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2011-12-19 FCST: SE NM, NW TX, SW OK

Joined
Apr 18, 2005
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207
Location
Norman
Possible cold-core tornado event for Monday December 19th anywhere between SE NM and SW OK: mid-level closed low ejecting out of the Southwest and over the southern Plains. There are many parameters, which have to fall into place to get a cold-core tornado event (much like any tornado event). My biggest concerns for the setup are timing of the mid-level closed low, cloud cover, and, almost always, low-level moisture. If the timing of the mid-level low is good and the moisture is there (only mid 40's to low 50's dewpoints) this event might happen. I've had my eye on this wave most of the week; the models don't handle closed-lows very well, but they've been relatively consistent with the forecast.


12Z NAM December 16th Forecast for 18Z on December 19th:

Nose of upper 40's-low 50's dewpoints into NW TX
Sfc temperature axis going through Childress, TX
-5 deg C 700mb temps advecting over NW TX
-20 deg C 500mb temps adevecting over NW TX
intense PVA over NW TX

12Z GFS forecast is very similar to the NAM, but slower with all the same parameters over SE NM/W. TX border.

Also, there is the possibility of a snow storm between Beaver, OK and Greensburg, KS that night, so that could be a double tornado/snow chase. There are still random aftershocks near Prague, OK, so an earthquake chase is possible if this setup doesn't occur.

Simon
 
Im not real good with Cold-Core setups, so feel free to enlighten me if any points I put out there don't make good meteorlogical sense. I agree completely that there should be some potential with this setup, however, my observations from both NAM/GFS lead me to want to lean toward potentially chasing in the east-central Texas region (even though terrain sucks for the most part). In this region, both models bring in upper 50's to low 60's TD's, greater CAPE values approaching 1000-1250, better Theta-E Advection, as well as some rediculous looking large clockwise curved Hodos and a more classic and rather impressive Skew-T, with good backing SE surface winds rapidly veering to SSW at 850 and SW from 700-300 from 60-80 knts. I do see where the better 500 vertical velocity is nearer to the NW TX/SW OK area, which is where my lack of a lot of Cold-Core forecasting could be throwing me off. However, LI's as well as LCL's also appear to be just as good in EC TX as they are very near the center of the Low. Is it just more likely to get those Low Topped/Mini Tornadic Supercells closer to the center of the super cooled upper low because of the more intense vertical velocities? Are there reasons I should not be looking at what look like more impressive parameters in eastern Texas for this particular type of setup? Either way....hopefully some of us will be enjoying some chase time on monday ;)

Source Data: TwisterData NAM/GFS Run 18Z Fri Dec 16, Valid 18-00Z Mon/Tue
 
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Not suggesting anyone ignore SE TX with reasonable instability and low-level shear, but I'm talking about the potential for a cold-core tornado event associated with a closed mid-level low.

Cold-core tornado events are very much the same as a typical warm sector tornado event; both need instability and low-level shear. Relatively cold mid-level temperatures associated with a mid-level closed-low are crucial for generating instability for a cold-core tornado event, and there is typically a warm front or occluded boundary to provide low-level vorticity. These events may, but not always, involve landspouts as well as supercell tornadoes. They can occur summer through winter; summer events typically have higher amounts of low-level moisture, and 40-45 deg F sfc dewpoints have been associated with some late fall/winter/early spring events. Examples of some notable cold-core tornado events include June 20, 2011, November 13, 2008, March 20, 2006, April 10, 2005, and May 17, 2000.

Monday: things appear to be falling into place; concerns are cloud-cover and the speed of the southward-diving polar front. If the front is diving south too quickly it will ruin the small sliver of a warm sector/occluded boundary. If the upper-level clear slot doesn't move over the favorable low-level environment in the late morning heating/mixing can't occur to clear the low-level clouds and get even a little surface heating (research found about 3hrs of sfc heating with mostly clear skies is sufficient in many cold-core tornado events). If all the parameters fall into place for this event I'd target the Plainview, TX region going off current data, but this target region can shift or disappear by Monday morning.

The snow storm/blizzard appears to be set for OK Panhandle/SW KS even if the cold-core tornado event doesn't occur. Hopefully, at least a few chasers can document the event if all the parameters fall into place. Unfortunately for me, I won't be able to chase this event.

Simon
 
Good eye on picking up the potential for a cold core event, Simon.

It prompted me to go back and read through Jon Davies' classic paper. There are quite a few parameters that seem to be "coming close" to those identified in his paper, which can be found here: http://www.jondavies.net/DaviesWAF_coldcoretors_dec06.pdf

Re: cloud cover, I notice this morning there seems to be a clear slot developing over west Texas so perhaps we'll have that brief period of surface heating. Certainly the proximity of the surface low to the 500mb low is conducive to a cold core setup, along with the strong deep layer shear. The major concern looks to be moisture. In looking at the RUC, I'm concerned that sufficient dewpoints may be too separated (to the south and east) from the boundaries. I realize you don't need tons of moisture in these kinds of setups, but I think we'll need at least 53td or so to advect up to around the Lubbock area to seriously support a cold core tornado. Will be interesting to watch.
 
I didn't post before because I just couldn't get excited about this setup. I thought the instability would be too weak. I still think that anywhere north of I-10. I just don't see how a surface-based storm is going to develop there given the cloud cover. Also, given latest visible satellite trends, I see a gravity wave train has developed across central TX, so obviously there is a stable layer there. It clears behind that, but there's only the narrowest of windows between the clouds associated with that gravity wave train and the dryline. around SW OK/NW TX the moisture is a tad better, but the mid-upper levels aren't really that cool, and I have doubts that cool enough temps will move over before the dryline passes.

As far as south Texas goes I see some serious potential for severe storms later today. Already, CAPE has climbed to 2000 J/kg, and there is a pretty favorable wind profile. I like the San Antonio-Waco-Houston triangle (nudged a bit northeast) for severe potential later on.
 
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