High Plains Drifter


disclaimer:  "The meteorological views/forecast thinking expressed are those solely of the author of this blog
and do not necessarily represent those of official National Weather Service forecast products,
therefore read and enjoy at your own risk and edification!"

April 9, 2009

Update #2 on 9 April 2009 “cold-core” setup forecast

Filed under: Chase Forecasts/Outlooks,General Weather & Forecasting — Mike U @ 10:23 am

Here is a 15z Surface plot with some subjective analysis of the temperature and dewpoint fields.  Subjective surface vertical vorticity max is encircled.  The short-term RUC and NAM suggest the surface vorticity max will strengthen and perhaps drift north through 21z…thus would expect moist advection to continue northwestward into the Wichita-Kingman area.  If I was off work today, I would be driving toward Kingman right now (although I probably would have left at 11am!). Visible satellite, not shown, does reveal a very promising pristine sky in this area, so direct insolation will only aid in increasing low level lapse rates (decreasing static stability) to help spin-up the surface cyclone even more across south-central Kansas.

 

 

Update on 9 April 2009 “cold-core” setup forecast

Filed under: Chase Forecasts/Outlooks,General Weather & Forecasting — Mike U @ 6:30 am

Early this morning, it appears the setup for possible tornadoes in south-central KS still looks pretty good.  In fact, I think it looks really good!  I just took a look at the 09z RUC 12-hour forecast for 21z, and I am pleased to see that it matches the NAM forecast pretty good in most of the fields supporting "cold-core" surface-based severe convection.  The only difference is positioning of the fields.  The 00z NAM forecast was a bit farther south from previous runs, however the 09z RUC is very similar to the previous NAM runs (farther north along Highway 54 corridor).  Below are a few of the 09z RUC figures I put together to illustrate:

Figure 1. 12-hour forecast of surface wind and dewpoint from the 09z run of the RUC model.  The region I am most interested is encircled dotted-black.  I observed tornadoes both on 26 October 2006 and 10 November 2008 in this same area, conceptually speaking in terms of the surface wind and dewpoint fields.  The western nose of the dewpoint/Theta-E field at the point of maximum surface vertical vorticity is the "place to be", in my opinion, for observing (a) tornado(es) given the tremendous source of vorticity and baroclinicity a storm has to work with. There will be a southeastward extension of this rich vertical vorticity along the occluded front, so as additional storms form southeast by late afternoon/early evening, there may be several storms producing tornadoes along the surface occluded front.  I feel quite confident the occluded front will be very productive!  500mb Temperatures are also shown in this figure.  Note how far east the -20C isotherm extends!

 

Figure 2.   The 12-hour RUC is generating convection in the exact area I expected it to, which leads confidence in the forecast for (a) severe storm(s) with tornado prospects.  This is even farther west than I was thinking yesterday, should this be a perfect prog.  Model forecast CAPE is higher than I typically see for the true "cold-core" events, with the RUC suggesting near 1000 J/kg CAPE nosing as far west as Stafford County, KS!.  Usually model CAPE doesn’t capture the true surface-based instability for these events very well.  This could be a signal that today could be a very productive "cold-core" day.

 

Figure 3.  The 00z run of the 4km WRF-NMM is interesting.  Hourly graphics of the simulated radar reflectivity show intense convection developing as far west as Coldwater-Medicine Lodge, KS at 22z… Wow!  They may have to watch this closely at work (NWSFO Dodge City, KS) for our eastern counties from in the 21-22z time frame.  I am scheduled to go into work at 21z!  

 

So, the 64-thousand dollar question.  Where would Mike target if he wasn’t at work this afternoon/evening? 
Pratt, KS by Noon and watching the sky/visible satellite/observations/short-fuse composite very closely, with eyes set east (or east-northeast or east-southeast??) of Pratt for the 21-22z time frame!

  

April 8, 2009

A “cold-core” setup in South Central KS on 2009 April 9?

Filed under: Chase Forecasts/Outlooks,General Weather & Forecasting — Mike U @ 11:20 am

I am intrigued by the setup for localized tornado event in south-central Kansas tomorrow.  It is shaping up to be an event with similarities to 26 October 2006.  I think (a) tornado(es) may occur farther west than the current Day 2 SPC (the 1st, 06z, issuance) outlook slight risk in a small corridor where upper 40s to lower 50s dewpoints will sneak west along the Highway 54 corridor from Wichita to Kingman.  Surface vorticity will be maximized in this area due to the presence of a significant middle tropospheric potential vorticity (PV) anomaly.  I like to look at 400mb for wind speed fields and related PV anomalies.  It is just downstream of a 400mb PV anomaly where surface cyclogenesis (in the wind field) is maximized (dZeta/dt at the surface for you meteorologists out there!).  I think if surface based storms form in this zone, it will take advantage of a tremendous source of vorticity in the low levels — both vertical vorticity and horizontal streamwise vorticity.  Given the substantial ageostrophic motions present in the low levels in response to a small scale jet streak like this, there will be an enhancement in ambient vertical wind shear as well as the atmosphere tries to restore itself back to geostrophic balance.  Okay, that’s some heavy meteorology, but that’s what is going on in these small space/time scales.  Timing is critical.  Like 10 November 2008 and 26 October 2006, the event occurred in a very short time window…usually centered around 21-22z.  If the current NAM model holds, then the best area at the 21-22z time frame will be along the Highway 50 corridor somewhere in a Cheney Lake-Kingman-Wichita area.  Below is a conceptual model I put together for an informal presentation back in January at a local AMS High Plains chapter meeting regarding these special events.  What is very interesting about my conceptual model is that the area I drew this conceptual model — south central Kansas — is exactly where I think things may unfold tomorrow (very near the yellow area on the graphic!).

 Below is the 33-hour forecast from the NAM valid 21z April 9th.  The graphic is of 400mb wind speed and surface wind barbs.  I annotated where the 400mb PV anomaly would be based on the wind speed field…as well as where the greatest vertical vorticity would end up being as well.  This all seems to point to the Wichita area or points just west at 21z:

 

 

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