May Chasing 2008

[Paul Knightley]

A major severe storm outbreak seems increasingly likely later next week across quite a large portion of the Plains.

You've gotta love the ECMWF - that's why we use it at work!

 

[Mikey Gribble]

I just copied and pasted this from my blog. I made this post earlier so it was based off of the 12Z GFS and yesterday's 00Z ECMWF...


Severe weather outbreak and possibly a tornado outbreak are becoming increasingly likely during the latter half of next week. The GFS has continued to trend towards the ECMWF, while the ECMWF holds pretty much steady from run to run. Both models are similiar with the upper air pattern and strength of the West coast trough, but there are significant differences in timing and evolution of the trough beyond Wednesday. Because of this is is virtually impossible to pin down a time frame right now. The ECMWF has been more accurate this year, but it's timing may be a little too quick this time. It depicts severe weather/chase days on Wednesday and Thursday. The GFS is much slower and stalls the trough over the Rockies as it deepens. I think the more progressive solution of the ECMWF probably makes more sense for several reasons. I also think ECMWF is a little too fast with the trough ejecting into the plains (it has a tendency to be too fast with the progression of closing troughs). And finally I think both the GFS and ECMWF may be a little too strong with the strength of the trough.

That being said, this is mostly speculative and my confidence is fairly low on the timing and evolution of next weeks trough. I am very confident there will be a west coast trough though and climatology in mind it should perk up our spirits. There should also be good moisture over the gulf, which provides another reason for optimism. My best guess at this time is that Thursday and Friday will be chase days, but it could just as easily fall on any other two days between Wednesday and Saturday. I will update the forecast again tomorrow morning.

Now that I've had a chance to see the 12Z ECMWF there isn't so much uncertainty IMO as to what days hold the best potential. The ECMWF is slowing down now and falling in line with the GFS (to some extent since the GFS is still very different with the evolution of the trough) on the timing of the trough affecting the plains. I still think the GFS is out to lunch on it's evolution of the trough and stalling it out over the Rockies, but whatever. Anyways, I think the 12Z ECMWF is fairly accurate now and should be fairly close to what will happen. This is starting to make the timing more clear too and I am fairly confident Thursday and Friday will be the chase days with this system, with Thursday being the day before the day and Friday being the more widespread severe wx event. So we are back to the traditional questions with these scenarios. Moisture return and the cap will likely be the issues on Thursday. The question for the main day (Friday) will likely be directional shear. It is way too far out to be nitpicking on details that are unclear at best, so I will leave it there. You have to like seeing a negatively tilted trough though after the crap we've been dealing with this season.

 

[Greg McLaughlin]

After a dismal chase season to this point I find it difficult to not get excited about the models this far out. For all of you out there planning your chase vacations over next week into Memorial Day weekend, you might end up striking gold. I am really interested in how the GooFuS has the trough evolving over the weekend. The slow weakening trend favors multiple severe weather episodes over a large portion of the Plains given the forecast broad warm sector to be in place.

You may have a chase in Kansas one day, be in eastern Oklahoma the next, then up in Nebraska/Iowa a day or two later. Unfortunately gas prices will make chase vacations bittersweet for some, but for all of you who are coming out next week, it looks like you picked a good time....assuming what transpires resembles something close to what the models are currently showing. Given favorable climatology I would be shocked if we don't get at least localized tornado events out of this forecast pattern. Lets hope the models aren't jacking with our heads trying to add insult to an already lack-luster 2008 year.

 

[Derek Weston]

I just copied and pasted this from my blog. I made this post earlier so it was based off of the 12Z GFS and yesterday's 00Z ECMWF...


Severe weather outbreak and possibly a tornado outbreak are becoming increasingly likely during the latter half of next week. The GFS has continued to trend towards the ECMWF, while the ECMWF holds pretty much steady from run to run. Both models are similiar with the upper air pattern and strength of the West coast trough, but there are significant differences in timing and evolution of the trough beyond Wednesday. Because of this is is virtually impossible to pin down a time frame right now. The ECMWF has been more accurate this year, but it's timing may be a little too quick this time. It depicts severe weather/chase days on Wednesday and Thursday. The GFS is much slower and stalls the trough over the Rockies as it deepens. I think the more progressive solution of the ECMWF probably makes more sense for several reasons. I also think ECMWF is a little too fast with the trough ejecting into the plains (it has a tendency to be too fast with the progression of closing troughs). And finally I think both the GFS and ECMWF may be a little too strong with the strength of the trough.

That being said, this is mostly speculative and my confidence is fairly low on the timing and evolution of next weeks trough. I am very confident there will be a west coast trough though and climatology in mind it should perk up our spirits. There should also be good moisture over the gulf, which provides another reason for optimism. My best guess at this time is that Thursday and Friday will be chase days, but it could just as easily fall on any other two days between Wednesday and Saturday. I will update the forecast again tomorrow morning.

Now that I've had a chance to see the 12Z ECMWF there isn't so much uncertainty IMO as to what days hold the best potential. The ECMWF is slowing down now and falling in line with the GFS (to some extent since the GFS is still very different with the evolution of the trough) on the timing of the trough affecting the plains. I still think the GFS is out to lunch on it's evolution of the trough and stalling it out over the Rockies, but whatever. Anyways, I think the 12Z ECMWF is fairly accurate now and should be fairly close to what will happen. This is starting to make the timing more clear too and I am fairly confident Thursday and Friday will be the chase days with this system, with Thursday being the day before the day and Friday being the more widespread severe wx event. So we are back to the traditional questions with these scenarios. Moisture return and the cap will likely be the issues on Thursday. The question for the main day (Friday) will likely be directional shear. It is way too far out to be nitpicking on details that are unclear at best, so I will leave it there. You have to like seeing a negatively tilted trough though after the crap we've been dealing with this season.

Wednesday really looks like a chase day to me and potentially the one with the best directional shear. Eastern half of Kansas area. Should be enough CAPE to get it done... this has been showing up for at least a few runs now on the GFS. Trick seems to be where the best 850s land...

I would definitely be there on Wednesday as of right now.

Directional shear on Fri is hardly there -- but definitely the strongest shear/CAPE setup. Thursday seems rather unidirectional as well. Speed shear will be interesting though. We've seen a few of these sort of setups produce already this season...

Strong enough system, but none of the GFS runs have been knock-my-socks-off sure-fire type setups. Love the CAPE, shear questions abound.

 

[Mikey Gribble]

You are going off of the GFS Derek and I would advise against that given it's performance as of late. The GFS digs the trough over the central plains on Wednesday and does portray decenet midlevel flow, but I'm not buying it. The ECMWF has been much more consistent with a trough digging over the Rockies and this makes more sense for several reasons. The GFS on the other hand has been all over the place. I obviously don't know what will happen (nobody does), but I fairly certain I'm right on this one.

Even if the GFS verfied (like you are going off of) pull this up and look at the cap that's in place http://www.weather.cod.edu/forecast/
That is assuming the GFS's miracle like moisture return takes place. Right now the GFS has dewpoints sky rocketing on Tuesday. The only problem is that there is nothing there to advect that moisture northward. Logically you won't have a LLJ until Wednesday. With good moisture residing over the gulf, you are going to be hard pressed to get that to central Kansas in 12 hours. This is all assuming the GFS's upper air pattern verifies, which isn't likely either.

Derek said...
"Wednesday really looks like a chase day to me and potentially the one with the best directional shear. Eastern half of Kansas area. Should be enough CAPE to get it done... this has been showing up for at least a few runs now on the GFS. Trick seems to be where the best 850s land..."

You should go back and read my last couple posts Derek. It is very typical to have good directional shear as the trough approaches, but you traditionally have questions regarding moisture return and capping. Check the unbreakable cap out on the GFS too. If you chased Wednesday (if the GFS verified) you would be looking at blue skies. Directional shear is great, but if you don't have a storm it doesn't do you much good. Again this is all based on the notion of the GFS verifying and you are braver than me if you believe that.

Derek said...
"Directional shear on Fri is hardly there -- but definitely the strongest shear/CAPE setup. Thursday seems rather unidirectional as well. Speed shear will be interesting though. We've seen a few of these sort of setups produce already this season..."

Again you should go back and read my last couple posts. You typical loose your directional shear as the trough ejects into the plains. That is normal. That is why I said Thursday (first chase day) would come down to moisture return and the cap and Friday (second chase day) would come down to how good the directional shear is.

Go with whatever you want to, but I would strongly advise against using the GFS on this one. We'll find out by next week what's going to happen, but I am fairly certain Thursday and Friday will be the chase days with this one (not Wednesday).

 

[Derek Weston]

You are going off of the GFS Derek and I would advise against that given it's performance as of late. The GFS digs the trough over the central plains on Wednesday and does portray decenet midlevel flow, but I'm not buying it. The ECMWF has been much more consistent with a trough digging over the Rockies and this makes more sense for several reasons. The GFS on the other hand has been all over the place. I obviously don't know what will happen (nobody does), but I fairly certain I'm right on this one.

Even if the GFS verfied (like you are going off of) pull this up and look at the cap that's in place http://www.weather.cod.edu/forecast/
That is assuming the GFS's miracle like moisture return takes place. Right now the GFS has dewpoints sky rocketing on Tuesday. The only problem is that there is nothing there to advect that moisture northward. Logically you won't have a LLJ until Wednesday. With good moisture residing over the gulf, you are going to be hard pressed to get that to central Kansas in 12 hours. This is all assuming the GFS's upper air pattern verifies, which isn't likely either.

Derek said...
"Wednesday really looks like a chase day to me and potentially the one with the best directional shear. Eastern half of Kansas area. Should be enough CAPE to get it done... this has been showing up for at least a few runs now on the GFS. Trick seems to be where the best 850s land..."

You should go back and read my last couple posts Derek. It is very typical to have good directional shear as the trough approaches, but you traditionally have questions regarding moisture return and capping. Check the unbreakable cap out on the GFS too. If you chased Wednesday (if the GFS verified) you would be looking at blue skies. Directional shear is great, but if you don't have a storm it doesn't do you much good. Again this is all based on the notion of the GFS verifying and you are braver than me if you believe that.

Derek said...
"Directional shear on Fri is hardly there -- but definitely the strongest shear/CAPE setup. Thursday seems rather unidirectional as well. Speed shear will be interesting though. We've seen a few of these sort of setups produce already this season..."

Again you should go back and read my last couple posts. You typical loose your directional shear as the trough ejects into the plains. That is normal. That is why I said Thursday (first chase day) would come down to moisture return and the cap and Friday (second chase day) would come down to how good the directional shear is.

Go with whatever you want to, but I would strongly advise against using the GFS on this one. We'll find out by next week what's going to happen, but I am fairly certain Thursday and Friday will be the chase days with this one (not Wednesday).

That was going off of the GFS. GFS hasn't been too sharp this spring. Speculative thoughts based on what the GFS was throwing out for the day. Would expect to see plenty more changes between now and then. Didn't look at capping issues. Yeah, certainly seem to be issues those first two days. Be interesting to see how strong the moisture return is. Have noticed that about the way systems tend to unfold. (directional to unidirectional) Sometimes the 'day before' gets some fun, sometimes not. Will just have to see how things evolve.

 

[cdcollura]

The key point here is that MANY of the models, not only the GFS, but others (like the ECMWF), are showing the trough and looking encouraging. Never look at just one model, but a general "composite" of many models.

Last week, the ECMWF was showing a trough but the GFS a ridge, total opposite, for May 22. Now, closer to the "event", both show a similar trough in that general time frame, and I decided to make plans to get out there at that point.

 

[Mike Hollingshead]

Hmmm, looking at the 0z ECMWF I may have to become more of a fan in the GFS now(lol "fair weather fan" here). The last ECMWF run leaves that western trough highly blocked in over there by the eastern big trough. Don't exactly want to see that! Now it looks a little like early 07....high plains or bust. All I know is the low level jet is going to be highly confused if it happens like that shows...all backed to se instead of veered to sw or worse. Thursday actually makes me think a lot of March 28, 2007 on there.

Now that we get the big trough, we just need to get the eastern one to be a little weaker. Coming out slow is fine, but at least come out some.

Edit: 12z gfs in....SIGH.

 

[Jason McKittrick]

I remember seeing someone ask when the last time there was such a strong extra-tropical cyclone in the plains( ECMWF sub 980 mslp prog). Well, I did a little searching on the NOAA Daily Weather map Archive. In the last 10 years I did not find any sub 980 lows. However, there were three sub 990 cyclones.

988mb May 11, 2003
989mb May 11, 2000
985mb May 5, 1999

Two of the three cyclones listed above were accompanied by significant tornado outbreaks. Most will recognize the 1999 date. The cyclone which produce the Moore, OK tornado went on to produce 113 additional tornadoes (SVR Plot data) over the coarse of 3 days and roughly 12 long tracks.

The May 11, 2003 cyclone occurred during the record setting first 2 weeks of May 2003. The specific cyclone listed above produced a significant tornado outbreak across SE Iowa and N Illinois. It produced approximately 63 tornadoes over the three day period and again roughly 12 of these were long track.

The last occurrence May 11, 2000 produced 13 tornadoes, 1 significant and 0 long tracks.

Climatology confirms that as most of us suspect the models are most certainly over forecasting the intensity of the impending storm. All of the occurrences that I found also occurred during the first 2 weeks of May. I think it is safe to say that until the models back off on the intensity forecast that we should be real careful how much we believe.

In my opinion it is likely that we will see a pattern change to a trough in the west. This will be much more favorable for severe weather. The models seem to favor a strong ridge over the eastern US and this should produce an extended period of convection and severe weather over the central and western plains (great chase country). It will take several days to decipher the details and I will not even attempt to do so until Monday.

At this point I am still anticipating several days of good chase opportunities somewhere from central and western Nebraska to the Texas Panhandle. My main concern is the strength of the EML since the preceding airmass has been responsible for such remarkable heat along the west coast and intermountail region.

 

[Mikey Gribble]

Well after seeing the new runs of the GFS and ECMWF I started to get a little emotional. This is when I always tell myself that you can't get hung up in run to run changes. It doesn't usually work and I still got caught up in each runs changes (which leads to a roller coaster of emotions), but we really know better than to do that. We've all watched trough after trough every spring jump around on the models and after it's all over with and the chase day has come and gone we realize how wasteful it was to get pissed when one run shows something completely different from the last. I know damn well I should just ignore run to run changes and focus on the bigger picture, but I can never seem to do it. Anyways, the latest runs of the the GFS and ECMWF look like crap, but the important thing is that the last 10 runs before this didn't look like crap. All we really know with some degree of certainty is that we are getting ready to have a trough over the Rockies and that is the first prerequisite for getting a chase day. The rest will iron itself out with time.

Derek said...
"Sometimes the 'day before' gets some fun, sometimes not."

Yeah I am a huge directional shear fan, so I am also a huge fan of the day before the day chases. Greensburg last year was a day before the day. When the moisture is there and the cap breaks there are usually pretty good results on those days.

 

[Michael O'Keeffe]

I'm not concerned about how the latest models haven't looked so good. The last five days have been showing good stuff and one or two runs out of 20 models runs isn't going to hurt anyone. I mean that is a monster system and the models have a harder time trying to place one day let alone 3 or 4 days. I will start to worry by Monday or Tuesday, but as of right now I'm still banking on 3 or 4 good severe wx days from Wed-Sat sometime.

Edit: Just to add a bit more to my rant, I have called off chases 48 hours before an event and then 24 hours later packed and in the car ready to chase, so what I mean by that is models change back and forth all the time and the thing we need to do is worry 5 days down the road.

 

[Scott Weberpal]

Another thing to note is you shouldn't just look at the GFS and ECMWF without looking at the ensemble means and spaghetti plots. The spaghetti plots and ensemble means also tend to agree with the most recent solution of the operational GFS and ECMWF cutting off the upper low over the southwest. Don't forget, even though this run may have been different than the last 4 or 5, we're getting closer to the event with each run and as we get closer the models will have a better handle, thought they won't have a complete handle until the system is on shore.

 

[Mike Hollingshead]

Well at least the Canadian model keeps it more of one big solid trough, not shearing out...and moves the east coast blocker a bit more northeast.

Canadian 12z Friday

I hope it moves real slow and lets a person just find a cheap motel and not rack up a ton of miles. I also hope it has day after day hope so I don't need to drive back home between any, since I can't stand boredom(looking around at plains things).

I'm worried a little at the recent runs though. Seems like it is in the time-frame where it flips back to the crap it had been showing, then continues with that till the event. What it's done today on the GFS is a pretty good move back towards where it had been most of the time...at least generally.

And about not worrying till the few days before...I don't think anyone is anymore worried than anyone else if you are reading the thread in the first place.

 

[Mikey Gribble]

When I looked at the GEFS ensemble the other day it looked like a spider web, so it wasn't much help. I rarely look at the Canadian just because it is usually all over the place with its ensemble members too.
edit - good point Hollingshead. If you're reading this thread there is some degree of worry in your mind, whether you know it or not lol.

 

[Chris Hayes]

We're currently heading west on I-70 toward Kansas City where we'll be staying for the night. I look at the situation coming up next week like this. The fact that there will be a big trough over the west is enough to give me hope. It will have to move out sometime. Be it next wednesday, thursday, or whenever. It will move out. If it were possible for it to become a high pressure system, then I'd be really worried I have 3+ weeks to chase this year, and we just left home, so I'm happy to see a more favorable pattern setting up, even if I need to wait a few days to get an even marginal chase in