Questions about CAPE and other meteorological questions.

[Raymond Mason]

For a while now I have been trying to learn how to forecast severe weather. So what I did was use a radar program along with Twister Data to try and figure this out (I don't look at national weather service forecasts or weather channel since I want to learn to do this myself.) I know CAPE stands for Convective Available Potential Energy. The higher the CAPE the more potential for severe weather. Today when I looked on Twister Data I noticed a large area from the bottom of Texas all the way up near Canada which had a CAPE for 4000. Then when I looked near Reno Nevada there was a system moving through there which had a CAPE closer to 500.

I don't get this; I thought the higher the CAPE the more potential for severe weather. Does this explain why the storms where relatively weak in the area? Does this also mean if something pops up near the higher CAPE area of 4000 could it be a lot stronger then say a storm in a CAPE of 500?

Also I looked at the dew point in the areas with high CAPE and noticed they where very high. The Theta-E 500mb - 700 and those figures where around 340 near Kansas and Oklahoma.

Today there was nothing on the radar and no severe weather in CAPE of 4000. I am I missing something? I would think the conditions would be highly favorable. Maybe I just don't quiet get this yet.

 

[Todd Lemery]

Most of the people on this forum have forgotten more than I know, but there is so much more to severe weather than just cape. The key letter in "cape" is the "p" which stands for potential energy. All that potential won't mean a whole lot without other ingredients like shear, the right kind of cap, some kind of convergence and much more.
Tim Vasquez has a book out called "storm chasing handbook". For a low price you could get that and probably many more questions answered on forecasting.

 

[Skip Talbot]

Today there was nothing on the radar and no severe weather in CAPE of 4000. I am I missing something?

Yes, we need four ingredients for supercells with significant severe weather: moisture, instability, shear and lift. You're looking at just one of them: instability as measured by CAPE.

In the summer we often have an excess of both moisture and instability (which is dependent on the moisture). What we usually come up short on is shear and lift because the jet stream migrates north in Canada. That jet provides much of the shear and lift we need. It makes sense if you think about it right? In the summertime we often have a lot of hot, humid air that persists for weeks: summer doldrums. We don't have the big weather systems, lines of storms, crashing cold fronts and surging warm fronts that we can get in the spring, because the troughs and active weather patterns that are associated with the upper level jet have pushed north during the summer.

On the other hand, in the winter and early spring, we've often got an excess of shear and lift, but all of our moisture and instability is stuck down south, so we wind up with a lot of weather, but not severe thunderstorms because it's too cold.

This time of year, the first thing I look at is the 500 mb winds. If they are less than 30 knots, I'm usually not looking any further. In the winter and early spring, the first thing I'm looking at are the dewpoints. If they're less than 50, I'm usually not looking any further either.

 

[Raymond Mason]

@Todd

I will check online for that book. Thanks!

@Skip

I suspected that the jet stream might of had an effect on sheer. I did notice the high CAPE was roughly relative to the moisture as well. 4000 was a typo I meant 3000. I understand now why you look at what you do first before you consider anything else. Now I can at least forecast a little better with these points.

I would honestly love to be a meteorologist but I am horrible with math lol. I am going to try and study old outbreak weather data and compare it with what I just learned. I think I understand now why the storms where weak today up north. Sure they might of had warm most air, lift, some sheer but the CAPE wasn't ideal at all for any severe storms; they where just mainly rain storms causing flash floods.

Also how do you find warm and cold fronts? I have been trying to figure this out but I am just not sure where to look.

 

[John Farley]

If you are looking at current surface data or at a forecast model that shows temperature and/or dewpoint along with surface winds, the fronts will usually be along an imaginary line where the wind directions are different on opposite sides of the line, and also there is a substantial difference in dewpoints and temperatures on opposite sides of that wind-shift line. Often but not always, a warm front will extend eastward from a surface low pressure center while a cold front will extend southwest. Surface winds will often be easterly in the area north of the warm front and southerly in the area south of the warm front, and southerly or southwesterly ahead of a cold front and northwesterly behind the front. You can see this in the wind barbs on surface data plots. These are just very general rules and the specifics will depend on the orientation of the fronts, how wrapped up the low is, and a variety of other factors. Hope this helps a little; definitely agree with Todd on the storm chaser handbook.

 

[Raymond Mason]

Thanks for the response John! I have been learning a lot. I have one more question: Do you think I should move out of Nevada before even considering chasing? I mean it is something I would like to do..but I am really far away. I guess I can try monsoon season chasing in the west for now as practice.

 

[Will Campbell]

@Todd
I suspected that the jet stream might of had an effect on sheer. I did notice the high CAPE was roughly relative to the moisture as well. 4000 was a typo I meant 3000. I understand now why you look at what you do first before you consider anything else. Now I can at least forecast a little better with these points.

Right you are sir. This is because the air temperature and the dewpoint are two key "factors" in the equation to determine CAPE. While the actual equation looks like a drunken eye-chart, including level of free convection, neutral buoyancy levels, virtual temperatures etc, an overlay of high T/Td will usually coincide with higher CAPE.

Locating cold fronts, warm fronts, and drylines (collectively boundaries) can be multi-faceted. Temperature differences and wind shifts will be your primary giveaways. When locating warm fronts SFC-850 temperatures and Theta-E advection can be used with wind shifts to determine the location of the boundary. With cold fronts I will typically look at temperature and winds. Drylines are pretty easy to pick out from models, especially when the boundary is nice and sharp. As the season progresses fronts can be less pronounced as you get less of a temperature difference after frontal passage.

 

[Rob H]

Try starting here, it's where most of us started: http://www.theweatherprediction.com/severe/ingredients/

The balance of ingredients, and the right mixture is what's important and why you can have EF-4s in 1000 MLCAPE and extreme shear, and EF-4s in 4000 MLCAPE and little shear.

As for where you live, you can start by taking a chasecation - May 20th through June 20th almost always have good storms in some part of the country. Or you can get better at forecasting and drive/fly out for those 2-3 setups a year that seem like slam dunks.

 

[Raymond Mason]

I made this little animation today of changing temperatures over 8 hours today I assumed this is a warm front moving to the north east. Storms are forming in front of it where severe storms where predicted to be. Now there seems to be action.

Thanks Will and Rob!

 

[Marcus Diaz]

Right now there's a pocket of 6500 SBCAPE in southern KS/northern OK. But you won't see a storm drop tornadoes around there since the cap is nuclear and LCLs are high. Not to mention the lack of good shear and a trigger.

 

[Raymond Mason]

Right now there's a pocket of 6500 SBCAPE in southern KS/northern OK. But you won't see a storm drop tornadoes around there since the cap is nuclear and LCLs are high. Not to mention the lack of good shear and a trigger.

I agree the environment doesn't seem ideal at all. On another note that system in North Dakota has gotten HUGE.

Tornadoes watches and hail the size of a half dollar reported. This system is pretty explosive if you ask me. I found the book and I think I am going to buy it very soon.

 

[Marcus Diaz]

There's a rare severe storm just east of Reno that looks impressive for Nevada standards. Hope you got a taste of it out there.

 

[John Bowles]

For a while now I have been trying to learn how to forecast severe weather. So what I did was use a radar program along with Twister Data to try and figure this out (I don't look at national weather service forecasts or weather channel since I want to learn to do this myself.)

This seems like kind of a backwards way of doing things. If you wanted to learn to fish, would you head out with a rod and fumble around until you figured out the tricks, or would you try to learn from what other people are doing? One way is a lot easier.

WFOs often post forecast discussions, and the SPC posts mesoscale and outlook discussions, explaining why they think a setup will behave a certain way. You can learn from them, and compare it with your own analysis.