Thermal Soaring Forecast -- anyone know how to read this? - RC Groups
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May 17, 2006, 11:17 AM
Slope elope
Cziltang Brone's Avatar
Question

Thermal Soaring Forecast -- anyone know how to read this?


Poking around at NOAA, I came across the Thermal Soaring Forecast for Santa Ynez, CA, which is quite near our main flying site. I'm not sure if this would be of any use in predicting conditions, as I don't really know how to read it. Specifically, how a high "lift rate" would affect the slope lift, perhaps 10 miles away.

Any thoughts?
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May 17, 2006, 11:33 AM
Fun ain't cheap!
droydx's Avatar
Quote:
Originally Posted by Cziltang Brone
Poking around at NOAA, I came across the Thermal Soaring Forecast for Santa Ynez, CA, which is quite near our main flying site. I'm not sure if this would be of any use in predicting conditions, as I don't really know how to read it. Specifically, how a high "lift rate" would affect the slope lift, perhaps 10 miles away.

Any thoughts?
(1) Get a good nickname, (2) if you got it - get rid of it, and (3) in Santa Barbara Always bring a weasel



Droydx
May 17, 2006, 11:51 AM
Slope elope
Cziltang Brone's Avatar
Very helpful I meant thoughts about the Thermal Forecast.

Quote:
Originally Posted by droydx
in Santa Barbara Always bring a weasel

Yeah, you're one to talk! I'm not convinced you even own a Weasel!
May 17, 2006, 12:32 PM
Registered User
Daemon's Avatar
That thermal forecast indicates that it's very poor conditions for
thermalling.
Compare with this one:
http://www.crh.noaa.gov/bou/include/...entdir=routine
Notice max lift rate of 791 ft/min.

Yesterday a paraglider pilot launched from Zion and flew 93 miles south.
HGs and PGs were topping out a little over 12,000 feet.
Today, probably more of the same.

ian
May 17, 2006, 01:16 PM
The lift is out there....
barefootbass's Avatar
Tomorrow looks even better!
May 17, 2006, 01:31 PM
PGR
PGR
Low AltiDude
PGR's Avatar
Quote:
Originally Posted by Cziltang Brone
Poking around at NOAA, I came across the Thermal Soaring Forecast for Santa Ynez, CA, which is quite near our main flying site. I'm not sure if this would be of any use in predicting conditions, as I don't really know how to read it. Specifically, how a high "lift rate" would affect the slope lift, perhaps 10 miles away.
I also poke around in the NOAA/NWS websites and I've never come across anything like that. But that's apparently because I never used "soaring" as a search term. Doing so just revealed the following link to information from the San Diego NWS office:

http://newweb.wrh.noaa.gov/sgx/data/aviation/soar.htm

Hmmmm .....

Different info, a little less detailed, but intriguing nonetheless.

I think Cziltang Brone is on to something here.

Now if someone would only come along and tell us what it all means.

Pete
May 17, 2006, 01:51 PM
Slope elope
Cziltang Brone's Avatar
Seems like Daemon might know, but he just provided more alphabet-soup.

HGs? PGs? CCL? I can't say I even understand the units: ft-msl ?
May 17, 2006, 01:56 PM
blah...
THUREN's Avatar
Need to know the meaning??

Glossary



CCL
Convective Condensation Level- The level in the atmosphere to which an air parcel, if heated from below, will rise dry adiabatically, without becoming colder than its environment just before the parcel becomes saturated. See Lifted Condensation Level (LCL).

MSL... Feet mean sea level..
May 17, 2006, 01:59 PM
blah...
THUREN's Avatar
I have the answer...

Don't try and pull any crazy thermals if it's socked in foggy or raining...


BTW..... 85 now in the valley, high of 65 today here.... I'll be up on the hill about 3-4 o'clock...

Up-valley Wind
A diurnal thermally driven flow directed up a valley's axis, usually occurring during daytime; part of the along-valley wind system.


Don
Last edited by THUREN; May 17, 2006 at 02:08 PM.
May 17, 2006, 02:49 PM
PGR
PGR
Low AltiDude
PGR's Avatar
Quote:
Originally Posted by THUREN
... adiabatically ...
Gesundheit!

Pete
May 17, 2006, 02:52 PM
The lift is out there....
barefootbass's Avatar
If you can check out Paul Naton's "Secrets of Thermal Soaring" video. Very informative and useful. Well delivered and with easy to use diagrams. You may not think that thermals apply to slope soaring and if you are on the coast they may not but inland they certainly do affect the slope dynamics. Also Karl (Predator) has a fantastic explination of how thermals and slope intermix on his site www.predatorwings.com
You can alway tell the difference between pure slopers and slermallers by who's walking and who's flying when the "lift" dies...
May 17, 2006, 02:59 PM
Registered User
Daemon's Avatar
To understand the numbers you need to understand the dry (unsaturated)
and moist (saturated) air lapse rates and it helps to understand Skew-T
diagrams. Lemme see if I can explain it.
Start with a background on lapse rates here
http://en.wikipedia.org/wiki/Adiabatic_lapse_rate

Then go to this link sometime mid morning on any given day although
today is best.
http://www-frd.fsl.noaa.gov/mab/soun...ta_source=MAPS
It's a Java based skew-T diagram for a location near Mt. Zion here.
(should be able to change the coordinates to some place near you).
The red line represents the temperature of the air at each
altitude. Pretend that it's a real sounding (a balloon rising up
that records air temperature as it goes). Now put your mouse
near the bottom of the red line, and a tiny bit to the right and
click. A pink line appears.

That line follows first the dry air lapse rate, then bends upward and
follows the moist air lapse rate. In both cases the air is cooling as it
rises. That pink line pretty much always follows the same shape, but
the point at which it bends will change depending on the current
dew point (represending how much moisture is in the air when
the parcel leaves the ground).

Here's how it applies to thermals. The sun heats up the air near the
ground. As long as the air temperature of that parcel of air is
greater than the temperature of the air above it, it'll rise.
The air doesn't heat evenly and it's influenced by wind and terrain
so instead of all the warm air rising straight up, there tend to be pockets
and small rivers/streams of warm air that flow together and produce
an organized thermal. The rising air in that thermal will follow the profile
of the pink line, first on the dry air lapse rate. While the parcel of air
rises, it cools (pink) but the atmospheric air also is cooler (red) so
as long as the pink line is to the right of the red line, the parcel of
air continues to rise. The further to the right of the red line
the larger the temperature differential and the faster it rises.

If the pink line stays to the right of the red line all the way until the
bend in the pink line, then that represents the temperature at which
the parcel of air becomes saturated (cold air can hold less moisture than
warm) and that's cloudbase. If the pink line crosses the red line before
reaching cloudbase, then that represents an inversion (the altitude
at which the air above the rising parcel is warmer than the parcel itself),
and the rising parcel of air slows and stops.

If you look at the red line carefully you'll notice that over the course of
the day (click on the different sounding times) that the very bottom of
the red line extends further right. That represents predicted ground
temperature. If the forecast is good, that point should pretty closely
match the temperature you measure yourself. If you click on
the chart at ground level at the current measured temperature
then that should give you a fairly accurate picture of how strong
the thermals will be, when they'll start, how high they'll rise.

The soaring forecast is built entirely on this info.
Take today's Denver/Boulder forecast.
Max temp: 82F (that matches what my thermometer says right now)
Time of trigger temp: 11am (This is the time at which the ground temperature will be great enough to cause a rising parcel of air to continue to rise to the right of the red line).
Maximum height of thermals: 18108 ft: (That happens to be cloudbase, so the forecast is calling for enough hot air to push the pink line to the right so far that it clears the inversion and gets all the way to cloudbase)
See that the cloudbase (short black horizontal line) on the skew-T
is pretty close to the soaring forecast max thermal top.

Time of overdevelopment: 3pm (That's when all the air rising to cloudbase creates so many clouds that it cuts off the sun and ground heating stops. It also can be the time at which the hot air is expected to break through the inversion (if it exists) all at once, causing sudden clouds/rain/thunderstorms)
Maximum rate of lift: 791 ft/sec (because the pink line is relatively far
from the red line (on a poor day they're almost on top of each other),
it means the thermals rise pretty fast).

Looking at the San Diego soaring forecast, notice that at all the
costal sites the max ground temps are low, trigger temps are high,
thermal tops are very low (the pink line would cross the red line early).
The inland sites though, have a higher max temp, trigger temps are low,
(putting pink line way to the right of red line) and thus the
soaring index is very high and thermal tops are also very high.
At 14-18k feet, thermals are probably rising all the way to cloudbase
there as well.

Neither of these scenarios is really normal for this time of year.
On a "normal" soaring day there'll be a bend to the right in the red line, that
represents an inversion. You click on the graph at the ground temp, and
find that the pink line extends up normally and then crosses the
red line at say.. 8-9k feet. That's the top of the inversion (aka "the cap").
A soaring forecast would initially say that the tops of the thermals are at 9k.
The cap keeps clouds from forming so the sun continues to heat
the ground throughout the day, pushing the bottom of the
red line further to the right (ground temp) and the top of the cap
(the bend in the red line) softer as the rising
warm air fills up that space (the pink line will continue to cross the
red line at about the same or slightly higher throughout the day).
At some point, if enough warm air is stored up below the cap, and
ground temperatures get high enough, some of the more energetic
thermals will have enough upwards momentum to push right through the
cap to higher altitudes. Not long after that, a few of them will
manage to rise higher up into the colder air (red line bends back to the left)
and then metaphorically speaking, all hell breaks loose.

If there's a lot of stored hot air below the inversion, and strong
thermals break through it into colder air, then they'll pull all that
warm air up from below the inversion all at once. You'll go from clear
skys to big black clouds in a very short time, and these are
the building blocks of thunderstorms. Storm forecasts will talk about
the CAPE (Convective Available Potential Energy) which represents all
the energy stored in the warm air trapped under the inversion waiting
to let loose and build a thunderstorm. When it does finally go the
storms cool the lower level air througout the evening, which creates
the inversion the next day. This is a "normal" monsoon season cycle.
Cool air in the morning with low level inversion, sun heating all day,
thermals rising to the cap until mid/late afternoon, thermals break
through cap, thunderstorms, cool low level air.. rinse, repeat.
Anyone thermal soaring (PGs/HGs especially) should think about getting out
of the sky as soon as the black clouds start forming anywhere, because
they'll create thermals that you can't get out of, and change the
wind direction for miles around.

ian
Last edited by Daemon; May 17, 2006 at 03:24 PM.
May 17, 2006, 03:07 PM
Registered User
Daemon's Avatar
Quote:
Originally Posted by Cziltang Brone
Seems like Daemon might know, but he just provided more alphabet-soup.

HGs? PGs? CCL? I can't say I even understand the units: ft-msl ?
HG = Hanggliders
PG = Paragliders
CCL = what Thuren said (I didn't introduce this abreviation)
ft-msl = ft mean sea level.. (sea level changes with the tides so they reference it as an averge, or mean over the last 19 years)
as opposed to
ft-agl = feet above ground level, (which varies for every location on earth)

ian
May 17, 2006, 03:15 PM
Rick Rogahn
Endless Sloper's Avatar
Ian, you are a bad a$$. Going to save this last entry for later when I can digest it further. Fantastic expaination, I'll see if I can find this for WA sites.
May 17, 2006, 03:18 PM
Registered User
Daemon's Avatar
On a side note, the above referenced Java skew-T diagram is not
a half bad tool for predicting wind direction. Notice the plot of wind
barbs on the right side? That represents the wind direction and speed
for all altitudes from ground level to 50 thousand feet.
Obviously the ground level values are the most useful. Can see
in the ground level chart above, the bolded numbers are showing wind
coming from 67 degrees at 12mph. That's ENE at 12 which makes
for absolutely phenomenal conditions on Zion's big 1000 foot face.

Here's the URL modified for the sounding location closest to Parker Mountain
(about 3 miles west of PM)
http://rucsoundings.noaa.gov/plot_so...ta_source=MAPS
For today it's showing pretty light winds from the SSW/SW throughout much
of the day and unless the temps are well over 90 degrees, I wouldn't
expect much in the way of thermal activity.

ian
Last edited by Daemon; May 17, 2006 at 03:41 PM.


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