Data is coming from PRISM National Weather data set.
COMET currently uses observed historical PRISM weather data, from the nearest weather station relative to the parcel defined, for all years in the baseline. The baseline years, at the moment, always begin in year 2000 and typically (default) end in 2021, the year before the current year. Assuming a user does not adjust the baseline end period, 2000-2021 weather included in the model run is the observed weather. COMET is not predicting any future weather patterns for the scenarios, which are on the timeline of 10 years following the end of the baseline, in the typical case, this would be years 2022-2031. Instead the weather from the last 10 years of the baseline are used for the next 10 years. For example, assuming a typical baseline 2000-2021, 2012 weather is used for 2022, 2013 for 2023, 2014 for 2024, etc...
So the weather that is used for the baseline and the future scenario is the same.