4/13/07 FCST: TX / OK / AR / MO / IL / TN

[Jeff Snyder]

So... painful... to ... look... at...
The 0z NAM initialized the big 500mb low near the southwestern Great Lakes region a little farther southwest than previous forecasts suggested. The mid-level jet stream is now forecast to remain ~100mi further south than previous forecasts indicated through Wednesday. I assume this is a result of the cold front current traversing Oklahoma and Texas being a little stronger than earlier forecast, which allows the front to move a little farther south into the northern Gulf of Mexico through Wednesday (thermal wind relation tells us that a southward shift in the baroclinic boundary would also lead to a southward shift in the mid- and upper-level jet, which is what we see). With slightly weaker ridging downstream of the Thurs-Friday system, it seems that return flow is also impeded (with terrible Td forecast for Thursday, at least in terms of tornadic supercells across the southern Plains).

The 00z GFS also forecasts a very elongated 850mb low to develop across Oklahoma and Arkansas Friday. This acts to veer strongly the 850mb flow, also shifting the axis of the LLJ well east of the dryline / front. Oy!

Personally, the area in southcentral OK ahead of the SFC low looks best to me. Shear vectors are forecast to be out of the southwest, so the most 'normal' / perpendicular orientation of the dryline relative to this shear vector appears to be along the apparent dryline bulge to the east and southeast of the SFC low (the position of which has just shifted southward ~150 miles from the 12z NAM run). Man, I can't believe how different the 2m and QPF fields look on the 00z NAM compared to the earlier 12z run. The 00z GFS is even farther south than the NAM in terms of the sfc low position. I'm very hesitant about a chase in the jungles near dark with 50+kt storm motions.

FWIW, the area of northcentral Texas west of Paris is pretty good chase territory. If something develops near or west of I35 down near Fort Worth by afternoon, the logistics of the terrain and road network may provide for a chase that wouldn't be terribly difficult. I'm terribly, terribly disappointed in the turn of events. But hey, it can't get any worse, can it?

Edit: It is worth noting that both the NAM and GFS are faster than the ECMWF and UKMET (at least the 12z/10 runs). I'm not too impressed with the run-to-run consistency of either of the primary NCEP models in this case, and, as the HPC suggests, the ECMWF may be a more likely solution.

 

[Jason A.C. Brock]

Never utter the words "It cant get any worse than this". Life will take the oppurtunity to prove you wrong every time. I have been worrying about this system being in the jungles since the weekend and it looks like it may very well still do that. We are jsut gonna have to do what we do everytime. Wait till the morning of and make a choice. BTW. The more you tell yourself "its still early in the season" the next thing you know its Late May and your wondering where the hell all the tornadoes are.
Ill be hoping for things to setup close to the I-35 corridor from OKC to Fort Worth and then just go where the storms lead until dark.

 

[Brian Stertz]

I am still on board with Friday's chase potential, particularly in vicinity of the triple point which should be near Gainesville TX at 00z. Backed surface winds should be in place along the Red River east of I-35...along and just north of the warm front...with the classic thermal ridge poke aimed between Durant OK and Paris TX. STP and sig. severe forecast parameters are very high across SC/SE Oklahoma and this is where the strongest 0-1km shear is forecasted along/north of the warm front boundary. This is all based off the 00z ETA run. Chances are that with this being a powerhouse system, the actual triple point position and theta ridge Friday afternoon may be further back west towards the Wichita Falls TX area...at least that's my speculation. At any rate...still a "green light go" for a chase Friday. Also, one more thing of note, there is a pretty high potential of some strong-intense tornadic supercells in C/SC/SE Arkansas...N/W Mississippi & possibly extreme N.Louisiana after midnight. The low-mid level jet criss cross is maximized in these areas with a strong surge of deep Gulf moisture indicated ahead of the approaching surface low moving due east across the Arklatex. This could mean quite a bit of trouble for some dangerous late night Lower MS Valley tornadoes...particularly along the boundary from SC Arkansas into NW Mississippi.

 

[matt patterson]

Wow... What a turn of events!!!!!! Anywho, the 6z wrf places the sfc low right on the red river at or near I-35 by 00z on Friday... Also to note that it has the 500mb winds farther south than the previous run as well.... Im still hoping for some northward progression of the system but it is looking less and less like that will happen... To make matters worse there is nothing (severe weather wise) in the forseable future as the GOM will take a very hard hit, but that is for another thread... I will still attempt to chase this system because i could not imagine going all april without a stormchase..... Start praying to the weather gods......

 

[Brandon Sullivan]

south south south.. i think im out boys... have fun with it.

 

[Jim Bishop]

I guess most of the pessimism on this boards is do to the crappier chase terrain. I'll give you that, but the setup still looks very good for tornadic supercells. I'm a little surprised the SPC doesn't at least have a hatched area outlined. Actually I expected them to have a moderate risk, but I suppose they are being caution at this stage in the game.

At any rate the shear, moisture and instability will all be strong. Everything's just been shifted further south and west. Living in Houston this is actually really helpful for me. Gives me a chance to leave work early, gun it up I-45 and catch a supercell.

 

[Kenny Drake]

I guess most of the pessimism on this boards is do to the crappier chase terrain. I'll give you that, but the setup still looks very good for tornadic supercells. I'm a little surprised the SPC doesn't at least have a hatched area outlined. Actually I expected them to have a moderate risk, but I suppose they are being caution at this stage in the game.

At any rate the shear, moisture and instability will all be strong. Everything's just been shifted further south and west. Living in Houston this is actually really helpful for me. Gives me a chance to leave work early, gun it up I-45 and catch a supercell.

With the models currently jumping around (which I think they will have come to a consensus by tonights run) the SPC will not center in on an area. I would definitely expect a slight risk to go up by tomorrow morning's 2nd day outlook based on tonights model runs if they are tending towards a consensus.

 

[mark plate]

I may be wrong on this, but if I understand correctly, the highest risk allowed in day 3 is a slight, and no hatched areas are ever indicated on day 3.

 

[matt patterson]

They can issue MOD risks on day three... they did this on June 12 or 13 of 2005 i believe out in the texas panhandle.... Anyway, the 12z WRF/NAM is out and it looks like it has backed it up to the west a bit.. I-35 seems like a pretty good starting point if i were to pick a Western extent at this time... I think the triple point will be the place to be in either case where the shear is maximized along the WF... Personally i would rather the solution stay like it is now as opposed to 100 miles north, which will keep us out of the Jungle in SE OK.. If im correct the area south of the Red River E of 35 is not bad chase country?

 

[mark plate]

I stand corrected...a moderate CAN be issued on day 3, but according to this below, it never has been done. Since I have seen MANY situations much more volatile and certain than Friday in the past and it has never been done, I certainly would have been shocked to have seen it used for the first time for this system. A Day 2 HIGH has only been issued once before apparently...see the details below.

As far as Friday goes, yes the WRF/NAM has the surface low back to the west, but closer inspection shows the better parameters for significant severe well off to the southeast...in far eastern TX, LA, and far SW AR.

________________________________________________________________

Day 2 outlooks, issued twice daily at 08Z and 1730Z, refer to tomorrow's weather (12Z-12Z of the next calendar day) and include only a categorical outline, textual description, and a probability graph for severe convective storms generally. Day 2 MDT risks are uncommon (only several times a year on average), and a Day 2 HIGH risk has only been issued once (for April 7, 2006).
Day 3 outlooks refer to the day after tomorrow, and include the same "break outs" as the Day 2 outlook. Higher probability forecasts are less and less likely as the forecast period increases due to lessening forecast ability farther in advance. No attempt is made to forecast general thunderstorms and a HIGH risk is never issued. While a MDT can be issued for Day 3, there are no known occurrences of such.

 

[Mikey Gribble]

I think the 12Z NAM makes northern Texas look quite a bit better. For one, temperatures recover better, warming into the mid to upper 70's. Moisture is slightly better as well. And most importantly to me, 850mb flow isn't veering as much as it was in the 00Z and the LLJ isn't as far away from the dryline as it was, which kicks low level flow up a bit. As a result, storms forming near the triple point (and slightly South along the dryline) could realize 0-3km helicity AOA 300m2/s2.
One thing that worries me is how narrow the window of insolation is in this target area. Temps are going to have to jump 10 degrees from 18Z to 00Z. There is a good dry punch wrapping in over the warm sector at 18Z, but I am still a little skeptical. I have changed my mind on whether or not I would chase though. I still will wait until tomorrow night to make the call, but if the 12Z NAM were to verify, I would target about 50 miles SE of the triple point and get on the first storm that had undisturbed inflow and I think it would have a pretty good shot at a tornado or two.
Storm motions of 45kts is not good for me. I already got two speeding tickets this season and apparently if you live in Kansas, number three gets your license taken away for a year. I wish I would have known that before and I would have rationed myself. If you see a black Xterra pulled over, please take one for the team and start swirving and speeding as you go by.

 

[Brian Stertz]

The 12z ETA shows a very well focused triple point over NC Texas by 00z Friday...it appears the strongest tornado parameters (steep lapse rates, good 0-3km VGP, lowered LCL's, decent inflow, 0-3km CAPE of 150-200 j/kg. to name a few) are in the Paris TX area. Just need to be sure that if a supercell initiates in the warm sector - triple point area that it will not immediately race northeast and over into the cold side of the boundary. If there can be that one rogue supercell or two that can ride eastward along the boundary (where obviously SRH and moisture pooling will be significant) then there may be that excellent chase where you can basically follow it along US-82 as it tracks eastward south of the Red River and ahead of the surface low. This is all speculating a forecast which the 12z ETA suggests. I like the decent focus presented in this new 12z ETA update, but storm motion trajectory will make or break this setup for Friday as it appears. Certainly do see a cause for concern overnight Friday into Sat. morning as things shift eastward into the Mississippi Delta area...for potentially some damaging tornadoes as deep moisture pools on the east-west boundary where 400-500 m2/s2 SRH is forecasted. Could be a wild and wooly night Friday night in this area as things shift eastward.

 

[Brian Stertz]

If 18z MesoEta...the big supercells on Friday are shown to pop in the area between Paris and Tyler TX...this seems to be a LLJ convergence area where southwest winds are hitting south winds...edge of cap...and in the area along the warm front which extends from NE Texas into SW Arkansas. Looks like tough chasing in the Arklatex if this holds true. The MesoEta does pop more isolated cells back west on the dryline from near Sherman down to the southwest of Ft. Worth...not sure if the shear will be sufficent to support tornadoes or not because the LLJ axis has shifted into the Arklatex. Just will have to keep monitoring things as Alex mentioned in his very good post.

 

[Ray Walker]

Well first off I just want to say that the SPC has issued a day three MODERATE risk before. It didnt really verify in the target area, it was June-12-05 I beleive. They had a moderate risk up for the eastern texas panhand and western oklahoma down into the texas south plains. However as we all know the south plains had a nice localized tornado outbreak that day, but anyways back on subject.
This system is really complicating things for me. I live in SC Oklahoma so Location isnt an issue here. But I really would like to see the moisture much deeper and the storm track further to the north and west. Even though I do think north texas and southern Oklahoma WILL see tornadoes I dont know how widespread or significant they will be, or how chaseable these storms will be. Cape values around 1200j/k and extremely powerfull wind feilds may not be a good combination, and yet if very well might given the extreme dynamics and lift with this system. But Honestly in an environment such as this one I have seen that not enough cape and to much in the way of wind shear causes the towers to be ripped apart. Also this system may generate to many storms all at once. However If Isolated storms form or even a cluster of storms can form and ride along the warm front and establish good inflow then We should be all set. This storm just represents to many quetions right now for me. I will make a choice on whether I will go or not sometime tomarrow.

 

[Jeff Snyder]

If 18z MesoEta...the big supercells on Friday are shown to pop in the area between Paris and Tyler TX...this seems to be a LLJ convergence area where southwest winds are hitting south winds...edge of cap...and in the area along the warm front which extends from NE Texas into SW Arkansas.

That's a possibility, but the 18z NAM also shows widespread precip and cloud-cover over northeast Texas, which removes any surface-based instability. Check out the 18z NAM CAPE forecast valid at 21z: http://wxcaster2.com/CENTRAL_MESO-ETA212_SVR_CAPESRHSWEAT_51HR.gif ... (that EEK is for the total lack of instability north of I20/I30)

Destabilization occurs (in the forecast, at least) rapidly after 21z, with >1000 j/kg CAPE developing northward into northeastern Texas by 0z and thereafter. That's a possibility, but I'm always hesitant of model forecast of strong destabilization after 21z. Kind of reminds me of the 3-30-07 bustola.

Of course, it's important to remember that this is just one solution from a model that hasn't been terribly consistent the past couple of days, so I'm not too confident in such a dire solution yet.