3/3 FCST: Wednesday - A system to watch closely

[Jeff Snyder]

First off, I'd have to say that there are some pretty major differences between last nights 0z run and the latest 12z run from the ETA. The upper trough is about 150 miles farther west by 6z Thurs (western NM instead of central NM), and is more positively tilted. On the other hand, there is significantly less rainfall (qpf) north of the warm front. Actually, with the trough being farther west, the sfc low is also a little farther west. This, along with the lesser amounts of qpf north of the boundary, has seemingly allow the warm front to move farther north by 0z thurs (Weds. evening), and has allowed the untable air (with CAPE >2000), to move into northern TX.

I do hold the same concern as Gabe... 850mb winds are farther east, for the most part. However, this seemed relatively common last year (strongest 850 winds well east of the dryline)... What is of more concern to me is the tendency for the ETA to shoot the low/trough out of the SW US too quickly. This has been in play the last couple of runs, as the systems has slowed down each run. Well, the system doesn't slow down, per-se, but the forecast position of the system slows down . At any rate, if this trend continues, we may run into a signficant timing issue, and evererything may pass through the area durng the night Weds and morning Thurs...

In all, each run seems to be getting sweeter, so we'll just have to see...
Jeff

 

[Tim Marshall]

Indeed. The morning models slow down this system. This will allow even more low-level moisture to advect northward. The 12z ETA now has 60 dewpoints all the way to Oklahoma City by Wednesday evening! The warm front still remains across north-central Texas. Yes, Wednesday is looking more and more like the day before the dynamics spill onto the plains. I agree with the concerns others have expressed over prior convection and the cap, and it now looks like the system is about 12 hours out-of-phase. But, Wednesday looks like the first chase day of the spring for me. Looking at the Junction-Abilene line right now. TM

 

[Joel Wright]

There's certainly no question this storm has WAY more moisture to work with. It will be interesting to see how things come together with this system.

 

[Jim Bishop]

The main concerns I'm focused on for Wednesday are a possible cirrus deck, and a lack of upper level support. Based on current water vapor imagery and backed up by the ETA, it appears there may be cirrus worries for Wednesday.

If there is no cirrus deck, then Wednesday will be a great chase day. If a cirrus deck prevails, this will keep surface temps down, and I'd then be worried about initiation. The current 850 temp forecast shouldn't be a problem, ~15C, but it could be with cirrus.

Otherwise, Wednesday looks great!

Jim Bishop

 

[Jeff Lawson]

Today's nice weather is having the usual effect, getting me excited about the coming setup despite previous concerns. The 12Z ETA isn't helping, either.

It now looks as if the warm front will prove more of an advantage than disadvantage, giving us a good boundary to work with in North Central TX. One of the biggest concerns I have is convective debris from storms Tuesday night limiting insolation for Wednesday. On the other hand, any storms Tuesday night might make for some outflow boundaries to work with. Dependant on what happens, it could be a tricky situation at the surface Wednesday morning.

I'm feeling more confident now that North Central TX will see some severe weather out of this system, but I'm not sure yet what my chase strategy would be Wednesday. Obviously, the warm front will be the primary player, but with storms potentially all over the place, picking a target is going to be tough. To be honest, I usually don't like to chase days when there are numerous clusters of storms in the muck, as your success really comes down to simply being in the right place at the right time. April 7, 2002 comes to mind...lots of decent storms that day, but only one that interacted with the warm front at just the right time and place to produce a significant tornado.

I'm getting in the mood to chase, but I'm not clearing my schedule for Wednesday quite yet. I want to see what transpires tomorrow (and especially tomorrow night, which could be interesting in itself).

 

[Melissa Moon]

I've been looking at everything and I agree that there is some promise.

However, I do have a question about helicity and the models. I'm not like reliant on the models or anything, but the forecast helicity in the North/Northwest Central Texas area is, like, 50 m^-2 s^-2. Don't you need higher values in order to even get weak tornados? How important is the helicity forecase relevant to everything else, and how good is the ETA for forecasting helicity anyway (in your experience)?

I always feel stupid asking questions...

Melissa

 

[Jeff Snyder]

Storm-Relative helicity is VERY dependent upon storm motion. While 50m2/s2 is weak in many regards, one must ask with which motion is this the result of? In other words, a storm moving northeast at 55mph may experience helicity of 50m2/s2, while a storm in the same environment, but moving east-southeast at 40mph may experience MUCH more. In cases of supercells, motion tends to be slower and to the right of the mean mid-level wind, which tends throw any model forecast helicity out the window...


I find that it is difficult to put much weight on model forecast SR helicity (make sure it is SR, too, and not environmental helicity, which negates storm motion). Oftentimes, the storm modifies the environment itself, or at least the environment is modified by mesoscale features that can hide in coarse model grids and go undetected by the models. Just something to keep in mind...

Jeff Snyder
KC0HJX
www.TornadoCentral.com

 

[Jeff Snyder]

Well, the 0z models are starting to roll in... Just from the 0z graphics, it doesn't look too good (well, as good as earlier runs at least). CAPE is meager (<800) across much of north Texas and points northward. Now, I think much of this has to do with the fact that the ETA convects across the area by 0z, and thus decreases surface temps and related instability at that time. This explains why there isn't progged to be much more CAPE across the area at 0z than 18z. So, I don't think I'd take the 0z CAPE too stringently.

Again, as has been the case, the system continues to slow down. The problem is, by the time the system kicks out on Thursday, upper forcing is very strong and will likely result in a strongly-forced squall line...

I think the best convection will likely be nearer San Angelo than SPS, I think, mainly because of instability reasons...

Any other thoughts?

Jeff

 

[Chad Ringley]

I second that Jeff. After looking at the 0Z Eta & GFS, certainly looks like the best chance of any solid convection & discrete storms is going to be in the SJT CWA. But with the 850 flow backing significantly NW of the upper level low (not sure how much I believ that, but there has been some run-to-run consistently), 0-1km SREH may be limited at initation time in the SJT CWA.

The Gulf is defintley open for business again though. High precip totals nonetheless for N. Texas/S. Oklahoma (0Z Eta has returned 60°F+ Dwps across the Red River) but it appears the severe potential will be limited thermodynamically north of I-20.

 

[Mike Hardiman]

I'm not too impressed with the chances for along the Red River at all... north of the warm front there is little instability... probably a lot of left over clouds from the previous day (elevated stuff?)...

Maybe in and around Junction and South.... that area of Texas. Better instability... decent shear, but both the AVN and ETA showing some mid level moisture getting pulled up from the Pacific... above a dry punch at ~700mb. I'd be concerned about mid-level clouds perhaps?

Laptop is still 2500 miles from here, won't have it for over a week. Perhaps the funds could better be saved for May/June. I'd be looking at a 6 hour drive from the Sun City, on a 3-day stretch off work, but right after an 3-12 shift. Intrigued, though I'll probably sit this out.

-Mike

 

[Joel Wright]

I wouldn't count this one out just yet. Things still look pretty good to me, very nice moisture return and favorable dynamics should allow some supercell activity late in the day Wednesday. At this point my early guess would be between Abileen and San Angelo. Minor details will need to be worked out but that's my first stab at it.

 

[Shane Adams]

I'll make a decision early Wednesday based on real-time data. I'm about modeled-out on this one already.

 

[George Tincher]

I'll make a decision early Wednesday based on real-time data. I'm about modeled-out on this one already.

Yep, when many of the relevant details are unclear and inconsistent from run to run, that's about all one can do. May severe weather is difficult enough to forecast, but these early season systems are enough to drive a person up the wall at times. I really have no clue about tomorrow, not a clue. LOL. I guess I'll try to watch and learn. With every system comes something new to be learned, and boy do I have lots to learn.

-George

 

[Kevin Scharfenberg]

I think cold ridging will hold firm tomorrow (Wednesday) in the Panhandles and western Oklahoma, even as moisture and heat try to return northwest in response to the approaching upper low. This will cause a warm front to sharpen up during the day somewhere near a Midland-Ardmore line. As the LLJ strengthens during the day, isentropic ascent will set up over the warm frontal surface and re-inforce the boundary with stratus and precipitation on the cold side over west Texas and western Oklahoma.

However, as the day wears on and deep forcing increases over the warm sector, thunderstorms will likely develop along the sharpening boundary. A Bunkers storm motion estimate for the SJT area suggests right-moving storms will have a motion out of about 235 degrees at 30 knots, which would carry them along the warm front or even slightly into the warm sector. If that happens, supercells may threaten the D/FW metroplex and surrounding areas by dark. Low level shear is still not progged to be incredibly strong, at least until after dark, so the threat for widespread/significant tornadoes doesn't look too high during the daylight hours.

The failure mode would be if the warm front got stuck in an east-west orientation, forcing storms into the cold air too quickly, and/or if the upper winds backed too strongly forcing the same result. The best hope for chasers is for the warm front to lift quickly into eastern Oklahoma, into a more north-south orientation, and for the low to not dig/eject too quickly, keeping winds aloft more veered.

As for which day is better: storms moving at 30 kts in north central Texas Wednesday currently look better for chasers than the possiblity of storms moving at 50 kts in southeast Oklahoma and western Arkansas on Thursday. Plus, Thursday has the potential to be a squall line setup with more unidirecitional shear and stronger forcing.

 

[Chris Sokol]

Current plan is to head to Abilene early Wed morning (6 AM), unless the systems outlook changes majorly. My main concern is getting drawn too far south. I don't think that this will necessarly be a Midland-Del Rio chase day.

Chris Sokol/KD5ILI
Mobile Weather Concepts
Oklahoma City, Oklahoma