3/23/09 FCST: NE, KS, OK

[mark plate]

I'm with Rich on this one...I can't see 60+ dewpoints overspreading the warm sector. I see no reason to argue with the mid-upper 50s dewponts shown by the 00z ECMWF and new 12Z NAM/WRF. Thus although temps will warm into the mid-upper 70s in the warm sector, CAPES will likely be in the 500-1000 j/kg range. It's looking like a high shear, low instability event, which more often than not are not very satisfying to chase.

 

[mark plate]

The 06Z NAM is showing MUCH greater heating at the surface by 1 pm than the GFS could have dreamed of. Instability might not be as much of a problem as some were thinking

That's because it's mixing out the moisture, so yes instability is still a big problem, especially given the strong shear.

 

[John Cameron]

At the very least this will be a nice "shakedown" event for me to blow the dust off. Since it will be in my neighborhood I can make sure all my gear works and my lines of communication are functional. Despite the less than ideal BL, I'll pray for a few hours of insolation and a breakable cap west of Vernon, perhaps 50-70mi northwest of Abilene. Spotters never want the first event of the year to be an outbreak anyway.

 

[Brandon Goforth]

It's looking like a high shear, low instability event, which more often than not are not very satisfying to chase.

That's exactly what it is. The NAM and GFS are in reasonable agreement...shear is VERY nice, and I don't think anyone is going to disagree with that...but instability is not good at all with only pockets of CAPE near 750 ahead of the dryline and tds mid-upper 50s...puke. We've played this game many times before and 99% of the time come away with nothing on these extreme shear, low instability setups. Dryline is setting up roughly along the W OK/TX border by 0Z, with a linear mess occurring north of I-40. South of I-40 may be waiting until after sunset. We'll see what the GFS brings to the table here in a few minutes.

 

[Andrew Pritchard]

Actually, that's not true: a warmer temperature profile below the LCL does help matters by increasing instability (c.f. a Skew-T). Intuitively, this makes sense. When you add solar energy to a "parcel," it converts the energy from kinetic to potential (through the addition of latent heat -- manifest by the breaking of water bonds from a liquid state to a gaseous state).

I understand that Gabe, I was mostly suggesting that surface heating is not the big "will it, or will it not" issue on this event. I think we're mostly in agreement that it will likely get warm enough. I was getting more along the lines that quality moisture return is the big issue Monday, not whether temperatures hit 70F or not.

I'm sure there will be severe storms along the dryline across Kansas into western Oklahoma, but the tornado outbreak scenario is eluding me too. Another day with a couple nice looking supercells on radar that leave chasers wondering "why didn't it produce!?". I'll tell you why...

EDIT: Side note for those who were wanting to compare the earlier NAM runs to prove the GFS was under-doing instability - the new NAM now has dropped your Sunday CAPE values to mostly sub-500 j/kg... more in line with what you thought the GFS was wrongly showing you. Great trough, wrong timing.
\

 

[Scott Bilyou]

Next week's weather

Has anyone seen this? I just came across this. How "accurate" is Accuweather? I am a "newbie", so I'm not trying to question what they predict and what I've been reading here this week regarding Monday's weather. http://www.accuweather.com/news-story.asp?partner=netvideo&traveler=0&zipChg=1&article=0

 

[Skip Talbot]

Yes, the WRF is agreeing with the GFS that we've got a waste of great shear. The WRF even has a deeper low and more of a negative tilt, but the moisture just isn't there. One interesting thing I saw on the GFS was that the CAPE continues to increase through 6z Tuesday. I guess the moisture advection will continue after dark. Perhaps anything that goes up in the afternoon can tap this energy later on?

 

[Andrew Stoller]

Yes, the WRF is agreeing with the GFS that we've got a waste of great shear. The WRF even has a deeper low and more of a negative tilt, but the moisture just isn't there. One interesting thing I saw on the GFS was that the CAPE continues to increase through 6z Tuesday. I guess the moisture advection will continue after dark. Perhaps anything that goes up in the afternoon can tap this energy later on?

I was seconds away from mentioning this Skip! By 06Z, there's a decent area of up 1,000 to 1,500 J/KG of CAPE across OK and KS, and dewpoints continue rising to near 60.

Bummer, if this system had just 12 hours for more moisture return, it might take it from a nothing event to an outbreak.

Interesting - the GFS isn't breaking out the big precip now until 18Z Tue, so with the shallow and insufficient moisture through the day Mon, it's going to take even more time for moisture return to sufficiently destabilize and initiate surface based convection.

:edit:
There's a tiny dot of 1,500 J/KG CAPE on the 06z NAM in an area of 400 m2s2 3km helicity, corresponding to a 3km EHI of 3, right on the KS/OK border by 00z. I think I agree with Mike Hollingshead - there'll likely be some tornadic supercells, just not widespread and violent, and possibly nearer towards sunset and afterdark.

:edit2:
12Z GFS now shows up to 1,750 J/KG CAPE and a tongue of 60 degree dewpoints right on the dryline through OK by 06Z. Could be a long night for folks in OK.

 

[Mike Hollingshead]

The thing about extreme shear with lesser instability is usually it's just extremely fast shear more than it is that with nice direction. You just don't see the type of shear forecasted on the NAM now that many times a year. More than it is extreme it is NICE. NAM on board with everyone else(minus GFS) with not backing the crap out of the mid-levels. So you got 65-70 knot sw mid-level winds over se sfc winds. A s or sse low level jet at 50 knots! Sorry but I'll take 750-1000 cape in that stuff any day.

I think given a 55TD in that setup you're still looking at several tornadoes on Monday. Or maybe it's just the chaser in me talking.

 

[Jared Farrer]

I agree with Mike here that given the current projected profile a 15-20 degree dewpoint depression with temps nearing 70s isnt a huge deal with the projected shear. I think what everyone seems to be getting at is that NO this doesnt really spell out huge outbreak potential. And I would agree with everyone. But I do see alot of potential for tubes in a few key areas

 

[Scott Bilyou]

Monday's storms

Okay, given that I'm new and all, I looked (cheated?) at a loop from UNISYS at 11:15 central time. To my very untrained eye, it seems to me that it is moving too fast to wait around until Monday. Wouldn't there need to be stronger winds to slow it down? Sorry, I'm still clueless about all of this. Maybe I just need a thump on the back of my head(see NCIS). I need enlightenment I guess. Humbly yours.

 

[Andrew Ryan]

Okay, given that I'm new and all, I looked (cheated?) at a loop from UNISYS at 11:15 central time. To my very untrained eye, it seems to me that it is moving too fast to wait around until Monday. Wouldn't there need to be stronger winds to slow it down? Sorry, I'm still clueless about all of this. Maybe I just need a thump on the back of my head(see NCIS). I need enlightenment I guess. Humbly yours.

I don't know what you model you are looking at. UNISYS is a data provider and not a model. Also, low pressure systems don't "move," they propagate from one location to another. It appears that it is moving but really it's just a new low pressure forming downstream from the original one. But really this a question for the weather beginners forum. So, if you have any more questions be sure to go over there and post!

But anyway, I agree that this won't be a total bust. It's completely reasonable for Tds to reach into the mid-50s or even reach 60 but 0z Tuesday. It's just not going to be a huge tornado day. Most of the previous setups this year have maximized their potential, why can't this one too? But this is the first "real" setup of the year, so it should be interesting to see how it evolves.

 

[Brandon Goforth]

I think given a 55TD in that setup you're still looking at several tornadoes on Monday. Or maybe it's just the chaser in me talking.

No, it's just the chaser in you talking. Look, I too wouldn't be surprised to see several tornadoes on Monday, but I also wouldn't be surprised to see zero tornadoes. Past experience tends to tell me that the tornado potential is going to be over-hyped. Yeah, we have great shear...the latest GFS just dropped instability a bit more...now we're in the 500-750 CAPE range with mid-uppers 50s tds, and the NAM is much the same. The GFS has also sped up the progression of the dryline a bit. Maybe it's just me and my past experiences with these setups, but I just have a hard time believing that there will be much of a tornado threat with shear alone.

 

[Chip Redmond]

I'm still holding on to the underestimation of CAPE by the models thus far this year. Looking at temperatures and Tds I think they are just fine, although maybe a little more upper-level moisture would be nice. I don't forsee a major outbreak by any means on Monday but it will really be a matter if whether things can get going before dark and beat that pacific front. I am afraid of this going linear fast and cutting off the chances of discrete cells.

Chip

 

[Skip Talbot]

I hate to be so negative, but another thing I don't like about this setup is how the WRF is depicting the dryline moisture convergence. The 55 Td isotherm is well off the dryline in KS and further north, even at 0z in KS. Storms will be firing on the 50 Td isotherm where the boundary is much sharper according to the qpf plots. With the better veered midlevel winds I think the storm can move off the dryline, into a better environment, and there is better moisture convergence on the dryline after dark. The storms need to stay discrete through this period, however, and the best opportunities for tornadoes look like they will be after dark.