Projected 5G Interference Can Degrade Passive Microwave Radiance Assimilation and Alter High‐Impact Weather Forecasts

Abstract Passive microwave radiances near 23.8 GHz constrain lower‐tropospheric water vapor, but this protected window lies adjacent to fifth‐generation (5G) telecommunications spectrum. We quantify how projected terrestrial 5G leakage propagates through county‐scale deployment projections, directional antenna geometry, synthetic contamination of AMSU‐A channel 1 radiances, and UFS–JEDI assimilation. In a representative 2040 scenario, radio‐frequency interference (RFI) over metropolitan corridors produces brightness‐temperature perturbations up to 3.75 K. For Hurricane Ida's extratropical remnants, low‐efficiency 2040 RFI altered the 12 hr forecast relative to a clean control, with local precipitation changes up to about 10 mm and 2 m temperature differences exceeding C. Forecast changes appeared near interference sources and downstream, including regions without mapped 5G infrastructure. The results identify two pathways by which adjacent‐band emissions can affect high‐impact forecasts: biased radiances retained by assimilation and RFI‐triggered quality‐control rejection. Forecast sensitivity depends on emissions, network efficiency, and RFI‐aware assimilation.