More Storms on the way

[USAF Pilot 07]

CAPE = Convective Available Potential Energy... In essence it's how much "lift" there is in the atmosphere... Generally, when you have very sunny/warm days, you will get higher CAPE values, as surface heating creates lift...

CAPE alone isn't the catalyst to trigger storms. For most storms you need a combination of several atmospheric "phenomena" to come together...

[hiss srq]

This stuff is wreaking havoc on my day. I am banging my head on the desk here in the towe. There are airplanes packedo n Bravo and CharlieCharlie and a jet was temporaraly stranded on double golf for a bit with a tire problem. Ahrgh!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

[NYARTCCFAN]

So basically it replaced if I assume the Lifting Index that I have heard of years back that listed in values of Negative numbers ??

[N790SW]

I got stuck in the rain yesterday wile driving the golf cart at my job, me and my co worker mike were swerving and got soaked- the cart had no top on it neither. I also almost got struck by the lighting and when it struck 20ft in front of me, you can smell the burnt trees in its place. That whole ordeal was like a never ending Splish Splash ride lol.

[Smartass Flyboy]

This stuff is wreaking havoc on my day.

Gee, and just 10 miles to the South I went home right on time. :mrgreen:

As of when I left the curfew was up to 02.30 so I guess you're probably still at work. :lol: :lol: :lol:

[hiss srq]

[quote=Smartass Flyboy]

This stuff is wreaking havoc on my day.

Gee, and just 10 miles to the South I went home right on time. :mrgreen:

As of when I left the curfew was up to 02.30 so I guess you're probably still at work. :lol: :lol: :lol:[/quote:3fa01]
(Throws food at Mike)

[USAF Pilot 07]

So basically it replaced if I assume the Lifting Index that I have heard of years back that listed in values of Negative numbers ??

No, the lifted index still exists. The LI and CAPE are similar in that they both measure atmospheric instability and generally when you have negative LIs you will have positive CAPE. When looking for the possibility of convection, CAPE and the LI are two of the first things you'd probably look at. CAPE is the available potential energy actually in the atmosphere, which can later be converted to kinetic (i.e real) energy. CAPE looks at the whole sounding, at all levels. The lifted index is more a measure of environmental instability, generally at 500mb. Negative LIs indicate an unstable atmosphere, whereas positive LIs indicated a more stable atmosphere. To find the LI you'd raise a parcel adiabatically and then take the parcel temperature at 500mb and compare it with the environmental temperature at 500mb. This is why LIs are expressed in degrees C, and CAPE as J/kg. The more negative your LIs are, the stronger "updrafts" you're more likely to have due to a more unstable environment. But, sometimes with LIs you neglect features at lower levels which could cap convection, which is why CAPE is generally a better measure to use, and when both CAPE and the LI are used then you have a much better "read" on the atmosphere.

Like I said above, CAPE/CIN is regarded as a better "product" to look at in terms of forecasting for severe weather due in large part because CAPE looks at the atmosphere at all levels. For example, you can have really high CAPE values, but if you have a strong inversion at the lower levels (CIN), surface parcels will be capped at that inversion and won't be able to be freely lifted to convect.

Some of the strongest storms are generally seen over the Midwest where there is a slight capping inversion during the morning, allowing CAPE to really build up just above this inversion. Once the ground heats up enough to break the inversion, surface parcels can now tap into this really strong CAPE region, and just shoot up and convection is initiated very quickly and very violently.

[adam613]

Except in southern Florida. In Miami during the summer, due to the high dewpoints and even higher temperatures, the CAPE is in the mid 3000s *on average*; I've seen it get well above 6000. But the afternoon thunderstorms down there aren't usually very strong; they get heavy rain and an occasional microburst, but large hail and tornadoes are extremely rare.

In the Plains, an MLCAPE of 6000 would probably trigger a PDS Tornado Watch even in the absence of any other forecast indicators :)

[USAF Pilot 07]

Except in southern Florida. In Miami during the summer, due to the high dewpoints and even higher temperatures, the CAPE is in the mid 3000s *on average*; I've seen it get well above 6000. But the afternoon thunderstorms down there aren't usually very strong; they get heavy rain and an occasional microburst, but large hail and tornadoes are extremely rare.

In the Plains, an MLCAPE of 6000 would probably trigger a PDS Tornado Watch even in the absence of any other forecast indicators :)

Yep. CAPE alone can't create a storm, i.e. induce convection. You need a trigger mechanism to do that. The plains don't need such a high CAPE value because they generally have other factors to work with, the main one being a strong baroclinic gradient. You don't really hear extremely severe storms in the plains during the Summer months. Instead, the severe storms, tornadoes, and hail all occur during the Spring. In fact, Tornado season for the plains is generally during the months of March-May. This is due in large part to the baroclinicity in that area. You've still got a very cold, dry airmass north of the Jet over Canada and the Northern States, pumping cold, dry weather Southward, and South of the Jet you've got a very warm, moist airmass pumping warm, moist air North. Where these two airmasses collide is where you get extremely severe Thunderstorms.

CAPE alone won't make a storm severe, or into a supercell, nor will it trigger a tornado watch. A supercell storm is defined as a storm with upward rotation. You've got to have rotation in the atmosphere, (shear observed through the Storm-Relative Helicity) to form strong/supercell storms. Tornado Watches are generally triggered when you have significant shear in the atmosphere, especially at lower levels.

Many of Florida's "afternoon" thunderstorms are created by the land-sea breeze. The difference in temperature between the ocean and land creates an unstable environment which causes wind to blow off the sea onto the land. That land sea-breeze will then converge with winds going the opposite direction further inland, and force air upward and induce thunderstorms. There generally just isn't enough rotation or upper level support in the atmosphere to support the formation of supercells. What you get is generally high-towering CBs which dump a lot of rain (because Florida is so moist), with lightning. The reason you rarely see hail in Florida, or any other tropical locations, is because the freezing level is above 10,000 feet. So in a lot of the storms in Florida you will have hail in the upper levels, but by the time it reaches the surface, it's all melted, back into rain.

[NYARTCCFAN]

Ah I knew someone would have an answer !!!

[adam613]

USAF Pilot, that was more informative than the answers I got on the storm message boards I used to read. :)

[hiss srq]

Not related to the satorms yesterday but all of the MD-80's or at least most were specials on departure meaning we were departing them on 31 the arrival runway instead of 4 the departure runway because the strong crosswind. The onlty thing I can think of as a reason they would do this is the JT8 tendancy to compressorstall with a crosswind on takeoff. Or so I recall if memory serves correct. I know that 727's had that problem and it led to alot of compressor stalls early on untill they learned about it. So it is the only thing I can think of because a good chunk of the Maddogs were shuttles for Delta and those from what I understand really are not too heavy. Temps were not high either and normally when temps are high the 737's go special as well at LGA from alot of carriers for lead out reasons but yeah. That is my weather rant for the day from the tower. Also, it was funny, we were watching the news and they were bashing the ATC operation at LGA today and most of our tower was booing the report. Damn new hires makeing the airport look bad!

[NYARTCCFAN]

No wonder the strange path over my house you guys were sending them out on. :o

[USAF Pilot 07]

USAF Pilot, that was more informative than the answers I got on the storm message boards I used to read. :)

Well I will take that as a compliment, lol... Weather is one of my passions, which probably explains why I majored in Meteorology. A LOT more physics than I ever thought possible; who knew weather involved stuff like triple derivatives, Laplacians, gradient functions etc... etc?! I'm more of a fan of the real life stuff though, rather than the math stuff, but it's important to know both...

A lot of the weather boards out there aren't that great. Personally, the only weather board I visit, OCCASIONALLY (i.e. maybe once a month) is the EasternUSWx forums. They've got some really good pro-mets on there who offer real valuable insight and the like. The only problem with boards like that is that many times they explain things in such a way that the "lay-man" (i.e. people with no meteorological background) can't understand. That always got to me, especially before I started studying meteorology, which is why I try to "dumb" things down as much as I can to explain it to people who may otherwise have no idea. Weather is such a fascinating science, and such an imperfect science, one of the only sciences that cannot be totally explained, but has such an impact on our daily lives (weather affects 1/3 of our GDP) that I believe it's important to educate people, especially those people who seek weather knowledge or are fascinated by it, as much as possible, and I love explaining weather phenomena and sharing my passion to those kinds of people.

People are always quick to point out how the "weathermen" on TV are wrong and the like, but honestly, I think that's more of an ignorant statement by those who don't understand weather and who cannot comprehend things that aren't just black and white. If we, as meteorologists and people who understand some of the science associated with weather, can explain the "why" behind weather phenomena, we'd have much more of an understanding and educated populous....

[PhilDernerJr]

Clark, excellent posts. I love reading your weather-related posts. Very educational and informative.