I have a time series data which increases by a certain value and then remains constant for certain period of time. The increase may be very high or a normal increase. I have to forecast the values for next two years. I have used ARIMA and Holt-Winters Method. Should i select the best fit model by minimum MASE value? Is there any other method to forecast such time series?
Original Time Series Plot
Forecasted using ARIMA
Forecasted using Holt-Winters Method
Edit 1 - After implementing the suggestion this is what i am getting.
Step 1 - Using Diff to remove the trend
Step 2 - Using Diff and log together to remove heteroscedasticity.
Step 3: Forecasting using auto.arima on diff of original time series. Auto.arima is not able to provide any recommended model (p=0,d=0,q=0)!!