2015-05-09 EVENT: TX/OK/KS/NE/CO

[Eric Bucsela]

I know that Saturday is on more than a few folks minds, so I thought I'd start a thread. Sorry if it's premature, but some of us have to make the go-no-go decision early!

This day looks like the culmination the current system. Both GFS and ECMWF have a healthy negative-tilt shortwave ejecting into the Plains duing the day/eve with 50+ kts shear. From a low in E CO/W KS, the dryline pushes down into the E TX panhandle with backed surface winds ahead of it. GFS dews are in the low to mid 60s. Looks like the surface low and triple point will set up somewhere near the W Cntrl KS border.

The GFS has been trending more meridional with the winds and this doesn't help hodos above 700 mb. CAPE has also been trending down. 12Z run shows it < 2500 J/kg. So there are obvious doubts whether things bode well for classic supercells/tornadoes.

This early, all is subject to change, but would love to hear opinions!

 

[Jeff Duda]

The biggest thing that worries me about pretty much all days this week, including Saturday, is early development of precipitation/convection across a widespread area covering the target. The GFS has been consistently developing precip between 15Z and 18Z up and down the dryline. This just kills the surface temps and really keeps instability pretty low. If that much precip really does overspread the warm sector and minimize sunshine and destabilization, I suspect this event will be pretty spotty and marginal.

 

[Tony Gilbert]

Jeff certainly has a point which I fully agree with. ...I currently see my earlier arranged chase partner flying out the DFW tomorrow early without me because I need to finalise some of my local customer contracts.
Though I am under no illusion regarding the forecast diagrams a few days early. This outlook could well be reminiscent of past localised stronger severe weather events?...........
The upper long wave trough according to GFS is trying to drop a short wave circulation down over New Mexico. If this can occur and pivot slightly further east we could well see a combination of steep lapse rates, strong shear and most importantly some very high 0-3km SRH values. All hypothetical of course but maybe worth keeping a very close eye on this one from this point onwards!
Now whilst a similar process may have already occurred around five times this season I do wonder if early season conditions truly get the warmest seasonal SST feed from the Gulf till mid May onwards?

 

[Stan Rose]

Huh...sure looks like classic outbreak material to me...Saturday and maybe even Sunday. SPC just put out a 30% day 4 which may be the first I've seen this season...
Storms will be flying both days though, typical early season madness.

 

[James Gustina]

Just took my first peek at the models for Saturday and holy hell. ~1000 mb SFC low lee cyclone in the SE CO sweet spot with moisture in place well in advance over W Oklahoma and Kansas aoa 65F. Deep-layer shear is decently strong and well into the upper 40 knot range, with the shortwave taking on a nice negative tilt by 18Z Saturday. Mid-level height falls look surprisingly modest but I'm not overly worried about getting enough lift to get through any inversions that might manage to stick around. Like Stan said, looks like steering winds are going to be very fast out of the WSW meaning these things are probably going to be flying off the dryline into the warm sector. All in all, looks like a very solid western Oklahoma day and a pretty synoptically-evident outbreak of severe storms.

 

[Andrew Stoller]

12z 5/6/15 NAM is out and in range to 00z Sun. Yea, looks epic, and the GFS is now in alignment with the NAM and the concern of unidirectional deep layer flow is mitigated. Both have southwesterly 500mb with due easterly/southeasterly up to almost 700 mb thanks to a cold front that drops down Friday evening and retreats northwards as a warm front Sat afternoon. This looks to be a classic triple point setup somewhere roughly from southwest KS southwards into the north TX panhandle. points further south along the dryline get away from the speed max in the 500 mb flow rounding the trough base. Looks epic to me and I'll be there bright and early.

:edit: Just checked the surface on the GFS and it has the warm front much further north into southern Nebraska which keeps the unidirectional shear profile issue in place, but better prospects further south along the dryline. it's model watching at this point; fine details will emerge closer to the event.

 

[Matt Hunt]

Now that the NAM is within range, I'm making the call to take the long trek out to the TX panhandle or somewhere in that vicinity. Not much to add with what was said earlier. The 12z and 18z NAM are nearly identical, with the dryline right across the center of the TX panhandle, SW winds behind the dryline pushing into SE winds in the warm sector. This should be a good one. Anyone else notice the depth of that moisture? All the way up to 700mb! Some pretty big curved hodo's in the PH also. I'm expecting some strong tornadoes on Saturday, and yeah they'll be moving pretty quick.

 

[Mike Marz]

Latest NAM can't really get a lot better in my opinion. It is showing great 850s out of the south/southeast at 0z on Sun at 35-40 knots over the warm sector. It is showing 60-70 knots of 500s coming over the dryline out of the southwest by 0z Sun and up to 80-90 knots at 250. The current run also shows plenty of cape developing behind some early afternoon precip and it fires precip along the dryline by 0z Sun. Hodographs look amazing and storms flying off the dryline into that environment could get real serious. Hopefully things continue to look this promising as we draw closer.

 

[Jeremy.Degenhart]

I'll be heading over after work Friday...looks like the haul will be worth it. Worth noting that there's very slow boundary layer showing on soundings through 06Z late Saturday night/Sunday morning. Could be a long night.

 

[Jeff Duda]

This event has bust potential. Veer-back wind profiles across much of the DL in OK. I've never had a good day when dealing with S-shaped hodographs. They lead to messy storms.

The veer-back has been consistent in both the GFS and NAM.

 

[Jeff Snyder]

Jeff Duda just mentioned my main concern for Saturday. Some mid level backing yields ugly veer-back wind profiles and S-shaped hodographs in most of the forecast soundings I've seen from the GFS and NAM. Yuck. I have yet to see a good tornado in such an environment. I'll post a more detailed forecast later.

 

[Mike Marz]

The veer-back was bothering me a lot earlier this week. It has been a pretty consistent element in the models, but I feel that it has consistently improved with each run also. It would be quite disappointing if S-shaped hodographs put a hamper on this event...

 

[Jared Orr]

I'd also like to mention the possibility of elevated convection or pre-mature convection in SW Oklahoma spoiling the fun in these areas until late in the evening when the air-mass finally recovers. Both GFS convective precip and NAM simulated precip are showing an MCS being present at 18Z...It may force me to target something closer to the triple point, even though I would have more of a concern that this area would not remain discrete as long.

I'm quite surprised that they are issuing a moderate already. It certainly has potential, but there seem to be some unknowns about storm mode that could really affect things. I'm still chasing of course! It's a freakin Saturday! I'll see you and you and you and your uncle and your housemaid out there.

 

[Stan Rose]

I'd also like to mention the possibility of elevated convection or pre-mature convection in SW Oklahoma spoiling the fun in these areas until late in the evening when the air-mass finally recovers. Both GFS convective precip and NAM simulated precip are showing an MCS being present at 18Z...It may force me to target something closer to the triple point, even though I would have more of a concern that this area would not remain discrete as long.

I'm quite surprised that they are issuing a moderate already. It certainly has potential, but there seem to be some unknowns about storm mode that could really affect things. I'm still chasing of course! It's a freakin Saturday! I'll see you and you and you and your uncle and your housemaid out there.

Im not at all surprised. It has 'High Risk' written all over it. That doesn't mean it will be a good chase day of course, since High Risk storm mode/storm motion often leads to epic chase busts, but there will be widespread severe weather Saturday. People can nitpick and find kinks in the hodos all they want, but the big picture (pattern recognition) says outbreak. I hope I'm wrong, cause it will be bad news for the people in the path...

 

[Brian McKibben]

I cherry picked this sounding from the 12z NAM from the area where the STP is approaching 10 (NW Okla.).

500 hPa trough looks negatively tilted and 850 hPa winds are progged 40+ from 190° to 170°. Looks like there is some pretty good diffluence at 250 hPa. Tds are in the upper 60s and low 70s across the warm sector. PW is approaching 1.5 so these should be pretty good rain producers (right?). It looks like the apex of the DL bulge will be in SW Okla. I am curious to see how much cloud cover we have in the morning and how long it takes to burn off.