11/05/05 FCST: MO/IL

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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...
 
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.
 
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.
 
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 :p 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 :D

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

Cheers,

Helge
 
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 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 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...
 
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.
 
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>
 
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. :D
 
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.
 
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...
 
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.
 
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)...
 
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.
 
One thing to be careful of is the Td increases. The winds may be out of the S or SW in the Ohio Valley, but "the air isn't of Gulf origin yet" as Dr. Smith said this morning. The real question here is going to be can the air get juicy enough in time to generate anything of interest. In the lower MS valley, sure. I'm not convinced as of right now that the Ohio Valley north to the Great Lakes will be moist enough to support severe convection this weekend.


BC
 
Originally posted by Ben Cotton
One thing to be careful of is the Td increases. The winds may be out of the S or SW in the Ohio Valley, but \"the air isn't of Gulf origin yet\" as Dr. Smith said this morning. The real question here is going to be can the air get juicy enough in time to generate anything of interest. In the lower MS valley, sure. I'm not convinced as of right now that the Ohio Valley north to the Great Lakes will be moist enough to support severe convection this weekend.

BC

Low-level wind trajectories are pretty favorable (current obs show southwest flow across this region) for deep moisture advection into the Missip. valley through the next 48hrs... By Sat., I don't find the progged 60F SFC Tds too hard to believe. As for later this weekend, I don't think the great lakes/Ohio valley will see much at all -- if anything -- as models have been absolutely clueless and completely inconsistant from run to run on how to handle the evolution of this trough once it lifts out of the Missip. valley by late Sat.
 
Latest 0z NAM run shows more hope for the area... Steep lapse rates and warm/moist boundary layer is forecast to support strong instability by early afternoon across northern AR/southern MO. Forecast soundings continue to indicate favorable low-level shear/thermodynamic profiles for rotating updrafts with a threat for large hail. I would expect initiation shortly after 21z across northcentral AR/southcentral MO -- imediately east of the surface low -- where a favorabley backed surface flow pattern exists (and gradually veering with height). Low-level shear is still rather modest, with 200-250m2/s2 overlapping the stronger low-level instability. Deep-layer shear profiles will support long-lived updrafts... While low-level shear is marginally supportive of an isolated tornado.

This looks to be a >8hr drive for me... So, I'll have to wait and see.
 
Nick,

You better watch that NAM. It hasn't been initializing well from the bouy data of TD's in the western Gulf. Wayyyy too high on initialization. I am not really buying too much of a severe setup attm. I think some isolated torandoes may be possible in N AR given SFC Low placement and maybe some deeper moisture advection.
 
Well looking at the latest 00z GFS with a nicely negatively tilted trough developing in MO and slamming into central IL/IN the SPC had this to say in SWODY 2.

STRONG VERTICAL
SHEAR WILL LIKELY SUPPORT SUPERCELL STRUCTURES...ESPECIALLY OVER THE
MS VALLEY REGION...BUT EVOLUTION INTO LINES IS ALSO PROBABLE.
INITIAL SEVERE THREAT SHOULD BE OVER THE MS VALLEY...SPREADING NEWD
INTO THE TN AND OH VALLEYS OVERNIGHT. AN UPGRADE TO HIGHER
PROBABILITIES AND POSSIBLY A SIGNIFICANT SEVERE AREA MAY BE
WARRANTED IN LATER OUTLOOKS ONCE UNCERTAINTIES REGARDING THE TIMING
AND EVOLUTION OF THE UPPER TROUGH HAVE BEEN MITIGATED.


day2otlk_0800.gif


They obviously are going with the 00z GFS.
 
Originally posted by Dan Cook
What's that showing?

Looks like vorticity at 500MB... It shows a rather sharp negatively tilted trough axis, with good vorticity. That would suggest rapid deepening of the SFC based system, and an increased threat for severe weather (possibly "strongly forced" convection, given the associated low SFC based stability).

Not that I got ALL of that from that single image, but I am remember bits and pieces of the 00Z and 06Z GFS run.
 
This situation is very intriguing. While I'm not sure I agree with the language of the SPC discussion (a little strong IMO and what a change from yesterday), I'm finding this forecast much more fun than a guaranteed outbreak.

At the surface it looks as if some higher dew points are sneaking their way up the Mississippi R. Valley on the west side of the surface high that's been sliding east and currently is over GA. That's good news for moisture, especially considering the 150mb deep moist layer on some soundings near the Gulf and just east of the Mississippi. However, just on the other side of the River, the moisture is much more shallow. The biggest problem I see is that wind profiles (except the surface) are all from the west-southwest all over the place, blowing that drier air towards the moisture and target area. Further, soundings in the target area are dry and any more dry air is not going to help. However, if a nice 50-100mb moist BL can set up in the target area, given the 40-45 kts shear (00Z GFS), I don't see a problem with some nice sfc based convection. It'll be fun to look at the 00Z soundings to see what happened through the day.
 
I will be headed out tonight, and will get a hotel somewhere in central IL... The 0-3km SRH is pretty good across a broad area (150-300m2/s2 overlapping moderate-strong SFC based instability) and it looks pretty darn good immediately south of the NAMs surface low placement across central IL. With the 30-40kt SSW 850mb flow, we'll see some pretty good low-level shear south of the frontal boundary. If we could have gotten some extreme instability and some 70F SFC Tds, I could have seen a high risk... As of now, it could indeed be a moderate risk day based on the latest runs. As inhibitation continues to weaken as strong short wave trough pushes through... Rapid severe thunderstorms are anticipated around 21z along/south of the front, as instability increases to widespread >2000J/KG and low-level convergance will support a few isolated intense and tornadic thunderstorms. Very favorable veering with height will result in very sufficiant deep-layer shear profiles for long-lived updrafts (35-50kts), while low-level shear (and low LCLs) is supportive of tornadoes.

Overall, the best threat for tornadic supercells exists across central/southern IL... Where strong SFC based instability will be coinsident with very sufficiant vertical/low-level shear profiles and surface moisture pooling. I will probably head to the Peoria area tonight...
 
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