I am sometimes asked what the datum, projection, or geographical coordinate system (GCS) the LOCA data use. I am far from being an expert in GIS, but this page tries to answer that question as best I understand it.
The LOCA data are not projected, they are in (geodesic) latitude and longitude. Geodesic latitude is only meaningful in reference to a specific datum. The datum used in LOCA is ultimately based the datum used in the meteorological training data that LOCA employs in the constructed analogs process. So the question really devolves to, what datum the LOCA training data sets used.
Temperature and precipitation downscaling use the Livneh et al. 2015 dataset as training data. Although that work does not specify a datum, it is based largely on co-operative meteorological stations run by the National Weather Service Cooperative Observer Program (COOP). So when a COOP station specifies a (geodesic) latitude and longitude, what datum is it based on? The Western Regional Climate Center at the Desert Research Institute has this to say on the subject:
Datum Info: NAD83. However, there is no strict verification for each site — we have found some of the older information is NAD27. This is usually distinguished by the lack of seconds in the position coordinates. Generally, we post the information we are given and sometimes the datum isn’t specified. citation
So the answer to the original question is that LOCA data are unprojected geodesic latitude and longitude based on NAD83. However, some individual locations (gridcells) may be influenced by stations using the NAD27 datum, which could result in a surface displacement (datum shift) of up to 100 m (see this figure on Wikipedia).