2015-11-11 EVENT: KS, NE, MO, IL, IA, AR, TN, KY, TX, OK, LA

[Justin Bailey]

several model runs in a row now have shown a strong storm system moving though the srn plains, mid ms river valley, tn valley, and ohio valley areas next wednesday and thursday. Some understandable uncertainty exists to strenght and timing of this system due to it still being several days away however, what seems to be consistent is that there will be no shortage of moisture and warm temps (very large warm sector), and very strong wind shear (both speed and directional). This thread isnt so much about pinpointing a target area and forcasting this to be a major tornado outbreak or anything of that nature, but is more to discussion of model trends and bringing attention to this late fall system as it approaches.

 

[Andy Berrington]

Definitely a seasonably strong system ejecting out the West from the looks of most guidance. Obviously the main question (as per usual this time of year) is going to revolve around the quality of moisture return and subsequent thermodynamic properties the warm sector has (500 mb temps probably will not be ideal partly due to influence of the sub tropical jet, which will likely hamper mid level lapse rates). The deep layer shear will most certainly be there with a 500 mb jet max AOA 100 kts, but that lead shortwave that ejects out ~72 hrs may rob it of better return flow for a longer period of time. This will also likely hinder the longitudinal extent of the warm sector.

I will say this one has more potential than the one yesterday though. Systems of this strength with any decent amount of BL moisture almost always result in at least a decent QLCS. If instability ends up being more appreciable over even a small area, then we could be looking at a more substantial event.

Also, I request moving this to TA.

 

[Jeff Duda]

Like Andy said, I think poor lapse rates are going to significantly reduce the extent and magnitude of the severe weather threat from this trough. There just isn't much cold air in the mid levels. If we were seeing forecast 500 mb temps of around -15 or so over AR, TN and southward I would say there's a good chance of a significant severe weather event. Definitely a strongly dynamic fall system, though. A 140+ kt jet core, especially that far south, is impressive at any time of year.

The other kinda negative about this system is the moisture. There's actually TOO MUCH. Forecast precipitable water values look to be flirting with record values over much of the mid-south, and profiles are nearly saturated throughout almost the entire depth of the troposphere. Not only does this limit potential instability from slab lifting, but it also means the entire area will likely be socked in with clouds during the majority of the event, thus limiting destabilization via insolation.

 

[Taylor Wright]

Like Andy said, I think poor lapse rates are going to significantly reduce the extent and magnitude of the severe weather threat from this trough. There just isn't much cold air in the mid levels. If we were seeing forecast 500 mb temps of around -15 or so over AR, TN and southward I would say there's a good chance of a significant severe weather event. Definitely a strongly dynamic fall system, though. A 140+ kt jet core, especially that far south, is impressive at any time of year.

I'm seeing -17 C 500 mb temps in central-eastern Iowa into western Illinois on the 12z GFS, just east of the surface lows where winds are backed. The GFS even hints at slightly higher instability in central Iowa. We had equally crappy lapse rates on Thursday up here in KS and still ended up with upwards of 1000 J/kg of CAPE. Given that low-level shear should be plentiful up near the surface low, that could be enough to get the job done. That being said, the GFS is showing it could be washed out by noon, with temps struggling to get in the mid 60s, and that surface low will be in Canada in no time. I'm hoping this system is slower than what is forecast so I actually have a chance to chase it. Wednesday is a day I could chase if it's within 2 or 3 hours drive. Time will tell.

 

[Jeff Duda]

I'm seeing -17 C 500 mb temps in central-eastern Iowa into western Illinois on the 12z GFS, just east of the surface lows where winds are backed. The GFS even hints at slightly higher instability in central Iowa. We had equally crappy lapse rates on Thursday up here in KS and still ended up with upwards of 1000 J/kg of CAPE. Given that low-level shear should be plentiful up near the surface low, that could be enough to get the job done. That being said, the GFS is showing it could be washed out by noon, with temps struggling to get in the mid 60s, and that surface low will be in Canada in no time. I'm hoping this system is slower than what is forecast so I actually have a chance to chase it. Wednesday is a day I could chase if it's within 2 or 3 hours drive. Time will tell.

The GFS is forecasting < 500 J/kg CAPE everywhere north of about 35 deg. N latitude, save for a spot directly under the upper level low across SW IA during the afternoon. Perhaps right up next to the upper-level low there may be enough cold air to get some instability. However, shear is strong enough that I think there will also be problems keeping storms from getting torn apart that far north. Perhaps not, but storms will also be moving at highway speeds, so actually chasing them is probably doing to be difficult.

Farther to the east (EC IA/IL) I see nothing but soundings with nearly 100% RH up through 600 mb. I can't remember seeing a major severe weather outbreak with profiles that moist.

Obviously the details are going to change as the event draws near, but if the GFS comes close to verifying, I suspect this is going to be similar to this past week's event in that there will only be a few scattered reports of marginally severe hail and wind. A tornado or two can't be ruled out, but I don't think there's going to be any sort of widespread outbreak of tornadoes. This wouldn't be an event remembered for its severe weather component.

FWIW, the 00Z FIM has a slower progression of this trough.

 

[Andy Berrington]

Considering the GFS almost always has problems with instability in cold season events, I've been looking more at the Euro for that aspect of this and it is showing 500-1000+ J/kg of SBCAPE over that area Taylor mentioned from Wed morning through Wed afternoon. Given the strong backing of the surface/low level winds in this area, I wouldn't be surprised if that is your relative max in severe/tornado reports. It has happened quite a few times in this region in particular.

 

[Kahner Cleveland]

According to the GFS, the RAP, NAM, and almost any weather model available, a strengthening cyclone will make its way into the states by the middle of next week. For the majority of information regarding this cyclone I have used the GFS weather model, as it's the most commonly used long-range model. At 12:00pm(18UTC) Wednesday, the GFS has the deepening cyclone creeping into the central plains. Winds out of the SW at 500mb from 50 knots all the way up to 100 knots. Vertical velocity and relative vorticity look to amp up across the Midwest near or in Iowa as the spinning system moves into the plains. CAPE is low, but not 0(around 500, but can't be disappointed-it is November.) The cyclone's spin looks to give plenty of twist in the atmosphere across the Midwest as it moves across the plains, giving bulk shear of 50 knots in Iowa to around 80 knots in parts of Oklahoma. At the surface, winds look to draw in moisture from the south-southeast (from the Gulf) and push dewpoints into the 50's and 60's throughout the Midwest. Lifted Index is shown greatest across Western Iowa at -3 along with a supercell composite of 1. Tornado producers in Iowa Wednesday morning-afternoon? Please feel free to offer opinions and analysis based on this data and the data you've seen.

 

[Jeff Duda]

The event is now in range of the 12Z NAM. The NAM is a bit friendlier overall with the severe prospects near the upper-level low. In fact, I now see a few forecast soundings that match the pattern of cold-season tornado events (i.e., very moist low levels with rather steep near surface lapse rates while the actual storm depth is much lower than you would see in the warm season). Interestingly enough, though, it appears the best instability and tornado parameters peak very early in the day (15-18Z) right near the low from SE NE into SW IA. There is some weak instability farther east along the DL into MO/IL, but things don't look quite as favorable as under the low.

Farther to the southeast (the mid-south region) lapse rates are so poor there's almost no CAPE at all. The GFS agrees with this. The GFS continues to generally say what it had been saying before - that instability would be hard to come by almost anywhere - although it may have tended slightly more favorable. It basically says upper-level low or bust. Neither model even produces much rain in the entire warm sector of the system. Lame.

 

[Andy Berrington]

I've noticed in some soundings that I've looked at closer to the surface low that there are some rather robust 0-3 km CAPE values showing up. This alone during the cold season is sufficient to pull tornadoes (and potentially significant ones) out of low topped storms, and these will certainly be low topped with equilibrium levels at or below 400 mb. When you blend that with very strong 0-1 km shear/ESRH and rather orthogonal shear vectors to the boundary, you have a recipe for a problem closer to the triple point. Events like 4/20/04 certainly speak to this potential.

 

[kevin-palmer]

I was initially thinking North Central Missouri looked like the place to be. But each run of the NAM today has trended the system slightly slower and further west into NW MO or even KS. I hope that trend reverses or it will be too far for me to chase, and it would be great to get one more chase in before winter. But there are a lot of things different about chasing in November. There's so much less daylight, and early storm initiation means it's best to be in place the night before. I almost forgot that you have to subtract 6 hours from the models now instead of 5.

 

[Andy Berrington]

Might want to take note of just how impressive the 0-3 km CAPE is progged to be with this. The Euro and NAM (despite being 3 days out) are pretty close with their instability values, and they really perform better in the cold season vs. the GFS.



You could really have some impressive, yet low-topped updrafts in this kind of environment.

 

[adlyons]

There has been considerable hype over the 30% day 4 from SPC. Forecasters are mentioning the possibility of supercells/ Tornadoes as well as wind damage with a potent 500 mb closed low and associated short wave. I am opting to look a little further north than the current main risk area.

Lets get to the point, moisture return and significant instability are going to be difficult to come by for this event. A gulf low has been lingering for the past few days which is blocking current return trajectories. That is expected to move out as a surface high sets up to the east of the CONUS. This will help push some moisture back north ahead of a rapidly developing lee cyclone across SW Colorado. As it stands right now, there are some timing differences between runs, but the overall consensus between NAM, ECMWF, and GFS is the trough/closed low will rapidly eject over the Eastern Central plains on Day 3 Wednesday. A 100kt progged speed max should continue to deepen the lee cyclone as it translates to the north east. Latest guidance has the low NW of the KC metro by early afternoon, with an arcing dryline to the south.






SPC has focused most of their risk on the southern target ahead of an advancing dryline and coldfront with crappy lapse rates and poor instability. It appears the best environment for chase able storms is the Northern target which also happens to be beneath the closed low. Immediately south east of the surface low, the environment looks very favorable for miniature supercells and possibly tornadoes. Low level lapse rates are quite steep thanks to the cold pocket aloft, which is helping to drive cape up substantially especially in the lowest 3 km. Given the great shear, if storms do form they will likely rotate. This sounding shows what I am talking about with the "short fat cape" concentrated very low in the profile favoring rapid updraft acceleration.

It does not trip the traditional supercell indicators, but good cape and strong shear is an indication that supercells will be possible. Further south, I expect a strongly forced QLCS with a tornado/ wind threat. If enough clearing is realized, and lapse rates steepen a bit, a few rouge cells might also be possible with a chance for tornadoes, but it does not at this time look likely.

To summarize, cold core appears to be the best target at this time.

Pros for this setup:
Strong speed and directional shear
Good lift
Deep surface low


Cons for this setup:
Weak instability over most of the area
Moisture return is not favorable.
Lapse rates are not ideal.
Strong forcing may favor linear storm mode
likely wide spread morning convection due to WAA
System is very fast moving and timing will likely speed up.
Storm speeds are fast.

 

[Royce Sheibal]

Local NWS Office in Omaha included the mention of a classic mini-supercell event in SE Nebraska and W Iowa from 9am into the afternoon. Tors look to be a distinct possibility. I'm expecting the SPC to highlight the area later today or tomorrow morning as models come in. Right now there is pretty good agreement among all but the GFS that we'll see action in the dry slot (should we get enough clearing after sun-up). I'll write a better forecast tomorrow morning, and I WILL get to chase Wednesday! Fingers crossed.

 

[calvinkaskey]

I am wondering about near Saint Louis, Mo. http://www.spc.noaa.gov/products/outlook/day3otlk.html http://climate.cod.edu/hanis/model/fsound/index.php?type=12|NAM|US|con|sbcape|60|*161,108*|false http://www.twisterdata.com/index.ph...iew=large&archive=false&sounding=y&sndclick=y The surface shear looks great along with hodographs. Cape is fairly low though. It will be near sunset though at the time for chasing.

 

[Jeff Duda]

Holy MAULs, Batman! The NAM is really gunning on steep lapse rates despite saturated layers. That's an artifact of the convective parameterization scheme, and I'm not sure how legitimate those lapse rates are. Guess we'll see.