October 12-13th "Potential" Severe Outbreak

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October 12-13th "Potential" Severe Outbreak

Post by emcf30 on Tue Oct 09, 2012 8:37 pm

The technical side of the event.

The main concern through this period focuses on a very strong upper-level storm system and its potential to bring severe weather to the Eastern Plains. Models are in very good agreement in bringing a closed upper low ashore across Southern California during the day Thursday and tracking it across the Four Corners region Friday.



Guidance agreement loses a little steam by Saturday morning, mainly as the GFS ensembles show a rather large standard deviation in the 500mb height fields across the Eastern Plains. But there is very good clustering of the GFS ensemble mean, GFS operational and the ECMWF showing the upper low moving into western Nebraska Saturday morning. Even the GEM is in the vicinity of the aforementioned cluster, although it appears to be a slow outlier at this point. Given the agreement of the models, confidence is high that an anomalously strong upper-level wave will affect many areas from Friday night throughout the weekend.

This setup will be enhanced by broad surface high pressure over the eastern CONUS which will allow for strong moisture return. Indeed, with several days of favorable flow over the Gulf of Mexico, dewpoints by Friday should be in the low 60s across the Southern Plains. As the upper wave approaches from the west, it will induce strong surface cyclogenesis in the High Plains allowing a front that moved into the region Thursday/Thursday night to lift back northward as a warm front Friday/Friday night placing the region squarely in the warm sector of this powerful synoptic system come Saturday. Aided by anomalously strong low to mid-level winds, strong warm and moist advection is expected which destabilize this region leading potentially to BCAPE values in the 1000 to 1500 J/kg range.



The upper-level jet streak will be seasonal but it`s the low and mid-level flow that looks to dominate this system. 925mb to 850mb flow is some +3 to +4 standardized anomalies and as a result low-level shear is forecast to be quite high, on the order of 50+ kts in the 0-3km layer. While surface winds may be veered in the the Plains, the strong low to mid-level winds will result in very high helicity values.



And, while the upper-level jet is not all that robust for this time of year, the flow becomes largely diffluent as the upper wave becomes negatively tilted during the day Saturday. So given the strong kinematics and marginal thermodynamics of this system, there is an increasing potential for at least strong storms and quite possibly severe storms affecting the region during the day Saturday. There are still uncertainties with the timing and ultimately the location of critical elements, but the large-scale pattern itself favors some strong to severe convection in the Eastern Plains given today`s suite of models.



So in short, things could get a tad bit interesting this weekend from Texas, Oklahoma, Kansas, Minnesota, Iowa, to name a few states. There's looks to be a good setup for cold air funnels/ tornadoes in the upper plains along the warm front, on Saturday. It is crazy to see models showing 60°F+ dewpoints in southern MN for this time of year.



GFS showing a nice "dry punch" pushing into SW MN and Western Iowa in order to steepen the lapse rates.
For Saturday's regional potential, I'm not sold, till higher resolution models come into play. Precip. maps are way to boisterous for any destabilization predictability. At this time, I am thinking the best potential for damaging severe weather will be between Dallas- Ft Worth and Tulsa, Oklahoma. However, some of the trends of the models indicate a more Southern component to the low over Texas. One thing to keep an eye on is the frontal boundary which will be passing through the Lubbock area and may make it south into Midland. It wouldn't surprise me if the front made it down to the I-10 corridor tomorrow which is further south than the models progg All the recent cold fronts that have moved through this area HAVE ALL moved further south than model progs by an average of 150-200 miles. I think this trend will continue. As always, timing and speed of the system will be everything as far as the end result of the severe potential will be. On the positive side, the areas that need the rain that were affected by the severe drought, will get some much much needed rain this weekend.

This is an excerpt from the NWS Lubbock.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LUBBOCK TX
455 AM CDT TUE OCT 9 2012


HOWEVER...FRI AFTN/EVNG
APPEARS TO HOST THE BEST OPPORTUNITY OF WETTING RAINS AS THE UPPER
LOW LIFTS INTO ERN COLORADO AND DRAGS ITS TROUGH AXIS OVER THE
REGION COMPLETE WITH A DRYLINE AND PACIFIC COLD FRONT. ADDED WITH
UNSEASONABLY HIGH PWATS OF 1.3" TO NEARLY 2" AND STRONG KINEMATIC
PROFILES...THIS PATTERN IS BEGINNING TO EXHIBIT A STRIKING
RESEMBLANCE TO THE ONE WE SAW ON OCT 21 2010
WHEN NUMEROUS STRONG
AND SEVERE STORMS DEVELOPED. MANY MORE DETAILS WILL NEED TO BE
SORTED OUT IN THE DAYS AHEAD...BUT BASIC PATTERN RECOGNITION DOES
WARRANT A MENTION OF SEVERE STORMS IN THE HWO

This was the result in many areas.



Stay tuned, much more to come on this.









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Re: October 12-13th "Potential" Severe Outbreak

Post by sangria on Wed Oct 10, 2012 6:11 am

Thanks for the new blog e!!

Very thorough analysis, as usual.... nader
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Re: October 12-13th "Potential" Severe Outbreak

Post by emcf30 on Wed Oct 10, 2012 6:14 am

Here is our storm coming into play.







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Re: October 12-13th "Potential" Severe Outbreak

Post by scouter534 on Wed Oct 10, 2012 8:51 am

Thanks for the update E. Great job!
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