11/05/05 FCST: MO/IL

[nickgrillo]

A neutrally-tilted shortwave trough will enter western/central MO by afternoon Saturday bringing in very strong wind fields and advecting deep moisture into the area. NAM is forecasting CAPEs in the 1500-2000J/KG range across a large portion of the forecast area (thanks to widespread insolation resulting into upper 60s/low 70s + low 60s Tds). At the surface, the deepening surface low may result in a more backed surface flow pattern... With a gradually veering profile (from southerly boundary layer flow to 80-100kt westerly flow at 250mb). Combination of increasingly moist low-level inflow and steep mid-level lapse rates suggest a favorable environment for supercells with large hail and isolated tornadoes (especially near the surface low where there is more backed surface flow / enhanced low-level hodographs).

I will likely head out on Saturday if the models continue this trend...

 

[Brett Adair]

Good call, Nick. The GFS has a descent bite on that solution but it's going back and forth. I would love to see this thing dive more towards the south and give me a deep south tornado event here.

 

[nickgrillo]

Good call, Nick. The GFS has a descent bite on that solution but it's going back and forth. I would love to see this thing dive more towards the south and give me a deep south tornado event here.

Seriously, I would love this thing to start slowing down more on the models (and let it mature and become negatively-tilted as enters the Ohio Valley)... I would really like to see the warm sector across IN/OH on Sun., which is what the ECMWF shows - but the GFS is acting nuts and blasting the trough off the northeast coast! On any note, Sat. could unfold a decent event (I'd have to say SPC would go with SLGT for SWODY3 tonight) across Missouri and Illinois this Saturday. By the way, have you checked the GFS past 132hrs? Nice return flow off the gulf with a 30kt SW LLJ, with raging mid-upper flow persisting throughout next week -- possibley a series of small scattered events in the upper Midwest.

 

[Helge Tuschy]

Hi Nick,

man I would love to have so much time for chasing....ok let's say I would love to have the Great Plains in front of my house Weather is so boring here in Austria....

YOu're right...the system looks pretty interesting, especially when the return flow will set up like models want to....at least a better airmass than the past few times

Wish you good luck and at least a few CGs ...

Cheers,

Helge

 

[beaudodson]

Moisture has been a huge problem across this area over the past few months. The models seem to want to bring something off the gulf but have failed over and over again. I will be a bit more impressed once I see that the moisture is ACTUALLY going to be there. Something to watch.

 

[John Farley]

I think this has some potential, but I'm not jumping for joy yet. According to the latest NAM, the areas of best CAPE (around 1500 just southwest of the STL area) and the best helicity (farther east) are not co-located, and most of the precipitation predicted by the NAM is even farther east from the best instability. Looks like dewpoints may be around 60, certainly adequate and pretty good for this time of year, but not ideal - and that's if the moisture gets as far north as the NAM says it will. I agree this is a slight risk scenario, but would like to see a little better instability, shear, and moisture coming together in the same area. Still, since this is in my backyard I will probably chase if it looks good. Of course, that would mean giving up watching football, so choices will have to be made. :wink:

 

[nickgrillo]

I think this has some potential, but I'm not jumping for joy yet. According to the latest NAM, the areas of best CAPE (around 1500 just southwest of the STL area) and the best helicity (farther east) are not co-located, and most of the precipitation predicted by the NAM is even farther east from the best instability. Looks like dewpoints may be around 60, certainly adequate and pretty good for this time of year, but not ideal - and that's if the moisture gets as far north as the NAM says it will. I agree this is a slight risk scenario, but would like to see a little better instability, shear, and moisture coming together in the same area. Still, since this is in my backyard I will probably chase if it looks good. Of course, that would mean giving up watching football, so choices will have to be made. :wink:

I'd have to agree on the low-level shear... Still NAM gives a good >250m2/s2 SRH by the late afternoon - and this will overlap moderate SFC based instability ( http://128.121.193.153/CENTRAL_ETA_SVR_CAP...HSWEAT_84HR.gif ) and I highly doubt moisture will be a problem... Both GFS/NAM put 60F Tds all across this region - which, in addition to insolation, is resulting in sufficiant instability. I think the moderate low-level shear / deep vertical shear (and the moderate low-level instability) alone is enough to support isolated supercells and tornadoes...

 

[Kiel Ortega]

Moisture has been a huge problem across this area over the past few months. The models seem to want to bring something off the gulf but have failed over and over again. I will be a bit more impressed once I see that the moisture is ACTUALLY going to be there. Something to watch.

I agree there. I have a big problem with the HUGE dewpoint depressions on soundings all around OK and TX. While this isn't the target area, that dry air has to go somewhere (and it's probably east). Futher, given the 30s and below dew points along the TX/LA Gulf Coast and the surface high pressure sitting over LA right now, I wonder where this grand moisture return progged by the models is coming from. A fast moving system won't have time to set up the wind fields to do this, IMO. Just checked some buoys and it looks as if dewpoints about 200 miles south of LA are low 60s...so maybe if all that dry air magically disappears 60 dew points will make their way north.

 

[nickgrillo]

After doing a memory check, and analysing archived data - this setup does have some strong simularities to the 10/18/04 event. On this event, a surface low formed in nearly the exact same location... Including a cold front stretching from the trough and then curving back down into OK, with a warm front located from central MO into the Ohio Valley and a surface dryline extending from southwest MO into TX. Wind fields were also very simuler, with >30knt southwesterlies at 850mb then >40kt westerlies at 500mb... With fast zonal flow remaining (improving 0-6km shear). Instability was also of the same magnitude! muCAPE values were a widespread 1000-2000J/KG along/south of the warm front, given 60-70F dewpoints across the area.

Sat. has some ridiculously simuler features to this event... And here is what that event produced:

<img src=http://www.spc.noaa.gov/climo/reports/041018_rpts.gif>

 

[Jim Bishop]

The NAM solution is intriguing. However I think it ejects the shortwave too quickly. I believe the GFS has been trending on a slower ejection of the this particular shortwave, trending towards the European solution over the past couple days. I'll look into the details of the NAM solution once I'm confident on the timing and placement of the system. The timing of ejection (and resulting tilt of the system) will play a major role on whether or not this will be a decent chase opportunity.

Having said that I really hope something similar (but better of course!) to the current NAM solution verifies. I really want to go chasing this weekend, even if it's a looooong drive from Houston.

 

[Andrew Khan]

I just checked out the GFS, and it looks like we might also get some things going on down here in TN, somewhere. Perhaps middle TN, to East TN?

Wind Fields do look pretty good in the OH/IL are, with winds at 35 kts. Daytime heating looks like will be in the 60's in that region, but may rise during the primary heating. TD's will be in the 60's which will aid in development, and looks like a mild Low Pressure system wil put off a boundary of it, which could aid to.

 

[nickgrillo]

This event is slowly looking awful with the past 0z and 12z runs... Latest NAM/GFS has cut low-level wind fields way down from where they were, surface low is way further south, instability is awful...

 

[Brett Adair]

I'm wishing the better upper support would push further south, but this thing looks like it may be a wash out before it reaches me. Instability looks pretty descent across WRN MS/LA but it probably still wont be enough to do much.

 

[nickgrillo]

Originally posted by Brett Adair
I'm wishing the better upper support would push further south, but this thing looks like it may be a wash out before it reaches me. Instability looks pretty descent across WRN MS/LA but it probably still wont be enough to do much.

As of the latest runs, the best area would probably be northern AR... SFC Tds are progged to get into the mid 60s which should result in sufficiant instability... With model forecast soundings indicating mean mixed-layer CAPE ranging from 1500-3000J/KG across the region. Belt of 40-50kt w/sw mid-level flow in base of broad shortwave trough is progged to overspread warm sector during peak heating hours... With isolated severe thunderstorms developing by mid-afternoon. As of now, the main threats from anything would be large hail... Moderate 0-1km SRH overlaps some moderate instability during the mid-afternoon and this could possibley support an isolated tornado.

I likely won't head out unless it starts to look better (this is a solid 600 miles from me)...

 

[Brett Adair]

Originally posted by nickgrillo+--><div class='quotetop'>QUOTE(nickgrillo)</div>

<!--QuoteBegin-Brett Adair

I'm wishing the better upper support would push further south, but this thing looks like it may be a wash out before it reaches me. Instability looks pretty descent across WRN MS/LA but it probably still wont be enough to do much.

As of the latest runs, the best area would probably be northern AR... SFC Tds are progged to get into the mid 60s which should result in sufficiant instability... With model forecast soundings indicating mean mixed-layer CAPE ranging from 1500-3000J/KG across the region. Belt of 40-50kt w/sw mid-level flow in base of broad shortwave trough is progged to overspread warm sector during peak heating hours... With isolated severe thunderstorms developing by mid-afternoon. As of now, the main threats from anything would be large hail... Moderate 0-1km SRH overlaps some moderate instability during the mid-afternoon and this could possibley support an isolated tornado.

I likely won't head out unless it starts to look better (this is a solid 600 miles from me)...[/b]

I know how you feel, that is quite a distance from me also. It's about the same distance for me as well. With this being such a risk, I wouldn't dare go out.