4/03/11 FCST: KS/OK/NE/MO/IA/IL

[Chris Allington]

Well looking at 12z model runs this morning I figured it was time to open a thread for this event as well. In my personal opinion it looks better than the day before (4/02) but has some of the same issues.

This mornings GFS run depicts a more focused surface low (994mb) across NW KS near GLD. With mid 60s dews streaming northward across Oklahoma and into SC/ SE KS by late afternoon. It progs SBCAPE values pushing 3000 j/kg by 00z with a nice focused area of lift along a sharpening dryline. So far... alot to like.

Then I looked at the 700MB temps and CINH progs... all I can really say is ouch. There has been discussion of the GFS over forecasting cap strengh this year but with the upper level support arriving and some nice SW mid levels all day bringing nice warm air off of the Mexican Mountains, there could be trouble. I'd like to see stronger surface winds as the low deepens to maximize surface convergence. If something can manage to go the shear profiles look fairly decent right along the I-35 corridor up into SE KS. 40 to 50kts of bulk shear would certainly get things done and it doesnt look like storm motions will be too crazy.

Ill be watching this one with interest...

 

[Ben_Jacobi]

I am still fairly new at forecasting, but I just looked over the 18z GFS and I was surprised. CAPE is a little less, but still around 2500 J/kg which is better then nothing and the CIN looks a little weaker as well now its down to -150 J/kg (in central OK) as opposed to the -3-400 it was forecasting earlier today. Everything else looks good. Nice curvature on the hodos and good moisture return with dewpoints reaching in the 60's. I'm not gonna write it off just yet.

 

[Greg McLaughlin]

The EML between 850mb and 700mb looks quite formidable. Hopefully there will be a well timed lead impulse, because that might be our only chance.

 

[Brandon Redmond]

12z NAM has some pretty favorable EHI values along the Missouri/Iowa border Sunday Evening - now if we can get storms to initiate is another story.

 

[Skip Talbot]

Beautiful shear profiles, ample moisture and instability, with a deep surface low and backed windows along a nice looking dryline... it could be a great chase setup. Unfortunately, both the 12z NAM and GFS are showing a cap bust:

http://www.twisterdata.com/data/models/gfs/3/maps/2011/03/31/12/GFS_3_2011033112_F84_CIN_SURFACE.png
http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_84HR.gif

In the absence of extreme forcing, nothing is going to breach that cap, and I don't think we have the necessary forcing with the 60 knot midlevel jet just starting to eject over the warm sector by Sunday evening. Watch the capping trends as the runs come in, as the rest of the parameters are there, but at this point we're looking at a pleasant yet boring Sunday evening across the Plains and Midwest.

 

[Darren Addy]

Correct me if I'm wrong, but while the GFS shows seriously high (save your gas money) 700mb temps at 12z it moves them way east by 0z. That leaves behind the nebulous 5-7.5C temps in the area just east of the surface low (which the NAM places closer to the NE/SD border instead of the NE/KS border). This is one that I'm hoping the GFS is righter on, because it would mean a nice overlap of parameters by 0z south and east of Fairbury, NE in the northern tier of KS counties. Still a long ways out, but right now is looking like it could be a triple-point play and less likely down the dryline. Certainly bears watching, particularly since it is a Sun. night (for me).

 

[Skip Talbot]

Correct me if I'm wrong, but while the GFS shows seriously high (save your gas money) 700mb temps at 12z it moves them way east by 0z. That leaves behind the nebulous 5-7.5C temps in the area just east of the surface low (which the NAM places closer to the NE/SD border instead of the NE/KS border).

Yes, the 700mb temps cool off as the day progresses. Its like going from a thermonuclear cap to an overly strong cap though. Check out the progression of the lid strength index from afternoon into the overnight hours as the GFS is plotting it:

http://68.226.77.253/models/GFS/CENTRAL/CENTRAL_GFS_ATMOS_LSI_78HR.gif
http://68.226.77.253/models/GFS/CENTRAL/CENTRAL_GFS_ATMOS_LSI_84HR.gif
http://68.226.77.253/models/GFS/CENTRAL/CENTRAL_GFS_ATMOS_LSI_90HR.gif

Generally you need some very strong forcing to breach an index of 3, and typically nothing goes up above an index of 5. The trend here displays an excessively strong cap through the daylight hours, that weakens a little over a very narrow region, before quickly filling back in after dark. Such a scenario will certainly preclude the initiation of daytime, surface based supercells. The NAM is right in the neighborhood with its numbers too. The 700mb temps might look workable at face value, but I think the cap index and inhibition plots are a lot more telling of the cap strength.

Also of note is the lack of low level instability:
http://68.226.77.253/models/GFS/CENTRAL/CENTRAL_GFS_0-3KM_CAPE_84HR.gif
Yet there is a good deal of MLCAPE in the warm sector:
http://68.226.77.253/models/GFS/CENTRAL/CENTRAL_GFS_ATMOS_MLCAPE_84HR.gif

All of that instability is elevated. This setup screams after dark, elevated hailers with little tornado potential. We have to hope that both the NAM and GFS are substantially off on their forecast cap strength for this setup to have a shot.

 

[Skip Talbot]

I hate to say it folks, but the 12z NAM is pointing to everyone's favorite state... Iowa.

An appreciable hole opens in the cap at 0z and stays open:
http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_60HR.gif
http://68.226.77.253/models/eta/central/CENTRAL_ETA212_ATMOS_LSI_63HR.gif

The NAM for the first time is firing off convection in the warm sector at 0z across central Iowa as well. A welcome site after seeing run after run with empty precip/reflectivity plots! All the other parameters look to be in place with sbcape plotting over 2000 and a nice pool of 3km in central Iowa. Directional shear will be maximized near the warm front, and a 60 knot midlevel trough should provide more than enough speed shear for supercells. The change is probably the result of the models taking on a more and more progressive solution.

Further south along the dryline, I still think we're looking at a bust for surface based storms. That cap is unrelenting. It would be one thing if we were looking at a cap index of 3 at 0z (that's a strong cap!) and it continued to burn off into the night. If that were the case we'd just be hoping we got initiation while there was some stil some light left in the sky. Instead, the cap fills back in after 0z (even though it never really erodes). I have never seen good surface based supercells develop in an environment like this. My experience is quite limited, but in the absence of strong forcing and good low level instability I just don't see how the dryline has any shot at a surface based storm. The trough is positively tilted with broad mid level flow. We'll get some lift out of that flow, but we don't have the diverging, deep, high risk type trough that we need for this cap. At the surface, winds are actually veered across Kansas. This is not going to aid the badly needed lift we need from convergence along the dryline, and dews might actually mix out further enhancing that inhibition. Winds back a little better into OK, but the cap is even stronger down there. When the cold front surges through overnight, we'll probably have the forcing we need for initiation, but as the cap continues strengthen, these storms are all going to be elevated. They might be good for some lightning and hail, but not tornadoes.

There's still hope, but the last half dozen runs have been very consistently saying that there will be no daytime, surface based supercells across Kansas and Oklahoma.

 

[Matthew Piechota]

It also looks like the NAM and SREF are developing two sfc lows, one being in KS and the other in eastern IA with the cold front looking like it helps in the forcing department and breaking the cap around DSM this run of the NAM. What jumped out at me is the serious increase in low-level instability on this run. As Skip said, shear would be maximized along the warm front with veered sfc flow ahead of the cold front (just like the IA day last week)

 

[Matt Hunt]

NAM has been pretty consistent now in placing a hole in the cap over northern MO Sunday 00z. CAPE values over 2000, even approaching 3000, bulk shear 40-50 kts. The simulated radar (though I usually don't pay much attention to this) shows an isolated cell right at the IA/MO/IL border at 00z. I'm starting to like Sunday evening better than Monday for a possible tornado threat in northern MO. Directional shear could be better, but it's not terrible. What do you guys think?

 

[Andy Jackson]

NAM has been pretty consistent now in placing a hole in the cap over northern MO Sunday 00z. CAPE values over 2000, even approaching 3000, bulk shear 40-50 kts. The simulated radar (though I usually don't pay much attention to this) shows an isolated cell right at the IA/MO/IL border at 00z. I'm starting to like Sunday evening better than Monday for a possible tornado threat in northern MO. Directional shear could be better, but it's not terrible. What do you guys think?

That's looking like the best spot so far,

The 03z radar composite is showing a storm firing just east of KC:

 

[Doug Drace]

Since the news station I chase for is based in Texoma, and there is a risk, I doubt im going to be headed into KS or MO for this one. Convergence along the DL is certainly going to be more of a problem tomorrow than those heading up to chase the WF. However I have noticed some interesting trends with regard to the hellacious CAP, particularly along the DL. Has anyone else noticed the gradual trend by NAM to weaken the CAP considerably from I-40, along and just west of I-35 in OK to the Red River? NAM/WRF indicating less than -50 CIN within that zone...and thats not just the 6z run this morning...this trend began on yesterdays 12z. It's a narrow cooridor before it strengthens again, but it is opening up a little more. Like I previously stated, convergence doesn't seem all that impressive along the DL until much later into the evening/night when the CF advances SE and overtakes it...but I don't think it's looking quite as impossible as it did from previous runs to get a storm or two to initiate in the late afternoon early evening before sundown from OKC to Ardmore. I haven't seen anything fire in that zone with the Hi-Res models, but that doesn't mean nothing will, while often pretty accurate, they aren't 100%. It's also nice to see SPC's 15% hatched zone running all the way to the Red River on this mornings Day 2. Not a great chance in Central to Southern OK, but enough that I plan on sticking around closer to home tomorrow afternoon and see if anything happens.

 

[Jim Parsons]

Northern MO, near the IA border still seems to be showing a weakening of the cap on the 00z run....The cap still seems the big variable with this event.

 

[Chris Allington]

Looking at the 12z runs this morning, a few things jump out at me. First, I like the fact that the NAM and SREF have consistently been latching on to the dual surface low and relatively consistent as to location. With a 988mb low over Central Kansas by showtime Sunday. This deepening secondary low might be the key to getting some localized backing helping both to increase hodograph size and increase surface convergence (badly needed). CAPE is not as bearish as previous runs but an axis of 2000-2500 SBCAPE still develops from the OK/KS border, NE along the coldfront to the IA/MO border. One thing I noticed that I really liked on this run... both 500mb and 700mb VV maps show an area of lift maximized near the triple point along the Hesston-Emporia corridor at 00z. The NAM hints at initiation in this area between 21z-00z. This area is also right on the nose of the cape axis with 0-3km EHI values approaching 6-7 in this area. That area is what I'm looking at for Sunday... Peabody, KS.

 

[Benjamin Rock]

The CAPE looks good at over 2000 J/Kg and higher towards 00z. However, I'm thinking like Skip. With the cap at almost 3 at 00z means that if it does break, I fear it will be after dark where everything will just weaken from there. Dew points are good, CAPE is good, but the Cap? Not so sure..