04/15/2006 FCST: NE, IA, MO, KS, OK

[Tony Laubach]

Models are indicating a negatively tilted trough plowing into the Central Plains over the weekend. Current trends have it a bit further east than most of us would like, but keeping in mind the previous setups which were slowed and backed further west, I'm thinking the same would apply. A pretty hearty cap seems to be in place, though, but if broken, wind fields and decent moisture could aid in severe storm development. Still many days out and a coupel days shy of my "diving into models", but definately worth keeping tabs on this week.

 

[Jim Bishop]

Glad to finally see a forecast post for this "potential" chase day. I've been watching the models closely and have my eye on Eastern Nebraska.

The 12utc April 11 GFS run has slowed down the progression of the shortwave closer to the European solution, though the European is still further west. The respective ensembles are similar so I have decent confidence that a deep surface low will be present over Central to Eastern Nebraska by 00Z 16th.

My first concern with this setup reflects back on April 6 in Northern Kansas/Southern Nebraska where 850mb dry air entrainment north of the dryline bulge mixed down to the surface, causing surface dewpoints to drop from the middle 50s to the middle 40s in 2 hours. If the GFS is right, the same thing could happen over Central/Northern Nebraska & Southeast South Dakota Saturday.

My second concern is the moisture return. GFS has a tonge of middle 50s dewpoints making there way into South Dakota, mixed areas of low 60s - which I believe will be scattered at best. However with such an intense vort max ejecting into Nebraska and cold temps associated with it, mid 50s may be ok.

My third concern is a very strong CAP. GFS is forecasting anywhere from 16 to 18 degrees at 850mb. The intense vorticity advection *should* take care of that cap (GFS still shows CIN by 00z), but it sure doesn't make me feel any better about this setup.

Setting asside my concerns, the shear will be great. Southeast flow at the surface and southeast to south-southeast 850mb winds at 45 know, with 50-60 knot 500mb flow from the south. About 1000 j/kg SBCAPE would support fast moving low-topped supercells.

This is any iffy setup, but like most chase days this year, it has major potential. Since it falls on Saturday I might be up there...but man that's a long drive from Houston!

 

[Kurt Silvey]

It would be nice if this pans out, but as of now I’m pretty skeptical. Until the moisture returns to the southern plains, I don’t see how we can hope to get any moisture advection up to the northern plains. Today is a great example, with a nice low and cold front moving through eastern NE, storms should fire later this afternoon, but with Td depressions anywhere from 20 – 30 points, the best we can hope for are some very high based hailers. At this time I’m not seeing anything that will change this all the way into next week. With May quickly approaching, it would be nice if the GOM would open for business.

 

[Jason McKittrick]

I too have been watching Saturday with some interest. Looks like a warm front set up. Low pressure near Norfolk with a warm front extending SE into SW Iowa. This would not be such a bad set up if upper level winds were not perpendicular to the front. IMO it looks like an elevated wind and hail event for eastern Nebraska and western Iowa.

I have decided not to get overly excited about any severe weather potential until our dewpoint machine is fixed. Something definitely wrong with the Gulf of Mexico return flow. Until I see near 70 dewpoints in Dallas I do not expect anything significant in the plains.

 

[Mikey Gribble]

I am not real optimistic about this setup, but it is certainly worth watching. With a quick moving cut off low, I just don't see us getting good moisture that far North. I think dewpoints in the mid to upper 50's are likely, but that doesn't get me terribly excited. Once again directional shear is going to leave something to be desired due to the stacked nature of the low. As Jim mentioned, the cap could be a problem as well. I won't take a close look at the models until the 12Z runs tomorrow, but from what I have seen so far there are several things to be concerned about with this system if you are looking for tornadoes. Then again, all it takes is one tornadic storm to make a great chase day and we are getting close to May, so who knows what will happen.

 

[Simon Brewer]

Looks like a fairly decent setup on Saturday. Dewpoints in the mid-50's will be adequate for at least one tornadic supercell given the strength of the shortwave, but the fast storm motion will make chasing difficult.

Between Kansas, Nebraska, and Iowa I expect there will be at least one area with a good combo of cape, shear, and weak-capping-inversion to produce a good tornadic storm, so it's good to keep an eye on, but if the budget is tight then I recommend waiting and saving for June, because May doesn't look so good.

 

[samuel stone]

I think that if the cap can break, eastern kansas could be the place to be, for one I think Jim is dead on with dry 850mb mixing down to surface further north into nebraska and I think that is less likely to happen further south into kansas. I watched the April 6th event from my computer and what I saw happen with dry air mixing down was just what I had expected to happen while watching the models leading up to that day, and what the models are saying to me now is exactly the same thing so I think the concern Jim has is a very serious one for the eastern nebraska area. Further south into Kansas there could be a show if cap breaks, 12z NAM forcasts plenty of upper and low level shear supportive of rotating supercells if initiation takes place. Also winds should veer with height more in kansas than in nebraska, and 60 degree dewpoints should be more widespread and CAPE in eastern Kansas is progged by the 12z NAM to be up to 2000 j/kg.
Where as in Nebraska CAPE should be lower around 1000-1500 j/kg Acoording to 12z Nam run.

The models However are nowhere close to agreement on the timing of this system as the 12z GFS takes it significantly further east. Although I would be inclined to beleive the Nam more considering the recent model trend of moving systems further west as we close in on an event.

Hope some of the big questions about this event can be resovled with newer model runs.

 

[samuel stone]

The difference in the timing of this system between NAM and GFS is ridiculous. GFS pushes the dryline way into Iowa and and extends ssw along the Kansas Missouri Border by 0z, while the Nam has it just east of the
I-35/1-135 corridor and north into central-eastern nebraska by 0z. I have watched the last several runs and this problem has not been resolved one bit yet. Once we get closer to the event we will see wich model has their stuff straight.

Latest Nam run has the bulls-eye of CAPE (2000 to possibly 2500 j/kg) moved further north into Nebraska rather than in Kansas where yesterdays 12 Nam run had it. Helicity will be supportive of Tornadoes throught the warm sector and deep layer shear appears supportive of suppercells. Aslo Nam forecasts Strong 500 mb Vort max all across Nebraska and well south into kansas if this verifies I think initiation along the dryline in Kansas is almost inevitable due to large scale acent associated with strong 500 mb shortwave/low.

Aain though models are very much in disagreement so we will just have to see what happens.

 

[Tony Laubach]

From my blog earlier this afternoon...

...I'm cautiously keeping my ears and eyes open for Saturday's setup. If you buy into the GFS, I'll be staying home watching a Rockies game. If you believe the NAM, I'll be eating at Wendy's in Salina by noon. Both models are way out of sync with each other, which pending on how you look at it, could be good or bad. But its bad if you're a forecaster trying to determine which is the right one.

The GFS has the low and our target well north and east into Eastern Nebraska and Western Iowa. The NAM has things further south and west, giving a likely and much more feasable target near and just east of I-135/I-35 in Kansas. If the NAM starts to verify more and the GFS can start to come to terms with the NAM, I think I'm going to start leaning back into chasing on Saturday. Otherwise I'll sit this one out.

I haven't gone into specifics or details yet cause I want to wait another couple of runs before I start to make my target. With the diverence of the models so much, its hard to take stock in anything, let alone specifics on CAPE, moisture, shear, etc. While I do have concerns of the moisture being overdone and temps well into the 80s creating large spreads in temp and dewpoint, its something that could work out. The cap remains an issue, but could actually play into our favor if enough forcing from above moves overhead in the right areas. If this occurs, it'll limit the threat of everything exploding up and into a massive cluster of storms right away and may actually keep isolated supercells going well into the evening.

Its definately bears watching and will be a last second choice. I won't up my alert status til later this evening as I get a chance to see which model is going to take the helm. And of course, whether or not I have a ride will play a role, too.[/b]

 

[Jeff Snyder]

Tough forecast with such poor model-to-model consistency. The 18z NAM continues to slow things down a bit, with a minor westward shift of the dryline, particularly north of ICT. I remain highly skeptical of the dewpoint forecasts as this point (given the model track records this year), but the 18z NAM has actually increased the td forecast, indicating a nice pocked of >65F Tds in central OK, as well as along the I70 corridor in central and northeastern KS. I think it will be vitally important to get this moisture in place by afternoon, as it'll help ease the CINH situation and bring the dewpoint deficits / LCLs into a more respectable range. Correspondingly, the 18z NAM shows <60 j/kg CINH over much of central and northern KS (though no QPF yet), which may allow for initiation given strong convergence along the dryline (check out the 850mb and 700mb UVV plots), as well as deep-ascent ahead of the vort max (i.e. DPVA). The 12z and 18z NAM runs also show cooler 850mb and 700mb temps compared to a couple runs last night and yesterday.

Flow aloft also looks more "doable" than the past few events, with 45-55kt 0-6km shear (instead of 60-75kt deeplayer shear, which may have been too much for the given amount of CAPE) and 40-45kt storm motions. The flow fields look to support tornadic supercells IF we can realize the forecast moisture. Right now, we're still experiencing modified continental air that's being recycled from the southeastern US, which means we may not see real Gulf moisture. A look at the knee-deep moisture at CRP at 12z today makes me cringe. At least we have 2 full days to see some return, because we're going to need all the time we can get. Dewpoints in the Gulf (per buoy obs) have recovered into the upper 60s, but I question how deep that moisture is given the trajectories.

Of course, this entire forecast is as good as gum on a sidewalk if the GFS verifies. I can't imagine that, given the current state of the upperlevel (cut-off off the southern California coast) that the system will come through too quickly. Models have a tendency to be too fast with these types of troughs/lows, so the trend may be w/in the favor of most Plains chasers. Then again, the core of the upper-level low/trough isn't even being sampled yet, so this forecast may change entirely still.

EDIT: Not sure why the NAM is aggressively raising Tds across the central US in the coming days. The real >63F dewpoints won't really be advected northward since they're still down in the Gulf (and looking at Td forecasts from TX/LA/MS don't show this stream of mid-60 dewpoints). That rather "out of nowhere" look to the model progs makes it seem like the NAM is cranking the evapotransiration contribution enough to punt the dewpoints upward 3-6 degrees. I don't know what the current state of the vegetation is in KS/NE/IA/MO and points east, but this seems a little dubious. Perhaps if it was June and the corn and crops were in full swing, but I'm not quite willing to buy >64F dewpoints in mid April w/o much of an advective contribution.

In response to Bill below: Yes, I do think there's a chance for isolated supercells south of I70 from southern KS into OK. The storms in OK may be high-based (not elevated, since they could still be surface-based) given a 25-30F dewpoint depression. The last couple of NAM runs have shown slightly cooler 850mb and 700mb temps, which argues for a little weaker cap. The GFS is much cooler at the sfc and in the low-levels, so I'm basing this on the NAM. I wouldn't worry about the lack of QPF on model grids 54-60 hours out... The best probs will likely be north of I70 (northern KS and into NE and western IA), but I'm hoping (as see as a slight to moderate possibility right now) that initiation will occur in a couple of places south along the dry line, at least to I40.

 

[Bill Tabor]

Anyone think convection can break out further south into OK/TX on Friday or Saturday? Both days show some very slight potential IMO, but precip / strong precip appears somewhat unlikely. I note that SPC has eliminated any potential for southern areas on both days. NAM breaks some precip in Tx panhandle and OK panhandle on Fri.

[Note I include both days because so far there is no thread for Friday and I didn't think this question was a good enough reason to start one. Also it's more of a question than a forecast, but we aren't really allowed to post anywhere else with 48 hours - right?]

 

[Kenny Drake]

The current model outlooks are, agreed, not in much agreement at all. What they do agree on is the moisture being in the low 60s. However, all the previous setups across the plains this year had models predicting relatively the same moisture, but a bias of ~+5F. At this point, I would say Td's will probably be in the mid to upper 50s which is definitely acceptable. However, too much boundary layer mixing may drop these Td's to the low 50s which is definitely an issue. This seems to be the case with 4-1-05 and as a result kept LCL's high. Lifting mechanisms seem to be in place, I would agree with the target zone as of right now being in eastern KS, maybe near the KC area as it is in the divergent zone of the jet max with directional (wind direction changes from north to NE as you move towards KC from the west) and speed divergence. This isn't one of my most thorough model overview as I'm somewhat in a hurry. Also the location of the dryline is a major factor. Models have consistently pushed the dryline farther east in the past this year in the plains, so I am going to lean more towards the NAM over the GFS at this point. The NAM and GFS in the last setups seemed to displace the dryline axis by about the same amount too, and both overestimated the eastward extent. I would not be surprised if the dryline makes it only to a Wichita line, with a nice dryline bulge north of there which should clear the skies for heating, but hopefully not too much. The current SPC convective outlook doesnt really go into any detail at all so I can't quite figure out what they are thinking, but it seems the models are persuading them. In conclusion I see two major concerns for this setup:

1) Moisture return - models have overestimated consistently this year over the plains.
2) Dryline location - models have moved too far east consistently this year over the plains.

Also, another thought that just came to mind. These two are probably related, the model is pushing the dryline too far east which in turn would increase the moisture pile-up ahead of it. A good case study could come out of this, why did the models push the dryline farther east than observed? If this happens consistently but hasn't in the past, what is different about this year? Only thing that comes to mind right now is the weak to mild La Nina event.

Chase-wise, I wont be going out. Too much classwork and not shaping to be a good enough setup. Please help us May, I don't like this ridge. This storms will be screaming along too. The more chasable storms will be along the warm front farther from the jet max, but warm front supes are more likely to be HP based in theory... but then again most storms have been this year across the plains if memory serves me right. Warm front or dryline, for some reason I have a bias towards dryline chasing.. but storms that fire along the dryline and move with the warm front can be very interesting (April 5 2003) but I doubt we'll see 63 degree Td's and a relatively stationary setup. Large hail, lots of rain, hopefully a tornado before they go outflow dominate thats what I would be hoping for.

ADD: Forecast soundings for OKC at 00Z Apr 16 show a highly capped environment. Temperatures are pushing over 30C at the surface (90'ishF). With such high temperatures Td's will need to be higher than forecasted low to mid 60's (and models have been overestimating recently). This shows up with quite a high CIN (124) and only 365 CAPE... Looks like a sunny day in Oklahoma given those.

ADD2: Just realized NAM has dryline over OKC at that time, duh, maybe I should look at KTUL. This is a bit farther north and actually ahead of the dryline in a more favorable environment. CAPE of just over 1000 and CINH around 5.5'ish. Problem still seems to be same as noted by OKC sounding. It shows mid 60 Td's at surface, so I will hope for 60 at best.

 

[Kevin Polston]

I have made a quick run through of the 00Z ETA and it looks quite impressive...especially for northeast KS by Saturday afternoon/evening. Many parameters look good and the synoptic pattern is looking "promising" to say the least. The only concern at this point would be the amount of cap strength. It looks to me that based on the strength of the forcing the cap should be broken in northeast/east central KS. Thermodynamic parameters and wind profiles would favor tornadic storms....in my opinion. Running through the forecast soundings over this area.....the wind profiles increase dramatically during the day so that by 00Z very favorable hodographs and shear are present. I would favor...based on the 00Z run which is still 48 hours out......an area bounded by Concordia - St. Joseph - Paola - Emporia - Concordia.

Of course...things change and what could go wrong. Well...the ETA and GFS are still at odds over the placement of the surface synoptic features...with the GFS still being too fast in my opinion. The cap strength could also be stronger than forecast....but I think the lift along with mid level CAA will help erode the cap by late afternoon.

 

[Scott Lincoln]

I'm not sure i agree with the SPC's outlook for tomorrow. Looks like the moderate risk is misplaced. It probably needs to be more of a KS/NE area. I dont think the system is going fast enough to take the area of possible strong tornadoes that far east. It looks to be after dark before the dryline makes it to western Iowa.

Looking at the BUFKIT ETA/NAM soundings quickly, Lincoln kinda looks crappy in general with unidirectional shear only during the afternoon and almost no CAPE; St Jo, MO looks like it has decent directional shear but it has a pretty much unbreakable cap; Topeka has an unbreakable cap and almost unidirectional shear.
According to GFS profiles, St Jo has a cap at 3pm and 6pm; Des Moines has decent shear and CAPE, but not until after dark.
These profiles were updated early yesterday, so i'm hoping that something has changed in the model runs and that when i get more updates it will look better.

 

[Kenny Drake]

Reading over SPC's Day 2 outlook for the 15th it looks like they are favoring the GFS model because of it's consistency with the track over the last few model runs. However, GFS did the same thing the last few setups and then within the 12 hour forecast starting moving it farther west. I, too, disagree with their moderate risk. They do mention the inconsistency between both models but do not mention moving the moderate farther west. As for Tds which I am watching closely, the core of the low 60+ Td's are still sitting down in Texas. Hopefully this will be able to advect northwards by Saturday afternoon. With dry surface conditions persisting throughout the western 2/3 of Oklahoma, and mid 50 dewpoints as of 8:45AM I'm still skeptical. However, surface observations over SPC's current Day2 moderate zone do show low 60 dewpoints. I don't think these will stick around and will probably drop as the boundary layer mixes out today with heating. I really think SPC agrees with what has been said here on location of initiation. But, I'm getting the idea that they believe moisture will not be rich enough until storms move into western MO/SE Iowa for low enough LCLs to really be supportive of tornadoes.