2013-04-17 FCST: TX / OK / KS / NE / MO / IL

[Brian McKibben]

This is still 4 days out, but the GFS is continuing to hint at a possible severe weather outbreak. 12z WRF tomorrow morning will bring this event into play as well. I just looked at the 00z NAM and it looks like moisture will be pretty good. It looks like we will have a nice dry line from KS to TX. The upper level support should be there are the right time. Directional and speed shear look great. Also, I don't think we will have any cap issues this time.

I am going to keep an eye on the run to run consistency to see if this system plays out. If so, it could be a big day for the southern plains.

 

[Chris Wilburn]

This day is something to keep an eye on for sure. Previous model runs had this day as a cold front crashing through OK which obviously isn't good for chasing. Now it has a cold front in western KS and developing a dryline from KS into OK like you mentioned Brian. Definitely looks like moisture won't be an issue by looking at the NAM. It will be nice to look at the NAM at 12z to compare. Will post again when the NAM picks up on this day.

 

[Brian McKibben]

Just looked at the 12z NAM. All i can say is WOW! Look at those winds. I pulled a forecast sounding for OKC and LAW. I thought OKC was impressive with helicity of 555 m2/s2. Then I looked at LAW... 636 m2/s2. Here it is:



Here is the link to bigger image: http://weather.admin.niu.edu/chaser/tempgif/27713.GIF


The models are still in disagreement with this system. I like the GFS because, well, the results are more chaser friendly. This is definitely a system in which one should watch closely. The ingredients could be possible for a tornado outbreak.

SPC has Mod Risk for day 3.

Anyone else have some more thoughts? I got all antsy looking over those winds that I have ignored many other factors

 

[James Gustina]

The only real problem with this one is the possibility of a "hot mess" along the front. The shear is definitely a lot better but the NAM has been hinting at overnight convection that may leave some clutter in the morning, which may bring down those insane-o-CAPE values the GFS and even the NAM to an extent, have been spitting out. Overall though it looks like a solid day if semi-discrete cells pop in and around that stationary front, because the upper level flow is so much stronger going a little bit past 18Z plus the nice shear and at least modest moisture. I just wouldn't throw outbreak out there yet even with what the SPC is tossing up.

 

[Chris Wilburn]

Hopefully some discrete cells can pop just south of the front and along the dryline. This will keep storms away from the front which like you mentioned James can be a "hot mess." Of course, storms can interact with the front and go nuts. However, I prefer more of the dryline play into NW TX and extreme SW OK. It's not a crashing cold front so undercutting shouldn't be an issue like last Tuesday. Wind shear values are very nice and moisture and instability is about as good as you can get. It definitely has outbreak potential, but still some things to be lined out. I definitely agree that the GFS paints a better scenario for chasing. It has more of a classic dryline setup. I am going with the NAM though since it has seemed to perform better so far this Spring. With that said, the NAM looks very good as well. Still a couple days to look things over though. It definitely is worth keeping an eye on for sure.

 

[Ethan Schisler]

I've been watching the warm front play across MO/IL as the 00z NAM showed very high EHI values and good helicity in that vicinity coupled with 2000+ SB CAPE. However looked at the 12z NAM and it didn't look as good. My only play looks to be the dry line across North Texas into Oklahoma/SE Kansas where significant severe weather will be possible if storms don't congeal into a hot mess quickly. The GFS screams outbreak with even great potential still along the warm frontal boundary from MO into IL, but the NAM looks like a hot mess to me in some ways and would be more conditional. Will be holding out until 00z to decide if I am chasing or not. Definitely think this setup has good potential with it.

-Ethan Schisler

 

[Derek Weston]

Loves: Wonderfully backed SE surface winds... leads to nice veering up through 700mb on most hodos I see. Robust instability should be realized for southern target.

Doesn't love: Precip signals from NAM show way too much junk convection early in day... especially north of TX/OK border region. Stalled out front (as depicted on NAM) a blessing and a curse.

Early plan: Play extreme SW OK down into TX to catch storms popping off dryline as environment to immediate north may be compromised. If environment to immediate north isn't compromised... we party hard.

 

[Jacob Ferden]

I still am wondering exactly where the placement of the front will be. The models did such a lousy job with the frontal surge last week that it is a bit difficult to give a great deal of trust to what they're currently showing for this Wednesday. Having said all of that, the parameters speak for themselves: powerful 500 mb system, screaming 850 mb winds out of just the right direction, CAPE > 2000 j/kg, great hodo's...it's all there...but as Derek said, what happens with convection to the north?

If the GFS is right, I think we're looking at a major tornado outbreak of the type not seen since April 14 of last year.

If the NAM and Euro are right, which is my inclination, I think we're looking at a localized but high end event in SW OK/ NW TX, with the threat spreading east depending on southward progression of the cold front.

If the latter case, better be ready for some off the scale chaser convergence...if the NAM's target was any more obvious, there'd be smoke signals going up down there.

 

[Logan Karsten]

While it's very easy to look at the GFS/FIM models, one has to remember what happened last week. The GFS did a lousy job of advancing the cold pool across the Southern Plains. This is why my confidence is placed on the ECMWF/NAM solutions. The kinematics for Wednesday look great, no doubt about that. However, my biggest worry is that the cold front will be crashing down the dry line across western Oklahoma during the afternoon/evening hours. While storms that can fire along the dry line will have a great environment to work with, tornado potential may not last long with the approaching cold front. The NAM is places the cold boundary farthest south, with ECMWF still placing a bulge into west central/northwest Oklahoma, with accelerated movement southward towards 00Z and beyond. The other potential problem is the persistent clouds/precip models place in the warm sector. This will not kill instability completely, but it will limit things. This looks like a good chase for chasers living in the Southern Plains, but a big gamble for anyone who has to drive more than 3-4 hours to get to the target. If 00Z NAM/ECMWF back off that cold front, then I would say Oklahoma has more of an outbreak potential. However, currently, it looks like a localized region that will see supercells/tornadoes, and it is conditional at this point.

 

[Derek Weston]

While it's very easy to look at the GFS/FIM models, one has to remember what happened last week. The GFS did a lousy job of advancing the cold pool across the Southern Plains. This is why my confidence is placed on the ECMWF/NAM solutions. The kinematics for Wednesday look great, no doubt about that. However, my biggest worry is that the cold front will be crashing down the dry line across western Oklahoma during the afternoon/evening hours. While storms that can fire along the dry line will have a great environment to work with, tornado potential may not last long with the approaching cold front. The NAM is places the cold boundary farthest south, with ECMWF still placing a bulge into west central/northwest Oklahoma, with accelerated movement southward towards 00Z and beyond. The other potential problem is the persistent clouds/precip models place in the warm sector. This will not kill instability completely, but it will limit things. This looks like a good chase for chasers living in the Southern Plains, but a big gamble for anyone who has to drive more than 3-4 hours to get to the target. If 00Z NAM/ECMWF back off that cold front, then I would say Oklahoma has more of an outbreak potential. However, currently, it looks like a localized region that will see supercells/tornadoes, and it is conditional at this point.

I'm ready for a big gamble. About 10hrs from a target location. I'm liking the fact that the NAM has kept the CF in approx the same position the last 3 runs. Doesn't seem to crash it too fast the next 3 hours either. Even if the northern areas of OK are limited due to junk convection a storm that right turns hard off the dryline down south could be quite a bit of fun as it marches down the red river valley region. Probably pull the trigger if tonight's run again hold's CF at bay.

 

[Chris Wilburn]

While it's very easy to look at the GFS/FIM models, one has to remember what happened last week. The GFS did a lousy job of advancing the cold pool across the Southern Plains. This is why my confidence is placed on the ECMWF/NAM solutions. The kinematics for Wednesday look great, no doubt about that. However, my biggest worry is that the cold front will be crashing down the dry line across western Oklahoma during the afternoon/evening hours. While storms that can fire along the dry line will have a great environment to work with, tornado potential may not last long with the approaching cold front. The NAM is places the cold boundary farthest south, with ECMWF still placing a bulge into west central/northwest Oklahoma, with accelerated movement southward towards 00Z and beyond. The other potential problem is the persistent clouds/precip models place in the warm sector. This will not kill instability completely, but it will limit things. This looks like a good chase for chasers living in the Southern Plains, but a big gamble for anyone who has to drive more than 3-4 hours to get to the target. If 00Z NAM/ECMWF back off that cold front, then I would say Oklahoma has more of an outbreak potential. However, currently, it looks like a localized region that will see supercells/tornadoes, and it is conditional at this point.

I have some concerns too about a crashing cold front. However, the NAM has been keeping it pretty much stationary until it begins to makes its move east and south overnight. Hopefully this is the case so we don't have to worry about a crashing cold front ruining the party. I too have concerns or early day convection along and south of the stalled/warm front. I agree the best play may be extreme SW OK across the Red River into TX for dryline storms.

 

[James Gustina]

NAM is starting to look more and more like an outlier. GFS, Euro, SREF and UK-MET all show a much more amplified trough with that frontal boundary a good way north (100-ish miles). If the majority of the models keep this trend up, could be a nice day in west-central Oklahoma with the kind of 0-1 km shear values (aoa 30kts) and instability profiles they've been throwing out. Will have to wait and see though.

 

[jeremy wilson]

NAM is starting to look more and more like an outlier. GFS, Euro, SREF and UK-MET all show a much more amplified trough with that frontal boundary a good way north (100-ish miles). If the majority of the models keep this trend up, could be a nice day in west-central Oklahoma with the kind of 0-1 km shear values (aoa 30kts) and instability profiles they've been throwing out. Will have to wait and see though.

Even if the nam is the outlier and it confirms, it still looks great imo. The only prob i see is massive chaser convergence if the nam verifies.

 

[James Gustina]

If the SPC ups it to a High, then it'll be an unholy derpfest. But if the other models verify then it'll be a much broader area to play in and hopefully there won't be a bottleneck in one corner of Oklahoma and/or Texas. Storm speeds will probably be decent looking at the steering winds, nothing above 35 if the Euro is hitting it right. Just becomes a question of how discrete everything is.

 

[Tim Supinie]

As others have said, my main concern is the cold air mass to the north and how quickly it will move southward during the day Wednesday. The ECMWF and NAM are giving us this really shallow air mass again, which means I don't trust the GFS solution, as it will probably not have a handle on that shallow an air mass. (Evidence: the GFS handled the shallow front last week the worst out of the three). One question is "Why is the air mass that shallow?" (related question: "Why is it that shallow again?"), and I haven't dissected the model output long enough to have a good answer to that.

I suppose the good news is that the NAM has no freezing rain signals in its 60-hour forecasts this time around, so that's something ...