2012-05-27 FCST: KS/NE/IA/SD/MN

[brice.coffer]

Over the next 24-48hrs, a shortwave trough will begin to dig and eject eastward towards the Northern Plains. The ECMWF has been very consistent over the past several days, so my confidence in this setup is pretty high. The southern vorticity lobes in KS/NE look the most interesting to me. Between 18Z and 00Z, the surface winds back and the dryline sharpens in response to a deepening surface low in W KS. A pretty stout cap is in place over the warm sector on Sunday, however the ECMWF has been consistently breaking out precip by mid to late afternoon in an environment of 80F+/60F+ with moderate instability and 35+kts of bulk shear. The UL support is NW of this instability axis, creating a difluent region favorable for cap erosion and thunderstorm development.

My main concern right now is moisture quality/depth and the effect that will have on LCLs. The tornado threat might be marginal because of high LCLs. Also, forecast soundings from the NAM are not as veered as the ECMWF. Nevertheless, isolated thunderstorms, most likely supercellular, are probable by late afternoon before evolving into QLCS as more UL forcing arrives later in the night. I hope to have time to look at the morning NAM later this afternoon .

 

[brice.coffer]

36hrs later, everything seems to still be on track. Surface low that develops in W KS looks to be the best play. The cap won't be nearly as strong as the previous two days. Forcing will also be greater, so storm coverage could be an issue. Discrete or semi-discrete supercells will likely develop, some more dominant than others.

The main concern for tornadoes is still high LCLs. The moisture won't be as good as Friday or Saturday. Localized areas of lower LCLs are certainly possible though.

 

[Justin Turcotte]

I'll be watching the surface warm front advertised to be in northeast ND and northwest MN this afternoon. SPC has thus far overlooked this area, perhaps because NAM doesn't really want to clear the area out behind early morning convection along elevated front. Convection does looks to depart quickly this morning and if the area can get a couple hours of solar then ample instability will coincide with robust helicity along the boundary this afternoon and early evening. The GEM and even GFS suggest discreet cell development is possible along the boundary this afternoon with cell movement largely parallel to it. Tornado threat would appear to be non-zero. I'd be more excited if the low cloud over SD at this early hour wasn't seemingly entrenched.

 

[Bob Schafer]

The main concern for tornadoes is still high LCLs. The moisture won't be as good as Friday or Saturday. Localized areas of lower LCLs are certainly possible though.

One thing I noticed yesterday was that the RAP did a miserable job with sfc Td's yesterday in NE. It said that all the 60+ Td's were supposed to be hugging the SD/NE and IA/NE state lines at 00Z, yet there were obs of 60+ throughout most of NE. I'd guess the average discrepancy was a whopping 5 degrees F. It's just something I intend to remember today and beyond. I'm curious whether was an anamoly or a trend.

 

[Bill Hark]

I am excited about the potential for today. There will be good but fast upper level support with 50-60 SW 500 mb winds across western Kansas and central Nebraska. I like the southerly 850 winds that increase into the night. Dewpoints will be decent, at least 60 with an area of 65 in Nebraska per 12Z NAM. Depending on the forecast model, convection is likely from Nebraska as far southwest as Dodge City; into Oklahoma overnight. Forecast CAPE 1500 to 2000 though surprisingly the higher forecast CAPE is in Nebraska. A low should shift from western Texas panhandle southwestern Kansas by 00Z per NAM with forecast backed winds .
I am sitting in Russell, Kansas checking data. I am glad that I blew off the Nebraska chase yesterday and chose to relax for a couple of nights in Russell. Right now, I see two potential targets which I will alter based on the position of the surface low and updated model precip outlooks. These are Dodge City and Hill City. Hopefully some nice structure and maybe a tornado.

Bill Hark

 

[Mike Smith]

Like, Bill I see two potential targets. The latest HRR shows cells developing near DDC and just NW of HYS. Things look better for the southern cell, but there will be less PVA working on that area.

So, headed to GBD to determine a final target. It is easy to get from there to either target.

 

[Kevin Walters]

Hopefully the surface winds do back with time...pretty much veered just about every where right now.

 

[Rob H]

The HRRR/RAP have been over-forecasting surface temperatures by 5-10 degrees the last few days and have had considerable difficulty with this system. Just look at how horribly the HRRR did with instability and reflectivity on 5/26.

My guess is that the best chance today will be north of Russell/Hays - anything that goes up near the secondary low will take a deep breath of air when the 60kt nocturnal LLJ kicks in. Moisture advection will increase with the LLJ, so as long as there's enough moisture to keep storms sustained until that time, there shouldn't be a problem. The spreads are certainly not optimal, but don't completely rule out tornadoes.

 

[Jason Persoff]

It's go time...Last day out for this season: forecast feels pretty
straightforward, so I'm missing something. But really I don't have much not to
like about today.

Very strong southerly sfc winds are blowing me over as
I navigate the car in Russell, KS. That's not saying much given my height and
weight, but still stronger than I expected. Sfc analysis and forecast models are
in synch with low pressure developing in SE CO moving NE over the next few
hours. Low pressure at 850mb will also evolve synchronously but north of the sfc
low. The right entrance region of a potent jet streak will move through KS at
the 500mb level. Though this won't result in a "stacked low", it leads to a
stair step of goodness: the sfc winds should back weakly in the northern region
of the low, the 850s will crank midlevel moisture into said area, and the 500mbs
will add to vertical and speed sheer. CAPE is expected to pool east of the
dryline.

Since I have to head west anyway, conditional target will be
I-70 around Quinter (hey, I'm a sucker for that town anyway after '08). Enough
inhibition should allow for conditional storms to form late in the day there.

 

[Scott Roberts]

I can't see anything I disagree with above. The HRRR evolution seems quite similar to Friday night, but with the higher bases we're calling it a hail/structure chase. Headed for Hays to start...I'm happy with that as a central point from which to evaluate. I'm thinking we'll shade to the north early, then move south down the line.