5/1/08 FCST: KS/MO/OK/AR/TX/NE/IA

[Ben Prusia]

GFS has been consistent for a few days now in bringing a deep surface low pressure system into the Plains States next Thursday. Both the 12Z GFS and the 0Z ECMWF model are in general agreement regarding the strength and position of the system, to be centered in the general area of the Panhandles/SW KS/SE CO (~990mb).

The GFS is showing a stalled out warm front on what looks like on a line just south of I-70 with an eastward moving dryline. While the models still disagree on the position of the upper level system, with backed surface winds and SSE-rly H85 winds for most of the length of the dryline, could see a decent shot of some severe weather. Storms are likely at the warm front-dryline intersect in Kansas, southward along the dryline, with SE Kansas and NE Oklahoma seeing the best shot of severe weather.

SPC already mentions of possible outbreak situation in the timeframe of April 30th-May 2nd.

Mods: Please change title of thread to include Nebraska and Iowa.

 

[Kenny Drake]

I found out about this possibility yesterday and have been keeping an eye on ensembles since. Given climatology and the ensembles very general agreement on troughing late next week (across the west) this will definitely be a day to watch. However, there is quite a big spread in location and timing. The operational GFS has itself been inconsistent in details (timing, location, etc) for the obvious reason being a 1 week prog. I have a Mesoscale exam on Thursday so this day will likely end up being a high risk.

 

[Bill Hark]

I have been watching this system and agree that there is the potential for small (geographic) tornado outbreak mainly in SE Kansas, NE Oklahoma. This is very far out and many facors can change. I do like the approaching trough with strong SW winds at the 500 level overspreading KS/OK, 60 degree dewpoints into southeast and central KS and backed surface winds though I really don't like looking at surface features almost a week away. These things often slow and Friday may be the better day. I am concerned that the GFS is forecasting only a narrow area of backed 850 mb winds in the area of best severe potential. Most of the backing is too far north. We'll see with future model runs since a detailed examination of surface feature is almost wishcasting at this point.

Bill Hark

 

[Brian Stertz]

Although the moisture is a bit on the uncertain side, the strong shear and incredible lift could mean a pretty significant severe wx event for W/C Iowa southward into extreme E. Kansas and W/C Missouri Thursday. At this point my target would be SW/WC Iowa and possibly NW Missouri for Thursday... but as per usual on the ext. progs there are likely to be other factors that may make the obvious not so obvious. It does look like a solid chase day....and I am going to put in my time off to chase. Easily within 3 hrs. of KC and can be in place for the action.

 

[Gerard Jebaily]

Im in the same frame of mind as you guys so far. Plenty of uncertain factors being 5 days or so out. I really like the overall size of the setup which has the potential to produce multiple days worth of severe weather. Usually when a steup like this comes through this time of year, one can expect one of those days to be an mod risk day. I'm going to be chasing on the plains from April 30-May 10 so im hoping it will wait for me till I get out there. In the mean time, Ill definately be paying close attention to this one.

 

[Brian Stertz]

00z GFS forecast sure paints a target of SW Iowa/NW Missouri to me. Pattern recognition of these types of deep/wrapped up lows in NC/C Nebraska just screams to me get up into that strongly forced area where the nose of the instability is poking. Although the shear will not be nearly as strong nor will the warm front be as big of a factor as the 4/8/99 outbreak, but there are a few similarities...with the low eventually stacking over C/NC Nebraska and the nose of the theta ridge poking into SW Iowa. Strong tornadoes do appear possible by Thur. late afternoon/early evening if this forecast pans out that is....

http://wxcaster4.com/gfs/CONUS_GFS_0-3KM_CAPE_120HR.gif

http://www.wxcaster.com/CONUS_GFS_700_GPHTMPRH_120HR.gif

http://wxcaster4.com/gfs/CONUS_GFS_LCL_GPH_120HR.gif

 

[Mark Blue]

I couldn't be happier as my wife and I will be chasing from May 1-5 and this looks like a classic mid-spring setup for severe weather. There are so many factors that could change this far out that it's not worth beating the ol' head against a wall, but I (as others) like the area of SW IA, NW MO, and along the Kansas/Missouri border as a target area for late Thursday. It appears the ingredients exist in this area for a severe weather outbreak (CAPE, dewpoints, forcing, etc.).

One other area piqued my interest and it's along the cold front where a secondary surface low appears as though it might form in Central Oklahoma, which will keep me watching as time goes by. All factors appear to be in good shape at this point (lift, shear, moisture, cap, and frontal setup) for a severe weather outbreak for this particular time frame. All we need is cheaper gas prices and everything would be perfect!!

 

[John Hudson]

I have also been monitoring this setup, and it looks as though it just might be interesting enough to make the trip from Manitoba. I still have a major case of SDS from such a long winter, and just hearing thunder would be delightful.

What concerns me is the progged location of the moist axis is somewhat removed from where the best shear is predicted to be, but I guess it is really too early to call the ball.

Additionally, I can't say I've ever chased extensively in IA or MO, and have really been wondering what the terrain/road network is like.


John

 

[Darrin Rasberry]

The road networks are fine around and W of the DMX area. Cell coverage, especially for AT&T, is not.

Returns seem fine on the GFS, except for some cruddy cape until you go into the extreme S/SW portion of Iowa. I doubt this chase is going to be local for me, but then again, I won't have far to go.

 

[Mikey Gribble]

I haven't looked over the models much today, but there are a couple things that are worth noting right now. Last nights GFS had the cold front over taking the dryline all the way down to southern Oklahoma by 7PM on Thursday. Today's 12Z is much better with the intersection being over Kansas. The dryline-cold front intersection placement is going to be very important on this setup (if the GFS verifies). If the cold front over takes the dryline over Kansas and Oklahoma the shear vector will parallel the boundary and we will probably be dealing with linear/cluster crap. If we can keep the cold front-dryline intersection further North over Kansas then storms should fire off the dryline where the shear vector is normal to the boundary. I'm sure most of you know this, but I figured it needed to be mentioned anyways since it could play an important role in this setup.
Another thing that worries me is the mid level low closing off and becoming stacked. Again the 12Z run today is a lot better with this. Directional shear over far SE Kansas and Oklahoma is still decent, but this will need to be watched.
On the positive side of things there are two things that really stick out to me. The first is that if we can get dewpoints in the mid to upper 60's, like the GFS is advertising, and temperatures only rise into the mid 70's (as advertised) dewpoint spreads should be quite low (low LCL). Slightly higher temperatures would be helpful for CAPE though, since the 00Z is only showing around 2000J/kg SB. The other big positive is very strong 850mb winds (around 40kts). That being said, very low LCL heights and strong 0-1km winds can be a deadly combination for tornadoes. Right now 850mb winds are veering slightly, but if they can back to southerly watch out. I am waiting on COD to update before I do my forecasting for today, so I haven't taken a very close look at this yet, but those are my initial thoughts. I posted a forecast here http://loadedgunchasing.com/blog.html

 

[Scott Lincoln]

Additionally, I can't say I've ever chased extensively in IA or MO, and have really been wondering what the terrain/road network is like.

The road networks and terrain in Iowa are great in most places. For most of central and northern Iowa, the terrain is better than large portions of Oklahoma and Kansas. Southern Iowa gets hillier, and by the time you get into Missouri its quite hilly and the road network isn't making much sense. I rarely drive into Missouri to chase - I always tell myself "never again", but then always get sucked in again during moderate and high risks. I've also encountered a lot more instances of flash flooding in northern Missouri than in Iowa - it seems like they dont grade their roads down there the same way.

I'm definitely watching this setup to see how it evolved. At first it looked like the dryline might make it across the Missouri River into Iowa, but on some later runs it doesn't look as clear. It's probably best to wait and see and not make specific geographic or temporal projections until we get closer. It is interesting to note, however, that a study at ISU showed that in instances when a dryline made it into the state of Iowa, tornadoes occured 50-60% of the time.

 

[Mike Hollingshead]

If I had to make a bet on this one right now, I'd bet it plays out much like April 15, 2006 Beatrice Nebraska tornado day. I could see a very small area winding up favorable for tornadoes, in a localized location right at the se edge of any dryline arc, right before it begins to turn s and then ssw.

 

[Michael O'Keeffe]

I have been watching this for a day or two now and I think we could finally have a somewhat of a more widespread severe weather event from E Nebraska/W Iowa south into W Missouri/E Kansas and reaching into C & E Oklahoma as well as possibly N Texas. This chase season as far as the Plains states goes has been just a few supercells producing a tornado or two and then that's it. However I think with the size and magnitude of this system as long as we could get good moisture return and some better CAPE a large severe weather event could be in the works. As of the latest 12z GFS I am liking the SE Kansas region, but that will continue to change as the system gets closer. I am curious to see what the WRF says.

Here is a quote from the 1pm EAX HWO:

IF SUFFICIENT MOISTURE CAN QUICKLY
RETURN BACK INTO THE REGION...THEN PARAMETERS WILL BECOME FAVORABLE
FOR A SIGNIFICANT SEVERE WEATHER EVENT ACROSS THE EASTERN PLAINS...
INCLUDING MUCH OF THE OUTLOOK AREA.

As far as the moisture return goes I don't think that is entirely out of the question given the strong LLJ expected to develop on Wed into Wed night. Though the LLJ is slightly veered I have seen plenty of tornado outbreaks in that region with less than ideal 850mb winds. Ex. May 4, 2003 LLJ was SSW and Jan 7, 2008 LLJ was WSW. Just a thought.

 

[Mikey Gribble]

Michael said...
"Though the LLJ is slightly veered I have seen plenty of tornado outbreaks in that region with less than ideal 850mb winds. Ex. May 4, 2003 LLJ was SSW and Jan 7, 2008 LLJ was WSW. Just a thought."

I agree Michael. You will never meet a chaser that hates veered 850mb winds more than me, but if they veer a little bit (like what the GFS is currently showing with SSW) then I don't think it is a terrible thing given the southerly surface winds-925mb winds. It will give us a little bit of turning at least in that lowest 1km.
The biggest positive for this setup IMO is the excellent wind speeds in the loest 1km. That is one thing most violent tornado setups have in common. This is spiking 0-1km SRH over SE Kansas with values >300 and significant tornado value of 7.6. CAPE is lacking somewhat for a violent tornado threat with surface temps only in the 70's, but this also keeps the dewpoint spreads very low. Here is a quote from my earlier post on my blog...

"I am still very worried about the lack of directional shear. Even though it's not too bad in the 12Z run, slight changes in the evolution of the mid level low could wipe out the directional shear we have. Right now things look OK though. It is certainly worth mentioning that very low LCL heights and strong 0-1km winds are a deadly combination for strong tornadoes. There are a few things that need to happen... the dryline needs to stay ahead of the cold front in SE Kansas and Oklahoma, we need to maintain or improve the directional shear we have, dewpoints need to hit the mid 60's, 850mb winds need to stay backed, and if CAPE can improve slightly watch out. If those things happen then storms coming off the dryline could pose a very serious tornado threat. That is a lot of if's, but any time there are very strong 01-km winds it's a huge flashing red light for strong tornadoes."

If the things I mentioned above (a lot of if's) come together, then this setup may have the potential to support violent long-track tornadoes. I haven't seen a setup since Greensburg where I thought violent tornadoes(EF4-5) may be possible and it is usually do to not having exceptional wind speeds in the lowest 1km. This setup has that and it certainly has my attention because of it.
On the flip side I have extremely low confidence in this coming together ATT simply because there are so many slight changes that could ruin this setup. It is unstable to say the least. I posted more on the setup here http://loadedgunchasing.com/blog.html

 

[Brian Stertz]

One thing I have been watching is that this may be a setup where the deep moisture nose makes it to the southern end of the strong wave....ie NW/WC Missouri and maybe SW Iowa as it looks right now. The area is in the classic LFQ of the mid/upper jet wind max...and is in that very favorable diffluent zone. IF the deeper moisture can make it to this area, then we may be talking a narrow corridor for a possible strong tornadic supercell threat. Further south across sections of SE Kansas and adjacent areas of SW Missouri and NE Oklahoma...you may have a bit of a stronger cap. The only saving grace is that this area may get the good juice before dark...so the cap may not be as big of a deal had only low 60 TD's been in place. All signs point to something of a news maker system, but where this "sweet spot" is....that will have to be determined Wed. or even Thursday morning. I plan on doing an archive on Vortex Times of my forecasts leading up to the event, and will have a map done for how I think things may play out. It will be an interesting one to watch develop on the models. Pressures should really start to plummet Wed. night/Thursday so there could be rapid changes forthcoming...