Interesting wind experience

I learned a new aspect of the weather yesterday.

There was a flight I wanted to make badly enough to promote poor decision
making. A friend from out west was in town for just a day. The weather here
in the northeast was predicted to be totally clear but with winds that
usually produce gnarly and rough conditions. I'm comfortable in 15G25 but
the NOAA site was showing 30 - 40 knots at 3000 feet and 40 - 50 at just
6000 and I've gotten beat up in less than that. With a low just off shore
working gear like against the high, I could envision air coming in from
different directions at different levels and really stirring things up.

I wasn't feeling 100% sharp due to fighting off a cold either so I
reluctantly told my friend that our years long attempt to fly together was
foiled again.

While he was driving up the next morning, I called ATIS and the wind was 12
knots straight down the runway. I checked the latest forecasts and the
predicted speeds were down slightly. I called his cell phone and told him to
meet me at the airport.

Just after engine start, ATIS reported more wind and higher gusts than
anything reported. As we taxied out, I told my passenger that it was a
classic case of aviation decision making. I never would have considered it
if I had those numbers at home but, since we were there with the engine
running, we were going.

The takeoff was uneventful and the flight was smooth. There was an
impressive sideways drift when we reached a couple hundred AGL that I failed
to correct for because it felt almost like taking off in a calm. All day
long, our ground speed and crabbed tracks showed us flying in strong wind
but it felt almost like early morning calm. There wasn't a cloud in the sky.
All the landings were effortless and smooth.

There is more to predicting this aspect of the weather than the wind speed.
The atmosphere must have been incredibly stable, the wind was like a laminar
flow and perfectly predictable. We flew up to look at Mt. Washington and
turned back when told the wind was near hurricane force on the summit. I've
been beat up and downdrafted at our turn around point when summit winds were
half the velocity.

I'm sure his has something to do with stability and vertical air motion. I'd
like to know more about it so I can make better predictions. It was
beautiful flying weather and we had the skies almost to ourselves, probably
because of the predicted winds.

--

Roger Long

Last night I went up for a bit to do some approaches last night. Winds were
either calm or up to 6 knots at the surface at various airports but the
winds aloft at 3000 were predicted to be 38 knots. I braced for some
low-level turbulence but found only trace light chop below 2000. I saw 26
knots at 2,500 so the potential for sheer was definitely there.

Like you, I've experienced worse with less.

Marco Leon


"Roger Long" wrote in message
...
I learned a new aspect of the weather yesterday.

There was a flight I wanted to make badly enough to promote poor decision
making. A friend from out west was in town for just a day. The weather
here
in the northeast was predicted to be totally clear but with winds that
usually produce gnarly and rough conditions. I'm comfortable in 15G25 but
the NOAA site was showing 30 - 40 knots at 3000 feet and 40 - 50 at just
6000 and I've gotten beat up in less than that. With a low just off shore
working gear like against the high, I could envision air coming in from
different directions at different levels and really stirring things up.

I wasn't feeling 100% sharp due to fighting off a cold either so I
reluctantly told my friend that our years long attempt to fly together was
foiled again.

While he was driving up the next morning, I called ATIS and the wind was
12
knots straight down the runway. I checked the latest forecasts and the
predicted speeds were down slightly. I called his cell phone and told him
to
meet me at the airport.

Just after engine start, ATIS reported more wind and higher gusts than
anything reported. As we taxied out, I told my passenger that it was a
classic case of aviation decision making. I never would have considered it
if I had those numbers at home but, since we were there with the engine
running, we were going.

The takeoff was uneventful and the flight was smooth. There was an
impressive sideways drift when we reached a couple hundred AGL that I
failed
to correct for because it felt almost like taking off in a calm. All day
long, our ground speed and crabbed tracks showed us flying in strong wind
but it felt almost like early morning calm. There wasn't a cloud in the
sky.
All the landings were effortless and smooth.

There is more to predicting this aspect of the weather than the wind
speed.
The atmosphere must have been incredibly stable, the wind was like a
laminar
flow and perfectly predictable. We flew up to look at Mt. Washington and
turned back when told the wind was near hurricane force on the summit.
I've
been beat up and downdrafted at our turn around point when summit winds
were
half the velocity.

I'm sure his has something to do with stability and vertical air motion.
I'd
like to know more about it so I can make better predictions. It was
beautiful flying weather and we had the skies almost to ourselves,
probably
because of the predicted winds.

--

Roger Long

Roger,

I find the conditions you describe (high wind velocity with low turbulence)
more commonly in the Winter months up here in New England, which would seem
to comport with your suspicions about atmospheric stability. Do you still
have the winds and temperatures from that day? You could look at the lapse
rate to see how it compared to the standard rate.

-cwk.

"C Kingsbury" wrote in message
hlink.net...
Roger,

I find the conditions you describe (high wind velocity with low
turbulence)
more commonly in the Winter months up here in New England, which would
seem
to comport with your suspicions about atmospheric stability. Do you still
have the winds and temperatures from that day? You could look at the lapse
rate to see how it compared to the standard rate.

-cwk.



Stability is a great part of the equation, and there is one other.

The High in the northeast is well established, to high levels. With
Anticyclonic flow all the way up through 500 mb (18,000 ft) that airmass is
generally sinking. Hence the clear skies, not even any CU, even though the
air is relatively cold. Warm ground would help destabilize it, but the low
sun-angle isn't doing very much.

The horizontal gradient of the upper-air temperatures is fairly flat at all
levels... At 5000 feet, it is only 6 degrees Celsius difference between
Quebec and Northern Florida. A flat horizontal temperature gradient, actual
leads to little vertical wind shear, and to some degree, to little
*horizontal* wind shear.... So the only shear you tend to get is just the
boundary-layer shear.

So we have no vertical currents (stable), and little horizontal and vertical
shear, (except for some vertical shear in the boundary layer).

Now I am no aerodynamic expert, but it would seem that vertical wind shear
(alone) is the least problematic for aircraft. With the horizontal wind
changes quickly, the only things that happen could be yaw, and a possible
change in overall lift, but there is little or no roll...the relative wind
changes more or less uniformly for the whole wing.

When we have those unstable summer CU days, and a similar sort of boundary
layer vertical shear, the increased winds reach portions of the wings at
different times due to the vertical currents helping to bring them down or
retard them, (as well as adding their own differential vertical
components...).... so the potential for roll is greatly increased. If you
add horizontal shear, you get yaw problems as well.

To summarize:
A stable airmass with no horizontal shear, in spite of the boundary-layer
vertical shear, is probably the cause of your non-problems. :-)
Horizontal wind shear (such as vicinity of a front), and/or stronger sun
producing convective currents, would have probably upset that significantly.