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

[E Hale]

I think people are being skiddish about this system and not trusting the models because of what happened last week with the crashing cold front undercutting updrafts. We have to remember that a scenario like that is quite rare, and rarer still to happen as we get further into the season. The GFS has had a better handle on this system so far, with the other models coming around to agreement. I have a feeling that as long as the convection doesn't get messy too quickly and overcrowd the warm sector, we should see at least 15+ tornado reports. Although the messy convection potential with this system has me recalling (albeit some major kinematic differences) April 26th 2009 which was a total bust.

http://www.spc.noaa.gov/products/outlook/archive/2009/day1otlk_20090426_1630.html

 

[Trey Thee]

I think people are being skiddish about this system and not trusting the models because of what happened last week with the crashing cold front undercutting updrafts. We have to remember that a scenario like that is quite rare, and rarer still to happen as we get further into the season. The GFS has had a better handle on this system so far, with the other models coming around to agreement. I have a feeling that as long as the convection doesn't get messy too quickly and overcrowd the warm sector, we should see at least 15+ tornado reports. Although the messy convection potential with this system has me recalling (albeit some major kinematic differences) April 26th 2009 which was a total bust.

http://www.spc.noaa.gov/products/outlook/archive/2009/day1otlk_20090426_1630.html

Apr26, 09 was a terrible day as a chaser.

At this point I had expected to see more agreement in the models. The NAM is still being a bit stubborn. Although after last week I think everyone should at least think twice about chasing this system. I agree that it becomes more rare as we go on through the spring but we're only a week later and these canadian fronts have been unusually strong. Each weather system is it's own and must be evaulated as such, despite the fact that having two such systems might be "rare" re: undercutting the updrafts.

I'm still pretty bullish on tomorrow though. At this point the data looks pretty good, the question really is how widespread will the supercells be? Will there be a few on the dryline or will we get numerous storms on the DL and perhaps a few out in the warm sector?

 

[Tim Supinie]

I think people are being skiddish about this system and not trusting the models because of what happened last week with the crashing cold front undercutting updrafts. We have to remember that a scenario like that is quite rare, and rarer still to happen as we get further into the season.

And lightning never strikes twice in the same place, right? My reason for throwing out the GFS (for now) is that if a shallow cold air mass is indeed the mode of failure for severe weather, the GFS won't pick up on it. Heck, there's a shallow cold air mass in place right now, and I'm not sure the GFS is handling it very well at all.

Last night's ECMWF did trend more northward with the cold air mass, but also had it actively advancing southward at 00Z Thursday, as opposed to staying largely stationary in the 00Z NAM and GFS runs (even though the NAM and GFS solutions were ~300 miles apart with respect to their boundary placement). The advancing southward part makes me nervous.

 

[Marcus Diaz]

Should be noted that the GFS HAD a better handle on the cold front passage this morning through TX. NAM during Monday's 0z and 12z runs showed upper 40 temps pushed way south and along I-35 in central TX. But the GFS had the front barely push through the southern sector of the panhandle. This morning's obs had low 60s just south of LBK, which is really close to what the 0z and 12z runs of the GFS had on Monday. Been watching the SREF paint a happy medium between the 2 models with the triple point sitting in NW OK and the dryline along the TX/OK border. I'm leaning towards this as the model to watch. I've kept tabs of what both NAM and GFS say the cold front say for 21z today, and going to compare it with what actually happens.

Also, this may or may not be related, but central OK had a small outbreak of earthquakes this morning, just like right before May 24 and Nov 7 in 2011

 

[Brian McKibben]

The 15z RUC seems to be more bullish than the 12z NAM in pushing the WF further north. This is a promising sign for expanding the warm sector.

What a messy uncertain forecast. I will chase from my couch (I have to watch over the family), but good luck to all. I would target SW Okla. If you are lucky you can just follow something up the turnpike.

Two Models I will be watching closely:
http://ruc.noaa.gov/RUC/Welcome.cgi
http://www.emc.ncep.noaa.gov/mmb/mpyle/spcprod/00/

 

[Tony Gilbert]

Certainly some uncertainties within the various model output has occurred over the past couple of days. Primarily noted from the GFS transit into the period covered by the NAM. ATM (subject to change) target zone looks to be around the SW most corner of OK by late afternoon. The outlook for me was always pretty much based on a high shear and relatively lower instability scenario. Prime upper forcing mechanism cannot be ignored here; Strong divergence at mid to upper levels. Ultimately storms may develop discretely then become progressively more powerful as the upper low pressure displacement is extended downward into the updraft. With up to 550 m2/s2 0-3km helicity we might expect to see a small number of tornado reports. Some of which may be regarded as strong! Main concern for me looks to be the strength of convergence derived from the dry line? This could well fall short when compared to the NAM predicted surface dew point!

 

[James Gustina]

The NAM continues to be unfriendly towards this. I think its interesting to note that the SREF was painting the NAM as an outlier though, while the other major models still have semblance of consistency and continuity with each other. I'm not too concerned about a crashing cold front considering the models sans NAM have been handling today's front movements pretty well and most have it rocketing back north sometime around the 6Z time frame tonight. We'll have to see though. For comparison though, here's two charts one from the NAM the other the GFS.

 

[E Hale]

Well, regardless of how the models are ranging in consistency, the SPC is hinting at going High Risk.
WHICH
RENDERS LOW CONFIDENCE IN MAKING ANY SUBSTANTIAL CHANGES TO HIGHER
SEVERE PROBABILITIES ATTM. WILL DEFER TO LATER OUTLOOKS WHERE
OBSERVATIONS WILL PLAY A LARGER ROLE IN ADJUSTMENT TO THE MODERATE
RISK."

Although if the NAM verifies then we could possibly slide back into a slight, I guess. I personally have faith in this system, as misguided as it may be, due to climatology. Mid-April systems like this with surging dew points and triple point/trailing dryline are notorious OK tornado producers. The further the warm-sector border and accompanying boundary can stay north the more chance of staying discrete along the dryline we have. Preliminary target for me is going to be Guthrie OK, hoping to catch a cell rolling along to the NW of the OKC metro and either staying with the cell of dropping south to catch another one.

 

[Logan Karsten]

Indeed, this system has a host of uncertainty about 24 hours out. I still think the GFS is way too bullish on the northward extent of the warm sector. The NAM may indeed be a bit too far south, but that remains to be seen. It's encouraging to see the newest RAP runs trying to turn the boundary north quickly, but for me, this is just too unknown to justify driving from MN to Oklahoma. As badly as I want to escape the cold here, I think I will wait for a more defined setup that doesn't have cold fronts of doom.

 

[Derek Weston]

Indeed, this system has a host of uncertainty about 24 hours out. I still think the GFS is way too bullish on the northward extent of the warm sector. The NAM may indeed be a bit too far south, but that remains to be seen. It's encouraging to see the newest RAP runs trying to turn the boundary north quickly, but for me, this is just too unknown to justify driving from MN to Oklahoma. As badly as I want to escape the cold here, I think I will wait for a more defined setup that doesn't have cold fronts of doom.

In the end I chickened out too. I may miss something quite nice, but a 10hr drive for a one and done chase is a bit to ask for this level of uncertainty. What I may very well do, however, is play Illinois if the WF lifts north far enough and adequate destabilization occurs. The shear profiles are more than adequate for rotating updrafts. I wouldn't mind bagging a few WF beauties on a day when everybody is playing down south. (and on most big days, if this ends up big... you have some gems on the WF nobody pays attention to)

 

[Jeff Duda]

And lightning never strikes twice in the same place, right? My reason for throwing out the GFS (for now) is that if a shallow cold air mass is indeed the mode of failure for severe weather, the GFS won't pick up on it. Heck, there's a shallow cold air mass in place right now, and I'm not sure the GFS is handling it very well at all.

Last night's ECMWF did trend more northward with the cold air mass, but also had it actively advancing southward at 00Z Thursday, as opposed to staying largely stationary in the 00Z NAM and GFS runs (even though the NAM and GFS solutions were ~300 miles apart with respect to their boundary placement). The advancing southward part makes me nervous.

Tim is right in that the GFS is not properly handling the current cold air mass across the SGP. However, the GFS currently uses 64 sigma levels in the vertical, with about 15 of those below 800 hPa, so it may not be a matter at least of vertical resolution keeping the GFS from properly handling the cold air mass. However, the NAM is handling the current cold air mass better.

I'm also very concerned about the progression of the cold air. I see deepening pressures in SE CO ATM, but not over a huge area (I think most of the current pressure falls are associated with daytime diabatic heating). However, winds are starting to veer more across the TX/OK PH (not so much the rest of TX or OK), so we may be starting to see at least some retreat of the cold air. Despite the thinning clouds over S OK, however, I'm not seeing a response in the temperature/wind field in that region to suggest the front really is lifting. Recent runs of the RAP show quite a northwestward progression of the front starting around daybreak tomorrow, and it is currently handling the temperature field pretty well, so there may be hope yet.

Bottom line: it comes down to two factors.
1) How much the front moves
2) How much precip overspreads the area in the morning and afternoon.

The more favorable these factors are, the more likely the MDT is to be appropriate. Personally, I think the MDT classification is too optimistic. However, I understand the momentum of governmental work. Once a MDT is put into place, it's tough for anyone to take it down. I would be surprised to see the risk classification change for the first few day 1 outlooks. I certainly don't see justification for a high risk at this time.

FWIW, the SREF and NAM had been in strong agreement yesterday about the placement of the front. Today, the SREF has backed the front up towards the WWD-ICT corridor by 00Z Wednesday evening. However, the NAM remains stubborn on its solution. I highly doubt the GFS or FIM solutions will be correct.

 

[Trey Thee]

Tim is right in that the GFS is not properly handling the current cold air mass across the SGP. However, the GFS currently uses 64 sigma levels in the vertical, with about 15 of those below 800 hPa, so it may not be a matter at least of vertical resolution keeping the GFS from properly handling the cold air mass. However, the NAM is handling the current cold air mass better.

I'm also very concerned about the progression of the cold air. I see deepening pressures in SE CO ATM, but not over a huge area (I think most of the current pressure falls are associated with daytime diabatic heating). However, winds are starting to veer more across the TX/OK PH (not so much the rest of TX or OK), so we may be starting to see at least some retreat of the cold air. Despite the thinning clouds over S OK, however, I'm not seeing a response in the temperature/wind field in that region to suggest the front really is lifting. Recent runs of the RAP show quite a northwestward progression of the front starting around daybreak tomorrow, and it is currently handling the temperature field pretty well, so there may be hope yet.

Bottom line: it comes down to two factors.
1) How much the front moves
2) How much precip overspreads the area in the morning and afternoon.

The more favorable these factors are, the more likely the MDT is to be appropriate. Personally, I think the MDT classification is too optimistic. However, I understand the momentum of governmental work. Once a MDT is put into place, it's tough for anyone to take it down. I would be surprised to see the risk classification change for the first few day 1 outlooks. I certainly don't see justification for a high risk at this time.

FWIW, the SREF and NAM had been in strong agreement yesterday about the placement of the front. Today, the SREF has backed the front up towards the WWD-ICT corridor by 00Z Wednesday evening. However, the NAM remains stubborn on its solution. I highly doubt the GFS or FIM solutions will be correct.

I think it's odd the NAM is hanging on with the front further to the SE. Either it's found something that the others haven't or it's wrong...ultimately they will all likely prove wrong to some degree. I could see the front backing off to the Ponca City to Enid type line basically splitting the difference. I guess we won't really have a handle on this until tomorrow morning...which means I'm unlikely to chase it given that I'd have to last minute get off work. I'll keep an eye on things this evening and see what the models show 8 to 10pm tonight...Just not willing to throw in the towel yet given the divergence.

 

[Jeff Duda]

Yes, Trey, it is very unusual. However, SREF plumes for stations in Oklahoma show that the NAM is a cold outlier. Also odd is that the GFS is typically known to have a cold and moist bias, which is not consistent with how its forecast falls into the distribution of all model forecasts for tomorrow. Bizarre.

 

[James Gustina]

The front looks like its sagging north a bit, but like Jeff said that might be a bit misleading. It looks like it was down by the Red River about three hours ago and now a portion of it is north of Ada. If it starts lifting north more rapidly in the nighttime hours like the RAP has it progged to, I can see it sitting around Enid to Alva-ish in the late morning/early afternoon. I can't pass up a day so close to Norman but hopefully the front does end up making it to northern Oklahoma.

 

[Mike Smith]

I'll offer a couple of thoughts:

Based on synoptic climatology, the main 500 mb trough is too far west (as forecast by the models) by about 150-200 mi. at 12Z tomorrow to see tornadic supercells along the I-35 corridor tomorrow afternoon. Yes, there is a band of PVA on the 18Z 4km but it is, I think, too weak to trigger much.

The westward forecast position of the 500mb trough is why pressures do not fall much during the day tomorrow -- good catch, Jeff.

I'm in HOU at the moment on business and I can attest the moisture coming off the Gulf is deep. Given that scenario, we might see an evening tornado event or even overnight if the trough turns negatively tilted as some of the models indicate. If it does go negative, watch the warm front, especially near or just ahead of the dry line intersection, for a supercell(s) with a strong tornado or two.

At 8pm CDT, the lowest pressure in the area is at Roswell, NM.That is not much of an argument in favor of the warm front moving very far north. The warm front is currently from FYV to MLC to just south of SPS. The two-hour trend at SPS is for the wind to become slightly more northerly -- again, not much chance of it starting to move north in the next few hours.

So, if I had to pick a target at this point it would probably be 70 E/S line from 15 N of CSM to 50 S of SPS. The warm front play in west central or southwest Oklahoma could be very interesting in the evening.

Good luck and stay safe.