5/13/09 FCST: IA/IL/MO/OK

[Andrew Pritchard]

In hindsight, this NAM run is not -too- much different than previous runs.

Will just have to watch the track and speed of the mcs as it moves across Iowa and into Illinois tonight and this morning. Watching the precip plots on the NAM, (which are never correct, anyway) it does more or less exactly what I'd hoped for an initiates new convection along and south of it's wake from eastern Missouri into south central Illinois. This seems about the best bet... along and south of that mcs's path.

Ideally that thing is not still in central IL at 18Z. If it moves out of here at a decent hour and we see some clearing along the ofb in it's wake we could still be on tomorrow. I'll continue to bank on my SW IL, Litchfield target at 3 or 4 PM. Shear is still phenomenal... be a shame to waste it all.

Hopefully the trusty 4 km wrf shows me a nice big red blob NE of STL at 21Z. Otherwise, I'll just find myself a new hobby.

 

[Greg McLaughlin]

After looking over 00z model data, I honestly believe tomorrow will not be a tornado event of any significance. The NAM continues to break out too much precip in Illinois during the day which will likely limit any instability needed for sustained supercells....a problem when you have too much lift and no cap.

As for Oklahoma, I think the storm(s) of the day will be here, however I believe it will be in the form of a severe MCS or derecho event. I will definately be playing the southern target. I don't expect to see tornadoes tomorrow, but its May so you never know.

If I felt confident about the tornado potential in Illinois I would have left for St. Louis today since I have tomorrow off, but I really see that area being a total wash.

 

[Jeff Russell]

It looks like to me that the 00z GFS just increased the speed of the CF. By 00z all the shear is pretty much gone in W IL.

Maybe I'm seeing something wrong.

edit: I agree with John, I just moved my target SE of St Louis, which also works better for me. I'm going to bed and will hit the road around 3-4am Eastern.

 

[John Farley]

I wouldn't be all gloom and doom yet. In the early afternoon it looks very linear in IL, but it actually looks more broken at 21Z - with the tail-end of the heavier precip moving into an area with an EHI of 6 or higher just SE of the STL area. And if that happens, it certainly wouldn't be the first time for a line of storms to become more cellular as it moves into an area of better helicity. The slightly southward positioning on this run actually works better for me. I do think the storms will be more linear than not, but if there are breaks in the line and embedded supercells, there will still be some chase opportunities - as there may also be when the storms first fire. Now granted it is still a bit far ahead to try to glean this much detail out of the models, but the general picture is good instability, excellent shear, storms a near certainty. That's a lot better than we've seen most of this year. OTOH, too many storms and the likelihood of a lot of linear convection are issues, but that's nothing new - see comments in the first few pages of this thread.

The GFS is coming in now and has better CAPE - up to 3000. It seems to fire two lines, one along the front and another farther southeast, but a little farther north than the convection predicted by the NAM. perhaps in a band about through the Jacksonville area. So Litchfield still looks like a decent compromise between these models, although if the NAM verifies the area just north of Alton might be a better starting point.

 

[Mike Hollingshead]

0z GFS is pretty precip friendly for the MO/IL target, even suggesting that area of ec MO/wc MO fires convection ahead of the cold front. It's making me feel a bit better about that whole idea happening. I'm actually more and more believing it will pan out good in that area. We need some stuff to be there to leave a boundary, any boundary, and I could see this....without being bonkers all day long.

The NAM seems a bit off with what will be there in central NE from now through 6z. It then goes nuts between 6-12z with that convection over eastern NE, which then translates east. I guess what I'm thinking is that I could easily see something tracking through there without being completely crazy with precip and left over junk...given it already appears overdone.

Edit:
LOL I spoke too soon, as central NE starts to light up. I still don't see this as terrible timing yet if it can race east without turning too hard se too soon.

 

[Joel Wright]

Still looks good to me. GFS looks fairly similar to it's previous runs. Keeps most of the major morning convection further north out of the main warm sector. The LLJ will likely feed elevated storm development during the morning though. I think the majority of this will remain just north of the main warm sector though.

I'm still liking the Galesburg/Macomb area tomorrow afternoon. It won't take very long at all to warm into the low-mid 70s with any partial sunshine that can manage to develop, and that combined with mid 60 dews will yield cape near 2,000j/kg. That should be enough for some tornadic supercell action in this area. VERY low LCLs will make any storm that takes off in this highly sheared environment very capable of producing a tornado.

 

[Jesse Risley]

It looks like to me that the 00z GFS just increased the speed of the CF. By 00z all the shear is pretty much gone in W IL.

Maybe I'm seeing something wrong.

It appears to me that the CF is still in East Central IA according to the wind profiles. The directional shear looks to be diminished, but the speed shear is still present.

TIME SENSITIVE
http://www.twisterdata.com/index.ph...nglemap&sounding=n&output=image&archive=false

 

[Derek Weston]

It looks like to me that the 00z GFS just increased the speed of the CF. By 00z all the shear is pretty much gone in W IL.

Maybe I'm seeing something wrong.

GFS has been quicker consistently with the CF... most folks here seem to be operating under the assumption that the NAM has it right.

As for the NAM's precip predictions... concerning, I guess, though, I still don't value them terribly highly. As another poster pointed out, western Ill, in the wake of an apparent bow echo in the early afternoon, somehow quickly regains CAPE upwards of 2000 j/KG.

 

[Mike Hollingshead]

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/

That is updated and pretty interesting. That would suck though, get suckered south of I70 into crapville.

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/tcolc_f26.gif

LOL looks like a busy night if that happens. Interesting how long it holds things off.

 

[Scott Weberpal]

This say "go to Kirksville"

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/tcolc_f24.gif

 

[Chris Allington]

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/

That is updated and pretty interesting. That would suck though, get suckered south of I70 into crapville.

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/tcolc_f26.gif

LOL looks like a busy night if that happens. Interesting how long it holds things off.

This say "go to Kirksville"

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/tcolc_f24.gif

hmmm... makes me rethink things a bit. Even so... it breaks isolated storms over extreme western OK in the 23-00z timeframe.

 

[Andrew Pritchard]

Well, I've seen that thing nail initiation mode and location but be off by 3 hours. Those images are -very- favorable IMO.

FWIW Mike - you don't want to go a TON south, but the terrain doesn't start to really suck bad until Interstate 64 in my opinion.

 

[Jarrod Cook]

Well I don't really know what to think at this point, LOL. Just gonna not worry and just look in the morning, since I'm not far from the action anyways. NAM and GFS both show inconsistencies from previous runs...NAM shows this MCS that Pritchard and others mentioned, but also shows a strong tonge of CAPE moving into W. IL over a pocket of strong LIs and shear ahead of the CF after this. GFS does not show much crapvection, but has MUCH less CAPE and further south with it, but tends to show some pre-frontal activity along the I-55 corridor.

And looking at H's links he just posted, that is interesting too...showing a classic MCS moving thru C. IL and clearing the Peoria area by 11 AM, but things hold off till 8 PM.

Will re-evaluate in the morning...but Quincy looks like a good bet perhaps, with possibly heading SE from there.

 

[Chad Cowan]

I'll be around central MO but I think western OK is the sleeper here. Pretty deep secondary low developing over the panhandles will back the winds there and given the extreme instability, any storm that goes up will be nasty. Cap will be an issue there but the 0z WRF is showing a nice dryline bulge.

I'm leaving early for Colombia, MO but I'm hoping to sit under blue skies for a good part of the afternoon. 3z RUC is keeping all the early precip north of I-70...

 

[Bill Schintler]

Chase Target for Wednesday, May13

Chase target (southwest target in OK):
Ponca City, OK

Timing and storm mode:
Storms will fire from northeast to southwest along and ahead of an advancing cold front after 4 PM CDT. The “tail-end Charlieâ€￾ storm may be the preferred target.

Synopsis:
An upper-level trough will transition E through the northern Plains while becoming increasingly negatively-tilted during the period as an 80-90 kt H5 streak rounds the base. A 40-50kt LLJ will extend from OK into the western Great Lakes while spreading a deep moist layer throughout a broad warm sector. The CF will push E and S while providing a focus for widespread severe storms in IL, MO, KS, and OK.

Discussion (MO, IL):
Storms will fire along and ahead of the SFC front, starting in IL and then building SW into MO. Strong instability will develop, with MLCAPEs AOA 2000J/kg by 21Z. Deep-layer shear of 50-60 kts will exist along the southern periphery of the aforementioned H5 streak. Large hodograph curvatures will result as a 50kt SWRLY LLJ surges over slightly veered SFC flow. Impressive LLVL directional shear and extremely low LCL levels should set the stage for a tornado outbreak. By evening, storm mode will transition from discrete to linear in response to strong forcing and convergence along the CF. Bowing segments will be likely along the line, with severe wind likely. Additionally, steep mid-level lapse rates will increase the risk of large hail.

Discussion (southwest target: KS, OK):
Strong but capped instability will develop ahead of the trailing CF. By late afternoon, convection will develop from NE to SW along the front. MLCAPEs of 2500 – 4000 J/kG will result from moderate mid-level lapse rates and SFC dewpoints around 70F. Overall wind fields will be weaker then further N; however, updrafts will rotate given the strong instability. SFC-3km helicities should reach 300m2/s2 despite veered LLVL flow. LLVL shear, along with LCL’s in the 1000-1200 range, will support a modest tornado threat. Later in the period, storms will evolve into a linear complex and surge SE into a strengthening LLJ

- Bill

11:59 PM CDT, 05/12/09