Soaring Forecasts

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Kenneth Voort
Posts: 36
Joined: Mon May 24, 2021 8:15 am

Soaring Forecasts

Post by Kenneth Voort »

I've been taking what I've learned from my power training and applying it to soaring. One resource I've used religiously is the NOAA predictions: https://rucsoundings.noaa.gov/

If you put in YSA's coordinates there (I use 43.84,-80.44), and the default Op40 forecast, you will get a graph back, with the dewpoint and temperature plotted against a skew-logT graph (I honestly have no idea what that means, exactly). I've found it very useful to predict cloud density and height during my power training, particularly the flights where we're some distance from our point of departure. I'm trying to apply it to soaring forecasts.

Take this predicion for example, it's for the 29th of May 2021, at 12PM local:
Image
The blue line on the left is the forecast dewpoint, and the red line on the right is the forecast temperature. The red numbers on the bottom, and the red diagonal lines, are temperature versus the ICAO standard lapse rate (afaik). The blue horizontal gradients on the right are altitudes in thousands of feet, and the left scale is atmospheric pressure. On the right is a "windogram", as I call it, representing wind speed and direction.

This looks to me like a very wide dewpoint/temperature spread on the 29th of May. You will also notice an inversion beginning at about 6,000 MSL, at which point the temperature is expected to increase somewhat faster than the standard lapse rate, before decreasing again.

But this is where it gets interesting for soaring forecasts. If I click on any point in this graph, I will be presented with another plot, representing a parcel of air rising from that point, like so, where I clicked on exactly the point where the red line met the field altitude at York:
Image
Look at the magenta line there. See how it goes more off to the left, until the black horizontal bar? Well, before the black line, it represents the dry adiabatic lapse rate. After it, you see the wet lapse rate. Were a column of air to rise, that black line is where a parcel of air would condense and form cumulus clouds, if I interpret this correctly. But because of the inversion just before it, the air warms, and thus, we will not see cumulus this day - especially considering the massive dewpoint/temperature spread at that point..

But, please let me continue as I zoom in...
Image
This tells me that the air will cool slightly faster than the adiabatic lapse rate, until just above 5,000', where the red and magenta lines converge - in other words, rising air will be warmer than stable air until 5,000', which tells me there will be lift out there to 5,000' tomorrow - if I can find it. This prediction in total tells me to expect clear skies and hard to find thermals, but if I can find them, I can expect to ride them to about 5,000 feet MSL.

This isn't an explanation, it's a question. Am I interpreting this correctly?
With grace and beauty, Strength and cunning She’ll stay aloft — until; Inevitably — she loses. And must glide earthward. And lie there helpless, Lovesick for the sky.
Kenneth Voort
Posts: 36
Joined: Mon May 24, 2021 8:15 am

Re: Soaring Forecasts

Post by Kenneth Voort »

As it turns out, I was pretty spot on with my guess for today. Yesterday we didn't fly due to wind, so I can't confirm or deny those predictions. But today, I checked the NOAA sounding and got this:
Image

The dry adiabatic lapse rate (magenta line, before the black bar) and predicted ambient temperature (red line) converge at about 7,500' - in other words, that is where a thermal's temperature is expected to decrease, due to expansion, to the same temperature as the surrounding atmosphere, and therefore stop rising. Given a margin of error, I was predicting the top of lift at 4:00PM (the graph is using GMT, so it's for 20:00Z) to be between 7,000' and 8,000', with some light cumulus at 9,000 (the black bar). And indeed, on my last flight with Tom, we got to 6,900' before the lift fizzled out on us - with a few cumuls about 1,000' to 2,000' above us. (A personal record for me!)
With grace and beauty, Strength and cunning She’ll stay aloft — until; Inevitably — she loses. And must glide earthward. And lie there helpless, Lovesick for the sky.
Kenneth Voort
Posts: 36
Joined: Mon May 24, 2021 8:15 am

Re: Soaring Forecasts

Post by Kenneth Voort »

Alright, I'm going to take a crack at the weather on Friday (Jun 4th 2021). This is what the atmosphere should look like at 12PM:
Image
The red line is the forecast atmospheric temperature and the blue line is the dewpoint. Where they converge, you can bet on non-convective clouds. The black bar is where I understand clouds should form, should a parcel of air rise from the ground. Before the black bar is the dry adiabatic lapse rate, and after it, the moist lapse rate. I don't understand why on this plot, clouds will form with such a wide temperature difference.

But here's what this graph does tell me, and I can understand: there will be zero lift that until around 6,000' at noon, because a rising parcel of air would have a lower temperature than the surrounding air. We can then expect a relatively thick and convective, but sparse layer of cloud between 9,000' and 14,000', after the lapse rate decreases significantly. There will be a low level inversion to about 2500MSL, or 1000AGL.

Then, here's what it looks like 2 hours later, at 2PM:
Image
Now there's some lift. In simple terms, the magenta line (rising air) is warmer then the red line (atmospheric temperature), until 5500'. Here's that same plot, zoomed out:
Image
See how close the lifted condensation level (Magenta line) is to the ambient temperature (red line)? That tells me to expect a thick layer of convective cloud at that altitude, from about 6,500' to 14,000', over top of some mediocre lift. But because of the large dewpoint/temperature spread above 10,000', I'm expecting mostly convective clouds, not stratus, at 2PM.

Here's 4PM:
Image
That's half decent lift up to about 6,500' and then another thick layer of cloud above it.

In totality, my prediction is a clear(ish) morning with no lift and no convective clouds, but a somewhat thick layer of stratus. Thickening convective clouds as the afternoon gets old, and a mid-level thinning layer of altostratus or something similar. Lift should start around 2PM and be relatively light throughout the day. I won't be there tomorrow but I'd love to hear back if my predictions are correct.

(uhh... for the record... don't bet on my predictions...)
With grace and beauty, Strength and cunning She’ll stay aloft — until; Inevitably — she loses. And must glide earthward. And lie there helpless, Lovesick for the sky.
Eitan Rotbart
Posts: 5
Joined: Tue Apr 27, 2021 11:14 am

Re: Soaring Forecasts

Post by Eitan Rotbart »

So basically it means that Friday is not a good day to fly.
How about Saturday and Sunday?
Kenneth Voort
Posts: 36
Joined: Mon May 24, 2021 8:15 am

Re: Soaring Forecasts

Post by Kenneth Voort »

Woah, hold on there... I'm only 50% confident or so in my predictions. This is a learning curve for me.

As for tomorrow, it looks like a very clear day, with okay lift, which is actually great for training.

Here's what the air over YSA will look like at 2PM:
Image

That tells me there should be some lift up to 4 or 5 thousand feet MSL, where rising air will cool to ambient temperature. Above that though, the air is very stable. Those green lines are a measure of "convective inhibition", which is marked as the second number from the top in the top right, -74. So, it is unlikely that clouds will form, as a thermal's temperature will be below ambient temperature long before it cools to its dewpoint - so it will stop rising, and therefore will not cool to its dewpoint. You'd need a helluva lot of solar energy to create clouds, but if they do form, the bases will at about 7,000'.

This is probably a result of a warm air mass from the U.S. midwest overrunning cooler air in southern Ontario, if I had to venture a guess. If you have a look at the continental surface winds, you'll notice that tomorrow, the winds coming over southern Ontario should all be coming from the midwest.

It does look quite windy tomorrow though.
With grace and beauty, Strength and cunning She’ll stay aloft — until; Inevitably — she loses. And must glide earthward. And lie there helpless, Lovesick for the sky.
Eitan Rotbart
Posts: 5
Joined: Tue Apr 27, 2021 11:14 am

Re: Soaring Forecasts

Post by Eitan Rotbart »

I see the wind, Sunday looks like a more calm day in terms of wind, I think that that;s what I'll do.
I really do hope to be able to get decent amount of air time... :)
Kenneth Voort
Posts: 36
Joined: Mon May 24, 2021 8:15 am

Re: Soaring Forecasts

Post by Kenneth Voort »

Well I didn't come up today, but the forecasting was interesting - mostly because I typically only check the forecasts on clear VFR days. There was a significant threat of thunderstorms over York today, and if you have a look at the NOAA sounding for 2PM today, you can see why:
Image
See the red horizontal lines? They represent the measure of convective potential energy. You'll notice that the magenta line, which represents a rising parcel of air, is warmer than the red line, ambient temperature, until about 35,000' - almost into the stratosphere. Here's what it looks like, zoomed in to 10,000' and below:
Image
So, a thermal will have no issue rising to the level at which it forms clouds. And then, we have what's called "free convection" - the rising air is warmer than the surrounding air for a long time. If you look at the numbers on the right, "iLCL", the lifted condensation level (cloud base) is also the iLFC - level of free convection. One other important number to note is the top one on the right (that's probably why it's at the top) - CAPE. That's Convective Available Potential Energy. Anything below 1000 and thunderstorms/CBs are unlikely. Between 1000 and 3000 and they get more and more likely and frequent. Above 3000, watch out - that's tornado territory.

Let's have a look at the GFA around the same time:
Image
There's a quasi-stationary front stretching about from Thunder Bay to Halifax. South of it, that double purple line, is an upper trough. Warm air moving northward is meeting cold air, and it's forced up. That seems like a TROWAL (Trough Of Warm Air Aloft) to me, but there's some kind of difference I'm unsure of. So what's happening here is that once rising air reaches the level of free convection, where it is free to continue upwards to the stratosphere, it meets some kind of stationary upper front that the quasi-stationary front is holding there. That to me explains why thunderstorms were so likely over southern Ontario today.

If you look at the text description for southern Ontario, it projects isolated CB rising to 48,000' with heavy thunderstorms and mist in the vicinity of the upper trough and front. That's a little higher than the skew-log-t graph projected, but close enough for me.

edit:
I called the London FIC asking what the heck the difference between a TROWAL (those red and blue hockey sticks by the Manitoba border) and an upper trough (double purple line). In the words of Mr. Spock, it was... fascinating...

double edit:
A friend sent me a picture of a funnel cloud over Orangeville, that didn't quite become a tornado. It was definitely an energetic boundary layer today.
With grace and beauty, Strength and cunning She’ll stay aloft — until; Inevitably — she loses. And must glide earthward. And lie there helpless, Lovesick for the sky.
Kenneth Voort
Posts: 36
Joined: Mon May 24, 2021 8:15 am

Re: Soaring Forecasts

Post by Kenneth Voort »

Looks like tomorrow will see some awesome lift.

Image

Looks like at least one forecast model is predicting lift up to 7,500', and a light cumulus layer above that. Thermals should also be considerably warmer than the surrounding air, as suggested by the magenta line (thermals) being further left of the red line than I usually see. This to me suggests some good, strong thermals, which should be relatively easy to find.

If I zoom out, I get this:
Image
The temperature doesn't get too close to the dewpoint at all - the highest the relative humidity gets is 75%, at 35,000'. So, we may see a few altocumulus and high level cirrus, but nowhere near enough to filter the sun significantly. It should be quite clear below 7,500' as well; we had a similar plot today for CYTZ, and the CN Tower wasn't the least bit obscured from Hamilton at 3,000'.

Best soaring weather I've predicted in a few weeks now, although it might be a bit windy - 20km/h or so from 230°, a good crosswind on 14/32.

(but then again, I've been wrong on a few occasions, so...)
With grace and beauty, Strength and cunning She’ll stay aloft — until; Inevitably — she loses. And must glide earthward. And lie there helpless, Lovesick for the sky.
Alex Upchurch
Posts: 1
Joined: Sun Jul 05, 2020 9:47 am

Re: Soaring Forecasts

Post by Alex Upchurch »

Kenneth Voort wrote: Tue Jun 22, 2021 5:25 pm Best soaring weather I've predicted in a few weeks now, although it might be a bit windy - 20km/h or so from 230°, a good crosswind on 14/32.

(but then again, I've been wrong on a few occasions, so...)
Dr Jack is also suggesting it will be a good day, so you're in good company.

http://www.drjack.info/BLIP/NAM/NE/index.html
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