2013-05-19 FCST: TX/OK/KS/NE/MO/IA

[Michael Riedl]

With the GFS continuing its trend of slowing down the storm system Sunday is a day that is looking better and better after each model run.

0z GFS progs Dryline along the I-35 Corridor in KS/OK with a warm front futher north in IA. Depending on trough evolution the Warm Front might have mode of convection issues with a Back-Veer-Back profile.

Cooling aloft should spread over the Target Area, so CAP might not be too big of a factor - though would like some EML to hold things off. Shear might not be off the charts, but it's definitely good enough.

Still 120 hours out, with mesoscale details to sort out in the last 24 hours, but right now, this looks like it has good potential.

 

[Logan Karsten]

Yeah, Sunday is indeed beginning to look like the more favorable day. I am hoping models slow the system down further so the dryline is further West in better chase terrain. A I-35 East chase is not too appealing to me at the moment. The upper level flow finally arrives, the main energy ejects, and moisture will surely be in place.

 

[Brian McKibben]

Sunday is beginning to have great potential. Just pulled a quick sounding for Watonga, OK. The thing that noticed most about the 12z GFS on 5/15 is that the 850hPa winds are a little stronger, more southerly, and further west than previous. Also, there should be great convergence along the dryline (Southeast winds up against due west).

It will be interesting to see how the NAM handles this setup tomorrow. Fingers crossed.

P.S. That is the highest Sweat that I have ever seen. Anybody else ever seen a SW > 700?

 

[Jeff Duda]

I'm sure I have seen a SWEAT index > 700 before, although I generally don't pay attention to it as I don't find it useful as a forecasting tool. The reason for that is that there is no set threshold at which severe weather and tornadoes are possible/impossible. Also, a given index value can be obtained in many different ways, so you don't really know why the value is what it is.

Anyway, I also began to take notice of Sunday after last night's model runs continued to reduce Saturday's apparent threat. The wave appears to be slowing down in the models so that it places mostly central OK square in sight of a decent severe weather threat. Mid-level temperatures are lower than on Saturday suggesting capping not being a problem, and moisture should be quite rich. I would not be surprised to see low-70s Tds in the area. This would make for excellent instability. Turning is also very good, with generally SEly surface winds turning towards the SW or even WSW by about 500 mb or so. I would like to see just a tad faster speed on the 500 mb flow, but I think even 40 kts would result in excellent shear and reduced storm motion. Definitely keeping a close eye on this day, as well as the next day, too.

 

[Russ Conlon]

NAM has come online for this day and it looks like there is good agreement with GFS. What does concern me though is the dryline nosing to or just west of I-35 by 18z before retreating and having some dry air filter in and mess with the initiation of storms or making targeting a little more difficult However, I am loving the CAPE values and the hodographs that are showing on soundings in central Oklahoma. CINH doesn't look to be an issue at all. Best set up I have seen so far this year for Oklahoma though and this looks to be a two day event comprising of Sunday and Monday. I wonder if I am crazy but this set up reminds me an awful lot of May 8-9 2003.

 

[Derek Weston]

Agree central OK looks pretty good and is the obvious target... although I wish it was setting up further west a bit.

Second target would be SE NEB/W IA area with the northern surface low.

While the 500s are more southerly, there is a significant easterly component to the 850s / surface... their strength being just as solid as what we're seeing down south. NAM projects better 0-1km helicity across IA as well. Moisture should be robust. My concern is the strength and coverage of 500mb shear on up, however. 300mb is weak and is oriented the same direction lower level shear is, which doesn't seem too ideal.

 

[Michael Riedl]

Things have gotten a little bit cloudier, at least for the spatial extent of chaseable area along the dryline. The 0z GFS and NAM both want to close off the upper level low at H5 and translate the surface low pressure and associated dryline around 25-50 miles east. Not only that but the orientation of the boundary is more NE/SW which I am not the biggest fan of. The 12z GFS was holding strong with a more due north-south oriented dryline. Due to this - it looks like there will be good parameters still in SW into SC/C OK but in a small area. Chaser Convergance to the extreme potentially. Where as with the previous runs of the GFS it was looking as if there was going to be a much larger area to chase - all the way up into KS even.

0-3KM Helicity isn't jumping off the page either. Overall though, it's still one of the best set-ups we've had in a while.

 

[brice.coffer]

I'm slightly pessimistic about this day as of right now. I looked through every major southern Plains outbreak that I could think of and not a single one had the trough arriving in OK by 12Z. The progged timing of the trough in the GFS slowed down a couple days ago, but since then, the GFS has been fairly consistent from run to run. The NAM paints a similar upper-level pattern. As the strongly negatively tilted shortwave trough approaches the region of interest, the strengthening ridge upstream in the MS Valley stays in place, causing the ejecting UL PV maximum to take a northward trajectory over W KS/MO/IA. Normally I'd be concerned about a morning MCS, but luckily a stout CAP will be in place, hopefully preventing any significant morning convection in OK/KS. By afternoon, the flow aloft over OK is nearly zonal but the hodographs over KS/MO/IA are pretty ugly, due to significant backing above 500mb from the northward moving PV maximum. At the surface, the position of the cold front moving southward from W KS into NW OK will be key. The 12Z NAM is aggressive with the southward progression of the cold front, more so than previous runs and especially compared to the GFS. Thus, low-level winds are more favorable in the GFS compared to the NAM. If I had to choose a location over 48hrs out, then I'd go with NC/NE OK around 21Z. Unfortunately, the roads east of I-35 and north of I-40 are not particularly favorable for chasing.

 

[E Hale]

This is going to be High Risk. 4000 CAPE 0-6 KM winds at 55KTs, Dew points in the low 70's. dryline mixing eastward and interacting with great helicity and CINH: We gonna get some naders.

 

[brice.coffer]

36hrs hours later, not much has changed from my previous post. Only thing I'd add is that it looks like a stronger upper-level flow/PV approaches the region around max heating. It's a different looking setup than normal, but nevertheless, it potentially looks like a big day. The key is still the location of the cold front. The NAM and GFS have a very different solutions, with the NAM being aggressive with the surging front. The low-level shear is thus more favorable in the GFS. At 18Z, the RAP seems more similar to the NAM. The morning models should be informative after the overnight convection dissipates and radiosondes sample the approaching trough. Right now, I'd stick with a target of NC/NE OK.

http://climate.cod.edu/data/forecast/NAM/00/SGP/namSGP_250_pvort_021.gif

 

[Trey Thee]

36hrs hours later, not much has changed from my previous post. Only thing I'd add is that it looks like a stronger upper-level flow/PV approaches the region around max heating. It's a different looking setup than normal, but nevertheless, it potentially looks like a big day. The key is still the location of the cold front. The NAM and GFS have a very different solutions, with the NAM being aggressive with the surging front. The low-level shear is thus more favorable in the GFS. At 18Z, the RAP seems more similar to the NAM. The morning models should be informative after the overnight convection dissipates and radiosondes sample the approaching trough. Right now, I'd stick with a target of NC/NE OK.

http://climate.cod.edu/data/forecast/NAM/00/SGP/namSGP_250_pvort_021.gif

Depending on what you read and how you see the models, I've noticed some are pretty pessimistic with regard to chasing and storms tomorrow. While the system isn't perfect they seem to never be "perfect".
The GFS and NAM are definitely handling this system quite a bit differently being 24 hours out.

To me it looks like a potent setup north of I40 and east of I35 which means I won't be going far tomorrow. The system is one of the better systems I've had in my back yard in several years.

 

[samuel stone]

Not much too add to the going target, other than that north of I40 and east of I35 chase country is complete ass compared to where I chased today, West central Kansas(best in the country if you ask me). I am hoping some supercells can stay discrete into the US 166 corridor in far southern Kansas since road options are atleast a little better there. but one must chase where the storms are.

 

[Jared Orr]

On RAP, I noticed a tongue of cooler temps (just a couple shades lighter) that becomes more defined around 21Z, a NNE to SSW tongue slightly east of I35. It persists, and the GFS shows hints of something similar. Is this the models compensating for convective cooling? It's not an outflow boundary showing up late is it?

 

[John Farley]

Agree with Trey and Samuel on the target - but I think a couple other conditions will make for a more challenging chase today. For one, the 500 mb wind is stronger - good for the development of severe storms, but it also means they will be moving faster than yesterday's storms. And, with the storms occurring closer to OKC, ICT, and TUL, I think the chase crowds could be bigger today, as if they weren't big enough yesterday. And as others have mentioned, the terrain is tougher once you get east of I-35. But it could still be a rewarding chase if you can maneuver through the trees, hills, and crowds, especially early on after initiation before the storms start to line out.

 

[Trey Thee]

DP's are only in the mid60s throughout much of eastern OK right now. Starting to make me think perhaps the NAM was onto something with the higher LCL's?