May 7th-9th Severe Weather Episodes

[rockchalk83]

A little mystified by the SPC saying sups on Sunday will be high based. While LLVL moisture quality may not be superb like it was for Tuesday, LCLs still are going to be below 1000m for the most part...

 

The 06z NAM shows 850 dewpoints in KS to be between 3-7 deg C at 18z Sunday, with the deeper moisture in W OK. Now, that may advect into the KS part of the target area eventually, but I can see the forecaster's concerns as it relates to moisture quality and depth. The wind fields are very veered out at that height across Louisiana and Texas. For this to be great moisture quality, that trajectory has to come off the Gulf at several different levels.

 

Maybe the NAM is picking up on the interference of the upper low across the Great Lakes that Brett alluded to earlier in the week? 

 

FWIW, the 06z GFS at the same time Sunday does show much richer 850 dewpoints across the body of OK into S KS, but moisture depth and quality are concerns farther north. 

[chase_stormz]

The 06z NAM shows 850 dewpoints in KS to be between 3-7 deg C at 18z Sunday, with the deeper moisture in W OK. Now, that may advect into the KS part of the target area eventually, but I can see the forecaster's concerns as it relates to moisture quality and depth. The wind fields are very veered out at that height across Louisiana and Texas. For this to be great moisture quality, that trajectory has to come off the Gulf at several different levels.

 

Maybe the NAM is picking up on the interference of the upper low across the Great Lakes that Brett alluded to earlier in the week? 

 

FWIW, the 06z GFS at the same time Sunday does show much richer 850 dewpoints across the body of OK into S KS, but moisture depth and quality are concerns farther north. 

 

That seems to be a reoccurring problem with some of these setups, quality of moisture depth. It's alarming when the NAM is the model showing less moisture depth an the GFS. It's going to be tough to find a significant tornado threat until this problem can be resolved. 

[Radtechwxman]

This blocky pattern is really a killer for classic tornado setups. These slow moving upper level lows are good for sporadic photogenic tors but for a widespread threat we really need to break down this ridge so the system can charge east instead of at a snail's pace. What has been the main driver behind this blocky pattern? Seems like the last few years have seen persistent ridging in the central US and troughing over the Northeast

[brettjrob]

Moisture quality is definitely a concern even for Sunday, but I think it's borderline in terms of whether it would seriously mitigate the tornado threat, if other ingredients are in place. This is the type of setup you could almost write off already in major High Plains drought years like 2011-2014. But with reasonably moist soils and seasonable ET along most of the dryline, model forecasts of 62-64 F surface dew points may actually be realistic. LCLs may be a limiting factor up until early evening in some spots, but it doesn't look like a total setup killer.

 

Many forecast hodos still have an unpleasant S-shape in the midlevels. There are subtle hints at VBV, but in this case, the more pressing issue seems to be the dreaded flow weakness around H7. On the whole, hodos still look a lot better than last Tuesday. Moisture obviously isn't in the same league, but I'm leaning toward Sunday being a more impressive event on the Plains than any day last week, with gradually increasing confidence. Moisture and suboptimal kinematics are likely to keep the event from getting too out of control, though.

 

Haven't looked too closely at Saturday yet, as the only area with moisture is where it pools along the WF in S NE/NE CO, and that seems like a quite a haul from here for the quality of the setup.

[JasonOH]

Let's just say the 84 hour nam had a fun run. Mid 60s dews along the dryline, with less weakness at 700mb, and well backed surface winds leading to high SRH. Typical 84 hour nam fixing everything wrong. Lol

[chase_stormz]

Let's just say the 84 hour nam had a fun run. Mid 60s dews along the dryline, with less weakness at 700mb, and well backed surface winds leading to high SRH. Typical 84 hour nam fixing everything wrong. Lol

 

Book it 12z GFS really ramps things up by 0z Monday as well in Western OK down to the Red River area.

[nrgjeff]

Saturday looks like northeast Colorado may come together at least for a time. Forecast east-west boundary is conveniently lined up with the Palmer Divide. Might take a cell some time perhaps until it moves closer to Kansas to produce. Then it might cross the boundary rather than ride it. Still might be worth a cycle or two.

 

Sunday has potential if the moisture can return well. Also the VBV question remains to be answered. NAM and Euro are not too bad. GFS is still harsh there. Perhaps it is timing of waves; or, perhaps a more sinister northern stream influence that far south. Upper Midwest short wave in the other stream is stout Saturday night, and still matters before May 15. Northern stream could also influence moisture return, though the main issue is the current East trough. Regardless the northern stream will influence warm front placement, and keep overall questions going longer than usual this time of year.

[chase_stormz]

The 12z NAM finally brought Sunday's threat into range. Typically the NAM is poor at this range but still can give us an idea of what's to come. There's an ever so slight VBV issue with this sounding pulled from somewhere near the OK/TX panhandle border. With surface winds backed very nicely to the East of the dryline and the NAM (35kts) and GFS (50kts) showing stronger 850s than we've seen lately, Sunday certainly has my attention at the very least.

 

[JasonOH]

Looking at sharppy sounding on the NAM in western OK, (there are more data points in sharppy than the online point and click), the VBV isn't too severe in western OK. The ammount of VBV shown in the last posted sounding can be easily overcome. Due to dryline orientation, the backing winds allow for increased SRH, which has been our big problem. Also, anvil level vent looks good to keep storms from being HP messes. Let's see how things go these next few runs, but this is a good start.

[chase_stormz]

Looking at sharppy sounding on the NAM in western OK, (there are more data points in sharppy than the online point and click), the VBV isn't too severe in western OK. The ammount of VBV shown in the last posted sounding can be easily overcome. Due to dryline orientation, the backing winds allow for increased SRH, which has been our big problem. Also, anvil level vent looks good to keep storms from being HP messes. Let's see how things go these next few runs, but this is a good start.

 

It's absolutely a good start. One thing that killed last Tuesday's tornado threat, other than the significant VBV issue, was the lack of low level shear. If a sounding similar to the one that I posted above were to verify, the threat level would instantly increase even if in a narrow corridor.

[KSWx]

The 12z 4KM NAM soundings look absolutely bonkers near the triple point at 0z Monday: 

 

[chase_stormz]

The 12z 4KM NAM soundings look absolutely bonkers near the triple point at 0z Monday: 

 

 

How were you able to see 4km NAM that far out?

[JasonOH]

How were you able to see 4km NAM that far out?

That's Sunday 0z, so Saturday at 1900. He probably said the wrong day.

[KSWx]

How were you able to see 4km NAM that far out?

 

 

Meant Sunday, I'll leave it unedited for transparency's sake

[jojo762]

Don't think that a 63DP at the triple point will be possible on Saturday... But that 0-6KM wind profile is insane, don't think that will happen exactly though.

[andyhb]

A lot of backing in the upper levels on the 18z NAM @ 00z Monday, although it's mostly likely because the NAM is slower in the ejection of the trough, since the WSW flow in the 400-200 mb level doesn't reach the warm sector until after 00z.

[chase_stormz]

A lot of backing in the upper levels on the 18z NAM @ 00z Monday, although it's mostly likely because the NAM is slower in the ejection of the trough, since the WSW flow in the 400-200 mb level doesn't reach the warm sector until after 00z.

 

18z NAM soundings in W OK/TX Panhandle between 0-3z looks fairly significant in a localized area. As Andy mentioned, the trough ejection is likely a bit too slow with the NAM. The LLJ is really screaming at this time which owes to the strengthening of the low level wind fields which are strongly backed at the surface off the dryline. 

[Superstorm93]

00z MPAS looked really nasty for north east Colorado on Saturday. About 60 knots of bulk shear and 2000 j/kg of SB CAPE to work with. Has some pretty intense updrafts that track into Wyoming. Definitely keep an eye on this region. 

 

[chase_stormz]

Should be interesting to see how this looks for Sunday as well once it comes into range. The one thing that could hurt Saturday is the trajectory of storms crossing the boundary but those are some intense updraft helecity tracks.

00z MPAS looked really nasty for north east Colorado on Saturday. About 60 knots of bulk shear and 2000 j/kg of SB CAPE to work with. Has some pretty intense updrafts that track into Wyoming. Definitely keep an eye on this region. 

 

[brettjrob]

A lot of backing in the upper levels on the 18z NAM @ 00z Monday, although it's mostly likely because the NAM is slower in the ejection of the trough, since the WSW flow in the 400-200 mb level doesn't reach the warm sector until after 00z.

 

Agreed. I think that's becoming the key factor to watch - the speed and geometry of the trough ejection, much like last Tuesday. It's fairly common for the NAM to have a slow bias at the end of its range, so hopefully that's the case this time.

 

12z GFS forecast hodos along the dryline at 00z Mon, while imperfect, didn't have too much to complain about.

[andyhb]

Agreed. I think that's becoming the key factor to watch - the speed and geometry of the trough ejection, much like last Tuesday. It's fairly common for the NAM to have a slow bias at the end of its range, so hopefully that's the case this time.

 

12z GFS forecast hodos along the dryline at 00z Mon, while imperfect, didn't have too much to complain about.

 

At least we're not seeing all that junk down low like Tuesday had, this is more of a case where the issues are above 600-500 mb, which is usually more manageable than having some huge kink down in the 800-600 mb layer.

 

If there's one standout thing this setup has going for it, it's that strong LLJ. 35-50 kts of flow at H85 before nocturnal strengthening is nothing to shake a stick at.

[andyhb]

18z GFS took things up a notch by 00z Monday in west-central OK.

 

Soundings across the dryline show mid 60s dewpoints, lowest 100 mb mean mixing ratios of 13-13.5 g/kg (not super high for the time of year, but certainly sufficient deep moisture), 8+ C/km mid level lapse rates and 250-300+ m²/s² 0-1 km SRH. Can't find too much to nitpick in the hodograph structure, and the venting aloft is excellent with 80-100 kt flow in the H3-H2 layer.

[jojo762]

Surprised by the lack of hype over this... If moisture was not as much as a concern as it is, I'm sure this would be pretty well talked about given the dynamics in place. Also, everyone's trying to be a little more calm given how the last system flopped... Still impressive to have a 50-70kt H5 jetcore punch into a relatively moist and unstable warm sector that also happens to have an impressive LLVL wind field.

[bjc3395]

Would rather there be less hype. With mothers day falling on Sunday aND Tuesdays disaster in recent memory I'd expect chaser convergence to be slightly less than what would normally be expected.

[chase_stormz]

Agreed! Overhyped systems never pan out from a chaser's perspective haha.

Would rather there be less hype. With mothers day falling on Sunday aND Tuesdays disaster in recent memory I'd expect chaser convergence to be slightly less than what would normally be expected.

[frontranger8]

I'm not usually a chaser, but I may get out Saturday and see how things go. Similar in ways to the May 2008 Windsor tornado setup, which also had storms tracking NNW.

[brettjrob]

Surprised by the lack of hype over this... If moisture was not as much as a concern as it is, I'm sure this would be pretty well talked about given the dynamics in place. Also, everyone's trying to be a little more calm given how the last system flopped... Still impressive to have a 50-70kt H5 jetcore punch into a relatively moist and unstable warm sector that also happens to have an impressive LLVL wind field.

 

I really think everyone is gunshy after last week. It's amusing how much psychology and human biases can still factor into forecasting, even with such awesome and relatively reliable NWP at our fingertips. Moisture is definitely a legitimate factor to consider when assessing the potential for a real high end event, which may be slightly out of reach - but relative to the hype levels from last Tue and Fri, this is being pretty heavily underplayed.

[andyhb]

Should probably note that the models seem to be trying to make an event out of Monday as well (especially the 12z Euro). That and the 00z GFS show a second shortwave impulse rotating around the base of the ULL that reamplifies the south-southwesterly LLJ by late Monday afternoon. I remember this same type of thing occurring several times in May, 2013. The Euro shows a sharp dryline close to I-35 with backed surface flow increasing the convergence along it and 40-50 kt westerly 500 mb flow on top of it.

 

Wouldn't sleep on this either, since the moisture quality will surely be better by then barring convective influence from Sunday.

 

I really think everyone is gunshy after last week. It's amusing how much psychology and human biases can still factor into forecasting, even with such awesome and relatively reliable NWP at our fingertips. Moisture is definitely a legitimate factor to consider when assessing the potential for a real high end event, which may be slightly out of reach - but relative to the hype levels from last Tue and Fri, this is being pretty heavily underplayed.

Would think if you take the 00z GFS' moisture (Euro is perhaps a degree or two less) and synoptic setup and add a bit more surface backing, you have a pretty robust event possible. There is a sub-994 mb surface low along the KS/CO border and the GFS barely gets the surface winds passed southerly E of the dryline? I don't think so.

[thewxmann]

I really think everyone is gunshy after last week. It's amusing how much psychology and human biases can still factor into forecasting, even with such awesome and relatively reliable NWP at our fingertips. Moisture is definitely a legitimate factor to consider when assessing the potential for a real high end event, which may be slightly out of reach - but relative to the hype levels from last Tue and Fri, this is being pretty heavily underplayed.

 

Last Tues went from a dynamic negatively tilted trough hitting an insanely rich, moist warm sector to a VBV mess. This is going from a ragged bowling ball mess with modified continental air, to becoming something a little more. A part of it is gunshyness for sure but I think the inertia factor plays into it a bit.

[andyhb]

50-60 kt WSW H5 flow overlapping the dryline in OK this Euro run, stronger than the last few runs. Real nice backing of the surface winds as well enhancing convergence (as opposed to the GFS).