4/23/08 FCST: TX/OK/KS/CO/NE

[Stan Rose]

Yeah, there's a lot of 'Ifs' and 'maybes' but Im somewhat surprised by the lack of mention of severe potential on Wed. Havent followed this season very closely until now, so maybe im missing something. Sure looks like a respectable dryline setup. Is moisture an issue? Probably, when isnt it this time of year. I see enough continuity between the gfs and nam last few runs to make me sit up and take notice, especially when the nam (admittedly hot) is coming up with 6+ sig tor values late wed afternoon-eve. WIth a shortwave coming in late from the west, seems to me a good chance of initiation. Nam really likes NE CO. SPC cautions about the lack of shear but im seeing 40-60 kts bulk. I aint holding my breath, but its worth looking at.

 

[Mark Farnik]

A potentially significant event could unfold over the OK/TX Panhandles and as far north as southwestern KS late Wednesday afternoon and evening. The setup is looking to be classic dryline, with a warm front lifting northward over the TX Panhandle and western OK throughout the day, with the dryline developing in the far western TX Panhandle Wednesday morning and moving eastward onto the Caprock during the afternoon hours.
A speed max in the southern stream is forecast to eject over the Southern High Plains mid to late afternoon, with a secondary impulse ejecting farther north over the Central High Plains in the evening. South of the warm front and ahead of the dryline, dew points should rise into the mid to upper 60's with surface temperatures in the mid to upper 70's, creating a nice, tight T/d spread. The latest GFS run paints LI's of -7 to -10 and a healthy area of 2000 to 2800 j/kg of SBCAPE and MLCAPE, creating moderate to strong instability in the warm sector as the boundary layer heats up.
Storm initiation should occur as the ejecting upper jet max enhances ascent along the dryline as it pushes eastward, and as the upper jet exit region passes over the target area, forcing should help to further enhance the low level jet. 40-60+ knots of bulk shear and favorable low level hodographs in excess of 250 ms/2 will create an environment favorable for discrete supercells, some of which may very well be tornadic, given the environment.
This event is still two days out and, as we've seen time and time again this season, the models haven't been consistently reliable; things change quickly and events that have looked extremely promising on the models from a few days out have turned out to be, well, less than spectacular (pardon the pessimism, April 3rd is still fresh in my mind).
But at this point, anyway, the setup looks like it has some solid tornadic potential, and SPC mentioned a potential upgrade to higher probabilities once mesoscale details have been sorted out. Given the environmental factors present, I wouldn't be surprised to see a Day 2 Moderate Risk issued tomorrow for the eastern parts of the TX/OK Panhandles, western OK and far southwestern KS.
I am tentatively planning on chasing this setup, with a final decision to be made tomorrow afternoon.
If I do chase, my initial train of thought is to drive down to Garden City, KS Tuesday evening, spend the night there, and then drive to my preliminary target of Shamrock, TX Wednesday morning, which would allow me plenty of time to adjust my target before convective initiation between 4 and 6 p.m.
This *could* be a really good setup, with isolated, discrete tornadic supercells moving at chaseable storm motions a distinct possibility.
Lets keep our fingers crossed that the models aren't toying with us yet again...

 

[James Aydelott]

I'm curious to see if nocturnal convection will fire Tuesday night in the panhandle/high plains. If that happens, the mesoscale will be critical on Wednesday.

 

[Andrew Stoller]

Based on the 12Z 21 April Nam, I doubt we'll see mid to upper 60s dews, but if we do get overnight convection Tue night that pushes outflow west, perhaps that will keep the boundary layer moistened. The Nam does seem to produce precipitation Tue evening in OK, so perhaps outflow will also contaminate the boundary layer Wed. The GFS is the same with dews in the low 60s and has a bit of a bulge right in the OK panhandle.

Unfortunately, CINH looks to be a possible fly in the ointment as the evening progresses, but as the waves come in, discrete initiation looks to be a possibility. Directional shear I think looks great, especially the 850 winds backed out of the southeast. I think veered 850 winds has been one of the setbacks the last couple of systems.

 

[John Peters]

60 hr GFS depicts a small 500 mb 60-80 kt wind max over (perhaps slightly east of) SPC's 30% on the day 3, along with a very small focus of 50-60 kt low level sheer (there is also a nice vort. max over this area); both of which NAM does not seem to reciprocate. These features correspond to an elongated region of heavy precipitation that seems to propagate west. I'm guessing this is predicting the formation of a MCC, perhaps a derecho event?

The little impulse corresponding to the LL and Mid Level maxes seems to propagate east into southern Illinois and dissipate.

 

[Dave Kaplow]

60 hr GFS depicts a small 500 mb 60-80 kt wind max over (perhaps slightly east of) SPC's 30% on the day 3, along with a very small focus of 50-60 kt low level sheer (there is also a nice vort. max over this area); both of which NAM does not seem to reciprocate. These features correspond to an elongated region of heavy precipitation that seems to propagate west. I'm guessing this is predicting the formation of a MCC, perhaps a derecho event?

The little impulse corresponding to the LL and Mid Level maxes seems to propagate east into southern Illinois and dissipate.

I'm not an experienced forecaster, but it seems to me that the compact vortex-like feature the GFS is showing in northern TX has to be an anomaly of some kind, it's too bizarre to be anything but an artifact. I suspect it will disappear in future model runs... If only it could verify, North Central TX would be in for some truly insane weather! But I don't think even a strong compact derecho could account for features like this:

850 winds
Sfc dewps/strmlines
850 VV
6 hour precip
(note: links will be invalid when model updates)

So what is this? A derecho? A huge intense supercell? The vort max to end all vort maxes? A small hurricane over the plains?
Whatever it is, I suspect we can safely disregard it, especially since none of the other models are showing anything like it there.

 

[Kenny Drake]

I'm not an experienced forecaster, but it seems to me that the compact vortex-like feature the GFS is showing in northern TX has to be an anomaly of some kind, it's too bizarre to be anything but an artifact. I suspect it will disappear in future model runs... If only it could verify, North Central TX would be in for some truly insane weather! But I don't think even a strong compact derecho could account for features like this:

850 winds
Sfc dewps/strmlines
850 VV
6 hour precip
(note: links will be invalid when model updates)

So what is this? A derecho? A huge intense supercell? The vort max to end all vort maxes? A small hurricane over the plains?
Whatever it is, I suspect we can safely disregard it, especially since none of the other models are showing anything like it there.

This anomally appears to be a s/w that GFS propagates all the way from the ITCZ in the middle of the Pacific west of Mexico. There are little to no observations for initialization in those parts of the model's domain. However, GOES WV over the Pacific does show a vortmax out in the middle of the Pacific. Apparently, the GFS wants to propagate this along the rather-weak subtropical jet into the S. Plains by Wed evening. The NAM picks up on this too. I think this feature does exist, but I cannot possibly convince myself or anyone that the NAM and GFS are handling it properly right now due to lack of initial data in that region. IF this pans out it will be the first time this year the subtropical jet had a key role in inititiating convection.

 

[John Peters]

The recent ETA establishes this feature more so than the last run, showing a small region of 50-60 kt 500 mb winds centered over a pretty unstable boundary layer (3000+ J/Kg), with a 30-40kt LLJ. The little impulse in question should track west across TX and OK Wed. afternoon and night. GFS is more bullish on LL sheer, depicting a 40-50 kt max corresponding to the impulse.

I suspect the presence of CINH may inhibit widespread convection initially and allow some storms to remain discrete.

Based on my knowledge (i'm still new at this): if the models continue to agree on the positions of these features tomorrow we could see a moderate risk extended further east than the current 30% along the OK/TX boarder.

 

[Jay Press]

The 0Z GFS is out with that same little vort max. It looks very similar to the NAM 12Z. I am definitely not the forecast master, but it's looking quite interesting.

The thing that has me boggled is that the GFS and the NAM show the CAPE getting shot down from 18Z to 0Z. Especially the GFS. I like that both models are showing 850 backing winds at the 0Z time frame. That's nice to see for a change. Too much veering going on these days. So would one position themselves NE of that little low? Say, Wichita Falls even Lawton?

I may come out from So. Cal for a quick trip on a buddy pass. Wondering what Thursday will look like, I would like to make it a two day trip, but that's another discussion for another thread. Would someone PM me about Thursday?

Thanks,

B.p.

 

[Mike Hollingshead]

I'm starting to think about heading to the Goodland area for Wednesday. The main deepening low levels is more up in this region, with decent mid-level flow trying to overspread a backing low level jet. I just really like that 35 or so knots at 500mb over a se low level jet about 35 knots as well. Sharp dryline right on the KS/CO border. I would think there'd be a small window for the dews to return nw to this region prior to early morning convection in the TX panhandle. Not the greatest hope for good moisture there, but I think it will be enough of one. The biggest thing I guess this area has going for it, is being close to what looks like a good day in KS on Thursday(nw to sc KS). Basing these thoughts mostly on the GFS as I'm still not a reconverted NAM fan yet, even if it did better with today's sfc. Both are pretty similar anyway.

 

[Dann Cianca]

I'm starting to think about heading to the Goodland area for Wednesday. The main deepening low levels is more up in this region, with decent mid-level flow trying to overspread a backing low level jet. I just really like that 35 or so knots at 500mb over a se low level jet about 35 knots as well. Sharp dryline right on the KS/CO border. I would think there'd be a small window for the dews to return nw to this region prior to early morning convection in the TX panhandle. Not the greatest hope for good moisture there, but I think it will be enough of one. The biggest thing I guess this area has going for it, is being close to what looks like a good day in KS on Thursday(nw to sc KS). Basing these thoughts mostly on the GFS as I'm still not a reconverted NAM fan yet, even if it did better with today's sfc. Both are pretty similar anyway.

I hear ya' Mike. I think this may be my first chase of the year ... but we may be on the Colorado side of the border. Models seem to be handling the dryline pretty consistently and I'll be looking for weakening cap and low cloud breaks that morning. Think we might find one or two and with the shear being as nice as it is, I think we could see some ... well beautiful weather.

 

[Tony Laubach]

I'm not entirely sure you throw out Colorado/western Kansas just yet for Wednesday. While I have nothing against going to Texas (as shown by my multiple trips in multiple weeks), it would be nice to play in my home turf for a change.

Moisture is a bit harder to manage, but high plains + dryline usually yields interesting results. The instability won't be as strong, but shear values will certainly be there. If dews can hit the lower 50s, we'd be looking pretty good up here. Hell, even upper 40s would suffice for some good storms.

What makes this an interesting choice are the potential negatives for the southern target. The timing of the upper-air wave and the overnight convection make for two questions. The warm front will definitely be the play for the southern target.

Beyond a quick glimpse, I haven't fallen too deep with the models just yet. All I know is Colorado can't be ignored and my plan of attack in terms of leaving tonight will reflect that.

More, as usual, on my blog...

 

[Andrew Stoller]

The models don't really depict dews as high as the 50s in northeast CO, but the Denver AFD seems to think things may pan out:

THERE IS SOME COLD ADVECTION ALOFT AND LARGE SCALE
LIFT WHICH WOULD HELP ERODE THE STRONG MORNING CAP. IF STORMS DO
FIRE...LOOKS LIKE WE WILL SEE THE REGIONS FIRST SEVERE STORMS AS
SUFFICIENT CAPE OF 1500 J/KG EXISTS IN COMBINATION WITH STRONG DEEP
LAYER SHEAR. 0-3 KM HELICITY IS UPWARDS OF 200 M2/S2 SO SUPERCELL
DEVELOPMENT EXPECTED ALONG WITH POTENTIAL OF TORNADOES GIVEN MOIST
ENVIRONMENT AND LOWER LCLS EAST OF DRYLINE.

The models really paint a ton of early morning crumvection in the southern target which I never have good luck with, so I hope the dryline can get stacked up around, say, Yuma, CO. It's always better to get the dews back up against the foothills around CO Spgs northward to Castlerock so the orographic component of the Palmer Divide can help out, but it ain't gonna happen Wed.

 

[Mark Farnik]

Seeing as the southern target has question marks all over it in regards to the timing of the shortwave and the likely interference of early morning crapvection, I have shifted my focus to the northern target, which is looking better and better with each model run and also happens to be much, much closer to home and viably chaseable than the southern target.
Things are shaping up for what could be a pretty decent regional severe weather outbreak over the Tri-State of east central Colorado/northwestern Kansas/ southwestern Nebraska on Wednesday afternoon and evening. While the instability won't be as pronounced as the southern target and the amount of moisture return is somewhat questionable, bulk shear values will be in excess of 50+ knots, with backed southeasterly surface flow in the 25-35 knot range under 35+ knots of westerly flow at 500 mb. This strong directional shear, combined with 1500 + j/kg of CAPE and 0-3 km helicity values in excess of 200 m/s2 has potential mini-tornado outbreak written all over it.
This particular event isn't dependent quite so much on the moisture return (while dews in the low 50's would be optimal for tornadoes, High Plains magic often still occurs with dewpoints merely in the high 40's) it hinges on whether we can get enough breaks in the stratus deck to get adequate surface heating to break the strong cap by early to mid afternoon along the dryline. If we can get convective temps into the low to mid 70's ahead of the dryline, the cap will be breached and we'll be in business. But if adequate surface heating doesn't occur, initiation is questionable, if it occurs at all, and a perfectly good setup will go to waste.
I don't have class until noon tomorrow, which will give me plenty of time to evaluate the situation and make a final decision. If I start seeing large breaks in the stratus deck by 11 a.m., I'm heading east to my prelimanary target of Yuma, Colorado to gather data and prepare for initiation between 2 and 4 P.M. along the dryline, which should be draped from north/south from Sterling to Limon to Lamar.
I'm praying that the storm gods will look favorably upon us and allow for adequate surface heating and dews in the 50's... I really, really want to see a daytime tornado in Colorado!

EDIT - 1730 UTC Day 2 Outlook has hatched severe probs along dryline from southwestern SD through western NE across eastern CO down to the OK/TX Panhandles and mentions isolated supercells with a localized tornado threat.

 

[John Peters]

The latest ETA keeps the higher winds from 850 to 500 north and south of the OK/TX boarder. I'd expect a corridor of optimal supercell parameters from the TX panhandle into SE OK. My biggest concern would be capping (there is a pretty significant pocket of CINH depicted over the TX panhandle at 0Z). The best sheer profiles look to be just south of FWS, and this will be coupled with pretty strong instability during the afternoon. If any storms can get initiated here, i would imagine a significant tornado threat.

Edit: GFS continues to be much more aggressive with LL and ML flow, showing a pocket of 60-80kts at 500mb in coincidence with 30-50kts at 850 mb (though it is less aggressive in terms of instability). If the GFS pans out, and storms initiate under the enhanced low to mid level sheer, I could see a high-end Mod-High risk scenario playing out, with a potential for several strong tornadoes over a concentrated area.

lol, listen to me try to sound like i know what i'm talking about.