Updated Forecast

041016 Day 3 Forecast Map

Just a quick map and a few notes on Sunday’s severe weather potential in the plains. I didn’t forecast much this afternoon so take it with a grain of salt. The tornado potential doesn’t look that good for Sunday, but there’s a chance so I’ll spend a little more time on the forecast tomorrow. The short of it is that shear profiles and convective evolution are problematic along the cold front and then a stronger cap and convective coverage are more of concern along the dryline where convective evolution would be more favorable.

Monday’s setup is looking better with the NAM than it has in previous days with the GFS. The NAM shows a surface low deepening over southern Oklahoma through the day with a triple point setting up over central Oklahoma. Rather than a cold front pushing south like we’ll have on Sunday, the frontal boundary takes on more of a warm front style wind shift thanks to the jet streak associated with the southern stream shortwave nosing into the plains/pressure falls. Having more of warm front style frontal boundary should improve low level shear for any triple point storms relative to Sunday and keep storms from getting undercut like they tend to with a cold front. So at the surface at least everything looks legit for Monday. Dewpoints are forecast to get into the mid 60’s near the triple point  which will keep LCL height low and CAPE should be moderate to strong (SBCAPE in the 2500-3000 range). The bigger concern regarding tornado potential with this setup appears to be with shear. Deep layer shear looks pretty solid with good length in the hodograph and only a little backing with height (around 5-6km and it seems insignificant). Low level shear however looks a little sketchy. This is a result of 850mb winds tending to veer near the triple point, which seems to be a consequence of the pressure field being elongated into more of a NE to SW trough with the northern stream trough over the north central/northeast US. At the same time you have the pressure falls with the southern stream wave over Oklahoma, so it’s kind of like you just get weaker flow in that .5-1km area (like the LLJ is a little unsure of which way it’s going) in addition to the veering. If it wasn’t for that and you had southerly winds in .5-1km area that were about 10-15kts stronger, then I think you’d be in business on Monday. I’ll keep an eye on it, but as things stand now I still think there is at least a lower end tornado threat. If SPC is buying into the NAM then I would think the threat area may shift back west a tad in their next outlook.

I’m not going to get into the more significant trough forecast for Friday-Saturday, but I think the tornado potential is trending up with it in the latest model runs. I took my first look at the ECMWF, which seems to kick the GFS’s ass as much as I hate to admit it and it’s showing what appears to be a more favorable tilt/evolution of the trough for tornadoes in the plains. The 12Z run showed the jet streak just starting to work around the base this high amplitude trough as it nosed into the plains at 12Z Friday (that’s as far out as the ECMWF goes right now). The trough had a neutral to slight negative tilt, which is timed much better than the previous GFS solutions which showed the jet streak already through the base of the trough and taking on a hard negative tilt as it came into the plains. The ECMWF solution is much more ideal and would make directional shear a heck of a lot better than it would be with a hard negative tilt. The 00Z GFS is also trending towards the ECMWF, which gives that solution even more credibility. Given that meridional mid/upper flow/hard negative tilt were the major concerns with Friday-Saturday’s trough, this is a huge relief. I’ll wait to see tomorrow’s runs before I get into any detail, but high amplitude troughs like that taking on a slight negative tilt as they eject into the plains is what you expect to see on upper air charts for the more significant tornado events in the plains. Definitely a trend in the right direction. Still a long ways out and there are a lot of other things we need to look at, but it’s a good thing if you’re rooting for tornadoes and has the potential to be the first major severe weather event in the plains this year. I will get into more detail on this setup tomorrow, so check back then if you’re interested.

Alright, so I may get in a warm up chase just because it’s a weekend and fairly close to home on Sunday. Monday may be a little more promising, but we really need low level shear to get a little better for a good tornado threat. The real deal may be coming next Friday though, so it’s time to get serious about making sure I have all my equipment squared away. I’m going to work on that Sunday morning. I need to run some more wires and get my other streaming cameras rigged up (which I’ve been blowing off for the better part of a month now). I’m tired and rambling so that’s all for now, but check back tomorrow afternoon for an update.

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