5/2/08 FCST: IA/WI/IL/MI/IN/MO/AR/TN/KY/TX/LA/MS

[Joel Wright]

Been keeping an eye on Friday for the last few days. After really speeding the system up yesterday, most of the models have slowed things back up again. Now keeping the surface low in northeast Iowa at 7pm Friday evening. Yesterday a few of the models had it way into Wisconsin by that time.

Unlike Thursday, moisture should certainly not be as much of an issue. What may be an issue is the usual worry about the previous night's convection/debris. I'm not all that thrilled with the surface low slowly filling in during the afternoon either, but it's nothing too extreme. I'd much rather have a deepening surface low however instead of a filling one. Sometimes the models can fill a surface low too quickly. Hopefully that's the case here lol.

With all that being said, it looks like the surface and 850mb winds should stay fairly backed through the day. Overhead, decent 500mb winds will be veered enough for respectable directional shear. Should be some impressive lift with the very impressive fanning out of the mid and upper level wind field.

Still a few questions left to be answered, but this is still two days out.

 

[Adam Lucio]

The day morning crapvection doesnt concern me for ruining the days setup around here is the day I sacrifice my left leg to the weather gods.

Anyways, I really like the scenario GFS paints for IL, especially the eastern part of the state.

It brings a nice tounge of 60s Tds along with 1000+ j/kg CAPE in by 0Z sat. I too would rather see a deepening low rather than one occluded at 996mb, but given the shear profiles I think that should still be plenty to get things going. Plus if it can remain at a negative tilt I would think that would increase chances of bringing in a dry punch to clear the skies.

ECMWF keeps the low way further south and at 995. WRF is a little more westerly with it but still brings in good moisture to the region. With all these differences I dont know what to think...but I think there could be a serious threat for Friday. I hope models line up with the GFS. If I had to pick an area right now Id say anywhere along the I-57 corridor would be my playing field.

Time will certainly paint a clearer picture on this one.

 

[Heidi Farrar]

Well I expect that this thread will get a little more attention now that the SPC has upgraded to a pretty large Day 2 Moderate Risk, complete with a 45% hatched area, for Friday. I was anticipating this after I saw this morning's runs, since they are all slowing the system down compared to how it was looking a day or two ago. The WRF, and especially the NAM, are showing the higher helicity reaching further south now, at least between 18Z-0Z, coupled with higher CAPE across the entire Mod. Risk area. The shear has been there all along, so that's why I say I was expecting an upgrade. There's some pretty strong language in the outlook, especially given the conservative approach they've taken lately:

GIVEN THE DEGREE OF LOW-LEVEL SHEAR AND DEWPOINTS WELL INTO THE 60S ACROSS A LARGE AREA...TORNADOES -- A FEW POTENTIALLY STRONG/LONG-LIVED -- ARE ANTICIPATED

Also, I am noticing that the WRF & NAM are not presenting the squall line until roughly 3Z-6Z. ... or, put differently, the precip is showing up as more-or-less discrete until that time. I don't think it would be a stretch to say an outbreak is possible in the mid-Mississippi Valley area tomorrow afternoon and evening.

 

[nickgrillo]

I'd also point out the risk for scattered supercells in the northern portion of the warm sector (meaning northern IL and southern WI/MI) -- closer to the surface cyclone which will move northeast into WI by late tomorrow afternoon -- backing flow at the surface and increasing boundary layer shear. NAM forecast soundings show considerable SBCAPE well into MI by late tomorrow -- in a zone of strong synoptic-scale ascent mainly from the low-level WAA. Forecast boundary layer hodographs exhibit strong cyclonic curvature even into western/central MI, yielding favorable 0-1km SRH supportive of low-level mesocyclones and tornadoes.

 

[Chad Cowan]

I agree with Nick. I think there is a good chance for a tornado or two in southern WI and northern IL in the early afternoon spreading north and west with time as the low stacks up. Very strong kinematics in that area and models are advertising a decent thermodynamic environment, but that remains to be seen. There will be a risk/reward tradeoff between the nrn IL and srn IL targets; IMO the northern target will have a better chance of TORs than the southern target but if the storm mode favors discrete supercells in the south, that would definitely be the place to be.

 

[Joel Wright]

Well, unless something changes between now and then, I think we'll be playing the northern target closer to home. Part of the reason is gas prices. More importantly I think the northern target (northern IL, possibly east IA) will have the best overall dynamics. It looks like the morning activity should clear on out of the way enough for some insolation. It won't take much to get temps into the 70s. Low-level moisture will be more than sufficient for this particular setup.

Obviously the northern target is fairly conditional. I think if the area clears out soon enough it may end up being a really good setup. The NAM has hinted that the areas that do clear out may see SBCAPE in the 100-1500j/kg range. More than sufficient given the overall kinematic setup.

I have a feeling this may end up fairly similar to last Friday's system. Storms may fire a bit further east this time into western Illinois, before pushing eastward. We may end up starting our chase very close to home, and then push east across northern Illinois.

 

[Jim Zandonai]

Yeah the N.IL region is looking better this evening and will probably stay put like Joel too esp with gas prices high but may chase a good supercell if it erupts in the area and I can intercept it.
Should have a pretty good idea how things may work out on Friday A.M..
While we wont have as much instability as to our south in MDT risk area but some sunshine early on would sure make the day even more a good bet..

 

[Brandon Sullivan]

Hmm... Well, browsing through the 00z NAM, it has really cut down on the CAPE values over the area.. Highest helicity values remain confined to the SE portion of IL, where the low level jet support is centered. The NAM continues to forecast low to mid 60 dp's which should be sufficient..

I dont know about a target... I mean, if the NAM were to verify I would head to Southern/Eastern IL, where likely more clearing will occur, and instability will be higher...

Im not sure about the degree that it could be over doing things, I will be waiting anxiously for the new GFS..

Edit: Well the 00z GFS is in, and I do like what I see.. 65+ Forecast DP's over SW and Southern IL.. A look at KSPI (Springfield) at 18z tommorow, shows some pretty low LCL's and some nice (AOA 1000 J/KG) CAPE...

Good Luck to all who go out... As of now, I am thinking head south/southeast... Things could change though...

 

[John Farley]

Commitments early in the day and in the evening require me to stay near STL. I am worried that this situation, like so many others, will be dampened out by the effects of overnight convection and widespread showers - which may be why the NAM is not showing much instability. If we do get instability the dynamics look very good, but either overnight convection or widespread precipitation during the day could interfere with instability. I will play a waiting game, and hope something fires within not too long a drive of the STL area early in the afternoon. If I did not have the evening commitment, I would probably play the SE IL area into maybe western IN.

 

[Brandon Sullivan]

Well, waking up to a nice 15 hatched % tor to the Southeeast, over the area that the NAM wanted to show the most helicity and jet support...

At this time, I will likely play somewhere near Springfield to Champaign.. This way I have road networks to head North Or South, although, I could possibly target somewhere else, depending on where clearing is able to occur.. As always, I will have a close eye on the latest MSAS before I go out, as well as while I am headed there!

 

[Jim Zandonai]

Looks like todays biggest factor to overcome in the north is sunshine to heat the air up again sufficiently after this morning activity moves through.
Despite favorable wind profiles it looks like this afternoon will be a big IF up here..
This morning some elevated storms are moving into the NW IL region but it doesnt look too good to get it out of here for the afternoon 'event' to develop if it does..

 

[Matthew Fischer]

well so far this morning isn't looking promising here in N IL, stupid sloppy seconds! Currently raining over most of N IL with Elevated crap! Hopeful that the MCS to the south will suppress some storms for later today and clear out this cloudy junk. Today in N IL its all about heating. If we maybe an hour or two of sun this afternoon things may change.

Futher south into S IL and Boot Heal of MO, AR, and KY, could be some promise to the supercells and tornadoes, but don't know what this MCS will do. Might have to play the waiting game. My chase partner won't get home till noon or later. So things may change by that time.

 

[Joel Wright]

Definitely don't like seeing the giant squall line arranged NE/SW from southeast MO into northeast TX. While not always a convection killer, it seems to greatly reduce the quality of the storms to the north.

Not much clearing behind all this grungy crap quite yet. If things don't look much better by noon or early afternoon, we may just sit this one out. There's still plenty of time for clearing to take place though. We all know how fast things can change.

 

[Chad Cowan]

Northern IL is looking up. 12z RUC has 500-1000 more joules of CAPE in IL than the 09z RUC. I'm concerned about the developing pre-squall convection slowing the forward progression of the line and keeping us under the deck for longer. I'm also concerned with the lack of a strong dry punch on WV imagery; hopefully it will come with the 500mb jet streak later this morning and help mix out any high clouds blocking that precious radiation. I think that 70 degrees could be the magic number, if we get to 75 in the Rockford to Debuque area, all hell could break loose.

 

[David Wolfson]

On the road now from Chanute, KS, toward southeast AR target area, Monticello. Models show reasonable late CAPE and SR helicity with chance for more isolated cells ahead of the slower moving front. Subtle polar/subtropical jet diffluence is a plus feature, too.