04/24/06 FCST: KS/OK/TX

Looks like a heavy precipitation event with some forms of severe weather coming up on Monday and Tuesday, though details have yet to be worked out.
 
GFS (12z Apr 20) shows shortwave ejecting out over Rockies by 12Z Monday. Associated jet max progged to enter NW TX/OK sometime between 12Z Apr 24 and 00Z Apr 25. GFS is also progging a pocket of enhanced (hopefully near 70F) dewpoints over SE OK by 00Z. Im still feeling that GFS and NAM are going to high on the Td's like every other system west of the MS river this year. Still to early for details but it looks like triple point will setup over OK somewhere. Probably expect initiation over OK and building southwards. More details later, class starting now heh.
 
As of 12Z this morning, each of the models (EC, GFS, ETA) are not showing good agreement in the progression of the 500 millibar shortwave as the GFS favors a much flatter ridge, while the EC a slower eastward motion barely overspreading the Panhandles by 0Z Tuesday. Even by f48 the ETA and GFS disagree with the position and intensity of the vorticity maximum as the GFS depicts a stronger but further south solution to the ETA. Given that the shortwave will provide the primary forcing mechanism for lift in the warm sector of its associated surface cyclone, it's going to be critical which one of these solutions ends up panning out. The event is just out of the ETA's forecast range, so hopefully this evening's run could give us a little more insight into the 0Z position of the feature. Hopefully the three will start to converge in runs leading up to the event.

While the CAPE maximizes in Oklahoma during the early evening and late afternoon hours, the location of the progged surface low in SW Texas and the cold front sweeping across Oklahoma by 0Z makes it look like a less-than-ideal chase scenario. I would also prefer a little more SEly return flow in advance of the event but the ETA seems to prefer more Sly/SWly flow which will inhibit the moisture availability (again).
 
Tomorrow could be fairly interesting somewhere between central Oklahoma and south-central Kansas if we can keep the cold front from surging southward too quickly.

With a strong cap in place, and sutained mass convergence associated with a slow-moving triple-point low northwest of OKC, low-level moisture should pool with dewpoints finally getting into the upper half of the 60s. Deep-layer shear looks sufficient for supercells. Low-level hodographs look pretty good east and northeast of the low (assuming the cold front doesn't surge south) so tornado potential should be there. The upper tropospheric storm-relative winds look weak with the remnants of a shortwave ridge over the target area, so storms may tend toward HP in structure.
 
SPC mentioned and I concur that forecast confidence is really low. THe 09z ensembles show anything from the crashing cold front to several versions of nice cyclogenesis in NW OK. I feel that the consensus ensembles should be realistic. That is a cyclogenetic event in NW OK with the cold air slowed. Reason I think so is that the entire western system is slowed. The sfc high would have to travel pretty far from its genesis region under the confluent flow in the N Plains in order to crash a cold front through OK in the face of upward forcing and SW flow from a slower than earlier progged trough.

Negatives for chaseable severe in either scenario still center around this rapidly weakening trough as it ejects through this permanent mean ridge position in the Plains. I believe the mean ridge will serve to put a sharp southern edge to the convection, probably north of Norman. Afterall, why should Norman get any rain this spring? ;)

Jim
 
I'm liking Monday more and more. The trend on the ETA is very nice for the area near or sw of ICT. By 0z the meso eta has wsw 500mb flow of 50-60 knots atop a sse 850 of 25-35 knots with nicely backed sfc flow. I'm assuming the dewpoints will be as good as they have been all year. When looking at it I can't help but think of Attica KS May 12, 2004. It looks like a pretty focused target in that general area. I think I am liking it more than any other setup all year(if the last couple runs of the eta are anywhere near right...especially the 18z run). I plan to leave very early Monday and get data around ICT.
 
The comparison to May 12, 2004 is striking in terms of the position of major synoptic features, degree of instability, and strong low-level shear (according to the 18z Eta forecast). Really, the only differences I can find are that the mid-level flow is forecast to be stronger for this event than 5/12/04, there won't be a coupled jet at 500 mb as there was on 5/12, and the magnitude of moisture/instability will be lesser than 5/12. Nevertheless, it appears to be a fairly potent setup, with a good possibility of tornadic supercells *if* storms can remain discrete.

The Eta is placing the important surface features further north and west with each run, which suggests to me that once again, Medicine Lodge to Pratt, KS will be good targets. My only concern at this time is the paltry 250 mb flow. Even in a storm-relative sense, mass evacuation will be difficult if winds verfiy AOB 25 kts. If this turns out to be the case, I would imagine briefly classic supercells will transition quickly to HP, and then to an MCS configuration. Even so, it appears that tornadic potential would be there for at least a brief window after initiation. I agree with Mike H, this is the most "chaseworthy" setup I've seen all year.

Gabe
 
Things still look good for Monday on the 00Z NAM/eta run. We should see the current MCS over southern Kansas move southeastward across northeastern Oklahoma, laying down a southeast-northwest boundary behind. As the surface low deepens west/northwest of OKC, low-level wind profiles should become very good to excellent with large curved hodographs developing during the afternoon...particularly in the vicinity and on the north side of the boundary. That will probably be in the Stillwater/Ponca City/Wichita area.

Deep shear will be more than sufficient for supercells, but the storm-relative winds at the troposphere could be quite weak. Instability should be sufficient assuming the overnight convection clears out. Dewpoints should be the best we've seen all year in this part of the world...possibly higher than 65 with pooling along the boundaries.

Assuming work duties don't get in the way, the initial plan is to look for the best low-level hodographs and err to the north...probably a trip up I-35 toward the Kansas border after lunch.
 
Based on the most recent ETA run, it looks like the corridor between Enid and Ponca City yields the greatest potential for tornadic development with a belt of 50+ 500 millibar winds overspreading the region just north of the deepening surface low. Looks like the cyclone will be rather intense at low levels, probably leading to greatly enhanced LL shear just to the ENE of the surface low where the 850 winds decide to veer slightly. If I had to pick a target it would be Ponca City based on the ease of access and Wifi options, with the choice to head west or east along 281 (IIRC) depending on the evolution of the system.

Off topic, but check out the Oklahoma Mesonet temperature field.
heat%20burst.png

Heat burst!
 
Deep shear will be more than sufficient for supercells, but the storm-relative winds at the troposphere could be quite weak. Instability should be sufficient assuming the overnight convection clears out. Dewpoints should be the best we've seen all year in this part of the world...possibly higher than 65 with pooling along the boundaries.


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Ive been looking at the ETA mysteriously kill the upper trop winds both this evening from 24hrs earlier and now forecast for tomorrow evening. Well, the trop winds are quite strong up there everywhere outside of anvils. Looks to me like a consequence of strong gridscale overturning in the BMJ scheme. I guess in one respect, the BMJ scheme is replicating reality. But it's spreading its influence too far away from the overturning. My bet is that upper trop winds will be strong outside of MCS convection Mon evening.

00 UTC ETA depicts a potential tornado day within two hrs of OUN, possibly in the metro. I suspect it'll be weighted a bit further northwest. Still, my hopes of big rain on Lake Thunderbird may be realized after a healthy diet of hopefully harmless tornadoes. Still some measure of uncertainty including lack of moisture given the hot conditions. I'd like to see 70+ dewpoints given these hot temps in the PBL. If the low-level shear can increase to 30kts or more, along with 50kts of 0-6km shear, kinematics may compensate for potential cold RFDs.
 
Hi,

I am chasing tomorrow given the moisture recovery should be complete. Shear is good and instability according to models ideal. I am a touch concerned about high cloud progged over the target region/warm sector? Anyone else see this? Well this is according the the GFS latest run.

Regards,

Jimmy Deguara
 
Things are looking a lot better now than a few days ago. Still not great by any means, but tonights convection (btw, very nice heatburst near Enid showing 85F readings and mid 40 Td's) should, as previously mentioned, lay a nice outflow boundary. Hopefully I'll be done with classes and work by 2:30pm and get there in time to catch something. Mid 60 Td's do look quite possible with this. Hopefully daytime heating (mixing out) wont be too much of a problem as it was today. I noticed dewpoints were only in the low to mid 50s across central Oklahoma today per Mesonet analysis. Also, I'm not quite sure of chasing storms being chased by a rapidly advancing cold front. Hopefully it wont turn into a MCS too quickly. Good luck to those going out tomorrow, hopefully Oklahoma chasing wont be as much of a dissapointment as it has been the last month. 00Z NAM KOKC Forecast sounding shows nice curvature with near 2000 CAPE, however thats with a surface Td prog of near 70 Td, which I do not believe. I expect CAPE to be closer to 1500-1800 by initiation.

With temps in the upper 80s and low 90s I'd really like to see Td's at or above 70F, but that is wishful thinking. Regardless, I can't pass up a chance within 2 hours of home. Hopefully work wont keep me past 2:30 because I'll need to figure out how to get through OKC traffic otherwise. Also, in response to a previous post, high cloud cover might be a blessing in this case keeping temps slightly cooler (but still supportive of convection). The forcing tomorrow should rule out any heating issues.
 
Everything seems to be coming together for a fair shot at tornadoes across Oklahoma. I think the NAM is still a little ambitous on the moisture, but dewpoints in the mid 60's aren't bad(and the moisture is plenty deep across Oklahoma). Deep layer shear will improve throughout the afternoon as a mid level jet streak approaches and will be more than sufficient for supercells(AOA 50kts). Low level shear will be quite good ahead of the dryline over central Oklahoma. The forecast sounding for OKC has a very nice curved hodograph by 00Z and CAPE >2500J/kg. If the NAM can verify, then IMO we have a good shot at a few tornadic supercells coming off of the dryline and triple point in central Oklahoma. As things stand now, I would target the area from Woodward to OKC. I will probably leave Wichita by 11 tomorrow and I am sure my target will change once morning data becomes available. Good luck to everyone out chasing.
 
I'm a little surprised at how far north the MDT risk is on the 6z. Given the latest model solutions, I'd think that the SPC will drag the MDT risk down to the south-southwest about 150 miles. With nicely backed flow east of the sfc low, good moisture pooling (advection being aided by 50-60kts LLJ noted on area VWPs and profilers across TX and OK), and sufficient flow aloft will yield a tornadic supercell risk by afternoon.

I'm a little mystified by the 0z NAM solution at 250mb this afternoon. AS others have noted, the 250mb flow is progged to be quite weak over central OK. However, this is right where the NAM blows up QPF (Jim LaDue noted a possible convective parameterization side-effect). This is also right where we see an enhanced 500mb and 700mb jet streak / shortwave. I'm a little suspicious of this... If we toss out the 250mb forecast as being too affected by a convective parameterization effect, then we should also toss out the 500mb and 700mb forecast as well, since those show suspicious-looking small-scale jet streak in the same area. Regardless, new 0z NCEP WRF indicates ~50kts at 500mb, though it too shows a weakness at 250mb.

Tds >65F not having much luck making it too far past Austin, for what reason I do not know. Regardless, we may see elevated moisture (with higher mixing ratio than at the sfc) that may actually mix down higher dewpoints this morning. Add in evapotranspiration (which has seemed to add 2-3F to the dewpoint the past few days) and moisture pooling along the front / OFB, and things could get interesting. I'm not as inclined to head into KS, but that all depends upon what the surface map looks like by noon-time (non of the models had widespread cold pool / very low Tds in KS associated with the pair of MCSs that have rolled through there in the past 8 hours).

The Norman NWSFO is starting to bang the drum for today:
<div class='quotetop'>QUOTE("Norman AFD")</div>
WE THINK THE COMBINATION OF ENHANCED
LOW-LEVEL SHEAR AND PROGGED INSTABILITY COULD EASILY SUPPORT
TORNADIC SUPERCELLS - AND PERHAPS SOME STRONG/VIOLENT TORNADOES -
ACROSS N HALF OF OK THIS AFTERNOON AND EVENING... BUT MUCH WILL
DEPEND ON MESOSCALE AND STORM-SCALE EVOLUTION PRIOR TO THAT.
STORM-SCALE FACTORS MAY BE MINIMAL AS THE MOST ORGANIZED STORMS
NOW ARE EXITING THE NE CORNER OF THE CWA...LEAVING ONLY ISOLATED
CORES ACROSS N OK. THIS ALL MAY MEAN AN ACTIVE DAY AHEAD. [/b]
--> http://kamala.cod.edu/offs/KOUN/0604240906.fxus64.html

I haven't heard the "v" word (violent) mentioned in regards to tornadoes by the Norman NWSFO in quite some time (May 29 2004 was the last time IIRC -- if not it was back on May 8 2003)...
 
I have no idea why SPC would place the mod. risk that far northeast. I am sure it will be corrected in the next outlook.
We already have dewpoints in the mid 60's across the target area and as Jeff mentioned, we may actually gain a few degrees with mixing. I noticed that last night when I was checking forecast soundings, but I didn't think too much of it. If the low and mid level flow is as strong as the NAM was forecasting, we should be in good shape today. A lot more will become clear as the day progresses, but so far so good.
 
I have no idea why SPC would place the mod. risk that far northeast. I am sure it will be corrected in the next outlook.
We already have dewpoints in the mid 60's across the target area and as Jeff mentioned, we may actually gain a few degrees with mixing. I noticed that last night when I was checking forecast soundings, but I didn't think too much of it. If the low and mid level flow is as strong as the NAM was forecasting, we should be in good shape today. A lot more will become clear as the day progresses, but so far so good.
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Mike, I think they are following the oldest Nam run: after looking yesterday 12Z Nam the most favourite place for chasing was just the zone south-est of Wichita, the zone of the 10% of tornadoes; now the low pressure is forecasted to be in a more south-west oriented position so I think that in the next run SPC will adjust the map.
Guys, I love Harper-Pratt-Medicine Lodge county....Anyone knows why? :rolleyes:
 
Mike, I think they are following the oldest Nam run: after looking yesterday 12Z Nam the most favourite place for chasing was just the zone south-est of Wichita, the zone of the 10% of tornadoes; now the low pressure is forecasted to be in a more south-west oriented position so I think that in the next run SPC will adjust the map.
Guys, I love Harper-Pratt-Medicine Lodge county....Anyone knows why? :rolleyes:
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Well after some extensive analysis and discussion, I will get to make my first chase of the season thanks to a combination of no class and work. Derek Williams and I will be setting up initially in Enid, OK and play the T.P. from there as it moves ENE across North Central OK. The flow at 250mb does seem to be a bit perplexing but with the other dynamics in place, I am less inclined to stress out about it. As we speak, the Mesonet shows dewpoints already in the mid 60s with a gradual rising trend from south to north. Looking out my window in East Norman I see some elevated TCU putting out quite a bit of lightning and precip which makes me feel even better about the day (any moisture at this point makes me happy...omens).

On a side note, is there anyone out there that would want to nowcast today?
 
I don't mean to get off topic, but I wanted to respond to Andrea. The 00Z NAM had the surface low in NW to west central Oklahoma. I am also pretty sure that even the 12Z from yesterday had the low in the same place. I don't remember seeing any runs within the last 36 hours that had the triple point close to Wichita. The same SPC forecaster was a little off on yesterday's first outlook as well. The moderate risk is in the right place now though so it's water under the bridge.
 
I don't mean to get off topic, but I wanted to respond to Andrea. The 00Z NAM had the surface low in NW to west central Oklahoma. I am also pretty sure that even the 12Z from yesterday had the low in the same place. I don't remember seeing any runs within the last 36 hours that had the triple point close to Wichita. The same SPC forecaster was a little off on yesterday's first outlook as well. The moderate risk is in the right place now though so it's water under the bridge.
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Mike, I remember yesterday 12Z Eta and low pressure was oriented in a more North-Eastern position than today: infact making a target I did agree with the moderate of SPC, ie it seemed that South East of wichita to the border with OK was an hot zone.
Now I agree another time with the newest position of the moderate.
 
The Enid area looks pretty good for a starting point... There are numerous 68F dewpoint readings in northern and central Texas at this time, with a few 70F dewpoints in central TX. With 50-60kts at 850-900mb overnight, plenty of juice was advected northward just above the stable near-surface layer. The 12z Lamont sounding showed 3700 muCAPE (for a parcel near 830mb), which is very impressive. I'm not sure if we'll see widespread 70-73F tds in northcentral OK like the 12z RUC is showing, but 66-68F seems reasonable given evapotranspiration. I also don't know as if I believe the forecast locations of the cold front this afternoon. Winds the OK Panhandle are NNW at 30-40mph right now, with strong (3mb/3hr) pressure rises. Pressures shoiuld fall east of the cold front this afternoon, so I really can't believe that the cold front will only move 2 counties to the southeast this mid-afternoon. This will just be another complication by afternoon, since I'm inclined to think 'squall line' if the cold front moves any faster. As it stands now, 0-4km shear vectors may be due east or even ESE by afternoon, which will mean that there may be a significant component of the deeplayer shear that is normal / perpendicular to the front.

EDIT: The 12z is indicating that the triple-point will set up in west-central/southwestern OK, with a dryline bulge running from near Shamrock TX to Frederick OK to just west of SPS. It does look like the low forecase is shifting southwest in time (12z NAM shows it just south of Vernon by 0z).
 
model trend seems to be pointing more toward the surface low setting up even further southwest - perhaps even south of the Red River. Solutions differ significantly in how the trough will set up north of there. In the 12Z RUC, an elongated trough extends NNE by 0z, which results in veered surface winds ahead of the cold front until you get all the way back into extreme SE KS, where the RUC and SREF both suggest a potential play as a weak shortwave skirts the ridge and leds to a weak mesolow tracking along to north of the OK-KS border, intersecting with the convective outflow boundary from ongoing storms this morning. Morning NAM looks far too agressive in developing precip in eastern OK this morning, so I doubt that model's solution of backed winds extending nearly down to the low. Some sort of compromise seems reasonable until the atmosphere settles down a bit - which isn't too far off from what the current SPC outlook seems to highlight, but wouldn't be surprised to see the tornado threat elongated eastward a bit on the northern end, with large hail stretched a bit further southwest.

Glen
 
Very complex setup this morning. The models, and this human, are having a tough time. The cold front appears to be stronger/faster than the 12Z NAM/eta suggests...and should extend from Plainview to Altus to Medicine Lodge by late afternoon. Meanwhile the outflow boundary in southern Kansas is getting shoved southward faster on its eastern end, and by later today should extend ESE to WNW from Tulsa to Medicine Lodge. Oh, and the dryilne will also be out there early but occluded by the front somewhere in the Childress vicinity.

So there could be low pressure centers at Childress, Medicine Lodge, or both. I suspect as the front advances, the northern target storms will be undercut, and the deep shear vector would be nearly parallel to the boundary, so I'm leaning toward the southwest at the moment. The best scenario might be the southern low being as strong as the NAM/eta suggests, which would hold the boundary at bay during the afternoon in western Oklahoma. Probably a second target along the old OFB well east of the advancing front, perhaps near I-35 in north central Oklahoma.
 
RUC breaks out supercells along the dryline by 21Z...more discrete cells the father south you get into TX. Also, RUC has CAPE values up to 4500 j/kg. Should the surface flow stay backed in Cent. Okla. I think that west on I 40 would be a good place to start.
 
Watching the obs for a bit - pretty well defined outflow boundary surged south across SC KS, and is now settling in on the western extent just south of the OK-KS border - with weakening pressure gradient to the north, and strengthening pressure gradient further east which should help the boundary sag further south into northeast OK. Trend in convection in OK seems to be toward weakening, except for those storms settled into the warm frontal trough - nearly aligned with the mean upper flow so slow moving. western extent seems to be weakening now though. Also noting the surface low, now over western OK, is indeed sagging southward - with veering winds to its east as advertised by this morning's RUC (which has the warm front much too far south though in the initialization). I'd expect the boundary to hold out around the northern tier of OK counties and provide a favorable environment by afternoon.

Glen
 
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