3/20/11 FCST: OK/KS/IA

[Mikey Gribble]

I'm putting my money on Sunday being the big day in the plains. The GFS tends to be a tad fast, so maybe Monday, but like I said right now I'm betting on Sunday.
The GFS and ECMWF are in remarkably good agreement with the upper air pattern towards the end of the week (considering we are 7 days out). Both are showing an extremely potent trough, so I doubt that they are way off on that. With a potent system like that, we are going to get good moisture advection ahead of it. The LLJ will be screaming for a good 36-48 hours leading up to the main event with a trough like this. The GFS is showing upper 50 dewpoints ahead of the dryline. Too early to get into those kinds of details right now, but I think low 60 dewpoints are reasonable for a couple reasons. Anyway, I think a lot of the tornado potential will hinge on the tilt of the trough as it ejects into the plains. The GFS looks really good right now with a neutral to slightly negative tilt (I don't want a hard core negative tilt). Still a long ways out, but this certainly has my full attention.

 

[Jeremy Den Hartog]

I agree Mike, I noticed this as well. It will be interesting to see how things play out and how far north good deep moisture gets. Even part of a Nebraska could be interesting if moisture can make it that far north...and I realize it would be a stretch but maybe even southeast South Dakota (maybe a cold core setup?) Something to keep an eye on anyway.

 

[Lanny Dean]

Totally agree with Mikey...in fact, it looks like we might possibly be looking at a 2 or 3 day event. Forecasted CAPE values increase starting Friday out west and then look "prime" on the day in question. With that kind of a trough setting up (providing it keeps somewhat of a neg. tilt) it looks like we may have a shot at some severe starting on Friday out west maybe even Thursday and then going into the weekend with Sunday/Monday being the "prime" day. Looks like Mikey was right with upper 50 to mid 60 dews ahead of the dryline. My only real concern and issue is the shape of the trough but it's so far out right now, who knows.

Wonder how it's gonna look right on the 35 corridor in my back yard @ 18-22z come Sunday afternoon!?!?!? I think I like Henessey to start lol

 

[Jeremy Den Hartog]

If I had to pick a target right now, which I don't but I'm going to anyway for the heck of it, I would target around Mitchell and/or Sioux Falls, SD for a cold core play...especially if the 500MB low can close off. The targets further south will have a greater chance of producing but due to work southeast SD is my only option . Its a risky play I know but sometimes with great risk comes great reward.

Of course I could be completely off on the cold core setup so if someone notices things not looking right let me know - still trying to learn how to forecast them

 

[Matthew Piechota]

It really isn't a cold core type setup up the ULL back to the west along the MT/SD/ND border. The GFS does show it closing off sunday evening but its well displaced from any good moisture that is into eastern NE and southeast SD. The H5 temps are only a tad bit colder up north in that area than they are down in the southern area.

 

[Skip Talbot]

This setup looked the main event of a two day deal across the central/high plains. The day-before-the-day took a big hit with the moisture return and might be constrained to TX/NM now. The main event on Sunday looked quite a bit better yesterday actually when the dryline was setting up towards the Colorado border. The 55 dewpoints are more than enough that far west. However, as the models push that dryline east that moisture becomes more marginal in the lower elevations and you can see the instability took a hit on the past couple of runs. Still great looking speed and directional shear with a strong trough, LLJ, and awesome veering wind profile. Instability axis looks fairly marginal constrained to a narrow axis and with a rather narrow opening in the inhibition that fills back in after dark across north central KS. If storms go up here they might hug the dryline with struggling updrafts and high bases. These details are all contingent on the last couple runs of the GFS verifying though, which they won't, so expect something quite a bit different to play out. The timing and strength of that trough has been showing up consistently run to run though so there is a good chance somewhere is going to get a play off this system.

 

[Andrew Stoller]

It looks likk the GFS is slowing the system down a bit; runs yesterday had the dryline about 150 miles to the east and the surface low all the way up into the dakotas. The latest runs have the dryline more to the west and the surface low setting up in eastern CO. That means Saturday is basically a dud, but it might help the moisture return for Sunday.

It's all a moot point this far out though! Either day will likely have a good chase opportunity somewhere in the central to high plains.

 

[Connor McCrorey]

The ECMWF is slower as usual, and I'm thinking a 3/21 thread may be needed pretty soon

 

[Kelly Sugden]

Well there is a bit more consistency with the GFS coming in line to the slower ECMWF solution so Saturday looks like nothing while Sunday and Monday could be active. Fairly good agreement with dryline placement Sunday with the dryline bisecting the DDC CWFA. I'm going out on a limb and putting up a prelim target near Great Bend, KS Sunday. Hope it pans out because I have the day off for chasing. Worried about slim axis of surface based CAPE Sunday. Can't complain for 55-60 deg f td's for March. Good enough for this early in the season.

 

[Skip Talbot]

The GFS has been quite consistent with this setup. The placement of the dryline at 7pm Sunday hasn't shifted much at all between this mornings run and yesterday morning's. Like Kelly, I too am worried about that narrow little ribbon of instability its plotting, as well as the cap, which opens for a brief window before filling back in. Something to take note of though is that the GFS, and the NAM have been under forecasting instability and over forecasting cap strength on the past few setups. If that's the case with this setup, we should definitely see some severe weather and maybe a few tornadoes across KS and into OK and NE as that trough and veering wind profile continue to look amazing. Another thing to note is that the NAM and GFS, while showing a very similar pattern out to 84 hours, are quite a bit different in their placement of the surface features. If the NAM is more on target, we may see Sunday's target shift south some, and if the GFS is still too progressive we might see Sunday become the "day before the day" and Monday transition in the main event instead of the "sloppy seconds" that are currently being plotted. Still I'm impressed with the run to run consistency, and if the models are in agreement at 84 hours, we'll probably have a good idea whether or not Sunday is going to be the main play.

 

[Mikey Gribble]

I'm just going to copy and paste from my blog. On a side note, I don't disagree with what others said above. The dryline location and other surface details have stayed pretty consistent. And even though the general theme with the upper air pattern has remained steady, the details and nature of the trough has jumped around a lot with the models. Anyway, I really haven't spent much time on this forecast so take what I say with a huge grain of salt. I figured there is no reason to spend a lot of time forecasting this far out, especially when we got March Madness starting soon. I need to focus on my bracket. Sorry too for the rambling and longwinded forecast post I'm going to copy from my blog. I am way too tired of being on the computer to clean it up right now. Here is a copy from my post on my blog...


This forecast is turning out to be a little more tricky than I initially thought it would be. The ECMWF has jumped around a lot with the upper air pattern in the last couple runs. The GFS has been very inconsistent too with details regarding the upper air pattern. The general theme between the two is to slow things down. I am starting to think that Monday might end up being the big day. It’s really tough to tell right now. The timing isn’t quite right to pin down Sunday or Monday as the big day. It’s kind of right in between going either way right now.
The models keep wanting to jump back and forth between showing a compact (more traditional) upper level trough and a wide trough that ejects as several smaller disturbances. The more compact trough would definitely be the better scenario IMO. That would tend to favor one big day. The other solution where the trough kind of widens and begins to break up as several small disturbances move through southwest flow over the central plains would be more of a multiple day event, with lower severe probabilities each day than you’d typically get with the more compact trough. I have no clue what to believe at this point. Synoptic scale meteorology is not my strong suit. I don’t even pretend to know what I’m doing on that. There’s not a whole lot we can do about it anyway, so might as well just sit back and let time sort these differences out. We’ll get a handle on how this is going to unfold soon enough.
There are a couple serious concerns for me right now (aside from the upper air pattern). That is moisture quality and cap strenght. I will get into those in more detail below. A lot of people are probably worried about the narrow CAPE corridor developing ahead of the dryline, but I’m really not. One reason that doesn’t worry me is because the models have shown the exact same thing with the last three setups this year and it hasn’t really be a major problem with any of them. You really can’t trust the models, especially this far out, on the amount of cloud cover and insolation you’ll get. So I don’t see any reason to sweat that. Plus, if we don’t get a more compact potent trough solution with this setup there are probably going to be some issues with warm 700mb temps and a strong cap. Storms aren’t going to be firing early in the day if that’s the case and you may not need a realy wide CAPE tounge.
On the moisture issue, I didn’t do much forecasting on it. Pretty much just scrolled through the forecast hours on low level widns and moisture return from Thursday through Sunday. At about 84 hours out, when moisture advection slowly starts to ramp up, there are already lower 60 degree dewpoints over the southern plains. That 60 degree dewpoint line actually retreats from Friday to Sunday. I’m really not understanding why, but the reason could be complicated. From the surface to 850mb trajectories are favorable to draw better quality moisture north. Because of that I don’t understand why dewpoints would drop over the southern plains over the 48 hours leading up to Sunday. It’s not like 850mb winds are veering and bringing in some dry air that’s mixing down. There aren’t forecast soundings available for that far out (that I’m aware of), so we’ll really have to wait until we get closer to the event to figure this out. Forecast soundings are really what you probably should be looking at to figure that out. It about has to be some sort of mixing down of the dewpoints I would think, but again we will figure that out later. We really shouldn’t be worrying about details this far out.
Regardless of the moisture questions, the models have been consistent in showing upper 50 degree dewpoints ahead of the dryline and that is adequate for this time of year. As I mentioned in previous forecasts I’d much rather see the models showing low 60′s, but upper 50′s aren’t a problem IMO. It’s the difference between great and good.
The other big concern I have is capping issues. There isn’t any way to get an accurate idea of the cap right now, especially when you consider the major swings with the upper air pattern. The more compact trough solution the models have shown would probably bring in colder mid level temps and the cap wouldn’t be much of an issue. If we get the wider trough solution where smaller scale disturbances move through the central plains over several days then capping may be more problematic. With that solution mid level temps never really cool much until the main portion of the upper level trough ejects into the plains. That is one of the reasons why I prefer the more compact trough.
No reason to get into any more detail than I have already. I keep forgetting how far out this still is since I started forecasting for it so early. After looking at this for several days now it seems like it should happen tomorrow rather than 5 or 6 days from now. I am still optimistic about this setup. Not nearly as optimistic as I was a few days ago when both models were consistently showing a traditional tornado outbreak scenario unfolding, but there will be a fairly potent trough coming so I can’t complain. I will keep an eye on it and update later tonight or tomorrow.

 

[Derek Weston]

3/16/2011 12Z GFS stays on track with poor CAPE over the region. Rarely do I see appreciable severe events when such narrow instability areas are depicted via models. (for obvious reasons)

That said... perhaps NAM will be more optimistic when it comes into range here... the past few years the NAM has generally been a bit more optimistic where CAPE is concerned.

Tis all a bit saddening considering the shear we've been blessed with, but, alas... it is only early spring.

 

[Brett Roberts]

On the moisture issue, I didn’t do much forecasting on it. Pretty much just scrolled through the forecast hours on low level widns and moisture return from Thursday through Sunday. At about 84 hours out, when moisture advection slowly starts to ramp up, there are already lower 60 degree dewpoints over the southern plains. That 60 degree dewpoint line actually retreats from Friday to Sunday. I’m really not understanding why, but the reason could be complicated. From the surface to 850mb trajectories are favorable to draw better quality moisture north. Because of that I don’t understand why dewpoints would drop over the southern plains over the 48 hours leading up to Sunday. It’s not like 850mb winds are veering and bringing in some dry air that’s mixing down. There aren’t forecast soundings available for that far out (that I’m aware of), so we’ll really have to wait until we get closer to the event to figure this out. Forecast soundings are really what you probably should be looking at to figure that out. It about has to be some sort of mixing down of the dewpoints I would think, but again we will figure that out later. We really shouldn’t be worrying about details this far out.

In my opinion, the position and orientation of the surface high over the southeastern U.S. is partially responsible for these moisture woes. Not only is it too far west; it's also rather north-south oriented, encouraging northerly low-level flow throughout much of the western North Atlantic in the 24-48 hours leading up to Sunday evening. The result is that cool, dry continental air keeps entering the Gulf at low levels from the E and NE throughout the weekend. If you look at the 850 mb map valid 00z Mon, you can see the problem even more clearly: a strong high is centered over GA, with air circulating around it coming down from New England, into the Gulf, and ultimately up into the Plains. (Granted, this assumes steady-state flow and equates trajectories with streamlines, but it's a close enough approximation).

Comparing sfc and H85 progs for this weekend with historic March events in the Plains like 1990-03-13 and 2007-03-28, it's apparent that southerly low-level flow extended deeper into the Gulf in those cases, providing more tropical trajectories. It seems to me that this early in the season, a lot of synoptic-scale features have to be positioned just right in order to see good moisture return. Oftentimes, this requires an extended period of broad ridging across the eastern U.S. and far western Atlantic leading up to the show.

With that said, I'm not completely down on this system just yet. We've all seen cases in recent years where mid-upper 50s sfc dew points prove sufficient for supercells and tornadoes, particularly across the High Plains (Panhandle magic, anyone?). For Sunday, it appears that dew points in that range will likely be present across portions of the Panhandles and W KS. My biggest concern is whether the trough axis can move far enough E to support mid-level cooling and increase chances of initiation along the dryline. The timing and evolution of this longwave trough has varied so much over the past several days that it's not even apparent which day(s) will prove most promising, but if it should progress faster than the 00z GFS indicates, I like the chances of supercells with some tornado potential Sunday across W KS into the eastern Panhandles. In all likelihood, actual CAPE values will verify higher than what the GFS indicates, as has been the case with every event so far this spring.

 

[Stan Rose]

I am somewhat skeptical of the quality of moisture for this event, it's not uncommon for the moisture to be overforecast for early season events. The GFS might generally underforecast the CAPE, but there havent too many cases to compare to so far this year, at least not as far north as Kansas. Still, the shear looks terrific, and I have to work the whole time, so something is bound to happen...

 

[Chris Allington]

I was initially very hopeful about this event but now have some very big red flags... First, I'll start off with the positives. As others have mentioned I'm not overly concerned with the forecast CAPE progs as the GFS has shown very little CAPE until the day or 2 before most of these springtime set ups thus far. Its also very encouraging that its consistently had the same general area as 'the target' with the best lift, dynamics, and cape in SW NE and W KS along a dryline bulge thats been showing up for days now. I also like how the GFS has been regularly insisting on an area of backed 850mb winds along the dryline bulge out there.

That being said... has anyone else noticed the changes in the intensity of the surface low? It was regularly showing the low deepening to 994-996mb by Sunday at 00z. Now we have a 1008mb surface low at showtime, which actually weakens as the night wears on. Not only this but CINH progs consistently have been weakening slowly by 00z and then rapidly filling in after dark. Also, a quick glance at the 12z NAM this morning shows how far being its lagging the moisture compared to the GFS which is concerning. If this trend continues I think youll struggle to get deep moisture to the dryline bulge in time and end up with some towers struggling mightily against the cap in paper thin moisture and a narrow cape axis. Hoping it trends back to a positive light with the next few runs though. We still have plenty of time.

EDIT: After reviewing the 12z GFS it has shifted the area of interest much further south. From SW NE/ NW KS down to the KS/OK border area west of ICT. This makes the forecast moisture return seem a little more realistic and has increased CAPE values. That being said, its holding the main piece of energy out west and as a result the flow in all layers is much weaker. Turning (directional shear) still looks good but the weakness of the flow is pretty concerning to me. Additionally the cap looks fairly stout and with weaker flow you might have problems generating any kind of convergence along the dryline strong enough to overcome that.