Saturday, September 20, 2008

Chase Forecast: Sunday, September 21st

Well, it seems like we might have some storms to chase over the next couple of days. Being that it is September and we are entering the "dark period", I think I need to be on the plains. Monday looks to be the better day, but to do accessibility, tomorrow might be the "easiest".

Right now, a modest negatively tilted trough exists in the Pacific Northwest. A couple pulses of energy rotated through today, setting off some thunderstorms. In fact, one moved through Denver a couple of hours ago, giving us a brief rain.

On the Eastern Colorado plains, moisture is on the increase. Strong southerly winds will continue to pump moisture in throughout the night and into tomorrow. There isn't a ton of moisture available, but there should be enough to give us some dewpoints approaching 50ºF, especially near the Kansas/Nebraska border with Colorado.

As tomorrow approaches, we will probably see a little drying off of the mountains, which will set up a moisture discontinuity. Couple this with the approaching upper level support and a lee-side pressure minimum, we could see a favorable area for storms ... especially if we see a few more shortwave pulses ride through.

With this system, we'll see an influx of mid to upper level moisture. Cold temps aloft and some decent heating on the plains will give us some nice lapse rates. Forecast CAPE is around 1000J/kg, which is enough for some fun. Directional shear is favorable for a few rotating updrafts (which could reach significant height). I would be surprised to see a tornado on Sunday, but some good-sized hail is definitely probability.

The WRF and GFS disagree on precip formation and location, with the GFS barely showing anything. However, the GFS has been dry all summer and hasn't responded well to convective situations in or near this area, so boo on the GFS.

This will not be an explosive severe event ... marginal at best. But hey, it is September ... I'll take what I can get.

I've focused mainly on Sunday so far, but I'll try and put together a forecast for Monday sometime tomorrow.


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