6/20/10 FCST: KS/NE/IA

[Matthew Piechota]

Well I know most are busy with the tornado outbreak going on now in the upper midwest but after tomorrow my attention is turning to sunday in Iowa as this is the next day I can chase.

Sunday is starting to look pretty interesting along a WF that is setting up in IA looking at the 12z NAM. We have nice mid level winds between 35-55kts at H5 with H85 winds out of the SSW at 35 kts and backed sfc winds along the WF. It looks as that morning convection with the MCS will have to be watched but that will hopefully go through and the boundary becoming reinforced later in the day with instability and moisture really cranking by afternoon with dew points pooling in the low 70's along the WF. The MCS goes through the area with re-development behind the MCS in western IA per the 12z run of the NAM

What I really like about this setup already is the LL shear the models are showing along the front and the nice theta-e axis into western IA by late afternoon. also the 15z SREF already showing siggy tor at 40 for central/northern IA sunday evening. I know its still a few days about but the threat is there and will need to be watched closely.

 

[Jeff Duda]

As much as it excites me to see a setup like this come around and close to home, and especially as good as the hodographs that I've seen look (AOA 300 1km SRH with AOA 500-600 3km SRH and sufficient deep layer shear for supercells), the thing I hate to see in Iowa is there...and Tony Laubach would love this...

...the CAP...

It's Iowa and it's June. Warm 700 mb temps move in from the west through the day. Although the temps suggest a breakable cap, soundings suggest a deep warm layer from around 900 to 700 mb, warm enough that some serious warming would be needed to reduce CIN to manageable levels. I'm seeing a lot of CIN in soundings of 50 - 100 or more through 00Z. One would need surface temps into the 90s (which seems possible south of the OFB produced by any early morning convection which would, of course, reinforce the warm front) to expect daytime convection.

Hoping for another big day.

 

[Jayson Prentice]

I agree with Jeff here... I'll be posting a full forecast on my blog later this afternoon/evening, but taking a look at things from the 12z runs everything looks like it could be a very nice warm front tornado day in Iowa. But, as it happens usually if you look at the soundings you will see a very stout warm layer that is centered around 825hPa for much of the warm sector that would likely prove to be unbreakable. Most likely scenario will be for the parameters to be through the roof across parts of central/western Iowa and into adjacent portions of Nebraska/South Dakota, with an unbreakable cap...

It will be of interest to watch, as morning convection will likely lay down at least a couple of outflow boundaries and perhaps somewhat of a cold pool that may prove things interesting during the afternoon. But, the way it stands now is that anyone in Iowa will have to wait for the massive MCS to roll through overnight for their thunderstorms.


EDIT: A little more detail available on my latest blog post - http://severeplains.com/blog/?p=956

 

[jshields]

i too have been watching this day for a couple of days now. extreme instability(gfs has been showing ridiculous surface based cape in excess of 7000 j/kg), and stp values of 12-15. effective storm relative helicity values are over 300 over most of northern part of the state. the cap looks breakable on the 12Z gfs anyways, it shows less the 25 j/kg of mlcinh remaining at 0Z over most of iowa and eastern nebraska. the lid strength index is also showing -1 to -3 over most of central iowa. 12C temps are mainly over the southwest part of the state. i am planning on being out in northern iowa somewhere!

 

[Jeff Duda]

After taking a look at tonight's 00Z models, I am surprised at the sudden up-turn of the scenario for tomorrow. I checked a number of soundings across western/central Iowa and eastern Nebraska, and both the NAM and GFS (but especially the GFS) show awesome soundings both thermodynamically and dynamically. If either of these model simulations verify, there could indeed be some serious severe weather tomorrow in the W IA/E NE area.

 

[jshields]

well the spc has pulled the trigger issuing a huge moderate risk area! outflow boundaries and the now stationary front that should start lifting north through nebraska, should be enough to initiate storms. i liked the wording of the spc, "a potentially volatile airmass". cape potentially in excess of 5000, shear over 45 kts, and effective storm rel helicity over 200 m/s2. discrete supercells with very large hail and a some tornadoes will be possible, before transitioning to a possibly devestating forward propagating mcs later in the evening. mid level temps are right around 12C at 700mb for most of the area on the gfs, so hopefully the cap won't hold. i will be out chasing somewhere in eastern nebraska/western iowa, after looking where the boundaries set up tomorrow. a word of warning, nebraska had a ton of flooding this past week so there may be a few roads in northeast nebraska that are "messed up"

 

[Fred Dearborn]

Currently sitting in Nebraska City and will continue over to the Interstate 80 corridor around the Grand Island area.After seeing models,this could be a good place to setup.Morning convection is starting to clear out.

Fred

 

[Trey Thee]

Currently sitting in Nebraska City and will continue over to the Interstate 80 corridor around the Grand Island area.After seeing models,this could be a good place to setup.Morning convection is starting to clear out.

Fred

That seems to be a pretty good spot, if I were chasing up there today, I'd plan to be in the Grand Island, you've got decent roads in numerous directions out of Grand Island.

The model data seems to suggest an enhanced tornadic risk which obviously most of us and SPC would agree with (see their 10% area). But I'm a bit concerned that Lincoln, Omaha and perhaps even as far east as Des Moines could wind up in a bad situation as the day unfolds. Those are densely populated areas and the potential of of strong tornadoes is perhaps a bit downplayed (at least in my opinion) at the present time. I was thinking we'd see a smaller hatched tornado area run basically from Grand Island or York back to just east of the Omaha area. I was also expecting that 10% area to be a bit further east...of course this could change with later forecasts, this just has a bit of an ominous feel to it, for me anyways.

Be safe out there today guys.

 

[Greg McLaughlin]

Just happened to look at vis sat and noticed the OFB draped across Kansas. It looks to be a potential play later today. 12C 700 temps can be easily overcome in June. With sufficient flow aloft and the extreme instability coupled with the vorticity of the OFB, I am considering heading up into Kansas. You just never know with outflow boundaries.

 

[Andrew Stoller]

Per SPC meso analysis, composite indeces are going through the roof near that boundary in central KS, with 5,000 J CAPE.

I'm really liking east central CO as will ATM. Supercell composite is up to 8, the area is just north of a developing surface low, there's a ridiculously tight moisture gradient along the I-70 corridor (dew point is 8 here in CO Spgs, and 62 in Limon), the area has remained cloud free (unlike areas to the north in NE), and a cumulus field is developing in southeast CO that will move to the northeast into the good environment. Only drawback is the nasty capping inversion...

 

[Kevin Polston]

Looking at mid afternoon observational data...it seems to me the focus area for supercells and tornadoes will be similar to yesterday....which is in northern KS and possibly southern Nebraska. The outflow boundary is well defined, the best forcing is along that boundary where it has destabilized similar to yesterday and I think the more significant events will occur in this area. It appears SPC is trending in this direction as well based on their 1930Z outlook....but I dont like the eastern Nebraska area where it has not destabilized much at all with the persistent re-development of storms and cloud cover here. The only thing that seems different about today than yesterday is I am wondering if the cap is a little stronger today....in the sense that the 700MB temps are +14 or greater from the CNK area westward and southwestward...and based on vis imagery it looks as if there are more billow clouds from the HSI area south to CNK. I suspect the cap will be broken with persistent strong low level forcing and afternoon heating....but based on such a strong cap/sfc cin from southern Nebraska northward I think the best area for tornadic supercells will be in north central KS. Just as I am finishing up this post I see a tornado watch has now been issued from north central KS westward to far eastern Colorado.

 

[Fred Dearborn]

OFB will stall in n. cntl Ks.,so we are headed south on 281 to Ks/Ne border.Not very much clearing near I-80

 

[Ryan Pfannkuch]

I've totally lost a feel for how today is going to play out, considering that things really look different than I thought they would 24 hours ago. Several things just aren't following the script.

1) Persistent elevated convection across SE Nebraska and associated cloud cover has helped keep the true sfc front squashed well down into northern KS, some 100 miles or so S of where it originally looked to be. As proof of the almost "unforecastable" mesoscale trends happening today, the fcst high in Hastings NE was 91, and its currently 73 and cloudy (granted its only 330 pm). As Jeff D correctly pointed out above, less than 24 hours ago it even looked like IA would have a respectable surface based threat today. Several hours later it's hard to believe this is even the same day we're talking about. With the surface front still that far south, I am even wondering about the fate of the high QPF forecasts/Flash Flood Watches farther north into west central/northwest IA (where I currently am)

2) I realize that 1 severe storm has already broken through in the hot, deeply mixed air over western Kansas. However, at least 90% of this new TOR Watch covers area with 700mb temps of 14-15C. I know it's VERY unstable out there, but these are usually some very formidable warm mid levels to overcome. Maybe I'll be surprised at the magnitude of the severe threat across southern NE/northern KS during the next several hours, but for the time being I have unusually low confidence in today's scenario.

I feel for many a forecaster across the NE/KS/IA/MO region in this very challenging June pattern.