A met question

[dublinpilot]

Ok, here's a question for you guys.

I recently read a book called The Weather Handbook, by Alan Watts. I thought it was excellent, and it improved my understanding of weather no end! But together with reading that and "Severe Weather Flying" has had a strange effect on me!

Now whenever I wake up to find a lovely morning with generally clear blue skies, little wind, I start to think. I see a few cirus clouds around, and maybe the odd lower cloud, and conclude that there must be some moisture in the athmosphere, in order for the few clouds to form.

Then I think, well if there is very little cloud, and little wind there is bound to be a lot of stong thermals in the afternoon, due to heating of the surface. This will lift the air, as the lifting air cools, the moisture will condence, and form a big CB cloud, and we'll have thunderstorms in the afternoon.

Yet that doesn't seem to happen. The odd thunder storm seems to be on days that start out with a cloud filled sky with a large amount of low level cloud.

Where am I going wrong? Am in incorrect in concluding that there is sufficient moisture in the athmosphere if there are just Cirus, and the odd lower cloud around?

Thanks for any insight!

dp

[Thrifty van Rental]

You probably need to do a bit more reading. You must remember the factors required to create a thunderstorm. They are quite basic weather theory

Moisture is one factor, as you are saying, but it is not the only factor. You fundamentally need an unstable airmass, otherwise when and if the air is lifted, it will not continue to rise and build into a CB.

Was this a serious question, or did I miss the joke? :bored:

TvR

[redsnail]

The things I look for when "predicting" TS's are moisture, warmish day, instability through a deep layer (ie altitude).

So, I look outside, cirrus? good, alto cu (even better!!) and warmish day. The alto cu is the cue (excuse my pun). That's the main cloud that shows deep instability.

[dublinpilot]

Thanks for the replies guys.

No tvr it was not a joke, but a serious question.

I've understood the basic factors needed for ppl met, but want to expand my knowledge to be better at being able to predict what is going to happen, rather than just understand what has already happened, and what the forecasts are saying. I want to be able to make my own forecasts to a reasonable degree.

Development of thunderstorms is something that I've never been comfortable with my understanding.

Thanks for the replies.

[bluskis]

Thunderstorms can be a factor in cold fronts, alternatively they can be the result of instability in an airmass, triggered by heat or topography. The latter usually occur later in the day as the surface heat increases enough to send the unstable air upwards, and can be significantly more agressive in lower latitudes .

The met men have ways of measuring the lapse rates and stabilities that eyeball earthlings do not have, so there is nothng like aviation met forcasts to predict what weather will affect your flying.

[redsnail]

How to predict when and where a thundery will appear. I used to rely on this when I was bush flying in the Kimberley (Australia).
Things I would look for.
Season. Wet or Dry. Has the met bloke predicted thunderies for the day. (summer/winter/etc)
Topography. Mountains, hills, cities, lakes, near ocean etc. A ridge will provide some lifting. As you know, you need that to kick off cu cloud and therefore (if conditions are right, a TS)
Weather. Humid, windy, front, clouds formed already.

Frontal cells will form up around the front. (yeah obvious. It pays to know what front (warm or cold) as to when they'll form.

Air mass. Usually in the arvo, peaking around 2-4pm. Usually dissipates at night unless very tall.

Monsoonal. Big version of the above. Can get them at any time of the day. Less chance in the morning but don't bet on it.

So, when flying around and there's no thunderies forecast, note where the Cu is forming any way. Odds on there's something lifting the air and kicking off the cu. If the conditions are right then it's a really good bet that there's where the TS will form up. This is especially true for air mass sparklers.

The books are great but it's useful to watch what's going on around you and pay attention to the weather report on tv. :D

[RodgerF]

If the Cu and/or Alto Cu is visibly growinng , ie you can see rapid growth at the tops then it indicates high lapse rates and instability

[dublinpilot]

Thanks guys!

I suppose I was reading a bit too much, and then forgetting the basics!! It's all very fine to have the moisture, and the heat to kick off some lifting, but I was forgetting the unstableness bit. After all, if the lifting starts, it needs to be able to continue to form a TS.

Thanks very much redsnail, for your tips on predicting them without forecasts. While I'd never fly without checking forecasts (and we're luckey enough to be able to speak to a forecaster over her for just €1.50 per min) I want to be able to develop my own understanding to the point that I can make reasonable predictions from what I can see myself when I look out! So your visual clues are very helpful.

Thanks guys for clearing this up for me, even if it was a bit of a silly question.

:ok:

dp

[witchdoctor]

Great to see the interest in the weather beyond simple reading of the forecast. Can't add much to what has already been posted except one anorak point which surprised me when I first studied met - you get more CBs in winter than in summer in the British Isles. Now not a lot of people know that.:8