3/30/08 FCST: OK/TX

[afischer]

Haven't looked at this super-close, but 12Z NAM/GFS consensus is still generally for storms to form ~00-03Z Sun evening as the nocturnally enhanced LLJ impinges upon the quasi-stationary front near the OK-KS border. The GFS has a significantly stronger capping layer maintained/moving northeast atop the moist BL in this area (700 temps 5-7C). This looks a little more reasonable to me given the overall pattern, and would be a negative for a more significant nocturnal tornado threat if convection does fire near the surface front. The mesoscale details may be easier to iron out by tomorrow morning. Should be interesting to see how it pans out.

 

[John Cameron]

Not happy with 12z NAM in the way its keeping my neighborhood capped 36 hours prior to the event, even hinting at a zonal 500mb flow at the time of peak instability. The GFS is more promising, advertising a more well defined trough at 500mb in the late afternoon-early evening.

This scenario makes our early-season mouths water...I'm to the point now where I would just like to see a distant supercell at sunset to verify that spring has arrived.

 

[Gabe Garfield]

I have a feeling that, despite the concerns regarding the cap, Sunday will be the better of the two days (as Jeff has said, “the day before the day”). Admittedly, convective initiation before sunset is a bit more uncertain due to the apparent lack of forcing for convection, but I've seen enough to know that these concerns are usually based on the lack of information rather than potential. In other words, we probably won't know if convective initiation will occur until probably the 20-23 Z time frame (i.e., when TCu/Cbs actually start to develop). Several other days in the past featured similar doubts regarding initiation, and due to factors beyond our real-time observation abilities, were able to produce. A couple that come to mind are: May 12, 2004 and of course, May 3, 1999. Granted, it could just as easily cap bust, but I strongly doubt it will.

First, I like the increasing flow over the mountains; this is a feature that is often present with regional outbreak events. This should enhance the strength of the lee trough such that the near-surface winds will pick up in a hurry (not to mention the ageostrophic response lending to stronger low-level shear). Should upper-flow be any stronger than progged (a la, May 3rd), this process should commence faster and lead to the potential for daytime supercells (since convergence along the dryline would be increased via downward mixing of westerly momentum behind the dryline). Also, I really like the strong moisture advection. Adding a few g/kg to the mixing ratio does wonders to increase CAPE and remove any remaining convective inhibition.

Overall, I'm very pleased with the setup, and I think at least a few tornadoes are likely on Sunday.

 

[Mikey Gribble]

As far as the daytime hours go I'm not terribly impressed. As everybody mentioned the strong cap and timing of the upper level support could pose a problem. I am starting to think we might get a storm or two off the triple point in the 00Z time frame. One of my biggest problems is with the hodograph. The lowest 2km look good, but above that it isn't so great. It does improve into the 06Z time frame, but during chasing hours it isn't that good. Solid low-level shear and decent CAPE in the overnight hours will combine for a respectable tornado threat, but I don't think it's at the higher end of the scale. With Greensburg composite indices were off the chart and the hodograph was a thing of beauty. This setup isn't of that caliber IMO (I understand that others weren't neccesarily infering that). If only we could get the overnight parameters to occur during the day. Anyways, I posted a longer forecast here...
http://loadedgunchasing.com/blog.html

 

[Bill Tabor]

NAM: Well, let me just say that if convection breaks out over night I would be a bit worried about folks in mid to western Oklahoma and perhaps Kansas along the warm front. EHI of -7.57 at 0Z and over -6 during over night hours. I still am not sure about daytime chaseable convection though it appears there will be quite a bit of heating from the sw. While the area of interest may have cloud cover from WAA and moisture and possibly elevated mist it seems there won't be any higher cirrus type clouds. Appears the dryline will tighten up and bulge significantly into the western parts of OK by 0Z. I see no reasonably strong waves at mid levels until 06z. It appears likely that this will spark off convection possibly from areas north of OKC through it and to the south with very strong tornado parameters near that time.

Personally I won't really leave just to night chase. I may 'play around' if I am already out there and have a decent target under the right conditions. You guys know how that goes. Not positive at the moment if I will bite. This reminds me of the Greensburg day in that I saw something very strong at night, but chose not to leave and chase because it looked like it would be an after dark event. My target that day was close to Greensburg btw . If coming from the south (as I am) - I would possibly initially target SPS just to get close to the action, and reposition as necessary.. - plus that seems to be a thermodynamic gradient that will increase and move a bit further ne into OK later in the evening. I'm not so sure the triple point would go. I may be tempted to wait for the dryline if it decided to go. The NAM doesn't seem to really indicate if convection will break out along the dryline or the warm front that I see by 0z. First stronger indication is nearer 6z with the mid level wave passage.

David if you're checking this I did get my engine misfire fixed. I'll probably take a look in the morning a bit and see how I feel. Will be interesting to see what the 4km NMM-WRF Precipitation looks like, and the opinions of the rest of you.

Note: A likely Slight to Moderate risk during the day and at night if convection can break out in OK, possible High Risk with significant severe for tornadoes.

 

[Jason Montano]

Well not sure that I am going to chase tomorrow or not. I am not up for night chases when it appears he main event will be. However, if I do I am thinking of an area along US 82 btw Gainesville and Henrietta. This in the area of max Theta-e. The surface to h7 shear looks good but h5 is a bit weak. This could make for a nice slow moving storm or it could force any convection to rain itself out. Interesting is there is a bit of slight precip in the area per model there from 18z through 0z. I don't know, I would really like to chase tomorrow being it is a Sunday and all but I will regret going up there just to get sucked into a night chase.

 

[Mikey Gribble]

I've only glanced over the 00Z run, but it doesn't look like a whole lot has changed. The NAM has convection by 06Z over north central Oklahoma and as Bill mentioned the focusing boundary for this is a bit unclear. It appears that the NAM is breaking out the convection once the LLJ kicks in and there is better convergence along the front (and approaching upper level support). Again my biggest problem is the lack of good mid to upper level winds. The hodograph looks great in the lowest 2.5km, but the top half leaves something to be desired. Deep layer shear will be in the 40kt range South of the front though and that should be adequate for supercells. 1km SR winds did increase a bit with the latest run which will help.
I still don't agree with the Greensburg comparisons. For Greenburg the EHI was double what it is forecast to be tomorrow and the hodograph was much better. I do think there is a decent tornado threat after dark with the chance of a strong tornado or two, but this is not EF5 material IMO. Anyways, any storms that track along or South of the front will pose a tornado threat tomorrow night. I think the 01-06Z time frame is when we'll see some tornadoes. I plan on heading to Enid tomorrow afternoon to fine tune the forecast. I posted a little more of a forecast here...
http://loadedgunchasing.com/blog.html

 

[Jeff Snyder]

Well, what looked like a relatively obvious target has been muddled by the latest model solutions. Earlier today, the relatively obvious, "took at glance at things" target looked to be just downstream of the triple point, near Buffalo and Gage OK in far northwestern Oklahoma (and adjacent areas of southern KS). The 00z NAM, however, appears to have gone a bit more towards the earlier GFS runs in showing rather significant capping along and immediately south of the stationary front / slowly advancing cold front, and it's maintaining strong CINH along the dryline. It appears as though it may be mixing out some of the low-level moisture up in that area, as the 00z GAG sounding shows a ~53-54F dewpoint with a rather stout cap in place. In addition, 850mb Q-vector forecasts from the NAM and GFS show Q-vector divergence from central and western KS southward into far northwestern OK and the northern TX panhandle. This is quite troublesome, since it directly indicates low-level subsidence in those areas. Earlier today, I was thinking that perhaps convection would develop in the dry air back in the TX panhandle (where CAPE was still >500 j/kg and CINH was nearly removed) and move out into the moist sector near 00z. I'm not sure it would survive given the CINH and weaker CAPE now forecast.

I'm becoming progressively more interested in an "ahead of the dryline" play in the open sector across the eastern sections of western Oklahoma and into central Oklahoma (including north-central OK), where the models indicate weak CINH collocated with the local instability axis (2500-3000 j/kg CAPE along and west of I35). Forecast soundings valid tomorrow evening (00z) at END, OKC, and LAW show almost no cap in place, along with a nicely-shaped hodograph (though it could be a bit longer). So, from purely an environmental standpoint, I'm quite intrigued with the area 80 mi N and 50 mi S of the area between OKC and CSM. However, as we are all familiar with, a supercell-favorable environment means nothing if convection does not develop in said environment. Interestingly, the 00z NAM does show spotty convective QPF in western OK at 00z, with more substantial 6hr precip accums from near LAW northward towards END in the 00z-06z timeframe. Though the GFS QPF doesn't match the NAM QPF, it does show light precip in southwestern OK in the 00z-06z timeframe. In addition, the GFS 700mb RH progs show >50% RH in western OK ahead of the dryline and front at 00z, which may indicate that the model is showing something in the way of convective initiation attempts.

FWIW, the NAM is also farther south with the cold front at 00z... For example, the 10C isotherm at 850mb from the 00z NAM valid tomorrow evening lies across the southern OK panhandle towards ICT and on towards Topeka. In contrast, the 00z GFS valid at the same time shows the same isotherm lying from near Garden City to Topeka, a considerable distance north of the NAM. Similarly, the GFS Td forecasts are higher in NW OK adjacent areas of KS as far as I can tell.

At any rate... I guess I'm slightly less optimistic about the NW OK play tomorrow, and I'm increasingly intrigued by the possibility of initiation in the open warm sector near Watonga and Hobart (and E) tomorrow. Though the environment may be better for daytime torns, I'm just not sure what would force the convection (i.e. not finding obvious sources of low-level convergence). I'd rather not try to rely on such subtle things as differential heating boundaries or HCRs, so I'm not sure what to think. The subsidence forecast at 700mb by the GFS in western OK at 00z does not make me jump with joy.


My primary target is still far northwestern OK (GAG?), but I'm becoming increasingly more open to an Enid to Watonga and Weatherford play in hopes of a supercell roaming the open warm sector... If only there were some sort of boundary apparent to act as a source for low-level convergence in central OK... If I don't see one on sfc maps tomorrow around noon, I'll likely head up the NW passage.

 

[Bill Schintler]

Chase Target for Sunday, March 30

Target:
Ingersoll, OK (40 miles northwest of Enid).

Timing and storm mode:
Storm initiation will be at 7 PM. Supercell storms with hail to golf-ball size will be the primary SVR threat. An isolated tornado will be possible early in storm evolution.

Synopsis:
The ULVL flow is undergoing a transition from a zonal to an increasingly amplified pattern as a WRN CONUS trough digs S as evidenced by H5 height falls concentrated over CA and NV. More careful investigation indicates as many as three branches of the ULVL jet, with the strongest to the N with an 80kt H5 streak entering the Dakotas in the NRN branch. A significant piece of energy is coming on the CA coast and is associated with the aforementioned amplification of the overall pattern. Finally, ongoing convection in ERN TX seems to be associated with lift in association with a SRN branch jet centered S of that area along with a mid-level wave in the TX panhandle with attendant mid-level cooling. Mid-level WAA is underway over NM while an upstream S/WV is moving E through AZ and will be a player in tomorrow’s WX in the SRN Plains with lift and mid-level CAA late in the day. A 35kt LLJ is transporting 10-15C H85 dewpoints into OK ATTM.

Discussion:
The primary FCST concern is capping and associated timing of SFC-based convection tomorrow afternoon and evening. In the near term, the LLJ will aid in the maintenance of elevated convection in ERN TX while additional convection should expand into ERN and SERN OK over the next several hours. By tomorrow morning, these storms will have moved E into MO and AR as the LLJ veers, and attention then turns to the second round of convection which will initiate during the early evening hours in NRN OK. Warm mid-levels and lack of insolation are concerns, as well as a lack of LLVL convergence along a developing WF near the KS/OK border. During the key heating hours, ST and SC will remain over most of OK and WRN KS, while the TX panhandle will remain mostly clear except for some thin or broken CI N of I-40. This will serve to enhance a thermal gradient along the WRN OK/TX boarder into the OK panhandle. Meanwhile, H7 temperatures will remain around 6-7C with continued WAA on SWRLY mid-level flow. Mid-level lapse rates in 7-8C/km within the EML will increase instability. Late in the period, assent will increase as the S/WV now over AZ spreads into the area. The most likely location for storm initiation will be near the WF oriented along US-64 in NW OK at 01Z. SFC flow will be weak, but a 40kt LLJ will enhance shear and hodograph curvatures in the H9-H8 layer, especially after sunset when a small tornado risk exists as the BL begins to decouple and LCLs decrease to 800m AGL. Later in the evening as the BL fully decouples, a SRLY LLJ will increase to 50 kts and maintain the convection into the overnight hours as it moves towards Wichita.

- bill
11:00 PM CDT, 03/29/08

 

[Brandon Lawson]

The SPC 4km WRF shows absolutely nothing in the way of convection. However, (FWIW, and I know this is not saying much) this past thursday the 4km WRF did not do a good job of handling any of the storms that broke out.

 

[afischer]

The 00Z models paint a picture about as clear as mud, with the NAM-WRF still looking more optimistic with regard to nocturnal tornado potential. The NAM shows relatively rich and deep low-level moisture flooding northward into western/central OK during the late afternoon and early evening... very similar in magnitude/character to what was observed on this evening's 00Z CRP/DRT soundings. The GFS shows moisture return that is significantly less rich and shallower, which won't cut it for strongly surface-based storms after dark. I'm not sure this soupy moisture from deep south TX will survive all the way to northern OK in 24 hours.. but if it does and storms fire within the nose of the accelerating low-level jet, it could get quite "interesting." Hopefully by tomorrow morning things will be more clear.

Though I'm still not too excited about initiation farther west before dark (and moreover about tornado potential there), it's interesting that the drier GFS model suggests high-based storms might try to fire along its diffuse dryline ~00Z.

 

[Kenny Drake]

I'm becoming progressively more interested in an "ahead of the dryline" play in the open sector across the eastern sections of western Oklahoma and into central Oklahoma (including north-central OK), where the models indicate weak CINH collocated with the local instability axis (2500-3000 j/kg CAPE along and west of I35). Forecast soundings valid tomorrow evening (00z) at END, OKC, and LAW show almost no cap in place, along with a nicely-shaped hodograph (though it could be a bit longer). So, from purely an environmental standpoint, I'm quite intrigued with the area 80 mi N and 50 mi S of the area between OKC and CSM. However, as we are all familiar with, a supercell-favorable environment means nothing if convection does not develop in said environment. Interestingly, the 00z NAM does show spotty convective QPF in western OK at 00z, with more substantial 6hr precip accums from near LAW northward towards END in the 00z-06z timeframe. Though the GFS QPF doesn't match the NAM QPF, it does show light precip in southwestern OK in the 00z-06z timeframe. In addition, the GFS 700mb RH progs show >50% RH in western OK ahead of the dryline and front at 00z, which may indicate that the model is showing something in the way of convective initiation attempts.

I've been thinking the same thing for the last day or so now since the NAM has been forecasting uncapped environments well ahead of the dryline (OUN @ 00Z for example.) You are most definitely correct in saying that this environment is all jolly if the initial forcing is there to get a parcel on a free ride to the EL. May 3, 1999 comes to mind with regard to the possibly of Horizontal Convective Rolls being the initiating force well ahead of the dryline. The key tomorrow with regard to HCR possibly is surface heating. If we do not get enough surface heating than HCRs are not going to happen. Now, I'm not sure what the critical surface heat flux required to produce HCRs is but I know the average wind speed throughout the PBL tomorrow should be plentiful to meet the wind speed requirements along with low-level shear requirements. In the end this just complicates picking out a target location even more. If something does fire in the warm sector ahead of the frontal or dryline forcing tomorrow I will likely be swayed to it.

 

[Ilya Neyman]

On a day like this what I would say is...if you can chase, and it's not too far of a trip (i.e. based out of central OK) then I would say go out.

If nothing happens at least it's a Sunday evening.

Having said that, I need to throw my hat into the ring and say that I believe initiation has at least a 50/50 shot, probably higher, of occurring. I like the moist advection, dryline bulge, strenthening LLJ and the trajectory of the fcst shortwave ejecting onto the high plains during the evening.

Now as far as daytime initiation, things may be a bit more uncertain with regards to that, however, I too have checked the fcst soundings, many of which show nearly uncapped profiles across SW-CNTRL OK by 00z-03z timeframe.

Sweat indices approaching 500 and Helicity values in the 400-500 range per latest NAM also make one wonder.

I think the strength of the flow from the ground up is actually very adequate for tornadic supercells, especially given the fcstd Cape values of >2,000+ across a considerable area. Furthermore, instability looks to last well into the night.

The one monkey-wrench in all of this, and I must admit it is rather significant is the lack of qpf in both the NAM and GFS through the night. The NAM has a pre-dryline convective zone near I-35 by 6z but not much after that, whereas the GFS comes in even more sparse.

I think this is precisely the reason that we've still got a SLGT on a day that otherwise is a solid MDT.

In regards to the 4km wrf, it wasn't initialized well AT ALL. It's prog featured the intense convection thats been occuring across NE TX, LA, and AR to occur around the Red River and up through OK just a few hours after it ran. Meanwhile, having nothing at all where the actual storms have been going up to the east. This is just 3 hours out, and we're speculating on its ability to see 24 hours further. I must admit this is somewhat of a surprise because I've been impressed by the performance of the 4km wrf in some of our recent events, particulary with respect to convective mode, location and timing.

This is gonna be one of those days where it'll just have to be played hour by hour, but if I had to pick a zone I'd say Altus up through Woodward, and it wont hurt to get there by 6, and if you gotta wait several hours after that, well you might as well do that waiting out in the field.

 

[Michael O'Keeffe]

I'm not sure if anybody has seen the 9z RUC, but it is showing the dryline well defined in W Oklahoma by 21z. If that verifies we could have some good forcing or at least a mechanism to initiate storms possibly in the daytime. As far as the cap is concerned I'm no worried about it. It seems every setup in the Plains this year has been, "wait there's a strong cap", but everytime it breaks and unfortunately it breaks too easily most times (ex. Mar 2, Mar 17). So all in all I will chase and I think there will be some good supercells with a few nice tornadoes.

 

[Jeff Piotrowski]

New 12Z Ruc

The new 12Z Ruc has three storms one on the triple point Major county Okla. The next storm on I-40 west of Clinton. Tail end Charlie SSW of SPS.
Tornados are likely in all three areas. The most impressive data from the 12Z Ruc is the 3000 J/KG cape in WC/OK. I would expect that as the LLJ increase after 0Z a few strong tornados are possible.

Target: Fairveiw OK