Predict Trend is always just linear

[DougBrowning]

Anyone had luck with the Predict using Trend Raster tool?  No matter what I try I just get simple linear trend.

Here is a temporal profile of my 37 year raster.

DougBrowning_0-1733864958820.png

Predicting out 30 years I get this for the same area.

DougBrowning_1-1733864995068.png

Expect Harmonic which is even stranger.

DougBrowning_2-1733865038666.png

DougBrowning_3-1733865202589.png

Any tips or tricks here?

thanks