Forecast Update

Not that excited about Wednesday’s setup, hence the silence. Lots of issues with this setup, but most of them come from this being a positively tilted trough. I’m going to skip past most of the details since this really shouldn’t be anything major as far as tornadoes are concerned. A positively tilted shortwave will move through the central plains on Wednesday with a surface low located over NE Kansas by late afternoon. A dryline will extend south from the triple point over NE Kansas/NW Missouri/SW Iowa area by late afternoon.

Cloud cover could be problematic through most of the day across the warm sector, limiting surface heating to the area ahead of the dryline later in the day. Favorable trajectories off the gulf/moisture advection should start up as early as tomorrow morning, but the gulf just took a pounding so it looks like moisture return won’t be that good. It looks like dewpoints in the mid 50’s should make it up to the triple point, with low 60’s only making it into SE Oklahoma by late Wednesday afternoon.

There are two areas of interest IMO. Keep in mind I haven’t forecasted much lol. One is near the surface low where directional shear should be a little better. Low level shear should be stronger along the warm front, however storm motions will be largely perpendicular to the front and there is a pretty sharp temperature gradient along the warm front so my thinking is that storms will tend to get elevated quickly as they move north and have very little residence time in the area of more favorable shear where storms are still surface based. The second area of interest is where all the composite indices are spiking ahead of the dryline in eastern Oklahoma. The boundary in Oklahoma will be oriented NNE to SSW, but storms look to be normal enough to it that storms should be somewhat discrete. With less forcing and ascent relative to the surface low target, storms will fire later in the day down south. The NAM isn’t showing much in the way of convection down there until around 00Z, but I trust the NAM about as far as I can throw it with precip. We should get storms along the dryline over parts of eastern Oklahoma, but I’d have to take a closer look before I’d want to venture a guess on timing. My biggest problem with the tornado potential down here (despite the sharppy forecast soundings showing a PDS tornado hazard type) is veering 850’s. Being a plains chaser I’ve always hated veering 850’s. They are bad for several reasons IMO, none of which that I care to get into right now lol. If you read my blog regularly you’ll catch my spiel on that soon enough. I bitch about it on at least a dozen setups every spring. Anyway, I’m not real impressed with the shallow sweep in the lower portion of the hodographs resulting from winds starting to veer above the surface and the poor crossover in the 850-500mb layer. On top of that this setup will be getting into sketchy chase country and with poor directional shear storm motions will be pretty fast. To top it off any chance for a tornado will probably be fairly late in the day. Just not a good tornado setup IMO.

You may eek out a tornado or two on Wednesday, but I just don’t see it being that good right now. I’ll check it out tomorrow and make the call on whether or not I’m chasing then, but definitely leaning towards sitting this one out at the moment. Beyond Wednesday, the next window of interest seems to be around Sunday as another compact wave moves through the plains. There is some divergence in the details with this trough between the GFS and ECMWF, so I’ll hold off on getting into that until tomorrow. The short of it is the GFS is showing a positive tilt trough (again), while the ECMWF seems to lean more towards a neutral tilt. BTW if you don’t forecast much virtually all our good tornado setups come from neutral or slightly negative tilt troughs (not a huge fan of hard negative tilts either). Again it gets kind of complicated, but the shear profiles and thermodynamics tend to be best for tornadoes in that neutral to negative tilt range. With a hard negative tilt the low starts to get stacked and you lose your directional shear, with a positive tilt you get veering low level winds and the thermodynamics don’t tend to be as good. So at least for me when I’m looking ahead in medium to long range forecasting the things I pay close attention to are the tilt of troughs, amplitude of the wave, moisture advection/recovery time and quality of moisture available. The tilt of the trough on Sunday is a bit of a question mark and moisture quality is another big question mark since the cold front associated with Wednesday’s trough is forecast to slam into the gulf later this week. That very well may slow moisture return into the plains down enough to keep Sunday from being anything worth while too. Anyway, enough rambling for now. I’ll try to update tomorrow sometime.

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