Does calm wind mean no bumps?

NealRomeoGolf

NealRomeoGolf

Final Approach
PoA Supporter
Joined
Apr 12, 2016
Messages
5,123
Location
Illinois
Display Name
Display name:
NRG
Probably a stupid question:

I might get to take my mother flying tomorrow. My dad said to try to keep the bumps down. Winds aloft are predicted to be less than 10 knots all the way up to 5k AGL. Skies will be clear. Does this mean good chance for a smooth ride? Any other predictors for smooth rides?
 
Winds are only one factor. Stability of the air is a bigger one. Check out the forecast soundings in Skew-T/Log-P form to get a better idea of air stability at various altitudes. There is a bit of an art to it, but basically the slant of the temperature line relative to the red and blue guidelines will give you a lot of information about stability of the air.

https://rucsoundings.noaa.gov/
Google “Skew-T Log-P stability” for a number of guides to interpreting the chart.

Or, if you don’t want to study so hard, just go in the morning when the ground is cool. Uneven heating of the ground leads to uneven thermal lifting that leads to the passengers feeling choppy air.
 
wind is but one component. the type of terrain you'll be flying over, humidity, barometric pressure all play a part. check whatever weather source you use for flight planning.
 
Even if the winds aloft are stronger, going up to 4-6k may get you above any thermal/mechanical mixing and result in a smoother ride.
 
Generally speaking, no wind and no clouds means few bumps. But bumps are about movement of air, either laterally (winds aloft) or vertically (unstable air, heating, terrain).

Good rule of thumb is to fly early for the smoothest air.
 
Spring time is notorious for thermals due to uneven heating of the ground. But yes, calmer winds usually means less orographic turbulence. Even with strong winds aloft, it is often smooth above 3000-4000 AGL.
 
No. Thermals and edges of clouds also make bumps.

Edited for clarity.
 
Last edited:
If you look at the upper winds forecast (FD), and look at the temperatures for the various levels, watch for temperature differentials over 2°C per thousand feet. If, say, the temp at 6000 is 12°C and at 9000 it's 6°C or more, the bumps due to thermals will be minimal. A differential of a lot less than 2°C per thousand means really stable, smooth air.
 
Clip4 said:
Low surface wind and high overcast.
Click to expand...
Not necessarily. At the moment we have absolutely clear skies here, almost no wind, and the lapse rate is between one and two degrees C per thousand. It would be really smooth.
 
the earlier you go the less thermal activity there will be....
 
Daytime uneven heating of the ground can cause bumps on sunny days even if the winds are calm. As others have said flying early in the morning can minimize this risk. A night flight will also generally be smoother.
 
Paul V said:
Daytime uneven heating of the ground can cause bumps on sunny days even if the winds are calm. As others have said flying early in the morning can minimize this risk. A night flight will also generally be smoother.
Click to expand...
A low lapse rate dampens the rise of heated air. As altitude increases, the air has less pressure on it, and since pressure is a factor in temperature, the pressure falls. A normal rate is 2°C per 1000 feet of gain in altitude. If we heat air over a black field, it will try to rise since it has less density than the surrounding air, but as it rises its temperature falls, and if it doesn't stay warmer than the air its rising through, it will stop rising. So the lapse rate has to be higher than normal so that the rising air stays warmer and continues rising.

Forecasters look at the lapse rate, the atmosphere's water content, and temperatures to determine the likelihood of thunderstorms. A low lapse rate means no thunderstorms. A higher than normal rate means the air will keep rising, and as its temperature falls it can't hold as much water vapor, so the water condenses and as it does so it releases the heat it absorbed when it turned from water to water vapor in the first place. This heat slows the cooling of the air as it rises and accelerates its rise, producing towering cumuli and thunderstorms. Once the air reaches the tropopause, the altitude where atmospheric temperatures begin to increase with altitude, the lifting stops and we see the classic anvil head on the thunderstorm.

Lots of interesting stuff in the weather textbooks for CPL/IFR students. This is only one of them. Around here we get chinooks, the spectacular warming of air as it crosses the Rockies, with spring-like conditions in the middle of winter. Another fascinating lesson in physics there.
 
NealRomeoGolf said:
Probably a stupid question:

I might get to take my mother flying tomorrow. My dad said to try to keep the bumps down. Winds aloft are predicted to be less than 10 knots all the way up to 5k AGL. Skies will be clear. Does this mean good chance for a smooth ride? Any other predictors for smooth rides?
Click to expand...
All other things being the same, a high overcast is generally better than a clear sky for smooth air, because the late-morning/afternoon thermals won't get as much fuel from sunlight.
 
Brad Z said:
No puffy clouds.
Click to expand...
If there's enough humidity, you might have little puffy clouds capping the summer afternoon thermals, but they can still be there with a clear sky. I just assume a sunny afternoon from May to September (around the Great Lakes/East Coast regions, at least) will be bumpy up to somewhere between 4,000 and 10,000 ft AGL, and I'm rarely wrong.
 
David Megginson said:
If there's enough humidity, you might have little puffy clouds capping the summer afternoon thermals, but they can still be there with a clear sky. I just assume a sunny afternoon from May to September (around the Great Lakes/East Coast regions, at least) will be bumpy up to somewhere between 4,000 and 10,000 ft AGL, and I'm rarely wrong.
Click to expand...

Sorry, I was just trying to provide a veeeerrrry simplistic assessment. Generally in the eastern half of the country it's rare that you don't have enough moisture to have at least a few to scattered cloud layer from thermal updrafts.
 
GRG55 said:
No convective clouds.

Some of the smoothest air days are under a high, solid overcast. Minimizes the solar radiation that gives rise to thermals.
Click to expand...
Yup. And a high, solid overcast is often due to an overrunning warm front, making for a really shallow lapse rate, too.
 
scottd said:
In other words, you can have 50 knot winds just a few thousand feet above the ground, but in a stable atmosphere, you get no mixing, and therefore, no bumps.
Click to expand...
Exactly. I rode a low-level winter jet down from CYOW to either KIAD or KPHL (I can't remember which) once at 9,000 ft with a 60–70 knot tailwind, and it was smooth as a misty morning. Another time, I was flying against 50 kt a winter jet back from Boston, and it was throwing up so much turbulence from the New Hampshire and Vermont hills that I was leaving head-shaped dents in my ceiling (not a joke; I hit hard enough to feel slightly stunned after one jolt; when I walked into the FBO after four hours fighting that with ground speeds around 70 kt, the woman behind the counter took one look at me and told me to sit down while she grabbed me a hot chocolate).

The difference was that the bottom of the first jet was high enough to miss the tops of the hills, while the second wasn't.
 
I've flown in 30+ kt winds and it's been smooth as silk. I've also flown in calm winds where you could barely keep from bouncing out of your seat. Winds and turbulent air have no correlation whatsoever.
 
Kevin Eggert said:
I've flown in 30+ kt winds and it's been smooth as silk. I've also flown in calm winds where you could barely keep from bouncing out of your seat. Winds and turbulent air have no correlation whatsoever.
Click to expand...
Not no correlation — they have a lot to do with each-other — but definitely not 100% correlation.
 
Kevin Eggert said:
I've flown in 30+ kt winds and it's been smooth as silk. I've also flown in calm winds where you could barely keep from bouncing out of your seat. Winds and turbulent air have no correlation whatsoever.
Click to expand...

Not totally correct. If the wind is GUSTY it will correlate with choppy air.
 
Where I live we’re surrounded by mountains. Wind makes bumps. Absence of wind may not be smooth as glass but chances are good it’ll be smoother than on a windy day. Wind direction matters, too.
 
All I know is if a 707-737 cap'n is kind enough to give a PIREP of light chop, you'll prolly wanna toss your cookies in a 150-152.
 
scottd said:
Wind is just one component of turbulence. If it is really hard to get air to mix, you can have relatively strong winds and smooth conditions. This is quite ubiquitous in the overnight hours when a surface-based nocturnal temperature inversion sets up. That's incredibly stable air and that allows the atmosphere to decouple from the surface and the winds accelerate freely creating what is called nonconvective low level wind shear. Winds can easily accelerate to 40+ knots just 2,000 feet above the surface with glassy smooth air in these situations.
Click to expand...
On the western prairies chinooks are common, and if the air at the surface is very cold the warm chinook flow will run over it rather than displace it. I've seen that wind shear at 200 feet AGL.

One morning one of our instructors took off with a student. The surface was at about -20°C. at 6000 feet it was +18°C (about 65°F). They thought they were having trouble with the cabin heat; they thought it was stuck on. Then they looked at the OAT. All that heavy clothing and springtime warmth outside the airplane.
 
scottd said:
Yes, gusty winds are typically the result of a convective process and unstable air that wants to easily mix. Throw in very stable air and the gusts disappear along with the turbulence even when winds are relatively strong.
Click to expand...
@scottd sorry I'm just in chapter 4 in your book. Looks like I need to skip to chapter 13.
 
You must log in or register to reply here.
Back
Top