| Abbreviation | Definition |
|---|---|
| ULJ | Upper- Level Jet |
| ULWRF | Upward Long Wave Radiation Flux |
| UMWL | Upper Mean Water Level |
| UNESCO | United Nations Educational, Scientific, and Cultural Organization |
| UNFCC | United Nations Framework Convention on Climate Change |
| UNK | Unknown |
| UNMA | Uganda National Meteorological Authority |
| UOM | Uncertainty of Measrument |
| UOP | UCAR ( University Corporation For Atmospheric Research) Office of Programs |
| UP | Unknown Precipitation |
| UPS | Un-interruptable Power Supply |
| URI | University Research Institute |
| USDOI | United States Department of the Interior |
| USHCN | United States Historical Climatology Network |
| USIABP | United States Interagency Arctic Buoy Program |
| USMC | United States Marine Corps |
| USWRP | United States Weather Research Program |
| UTC | Coordinated Universal Time (Temps Universel Coordonné) [language-independent abbreviation, French: BIPM-verified.] |
| UTH | Tropospheric Relative Humidity |
| UTM | Universal Transverse Mercator |