| U/S |
Unserviceable |
| UAB |
Until advised by ... |
| UCP |
Unit Control Position |
| UDDF |
Up and down drafts |
| UFN |
Until further notice |
| UIR |
Upper flight information region |
| UKMET |
United Kingdom METeorological Agency |
| ULJ |
Upper Level Jet |
| UN |
Unable |
| UNA |
Unable |
| UNAVBL |
Unavailable |
| UNEC |
Unnecessary |
| UNKN |
Unknown |
| UNL |
Unlimited |
| UNREL |
Unreliable |
| UNRELBL |
Unreliable |
| UNRSTD |
Unrestricted |
| UNSATFY |
Unsatisfactory |
| UNSBL |
Unseasonable |
| UNSTBL |
Unstable |
| UNSTDY |
Unsteady |
| UNSTL |
Unsettle |
| UNSTLD |
Unsettled |
| UNUSBL |
Unusable |
| UPDFTS |
Updrafts |
| UPR |
Upper |
| UPSLP |
Upslope |
| UPSTRM |
Upstream |
| URG |
Urgent |
| USACE |
U.S. Army Corps of Engineers |
| USBL |
Usable |
| USBR |
U.S. Bureau of Reclamation |
| USFS |
U.S. Forest Service |
| USGS |
U.S. Geological Survey |
| UT |
Utah |
| UTC |
Coordinated Universal Time |
| UV |
Ultraviolet |
| UVM |
Upward Vertical Motion. |
| UVV |
Upward Vertical Velocity |
| UVVS |
Upward vertical velocities |
| UWNDS |
Upper winds |
Acronyms
