5/1/08 FCST: KS/MO/OK/AR/TX/NE/IA

[Chris Hovanic]

I'm thinking the triangular area of Kansas from Emporia to Winfield to Coffeyville has the best chance of breaking the cap tomorrow.

Two huge concerns however...

1) Moisture return, discussed ad-nauseam already. I think low-mid 60s advecting back into the above mentioned area is reasonable, but anything less will lead to far more negative buoyancy than indicated on present forecasting soundings.

2) Potential for a stratus-marred warm sector through the day. The NAM has been indicating the potential for a thick stratus deck through much of the afternoon across SE KS. This is rather disconcerting, as every bit of surface heating will be crucial given the strength of the EML that is forecasted. For whatever reason, a stratus deck beneath the EML inversion has been quite prevalent so far this chase season. We'll see if it decides to foul things up for tomorrow. It should be noted however that the GFS is much more aggressive with boundary layer mixing tomorrow, and would keep stratus concerns at bay.

It's also interesting to note that the 4km WRF appears to keep the dryline much further west tomorrow, back toward the Wichita area, will be interesting to see if that verifies.

All the above being said, IF thunderstorms are able to form before dark tomorrow, they should be isolated, and have a high potential of becoming tornadic after 7-8pm.

 

[Mike Hollingshead]

I'm still having conflicts with the banana type look the NAM and GFS both want to do. It'd be really nice if that sw-ne orientation to the sfc low would vanish on tonight's run and tomorrow.

Just looking at the 12z UKMET and it still looks a lot better. It and the ECMWF have been as consistent as the NAM/GFS, but nicer with the low level organization.

0z 850 Jet

0z sfc pressure

I'm sort of counting on things being closer to those models.

500mb winds

Probably wish casting on my part, but it just sounds nicer...and they too have been consistent.

Edit: Jeez, look what the RUC does with the sfc low tomorrow.
http://ruc.noaa.gov/disp2.cgi?/w3/rapb/plots_13km_dev/.//+sa5_ppt+am+33
http://ruc.noaa.gov/disp2.cgi?/w3/rapb/plots_13km_dev/.//+sa5_ppt+am+36

http://ruc.noaa.gov/disp2.cgi?/w3/rapb/plots_13km_dev/.//+rh850mb+am+33

http://ruc.noaa.gov/disp2.cgi?/w3/rapb/plots_13km_dev/.//+sa5_p500mb+am+33
Nuts.

Better air must be starting to cross Buoy 42002. TD been holding steady around 60 all day, has jumped 3 degrees in last 2 hours. Too bad more of it can't be onshore by tonights soundings.

 

[mark plate]

The quality of moisture remains suspect prior to 00Z. Dewpoints may reach the lower 60s in SE KS but that's about it. There may be a storm or two along the dryline around 00Z...likely LPish in nature. After 00Z, the UKMET clearly shows a retreating dryline which usually is not favorable for sustaining storms to its east. It's not until 06Z and beyond that the dryline/cold front start punching east and an eventual squall line is likely to develop and sweep across the area. Tornadic potential is iffy to me the way it looks now before dark in the southern target area. Northern/Central Iowa may actually be a potential sleeper area late tomorrow and tomorrow evening. Dewpoints should be as high there as they are in SE KS and the chances of a storm before dark are probably better.

 

[Derek Weston]

Northern/Central Iowa may actually be a potential sleeper area late tomorrow and tomorrow evening. Dewpoints should be as high there as they are in SE KS and the chances of a storm before dark are probably better.

Based on what model runs? 500s really seem to die out over that Iowa so I've been writing it off. (shear doesn't seem to work according to NAM)

 

[Jason McKittrick]

Buoy discussion 24 hours in advance of the event? That says it all.
April Cyclone + June EML + March Moisture = Sunshine and Wind. I will definitely be staying local for this one and if we don't have 60 dewpoints in SE Kansas by 6 AM I will probably cash it all in.

 

[Ilya Neyman]

One thing you gotta keep in mind, is the Gulf is a warm body of water, and any dry air blowing over it will be modifying substantially, especially the longer its over the water.

It seems like this modification is well underway across the central Gulf with dewpoints already rising despite continued easterly flow. Furthermore, pressure falls are commencing across much of the Gulf, with rises noted off the East Coast. Trajectories are veering with earlier E flow now more SE and SSE, especially the further west you get. In addition, the richest and most intact moisture to be found would be over the SW Gulf, west of the Yucatan where the frontal intrusion had its shortest effects. It's out of this area in particular that most of the moist advection will be taking place into the Plains. Speed transfer will be increasing tonight as near surface flow will be increasing to 30-40 kts at 925mb. This should allow the really rich air to make a move to the north, and which is why 60+ dews crossing the Red River by midnight isn't that unreasonable.

I am not at all concerned about the amount of moisture moving northward as I would be how much, if any, may mix out. That, will have to do with the 925-850 flow more than anything else tomorrow afternoon.

There will be a lot of dynamics coming out of a very intense and well organized negatively tilted trough. The capping will be quite strong, and the lack of moist sector and daylight qpf signals on latest model runs is a concern. CIN is, however, forecast to weaken substantially east of the dryline by early evening, and if there is enough convergence, and the 850 flow backs faster than it did last Thursday, a storm or two may pop. If that happens, significant shear and very strong instability will no doubt be supportive of significant severe weather from central-eastern OK northward across E KS.

If the cap holds, all that stuff wont matter.

This once again, will be a question of initiation.

 

[Adam Penney]

I am totally with you Jason. You really put it into perspective. When we are discussing dewpoints that are not even on shore yet, yes, that says it all.

I see the CAP as a major inhibiting factor. With dewpoints likely being overdone by current model progs, and the slight veering of 850 winds tomorrow, I am concerned that moisture quaility will be a significant problem, and thus being a lesser factor in helping to burst the CAP. I do see how the 850 winds are expected to start to back a little come late afternoon, but any veering at all could cause that dryer air from the SW to be pulled in and mix out our dewpoints at the surface. Considering the fact that dewpoints may only be meager at best, any mixing at all(a few degrees)could be devasting, IMO.

I am in between both targets, so I will check things in the morning and make a call around noon to chase or not. It would be terrible to see so much potential go to waste. But hey, this is mother nature we are talking about. When does she ever make sense?

 

[mark plate]

Based on what model runs? 500s really seem to die out over that Iowa so I've been writing it off. (shear doesn't seem to work according to NAM)

UKMET and ECMWF. GFS and WRF-NAM are both weaker. 30 knots at 500 mb is just enough so the chances before dark there may be as good as they are in the southern target. The southern target will be better by 06Z, but by then it's too late.

 

[Shane Adams]

Moisture concerns aside, am I the only one who sees this being a nocturnal event all the way? The main upper support at h5 doesn't even arrive until 6Z. Maybe I'm missing something.

 

[Rich Thompson]

Mid 60s are onshore from Matagorda Bay into the lower valley, and 60 F Tds have now reached SAT-AUS. We have ~24 h to move the moist boundary layer to OK and KS, which means we need about 20-25 kt mean low-level flow through that period. That won't be a problem.

The moist layer has been somewhat resistent to mixing today because of a sharp EML above the boundary layer, and moisture transport has exceeded any small mixing impacts. That should continue through tomorrow, which is why 62-64 F Tds should be reasonable across the ern half of OK into at least SE KS. The tough part of this forecast will be the weakening of the EML from the west tomorrow. I suspect tomorrow's 12z soundings will look awful in terms of CIN, and the rate of cooling at the base of the EML will be a bit uncertain given the missing ABQ sounding.

I wouldn't worry about the "veered" low-level flow killing the moisture through daytime heating/mixing, because the veered flow will be part of the EML and somewhat decoupled from the moist layer. The real trouble will be the moisture depth in relation to the LFC height. A "shallow" moist layer will require stronger and more focused ascent to shelter the lifted parcels from dilution. The veered flow above the surface suggests that lifted parcels will detrain more quickly from the zone of ascent along the front/dryline, unless the front or dryline is strung out NE-SW which wouldn't really help for other reasons.

I'll keep watching and assume that this will be a late decision tomorrow with substantial bust potential. My first guess is the same as many others - roughly the KS/OK border somewhere between Arkansas City and BVO (can't go any farther because of work that night). Forecast soundings from the NAM and GFS come up with some nice sigtor analogs for that same area tomorrow, FWIW. This situation would be much more interesting with 66-70 F Tds.

Rich T.

 

[Mike Hollingshead]

Buoy discussion 24 hours in advance of the event? That says it all.
April Cyclone + June EML + March Moisture = Sunshine and Wind. I will definitely be staying local for this one and if we don't have 60 dewpoints in SE Kansas by 6 AM I will probably cash it all in.

Yeah some of us are crazy, looking for that wall of good juice(not March) that will ride the dynamics from that "April" cyclone north, and reside under 6c at 700mb in the afternoon(that'd be a breeze in June ).

BTW, 42002 now at 66.4 dew, up 6 in 4 hours. I'd say the wall is near there.

And as for 60 TD in se KS. I'd think you could look at midnight and see those.

 

[Adam Penney]

Mike,
I sure hope you are correct. Everyone is certainly entitled to their own opinion. If we see 60 Tds in SE KS and midnight, that would pretty much make up my mind for chasing tomorrow. Hopefully we can get enough convergence along the dryline to get it to pop before dark. I chased the event last Wednesday in Texas, so funds are a little short this week. However, considering its less than a 4 hour drive to any one of the target areas tomorrow from KC, if we get that kind of moisture return by midnight, I will definitely be chasing tomorrow.

Heres to hoping your optimism wins out Mike....

 

[Jared Farrer]

Yeah hoping for moisture as far north as central IA seems at this point a little loopy! But as for shear, dereks right its good until you get up to around 500mb then it is just weak to say the least. Not sure if that profile would be enough given there was any moisture? Looks good though if things could speed up a bit!

Hard to play this one out! I guess we will just have to see how far the moisture will get by around 00z friday.

Ohhh yeah and I forgot to mention gas is up to 3.70, LOL. Not fun for me I live in IN. And if I see any miracles in the moisture department I will be on the move again like always! Talk about an expense I envy all of you who complain about driving say as far as central OK from KC

 

[Michael O'Keeffe]

I agree with Mike. Looking at the lastest RUC at 23z it is barely showing 50F tds pushing into Kansas (which is exactly how it looks now) and as the night goes on it increases fairly quick and I assume that is from the relatively strong winds at 925mb that will dramatically increase after 01z tonight. With a 40-50knt streak stretching from S TX into E Kansas. By 10z tomorrow we could see 60F tds poking into SE Kansas. I haven't been able to trust the RUC lately after last weeks embarressment, but it just seems very believable to me this week. Also we don't have storms on-going now that would scour out the moisture which I am pretty confident was what happened last week. We will have at least 18 hours of good strong winds near and at the surface to bring the moisture up.

RUC surface map at 01z tonight. Check out those isobars!!!
http://www.rap.ucar.edu/weather/model/ruc06hr_sfc_wind.gif

 

[Mikey Gribble]

64 would be pretty damn good for March.
I agree with Rich that low to mid 60's should make SE Kansas by 22Z tomorrow. 925mb winds are screaming out of the South at 40-50kts and at those speeds you can make some serious progress with moisture advection in 12 hours.
I also agree on the veering 850mb not being as damaging to the moisture as it was with the setup where the storm fired south of Norman. Forecast soundings show that winds don't really start veering until you get above 900mb. With the inversion starting at 900mb the dry layer should be decoupled from the boundary layer moisture (as Rich mentioned) keeping mixing to a minimum. So dewpoints aren't much of a worry, but the depth of the moisture is a slight worry. Since we have veered 850mb winds virtually all the way from now through Thursday night (small window where they back tonight), the moisture advection will take place below this level. Normally I like to see moisture depth up to 850mb or so, but I don't think the moisture will be shallow enough tomorrow to cause significant problems. Rich mentioned a good point on the shallow moisture increasing the distance from the moist layer to the LFC, which will make it even more difficult to break the cap. In a normal year I would have some optimism strictly because historically when the cap has been an issue it breaks more times than it doesn't. Well that certainly hasn't been the case this year. I am about one bad chase away from setting a season record for cap busts. Tomorrow could very well be the record breaker unfortunately.
If storms do manage to fire along the dryline between OKC and Wichita there is a very good chance they will be tornadic. From 00Z-03Z strong tornadoes would certainly be a threat with any storm in this area. My target as of now is Bartlesville, Oklahoma. I want to get there early enough to forecast and adjust if need be, so I plan on being there by 3PM or so.