Resolved OAT always too high at high altitude

[alpinebravo]

HI there, I've noticed that ActiveSky is giving higher than expected temperatures at altitude. This is happening consistently across a number of flights now and has a noticeable impact on aircraft performance.

I first noticed it as the CJ4 was not able to achieve its normal cruise speed of M.74 at is usual cruising altitudes of FL400-450, even in climb power. In MSFS live weather that would lead to an overspeed.

So I started to pay closer attention to the OAT and conducted some test flights. In my current test Im in the CJ4 flying from KTEB to Chicago Executive SimBrief was giving an OAT of -52 at FL430 (ISA +5).. At that level/waypoints

Active Sky was giving OAT -41, ISA +16
MSFS Live Weather was OAT -49, ISA +8

The attached screenshots show: the OAT with ASFS, OAT in MSFS live weather from the CJ4 MFD and the SB flight plan forecast for that segment of the flight.,

I've replicated the issue on a number of different flights in a number of different regions of the world and it is consistently some +14degC higher than what the forecast/MSFS live weather gives.

Regards

Brendan

(PS - posted as its own thread as I originally did it at reply to a beta thread, which may not have been the right place to log the issue)

 

[alpinebravo]

Some more data - this time in the Learjet 35A. ASFS still producing temps higher than forecast in the high flight levels with the corresponding impact on aircraft performance. 1st image from the tablet using MS Live Weather, Second ASFS. Third shows the SimBrief forecast OAT at that time, location and altitude (-52degC). Live Weather has that. ASFS had - 45degC.

 

[damian]

We have found an issue which looks to be related to an apparent recent MSFS2020 change regarding lapse rate calculations above FL365.

Here is a test build which attempts to resolve this, for anyone who would like to try. Thanks in advance for your confirmation of fix or reports of any continued issues.

https://www.mediafire.com/file_premium/ai1w1s79mk24hck/AS_FS_Install.exe/file

 

[alpinebravo]

Thank you for responding and issuing the test build.

First test indicates a definite improvement - flying out of KASE using live weather. SB gave a forecast of -50 at FL390. Aircraft was registering -53.

 

[damian]

Thank you for responding and issuing the test build.

First test indicates a definite improvement - flying out of KASE using live weather. SB gave a forecast of -50 at FL390. Aircraft was registering -53.

Thanks. A small variance from direct layer forecast in some cases would be normal, due to newly improved and more dynamic inter-layer and inter-spatial vertical/horizontal interpolation in the depiction (also included in this test build). This would explain the 3 deg difference at your screenshot point in time.

 

[damian]

https://forums.hifisimtech.com/threads/b8942-open-beta.15068/

 

[alpinebravo]

Another update to test? I found the previous build was always reading a little low (-2/-3), but well within the expected variance.

 

[damian]

This is same build, it's now posted as open beta. The +/- 3 deg variance would be expected, but always the same variance is not (especially if you're flying much different areas around the globe and/or with different historical weather beyond a week or two). Please keep us updated.