellite imagery shows a well-defined gravity wave train trucking southward across KS. The actual surface OFB lags it pretty good since we're talking about trapped gravity waves at this point, but there is an awful amount of low level cloudiness over far W KS and much of E CO. I'm sure that will burn off throughout the afternoon, but it will limit destabilization somewhat.

I think the best play is along the traditional areas of the DCVZ and Cheyenne Ridge areas across NC/NE CO and SE WY. Those areas are pretty clear right now with dewpoints in the low-mid 50s. At that elevation, that's enough to get stuff going (surface dewpoints near the Goshen County, WY tornado on 5 June 2009 were in the mid 50s). There isn't exactly a strong upslope component near the foothills, but there is a good component along the I-70 corridor. Not sure how long that will persist, though.

 

[Caleb Grunzke]

I'm currently stationed in Kearney, NE with PECAN. Been nice and sunny all day and temps have risen to 80. Surface winds are light but easterly. I'm hoping that supercells initiate somewhere near me like the 4kmNAM is advertising but, I'll take what the HRRR is saying also with the MCS in the late evening hours. Just want some storms please.

 

[Royce Sheibal]

I'm currently stationed in Kearney, NE with PECAN. Been nice and sunny all day and temps have risen to 80. Surface winds are light but easterly. I'm hoping that supercells initiate somewhere near me like the 4kmNAM is advertising but, I'll take what the HRRR is saying also with the MCS in the late evening hours. Just want some storms please.

Caleb, it seems, based on surface obs and hi-res sat, you may have a boundary just to your south, and storms are starting to fire backwards from NE KS toward SC Neb. It may be a bit early to jump the gun, but I'd head south toward Red Cloud or SE toward Hebron for a better shot. Then again, there may also be a jet streaking right over your head based on sat data, and a couple of associated blips on the radar, so it's a tough call. I tend to favor the area just to your south and east, personal preference.