Figuring out perfect inversion

[Todd Lemery]

I'm having a difficult time trying to figure out some kind of formula for determining when I'm staring at a cap that's going to give me a "blue sky bust" or maybe and MCS. I can look at a skew-t and see how much of an inversion there is along with the cape. If everything else was always equal, I could have a pretty good idea where I could find isolated supercells, but with different strength and kinds of lift, variables in cloud cover, previous days convection and everything else I have a hard time trying to pinpoint target areas.
I'm wondering how everyone else picks their target area. Are there some factors you add more weight to or others that are somewhat disregarded? I know there isn't a magic formula out there, but I would like to better be able to choose an area that isn't going to instantly blow up into a big ball of crap or leave me without anything at all busting the cap.
Bottom line is that I can generally put myself in an area where storms are going to pop, but really wouldn't mind if a little more often I could chill out at my target area until the late afternoon and have towers shoot up in front of me without having to make a big late adjustment to get in position. I'd love some help/insight

 

[Jason Boggs]

Personally, I'd rather have a cap that's too strong instead of too weak. Different mechanisms can weaken the cap such as a shortwave, increased surface temps, lack of cloudcover, increasing moisture, etc. If the cap is over 13C, it's pretty much over, but not always. Often times, if there is a strong cap with great dynamics, I will still go out. I've seen multiple times where one lone supercell would go up and put on a show for hours. Having that loaded gun sounding on a big day is great so see.

 

[Jason Boggs]

Here are a couple of links that may help out...

http://theweatherprediction.com/habyhints2/503/

http://www.theweatherprediction.com/weatherpapers/070/index.html

http://www.crh.noaa.gov/lmk/?n=cap

 

[Jason Boggs]

I will also point out that the further down the dryline you are (south), the more isolated the storms usually are. This is not only due to a stronger cap further south, but it's also due to the minimal lift that's usually associated with a dryline. Further north, it's generally a better bet for storm development on a strong cap day due to the better lift that's usually associated with a triple point, cold front, warn front, closer to the low, etc. I love dryline chasing for the simple fact that the storms are generally much more isolated and photogenic than storms further north.

 

[Todd Lemery]

Thanks for the tips and links Jason. I'll be digging in to them tonight.

 

[NealRasmussen]

You can look at cinH forecasts. That's a measure of the cap. Or precip forecast.

I would still vote Yes to allow realtime cinH maps to "go positive", which is
against the law, but might show the area where it's weakest.

And yes, I'll take a strong inversion. One where only one hole gets poked through
it. Or one hole per 60 miles. Poked being the word, as the inversion is most often
never broken. Just really close and then moisture convergence takes over

Neal.

 

[Jeff Duda]

I'm having a difficult time trying to figure out some kind of formula for determining when I'm staring at a cap that's going to give me a "blue sky bust" or maybe and MCS.

This is why analog/human weather forecasting is so hard. There is no one single formula that always works. Hell, there is never guaranteed to be any formula that will work on any given day. However, many replies so far have mentioned the same keys I would also use to determine the likelihood of CI and the areal spread of it. One additional parameter to look at is convective temperature. The convective temperature is the 2-m temperature that is needed to be exceeded for convection to develop essentially without forcing (no real lift needed). That doesn't mean that when the convective temperature is reached the entire atmosphere blows up. You really still do need some kind of lift, but when the convective temperature is reached, even the slightest push somewhere in the column is theoretically sufficient to get a parcel to its LFC, and with active turbulent eddies pervasive in the PBL during heating during the day, there's pretty much always some sort of lift, even if weak and on a small scale. The convective temperature is calculated assuming only the PBL mixes out, i.e., it does not include any impacts from temperature changes above the PBL from say...large-scale ascent, or from advection. Generally, the higher the convective temperature, the stronger the capping (because more heating is needed to break it). However, if the convective temperature is at or below the forecast maximum temperature for the day, that means there is hope of breaking the cap (assuming no large-scale ascent is going to help out). Even if the convective temperature on the 12Z sounding is higher than the forecast maximum temperature later that day, if there is a strong trough coming in, that may be sufficient to lift or weaken the cap enough to get CI. However, if it's June and an 18Z special sounding comes out and gives a convective temperature of well over 100 F (for example: http://weather.uwyo.edu/upperair/bimages/2009060718.72456.skewt.parc.gif), there's a good chance the cap is going to win.

 

[John Shewchuk]

That's a great question. Defining a perfect inversion is hard. NWS numerical products don't immediately provide all the necessary information needed to evaluate inversions, such as temp/dewpoint spread, thickness, height, mean humidity, and other related parameters. The above rules of thumb and advice (along with personal experience) help greatly for quick decisions. The only advise I can add is to also use other parameters in your decision making process: such as CAPE, VGP, SWEAT, LI, any other relevant indices. The more parameters used the better. This is similar to the WeatherChannel's TORCON, which is a composite algorithm of key severe weather indicators.

John

 

[Todd Lemery]

Wow! Great stuff guys....I can almost feel my IQ going up. Makes me realize how much more I need to learn. Thank you

 

[Brian G]

That's a great question. Defining a perfect inversion is hard. NWS numerical products don't immediately provide all the necessary information needed to evaluate inversions, such as temp/dewpoint spread, thickness, height, mean humidity, and other related parameters. The above rules of thumb and advice (along with personal experience) help greatly for quick decisions. The only advise I can add is to also use other parameters in your decision making process: such as CAPE, VGP, SWEAT, LI, any other relevant indices. The more parameters used the better. This is similar to the WeatherChannel's TORCON, which is a composite algorithm of key severe weather indicators.

John

Nice. The RAOB Program guy just posted to Stormtrack. I hope to see more posts from you in the future John!