Forecast Update

Looks like there were quite a few tornadoes today. Most of them look weak and a lot were rain wrapped, but a lot of reports none the less. That’s what happens in May and it’s why you chase whenever you can this time of year even if it doesn’t look that good. Unfortunately I did not chase today lol. It’s not that I didn’t think it was worth chasing. I’m just busy at work right now so I am a little more selective in when I play the bail on work card than I might otherwise be.

I haven’t been watching the models real closely. I had to do a bunch of computer work for my real job last night, so that took away from my forecasting time. I just glanced over the ECMWF and GFS for this weekends system. The kinetics are definitely weaker than they were in previous runs, but it still bring decent mid level winds into the plains Saturday. The GFS has backed way off on the hard negative tilt trough ejecting into the plains a few days ago. Instead it has the trough taking it’s negative tilt over the Rockies Friday night and by the time it arrives in the plains it kind of past the negative tilt phase and more of a decaying trough (for lack of a better term). On that note, I had a couple emails asking about what exactly the tilt of the trough is so here is a link to a very brief explanation of what the tilt of a trough is and how it can affect a setup.

http://www.theweatherprediction.com/habyhints/127/

So, with the trough past it’s maturity and decaying the wind fields associated with it are much weaker than previously forecast for Saturday, which will mitigate the severe weather threat quite a bit. The only good thing I can say about this change is that since the trough doesn’t have a hard negative tilt the mid levels winds don’t have as strong of a meridional component to them giving us decent turning in the 0-6km layer. With the GFS only showing about 40kts at 500mb I’m not sure the good kinetics was a good trade for better directional shear lol, but I’ll take whatever I can get at this point.

I don’t care to get into much detail at this point because I don’t trust the GFS that much and the NAM picks up on this tomorrow. I will say morning convection is still a bit of a concern, but maybe not as much as it was before. The GFS only shows moderate instability, but that should be good enough for at least a lower end tornado threat on Saturday as long as it verifies. We’ll see what the NAM has to say tomorrow. Generally speaking I think the GFS tends to under forecast severe weather parameters while the NAM tends to be too aggressive, but I think the NAM tends to be more accurate. Anyway, I’ll take a close look at the NAM tomorrow and start to get into details.

I did glance at Friday too, but it looks like moisture return may be a bit problematic so I’m going to leave it out of the forecast for now. I’m keeping an eye on it though.

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