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

[mark plate]

Gulf bouys show mid 60 to low 70 dews in the southern portions. The northerly flow turns around tonight and there's really good return flow for at least 36 hours before 7pm Thursday.

http://www.rap.ucar.edu/weather/mod...25_wnd&hours=hr36hr42hr12hr48hr18hr60hr24hr30


I don't think moisture will be too big of an issue.

I hope the UKMET or ECMWF are a lot closer on this. If the UKMET is right I'll be heading towards se KS Thursday. If the NAM or GFS are onto things, I don't know that it will be worth it or not.

I can't see what it does with the sfc winds where I'm looking at it, but the 850 500 cross over looks like it would be pretty sick in se KS. The sfc low looks better on there and I would guess they'd be a little backed.

SFC winds on the UKMET are about 160-170 at about 15 knots at 00Z in SE KS. You're right about the 850/500 cross over and if the UKMET verifies, SE KS does look best. No need to rush down there though...this will not be an early show the way it appears now.

 

[Adam Penney]

This far out. I will keep it brief. Lets just say that ATTM I am less than impressed. I have not seen the ECMWF, but according to the NAM only ~60 degree dewpoints make into SE Kansas around 0z. Looking at observations across southern texas and the Gulf, this seems much more realistic than the GFS which IMO is overdoing(again)the dewpoints. To make matters even worse, both models have 850 winds veering badly which would advect drier air and cause significant mixing down at the surface.

I am VERY much hoping I am wrong, but as of now, count me as on the pessimistic side with this set-up. Someone please show me how I am wrong, and turn my frown upside down.....lol

 

[davecarlsen]

I, too, am very concerned about the moisture return. I would need to see better evidence of moisture return before I would embark on a 3-day round trip for this setup.

 

[Michael O'Keeffe]

Like Mike mentioned in earlier post. We will have at least 36 hours of uninterupted flow from Gulf before Thursday afternoon. Here in KC we have a nice SSE wind now with winds out of the south; tomorrow we will see south winds once again with stronger winds with gust around 35mph. Over the next day and a half we could easily see a nice rise in the dewpoints at least suffient for tornadic sups in NE Oklahoma on Thursday afternoon/evening.

 

[Shane Adams]

Like Mike mentioned in earlier post. We will have at least 36 hours of uninterupted flow from Gulf before Thursday afternoon. Here in KC we have a nice SSE wind now with winds out of the south; tomorrow we will see south winds once again with stronger winds with gust around 35mph. Over the next day and a half we could easily see a nice rise in the dewpoints at least suffient for tornadic sups in NE Oklahoma on Thursday afternoon/evening.

We've had gusty south winds all day (10 hours) and our current ob in Norman is 79/34. I don't know what the 8am ob was, but after getting blown away all day by these strong south winds and coming home to a dewpoint of 31 (at 4:30pm) doesn't inspire much confidence in the trajectory/quality of this moisture return. I'm not playing the model game with everyone else this week so I'm only going off reality.

I glanced the overall synoptics a few times and fwiw, the whole thing looks mistimed to me.

 

[Mike Hollingshead]

We've had gusty south winds all day (10 hours) and our current ob in Norman is 79/34. I don't know what the 8am ob was, but after getting blown away all day by these strong south winds and coming home to a dewpoint of 31 (at 4:30pm) doesn't inspire much confidence in the trajectory/quality of this moisture return. I'm not playing the model game with everyone else this week so I'm only going off reality.

I glanced the overall synoptics a few times and fwiw, the whole thing looks mistimed to me.

Well reality did contain a big chunk of cool dry air moving south, well past the gulf coast, so it shouldn't be too shocking today's southerly winds remain dry. They don't even start to touch the good stuff till late tonight. The forecasted return flow looks quite strong and over plenty of time though. I only hope the later periods of reality don't contain strongly veered 850s above the good return flow.

 

[Mikey Gribble]

I'm starting to think this is going to come down to moisture and the veering 850mb winds. Surface to 925mb trajectories are very favorable for good moisture advection from tonight all the way up to Thursday afternoon (as Mike mentioned). 850mb winds are veering for virtually this entire time frame though, so I am having questions about how deep the moist layer will be. Forecast soundings show the moisture depth up to about 900mb in the Okmulgee, Oklahoma area. I would like to see it deeper, but that is good enough IMO, but when you figure in that 850mb winds will probably be advecting in dry air during the day on Thursday it worries me a bit. How much are our dewpoints going to mix down because of this? I have no idea, but maybe somebody else could answer that. I know the models did a terrible job with this the last time we had a similiar setup and the dewpoints were 5 degrees less than what was forecast.
The other concern I have is the 850mb flow, which is veering more in the latest runs of the NAM and GFS. Below 850mb winds stay backed pretty good so long as you stay South of the boundary intersection, so I'm not too worried about this layer. I don't think a little veering at 850mb will hurt us, but if they veer badly it could be trouble. Hodographs from Okmulgee look pretty good and I would think they would be favorable for tornadic supercells, but the idea that good tornado days rarely occur on veering 850 days sticks in the back of my mind. There obviously are exceptions (ex. 5/04/03) so I think I will chase regardless. I just don't know what to expect though if the 850mb winds veer badly.
If we can get dewpoints in the low to mid 60's I still think we are in good shape for a couple tornadoes, but this is a very fragile setup IMO where one or two things changing slightly could seriously damage the tornado potential.

 

[Michael O'Keeffe]

The 00z WRF is back to almost the way it was. The moisture advecting during tonight into tomorrow looks more believable showing 50F tds barely on shore at 06z, but slowly yet surely make their way north, showing a plume of 65+td into E Kansas by 00z Thurs though I don't it will be that high we could at least see low to mid 60s up to the KS/OK border. CAPEs are exceeding 3000j/kg once again, but the 850s are still veered a bit, but better than before and as for the cold front it looks the dryline will extend from near Wichita down into Oklahoma. Other than that everything still looks the same. I am a bit encouraged to see the models go back. I'm guessing the 12z was just a fluke as the 00z WRF looks like it did last night and the day before. Still could go either way, but I have a bit more optimism for SE Kansas/NE Oklahoma with a good threat for tornadic sups Thursday afternoon/evening.

 

[Darrin Rasberry]

Up here in the North, the winds don't seem as bad, but the 0-3 and 0-1 helicity appears a bit embarrassing. Nonetheless, E/SE Nebraska through SW/SC Iowa down through NW/NC Missouri looks like a decent area, and the potential should arise for a decent choice of a chase target when the warm front/cold front/dryline setup decides where it's going to end up. Right now, I'd like to sit in Council Bluffs at around noon and munch on burritos until I see what happens.

The supercell potential seems decent up here. I hope we can get just a bit stronger winds and some f&#* helicity as a nice gift when the setup arrives, but I'm excited. That is, at least, until the day actually happens and a huge, messy MCS lumbers through like the last few times.

 

[Mikey Gribble]

I totally agree with Michael. The 00Z is back on track with 850mb winds backing more than in the previous run. 925mb and surface winds are backed nicely and aren't veering as bad as they were near the boundary intersection too, so this definitely makes the southern Kansas area more appealing. If this can hold I think we are in good shape ahead of the dryline in a North-South area from OKC to Wichita. I still feel like this is really going to come down to 850mb winds and moisture. The 00Z NAM really has me feeling better though after the poor low-level shear with this morning's run.
edit - with slightly better directional shear and slightly stronger winds in the mid levels the 00Z NAM also picked up 0-6km shear to 40kts (better than that if you cherry pick soundings). It had kind of been a weak point IMO with only 35kts up until now.

 

[Van DeWald]

I'm thinking of an area between Winfield and Coffeyville, KS as a target. Looks like the cap is almost gone by 00z, and could get discreet storms in this area where parameters are very impressive before the rest of the front lights up southward through 06z.

Check out the 48hour Nam sounding for the area.
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=048&STATIONID=kcfv

 

[afischer]

There are clearly still some big question marks with this system. The tornado threat will depend on mesoscale details (how low-level hodographs/buoyancy and LCLs shape up ahead of the dryline/cold front) that will be much easier to iron out by the morning of the event. What I'm more concerned about is that the ECMWF/GFS/NAM models seem to keep hinting that the strong dynamic forcing/DPVA that will be required to lift and cool the intense capping inversion is forecast to intercept the moist axis fairly late in the day, if not actually move along behind the dryline near the surface cold front. This could be a major problem for achieving initiation in the moist axis before sunset, especially (seemingly) for more southern targets where hodographs will probably be most supportive of tornadoes. If moisture ends up being more paltry than forecast, I assume that will only compound the problem of breaking the cap.

 

[Kevin Rider]

Here is a sounding I found in Cushing, Oklahoma for 0z 48 hour NAM forecast. Looks like the 850mb winds are out of the SSW but CAPE is approaching 4000 and 0-3km SRH is near 340.
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=048&STATIONID=KCUH
Hopefully the veered 850mb winds will not be an issue the day of and we can get off some convection before dark.

 

[Jeff Snyder]

Hopefully the veered 850mb winds will not be an issue the day of and we can get off some convection before dark.

Or any convection south of Emporia, KS, period! I'm becoming increasingly concerned about cap bust potential on Thursday, a risk that is being elevated by the fact that there's a considerably better chance the models are overdoing moisture return than there is the models are underdoing moisture return. A couple of days ago, it looked like 850mb Ts would stay in the 15-17C range across most of the area, but the latest NAM and GFS forecasts are pushing that ever-so-scary 20C 850mb isotherm a tad farther to the E. Accordingly, the last couple of NAM runs has kept the warm sector S of Emporia, KS, dry until after 00z, and the new 6z NAM has the warm sector S of EMP dry through the entire evening. Fortunately (for the southern target chasers, at least), it looks like the cold front is not going to move as far SE as previously forecast, which should keep things from going linear too soon. That said, I really, really would like to see the 850mb winds back even 10-20 degrees -- the idea of 850mb trajectories from W TX is not appetizing to me right now. We've seen the effects of veered 850mb flow several times this year, and it certainly isn't pretty.

FWIW, it also will help that there will be a strong LLJ in place across the southern and central Plains from tonight all the way through Thursday night, which will certainly help advect northward any moisture that is able to modify the cP air currently in the Gulf attm. I will be paying very close attn to Buoy 42002 (ESE of Brownsville, TX) and Buoy 42035 (SE of Galveston) over the next 18-24 hours --> http://ndbc.noaa.gov/maps/WestGulf.shtml ... I better see mid-60F tds at those buoys by later this afternoon, or else there could be problems. FWIW, the current Td at 42002 is 58.6F, up from 51F about 21 hours ago. Water temp at that buoy is 77F, and the Td before the last cold front was in the 71-72F range. 00z NAM 12 hr forecast (valid 12 UTC today) is showing 65F isodrosotherm along or just southeast of the TX Gulf coast... Unfortunately, buoys in that area show that such a forecast appear highly unlikely to verify. For example, buoy 42020 (50 mi SE of CRP) just cracked the 60F Td mark, and I find it unlikely that Td will rise at least 5F in the next 3 hours. Then, the 00z NAM brings >65F tds into southeastern TX by 18z today... The 00z GFS looks a little more reasonable at 12z and 18z today, but it too ends up bring >65F into southern TX by 00z this evening. Buoy 42055 between mainland Mexico and the Yucatan peninsula is rebounding at a rate of ~0.75F per hour the past 4 hours (now up to 67.1F). The buoys are really all we have in the western Gulf, and they should be able to provide some insight into the moisture return off the coast of TX today.

The forecast 250mb charts show beautiful diffluence over the risk area as the upper-level jet streak fans out over the Plains, which I certainly like to see. This too made me question the previous forecasts of a farther east cold front, since there should be respectable pressure falls occurring over the western Plains as the jet streak noses out from the Rockies. My eyes are solidly focused on northeastern Oklahoma, where kinematics are nice and where moisture return should be slightly lesser of an issue (compared to locales farther to the N). One possible problem that's been in the model fcsts for the past few runs is relatively marginal deep-layer shear in eastern KS. Even farther south, some model runs aren't showing a whole lot of shear in the 3-7km depth, but the last few forecast soundings I looked at showed this to be more apparent in KS.

 

[Mark Blue]

FWIW, it also will help that there will be a strong LLJ in place across the southern and central Plains from tonight all the way through Thursday night, which will certainly help advect northward any moisture that is able to modify the cP air currently in the Gulf attm. I will be paying very close attn to Buoy 42002 (ESE of Brownsville, TX) and Buoy 42035 (SE of Galveston) over the next 18-24 hours --> http://ndbc.noaa.gov/maps/WestGulf.shtml ... I better see mid-60F tds at those buoys by later this afternoon, or else there could be problems.

I think Jeff's concerns about the moisture return pretty much sums it up right now. If the current upper air disturbance in the north central region of the CONUS can kick out soon, hopefully the Gulf of Mexico will be open for business again. One look at the water vapor imagery this morning validates the fact that the moisture return will be a key factor in this whole set up.

http://weather.cod.edu/loops/Southcentral-WV.loop.html

The timing of the LLJ kicking in and the Gulf opening up for business will be key for this system to give us what we've all been patiently waiting for. I believe it can still happen by tomorrow evening, but it's looking more and more like a late show to me (0-3Z?).

Mark