Post by Tom Goodrick on Mar 14, 2010 16:08:42 GMT -5
When we get Real Weather data in FS9 and go for a flight, once we leave the departure airport and until we get near the destination airport, our flight is at the mercy of the "winds aloft" provided by Microsoft. They get data from Jeppeson showing measurements made at several stations around the world. The measurements are accurate when and where they are made. But the problem is there are only a few places they are measured, and they are measured only twice a day - 8 am and 8 pm local time. This puts the winds we fly in on a much poorer basis of accuracy than the airport surface data which is measured every 15 minutes, 24 hours a day. (That might change after some more Federal budget cuts.) My son Scott provided the info. He is a research scientist for the US Dept of Forestry, specializing in Fire Weather.
To get an idea of the quality of winds aloft data, go here:
weather.uwyo.edu/upperair/sounding.html
This shows locations on a map at which upper level wind data is measured. The data is collected and displayed by the University of Wyoming under a Govt contract.
One thing not shown is the frequency of measuerment: every 12 hours, typically 8 am and 8 pm local time.
I jotted down several stations across the country. You can look at the map and move your mouse pointer around to get the precise locations near you. unfortunately, the codes you see are codes for the met stations which may not be for the nearest airport. It may take some detective work to figure out the closest airport or waypoint you can use for a flyover.
At Huntsville, AL, I am right between several places: LZK (KLIT), Little Rock to the west, BNA (KBNA) Nashville to the north, BMX (KEET) near Birmingham to the south and FFC (KFFC) near Atlanta to the east. South of Birmingham there is LIX Slidell to the southwest and TLH Talahassee to the east. North of Nashville ir gets a little spread out. There is ILN Wilmington OH to the northeast and ILX Lincoln IL to the north,northeast.
So these are the only places wind at altitude is measured. It should be interesting to get RW and then fly between the three or four places near you while noting the wind speed and direction over various waypoints near your path. I'll check Little Rock to Atlanta and Nashville to Birmingham.
The thing to look at is how smoothly the wind data change as you fly. That smoothness reflects the quality of the interpolation scheme.
At these stations, wind data is measured using a balloon that caries a data package and radios data back to the station responsible for that balloon. Included in the data area altitude and position data from a GPS device. Speed and direction of motion from the GPS device are considered to represent the wind speed and direction - a reasonable assumption.
This data is measured for scientific purposes using scientific units. Altitude is shown in millebars of pressure and translated into meters. You can get feet by dividing meters by .305. The data goes to about 100,000 ft.
I don't recommend getting wind data from this source. The only reason I mention it is that it gives us a clue to where we can expect the wind data to be accurate. It will be fairly accurate over these locations and mathematucal guesswork everywhere else. That is not the same as forecast winds aloft. To make a forecast, you must start with the measured data and then apply computer models that take into account other atmosphere data. But we should find good accuracy in FS9 over these location. Everywhere else what we see is a product of Microsoft's interpolation scheme.
An interpolation method is a method that tries to use a reasonable math function to guess the values of wind speed and direction at locatiions between the points where it is measured. We have all seen sudden changes in the wind as we fly. The higher you fly, the more severe the effects of these changes. They will break your airplane if you allow structural failure. (I always keep that OFF.)
To get an idea of the quality of winds aloft data, go here:
weather.uwyo.edu/upperair/sounding.html
This shows locations on a map at which upper level wind data is measured. The data is collected and displayed by the University of Wyoming under a Govt contract.
One thing not shown is the frequency of measuerment: every 12 hours, typically 8 am and 8 pm local time.
I jotted down several stations across the country. You can look at the map and move your mouse pointer around to get the precise locations near you. unfortunately, the codes you see are codes for the met stations which may not be for the nearest airport. It may take some detective work to figure out the closest airport or waypoint you can use for a flyover.
At Huntsville, AL, I am right between several places: LZK (KLIT), Little Rock to the west, BNA (KBNA) Nashville to the north, BMX (KEET) near Birmingham to the south and FFC (KFFC) near Atlanta to the east. South of Birmingham there is LIX Slidell to the southwest and TLH Talahassee to the east. North of Nashville ir gets a little spread out. There is ILN Wilmington OH to the northeast and ILX Lincoln IL to the north,northeast.
So these are the only places wind at altitude is measured. It should be interesting to get RW and then fly between the three or four places near you while noting the wind speed and direction over various waypoints near your path. I'll check Little Rock to Atlanta and Nashville to Birmingham.
The thing to look at is how smoothly the wind data change as you fly. That smoothness reflects the quality of the interpolation scheme.
At these stations, wind data is measured using a balloon that caries a data package and radios data back to the station responsible for that balloon. Included in the data area altitude and position data from a GPS device. Speed and direction of motion from the GPS device are considered to represent the wind speed and direction - a reasonable assumption.
This data is measured for scientific purposes using scientific units. Altitude is shown in millebars of pressure and translated into meters. You can get feet by dividing meters by .305. The data goes to about 100,000 ft.
I don't recommend getting wind data from this source. The only reason I mention it is that it gives us a clue to where we can expect the wind data to be accurate. It will be fairly accurate over these locations and mathematucal guesswork everywhere else. That is not the same as forecast winds aloft. To make a forecast, you must start with the measured data and then apply computer models that take into account other atmosphere data. But we should find good accuracy in FS9 over these location. Everywhere else what we see is a product of Microsoft's interpolation scheme.
An interpolation method is a method that tries to use a reasonable math function to guess the values of wind speed and direction at locatiions between the points where it is measured. We have all seen sudden changes in the wind as we fly. The higher you fly, the more severe the effects of these changes. They will break your airplane if you allow structural failure. (I always keep that OFF.)