An empirically based statistical method has been created to predict the relative change in modulus for a sealant exposed to outdoor weathering. This method has not been validated. The underlying high-precision data supporting this method was obtained using the National Institute of Standards and Technology simulated photo degradation by high-energy radiant exposure (NIST SPHERE). The NIST SPHERE can independently precisely control each of the four primary components of the outdoor exposure: temperature, humidity, ultraviolet radiation, and mechanical loading. The time-dependent modulus of the sealant samples were characterized using ASTM C1735-11 [ASTM C1735-11: Standard Test Method for Measuring the Time Dependent Modulus of Sealants Using Stress Relaxation, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA] before and after each exposure period. The resulting empirically based method produces a relative prediction of modulus change for any location, provided a historical weather file is available. Additionally, the relative geographical predictions allow for future independent verification of this approach. It is important to state that these are only predictions that have not been validated with the corresponding outdoor data.