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

[Alex Lamers]

Well I have classes, so once again I'm held back in Norman (can we get something not on a Monday or Wednesday please ). Anyways...I digress...

Even if I could go, I'm not entirely sure I would. I am concerned that this lead shortwave is going to kick off too much activity and the atmosphere in its wake over SW OK, NW TX and TX Panhandle will be convectively overturned to the point it cannot recover by dusk. Looking at the 12z models that have completely come in now...there is a general agreement that thunderstorms will begin developing as early as 14-15z in West Texas as the upper level wave interacts with low-level boundaries and increasing moisture situated thereabouts. That will then gradually progress east-northeast through the day. I think that will be the main show as far as thunderstorm activity goes. Models project the LFQ of the upper level jet streak to reside right over OK and N TX where winds in N TX are nearly westerly and winds in the TX Panhandle are nearly southerly (holy difluence Batman!). The timing of the shortwave is just all wrong.

It actually looks set up pretty nicely for the morning convection to sort of congeal into some flavor of QLCS and then ride east-northeast along or just north of the Red River. The NAM is especially impressive in this regard. 65-70F dewpoints pooling right along the Red River along a boundary. Essentially easterly sfc flow across OK and southerly sfc flow across TX. Nice axis of SBCAPE 1500-3000 j/kg straddling the Red River as a result and I think we could see a nice linear system plow eastward in that environment. Definitely not the most classic forward propagating QLCS setup I've ever seen but I wouldn't be surprised if we saw a nice swath of hail/wind reports along or near the Red River tomorrow afternoon. NAM & GFS agree on keeping a belt of enhanced 35-45 kt 850mb flow over C TX that slides slowly east during the day. Best threat area is on the nose of this LLJ in the associated thetae advection maximum.

Meanwhile, behind this system, the atmosphere should still be juiced and there will probably be a dryline sharpening up somewhere in W TX, but looking at upper level wind progs, they should be somewhat convergent. There very well may be some nice development behind the morning activity, but I would be skeptical of chasing (especially with gas near $3.50) under convergent flow aloft.

That all being said...with expected linear system to trek near the Red River during the afternoon...and associated subsidence behind it...if thunderstorms can overcome that negating factor, there could be some very interesting supercells roughly in the Plainview-Childress area of W TX.

Very nicely curved hodograph forecast at Childress at 00z Friday with ~2500 j/kg of CAPE. The thing that has me concerned is that the models take this isolated activity in the late afternoon and promptly squash it just after dark (including NAM and 4km NMM core WRF from NCEP). However, there may just be enough there to squeeze out a pretty nice supercell for a few hours right before dark.

AJL

 

[nickgrillo]

Forecast soundings along and ahead of the dryline in the TX panhandle for late tomorrow afternoon are extremely favorable for tornadic supercells. Only a thin layer of SBCINH exists on the 00z CDS sounding--with very favorable low-level wind profiles--yielding an enlarged and cyclonically curved boundary layer hodograph. With southeasterly boundary layer flow, moisture shouldn't be a problem, with SBCAPE progged >2000j/kg, assuming convective mixing isn't too strong in the afternoon.

I haven't really looked at tomorrow in-depth, but I wouldn't be too worried about the morning convection--with the southeasterly flow at the sfc advecting moisture into the warm sector, and spots of diabatic sfc heating later in the afternoon being able to deepen the BL and eliminate the inversion. Convergence at the sfc along the dryline and some weak mid-level DPVA aloft will likely be enough to release a SB parcel. Further north, there might be a chance for a few supercells closer to the sfc cyclone--but if I was chasing tomorrow, I would probably target somewhere in the western half of the TX panhandle, where the overall deep-layer kinematic and thermodynamic profiles are quite favorable for isolated cyclic supercells.

 

[Mikey Gribble]

That was a nice forecast Alex. I think you made some great points.

I just started my forecasting today for Wednesday because I was preoccupied with yesterday's setup, but I think tomorrow holds a decent chance of strong tornadoes if the NAM verifies. I only looked over the NAM because I was crunched for time getting a forecast posted on my blog, but now that it's up I started glancing over the GFS and there are definitely some major differences between the models. That being said what I am about to say (and everything I said in my forecast on my blog) was based on the NAM. It is certainly a tricky forecast to say the least with early morning convection when the jet streak (with the subtropical jet) comes through and CINH still along and ahead of the dryline either side of Plainview at 00Z, but I am starting to think things might work out.

The best tornado threat tomorrow should be with storms firing along the dryline in the (North-South) Happy to Lubbock area. Storms coming off the dryline in this corridor should realize the strong SRH along the warm front. The persistent CINH keeps sticking in the back of my mind for some reason. Assuming storms do come off the dryline by 6PM and don't struggle with the cap, I think we could see a couple strong tornadoes and possibly a tornado cluster in and around a Happy to Childress to Lubbock triangle. If the 00Z runs hold steady on what the NAM is advertising I would think the tornado threat (and concentration) in this triangle certainly justifies a moderate risk in the early morning outlooks. I posted a forecast here if you're interested http://loadedgunchasing.com/blog.html

 

[Shane Adams]

Nothing scientific, but tomorrow reminds me of April 9. I guess I'm just too ignorant meteorologically to be worried about the subtleties. I just remember a strong negative forecast vibe leading up to that event as well....followed by most of those forecasters chasing the event.

 

[Mikey Gribble]

Ouch! The 00Z NAM isn't looking too hot. I would forget about that moderate risk if I were SPC, at least until the later Day 1 outlooks when the picture becomes a little more clear. I am shocked with how poorly the GFS and the NAM have been performing lately.
The dryline front intersection has dropped a lot farther South. One of my favorite things about this setup was that the 12Z NAM had surface winds backing hard along the front which spiked SRH. They aren't backing so hard in the latest run which dropped 0-3km SRH off. I haven't seen 1km yet because the site that have it (that I know of) haven't updated. 700mb winds dropped off 5-10kts across the area I mentioned in the earlier forecast.
I need to wait till COD updates so I can get a more detailed look, but what I've seen so far isn't good. That pretty much makes my mind up for me on chasing tomorrow. I'm not going to make a 9 hour drive with this much uncertainty.

 

[Shane Adams]

Ouch! The 00Z NAM isn't looking too hot. I would forget about that moderate risk if I were SPC, at least until the later Day 1 outlooks when the picture becomes a little more clear. I am shocked with how poorly the GFS and the NAM have been performing lately.
The dryline front intersection has dropped a lot farther South. One of my favorite things about this setup was that the 12Z NAM had surface winds backing hard along the front which spiked SRH. They aren't backing so hard in the latest run which dropped 0-3km SRH off. I haven't seen 1km yet because the site that have it (that I know of) haven't updated. 700mb winds dropped off 5-10kts across the area I mentioned in the earlier forecast.
I need to wait till COD updates so I can get a more detailed look, but what I've seen so far isn't good. That pretty much makes my mind up for me on chasing tomorrow. I'm not going to make a 9 hour drive with this much uncertainty.

COD is updated...IMO it's an easy choice...April 9 all over again. You can't really forecast helicity, but if the NAM even comes close to verifying, holy crap. We'll have our butts parked out west along I-20 tomorrow. I don;t know how to forecast, but all the right colors I like to see on each parameter are stacked just the way I like them west of Abilene.

 

[Adam Penney]

Well I made the drive from Kansas City down to AMA today(Hey, you only live once right? Might as well enjoy it...lol). Mikey I can understand your pessism in regards to the drive tomorrow with the uncertainties at hand, however, the latest run of the NAM has me in complete 100% agreement with Shane. I-20 just west of Abilene looks very sweet at 0Z tomorrow "IF" this run of the NAM verifies. As Mikey stated, the model continuity has been just downright horrible over the past few weeks, so the setup could look completely different in the morning. We are also going to have to hope that early morning convection and rain cooled air doesnt inhibit instability parameters too much.

As of this moment I am going to target Sweetwater,TX along I-20. This can and will likely change in the morning, so this target is only pre-liminary. I will update in the morning.

Here is to hoping we finally get some backing of the winds and good tornado chances tomorrow!

 

[Mikey Gribble]

I'm on board with you and Shane. COD and Earl's page show two very different things. Same model different graphics/sites. That's ridiculous. If you look at Earl's page 3km SRH is is 280 ahead of the dryline bulge. I only checked Earl's because it updated first. I usually like to use COD. Now that COD is updated it shows >500 bullseye on 3km SRH. Earl's also doesn't have suface winds backing to almost due easterly like COD shows. How does that work out? I know COD is a little higher resolution, but those things shouldn't be different. After seeing COD though I pretty much agree with my previous forecast, only shift it South 150 miles LOL.
My god the NAM has shifted South. This is Monday's setup all over again with the models jumping surface boundaries all over the place. We are only 24 hours out. The front dryline intersection shouldn't be shifting South 150 miles from one run to the next.
Basically everything has shifted South down toward I20. It looks like it still wants to develop convection along the front earlier in the day. It's tough to tell but surface temps jump back up behind the early convection coming off the front right ahead of the dryline bulge and the 00Z precip. shows convection backed up to the dryline again, so I guess the earlier thoughts on a window of clearing/insolation still stands. Once again there is a respectable amount of CINH left at 00Z along the bulge in the dryline.
With the new 150 mile further South NAM I would target Colorado City. If 00Z NAM verified (which I am 99.999% sure it won't) the best tornado potential should be along the I20 corridor from Colorado City over past Abilene.
I guess we'll just have to wait till early afternoon tomorrow to figure out exactly where the dryline front intersection will set up. Wherever that is I would put myself just East of there. Ideally I would want to get on a storm firing along the dryline just South of the intersection to give it time to mature before it hits the backed surface winds along the front.

 

[Mark Farnik]

With all the hubbub surrounding the southern target, the northern target has largely been forgotten in the discussion of tomorrow's severe potential. While I can't deny the southern target looks potentially amazing for tornadic potential, you can't ignore the severe parameters further north in the central High Plains. The more I look at the most recent model runs, as well as tapping into my inner High Plains severe intuition, the better I feel about the sleeper potential of the northern target (northeast CO/northwest KS/southwest NE) for tomorrow. The latest runs of both the WRF and the GFS show a tongue of low to mid 50's dewpoints advecting northward along the dryline as far north as Ogallala, NE by 0z Thursday. Also, both are consistent in painting SBCAPE and MLCAPE values of 1500- 1800 j/kg and LI's of -5 to -7 across eastern Colorado and far western Kansas by 0z. Also promising is the fact that they show a fairly stout cap at 18z Wednesday and similarly erode it to nothing by 0z. Surface winds will become moderately to strongly backed along the dryline by 0z, and bulk shear values are in the 40-60 knot range with 200 to 250 ms/2 0-3km helicity values.
All the ingredients are in place, or at least so it appears with this particular set of model runs (with the consistency, or lack thereof, that they have shown lately, who knows what they might show by morning, lol) for a regional severe weather outbreak over the west central High Plains tomorrow afternoon and evening.
Given the models' unreliable track record of late, I'm basing my forecast more on what I know about High Plains severe climatology as well as basic severe forecasting skills.
Given the strong directional shear, backed low level winds and moderate instability, isolated to widely scattered supercells will likely be the primary convective mode with the potential for very large hail, damaging winds and the distinct possibility of a few tornadoes.
The potential limiting factors to this event are moisture and surface heating. If copious amounts of convection fire in the overnight hours in the Southern Plains, the quality and quantity of the moisture return could be affected and result in mid to high 40's dewpoints, which, while still sufficient for supercells, would definitely hinder tornadic potential. The most important factor, and the key player to convective initiation, is going to be adequate surface heating. A stratus deck is forecast to overspread areas along and east of the dryline by early morning and persist into the early afternoon hours. If enough large breaks occur in the deck by the late morning hours and we can get surface temps in the low to mid 70's, the atmosphere will be primed for initiation by early to mid afternoon. However, if the stratus deck persists and surface temperatures fail to rise out of the mid to high 60's, atmospheric instability, as well as the overall severe threat will be reduced significantly.
As of now, my train of thought is to analyze the situation again in the morning and monitor it through the morning hours. By noon, I should have enough information to finalize my chase plans and target and, if the storm gods are kind and the stratus deck erodes by late morning, head out the door and be to my initial target by 2 p.m. and make necessary adjustments from there.
If I had to pick a preliminary target at this moment, I would select Yuma, Colorado, seeing as that it will be about 15 to 30 miles ahead of the dryline at mid-afternoon, has excellent road options in all directions, and numerous Wi-Fi hotspots for data gathering purposes.
With everyone else's attention focused on the Texas end of the dryline, looks like I might be one of very few chasers on this northern target. Which is just fine with me.

 

[Alex Lamers]

Well I kind of thought this would pan out as a messy day and it still is looking that way. New 4km SPC WRF run (http://www.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/) bears this out well. The problem is there is a huge area of decent CAPE values >1000 j/kg that stretch from SW SD all the way to SW IA and southward to the Gulf.

There's a pretty significant shortwave pushing into the Plains early in the period. It just seems like one of those events where a massive amount of convection develops...tending to lead to a predominately linear mode. So I think that there will be a lot of areas that have severe weather potential...but as far as pinpointing any particular area to chase...that seems nearly impossible at this point. A lot will depend on where morning convection develops and where boundaries are situated in the 21-03Z timeframe.

I-20 corridor west of DFW and perhaps northwestward towards LBB seems to be where the best chance of discrete storms seems to lie. I'm glad I'm not able to chase...I'd be pulling my hair out right now.

AJL

 

[Brian McKibben]

Starting the day off with 4000 j/kg of MUCAPE in SW Okla. NW Tex. Storms are already popping due to the sw moving through W. Tex.

RUC forecast keep CAPE at or above 4000 throughout the day. h5 winds look to pick up to near 50kts as the next sw approaches the region. Also h85 winds increase to near 50kts. Things could get interesting if the wind fields materialize this evening.

Large hail seems very likely given the steep LR and cold temps at h5.

SPC is going with a Moderate Risk on the 13z outlook.

 

[Rocky Rascovich]

Today is a big gamble for a successful chase due to convection already breaking out across much of the target area between CDS and LBB in response to the lead wave. I suspect this could lead to a period of subsidence behind that wave and this dense cirrus shield that I suspect won't clear that area until at least 23Z. I would think that could further limit insolation. Still, based on the RUC, that next wave affecting that area west of CDS looks fairly stout as helicity values of about 400 m/s are projected along with 3500 j/kg cape. Another issue is that I'm officially spotting with KFOR now so if they call me, I'll need to be at least close to their viewing area, and once they call, my gas is more than taken care of for the day. I'm more skeptical of anything note worthy happening at least before sundown in western or southern Okla. If storms do manage to fire, lapse rates are steep and some big hailers are quite likely.

If I chase, I'll be heading out with Charles Edwards and Michael Ratliff and depart Yukon, Ok. shortly after noon.

 

[Gabe Garfield]

It seems like the target area for today is fairly unambiguous. The left exit region of the 250 mb jet, the nose of the 500, 700, and 850 mb jet maxima, and the north side of the dry bulge are forecast to be juxtaposed somewhere between ABI and CDS. Thus, my target for today is Jayton, TX.

Instability continues to be a concern, though, as a large subtropical cirrus canopy overspreads most of the Southern Plains. Nevertheless, I believe the abundant moisture and very steep lapse rates could make up for what would normally be a large fly in the ointment. Also, I am heartened to see that there is very little elevated convection this morning. Satellite and radar imagery should be the hot products today; satellite for clearing and radar for "seeing" through the grunge.

EDIT: Never mind about the lack of elevated convection over the TA. I was looking at an old radar image on COD.

 

[Adam Penney]

Sitting in AMA this morning, and am planning to head down to Lubbock in about an hour. I will get some data there and with a decent road network, I will make a decison from there. The latest RUC does show some oppurtunity last this afternoon and evening in the corridor that Gabe just mentioned.

0-3km SRH values are spiking between around 450 or 500 in this area(WOW) and SBCAPE is still forecasted to be around 3500 j/kg. Also, LI's are forecasted to be between -6 and -10. We also should receive backing 850mb winds at around 25-40kts. 500mb winds should be between 35-45kts and streaming in out of the west.

Obviously the concerns of early morning convection and subsidence behind this is a concern. Hopefully the picture will begin to become clearer in the next 2-3 hours.

Good luck to all today!

 

[Bill Tabor]

Today was looking good, but after reviewing this morning's NAM it is a fairly mixed bag it seems. The wave is coming out early which is never good. Winds are various levels don't all jive supercell / torn wise until nearly 0z and then seem to be weaker when viewing the 6z again later. Obviously the play is along the frontal boundary. I'll probably chase it but will likely be a mix and match day. I'd put my odds at getting a tornado at a fairly low level 2% to 5% (SPC standards) unless there is a long tracked gob monster sitting on the boundary after some decent clearing / heating in the right place during the window where best parameters are maximized.

Best of luck to the rest of you. I will most likely be running Spotternet and streaming video if there is anything worthwhile to stream. This could be one of those days where it isn't that great until almost dark and until 3z.

Good luck to the rest of you. I'll try and say 'Hi' to whoever I run into.