Update on 1/13 svr; major Santa Ana could also on tap

I don't feel like writing much more, but the following has been written on the Eastern US Wx thread the past few days:
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Jan 7 2007, 09:31 AM

The northern wave that goes into Canada will do its job in helping advect moisture northward, so that's a good thing for svr wx. But it will also leave a cold high behind. Where this high sets up could be important. Somewhere, there could be a blizzard (I agree with LC* on this) with a 32mb gradient across the Denver area. Ice could also be a problem as the warm air overrides the cold air of the high.

The low should intensify and draw in enough warm air to weaken the high - but is the 12Z overdoing it? The boundary starts to become more S-N rather than W-E, but a 1036 high doesn't dissapear like that. Nevertheless, I still think the severe threat could extend up to the OH Vlly.

Lapse rates still stink, no need to explain there. Of course clustering/excessive convection will need to be watched.

*Meterologist Larry Cosgrove

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Jan 7 2007, 06:03 PM

A couple of things to note: one is that the reason 12Z has it more positively tilted is the shortwave dropping down from northern Canada. Much stronger and pulls the vort max northward, leading to a more positive. One thing I've noticed about the GFS is that these little shortwaves can passed unnoticed only to show up around hr 120-180 and then have a big influence come the day of the event (April 2 comes to mind). Now, this could be spurious as well, so don't take my word for it.

The strength of the SE Ridge will also be very important again in dictating lapse rates and tilt of trough, and the Euro, GFS, and their ensembles (I heard that 12Z Euro and GFS ensembles were similar) still have slight differences.

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And then what I just wrote now:

Ensembles are still in disagreement. Again it is all up to the piece of energy in Canada and also the strength of the SE Ridge which will dictate if this will be a strong closed low or a weak positively tilted system. I suspect a compromised solution - which is similar to what the OP GFS and Euro are showing, is the most likely outcome.

With that said, the 12Z GFS is extremely ominous. Of course, two model biases to be concerned about.
1) Arctic air often underestimated in strength and southward advection.
2) Too fast in ejecting lows into the Plains.

With regards to the first one, there's a 1038 high in the Dakotas which suddenly dissapears 12 hr later. Maybe a bit unrealistic. That has to be watched in intruding on the warm sector, and I suspect that the models are overdoing the width of the warm sector on the 12th (Friday). 12Z has trended slower with the low, BTW.

Suspect that the 12th could verify as a marginal slight, but nothing too much more with shallow moisture. Maybe some elevated storms invof the warm front.

The big day should be the 13th. Strong WAA could be stronger than anticipated, depending on the strength of the low, causing the warm front to lift up into northern AR. As the dryline advances eastward in the day, strong deep layer shear and so-so low level shear will promote the growth of supercells with tornado potential. My thinking right now is right along the I-35 corridor, and maybe even further west given the current model trends. Lapse rates will be weak though, and that could be a limiting factor for instability. Another big problem will be the cold high following the system. Again, as I said, models tend to underdo CAA just as they can underdo WAA. That could prove disastrous to this setup if the warm front does not lift as far north as anticipated. From past observations, this type of a setup often can be ruined by that.

Minimal threat on the 14th with lapse rates continuing to weaken and the main energy moving northward.

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With regards to the Santa Ana event here, models are painting a downright scary setup on the 13th (same day as the possible severe wx outbreak). ~1030mb high parked over the Great Basin with extremely strong, northerly cold air advection. Once again, the brunt of the wind could bypass San Diego and slam Los Angeles due to the geography and the orientation of the inland mountains (N-S vs. W-E, respectively). 2m temps are progged to be around freezing, 850mb temps around -5. That's rare for southern California, and portions of the coast could even see a bout of freezing temperatures.

Stay tuned, exciting weather times ahead seem likely...