Weather Glossary - U

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UKMET

A medium-range numerical weather prediction model operated by the United Kingdom METeorological Agency.

Ultraviolet radiation

Electromagnetic radiation with wavelengths shorter than visible light, but longer than x-rays. Exposure to too much UV radiation can cause skin cancer.

Unsettled

Changeable or variable weather.

Unstable air

Air in which static instability exists. This condition is determined by the vertical gradients of air temperature and humidity.

Updraft

A small-scale current of rising air. If the air is sufficiently moist, then the moisture condenses to become a cumulus cloud or an individual tower of a towering cumulus or Cb.

Updraft base

Alternate term for a rain free base.

Upper level

The portion of the atmosphere above the lower troposphere. It is generally applied to levels above 850 hPa.

Upper level system

A general term for any large-scale or mesoscale disturbance capable of producing upward motion (lift) in the middle or upper parts of the atmosphere. This term is sometimes used interchangeably with impulse or shortwave.

Upslope flow

Air that flows toward higher terrain, and hence is forced to rise. The added lift often results in widespread low cloudiness and stratiform precipitation if the air is stable, or an increased chance of thunderstorm development if the air is unstable.

Upslope fog

Fog that forms when warm moist air is forced up a slope by wind.

Upstream

Toward the source of the flow, or located in the area from which the flow is coming.

Upwelling

The rise of colder, deep ocean waters along a coast due to the movement of surface water away from the coast.

UTC

Abbreviation for Universal Time Coordinate. See also Zulu, GMT.

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Weather News

Cyclone Trevor prompts mass evacuation from NT communities as it heads across Gulf

00:42 EDT

A state of emergency has been declared in the Northern Territory as Cyclone Trevor tracks across the Gulf of Carpentaria, Northern Territory Chief Minister Michael Gunner says.

Utes packed to the brim as coastal residents flee Cyclone Trevor

00:34 EDT

Mattresses, blankets and other precious items are being packed tight into utes in the Gulf of Carpentaria town of Borroloola as residents flee ahead of Cyclone Trevor's arrival.

Cyclone Veronica rapidly intensifies off WA's Pilbara coast, expected to reach category five

23:30 EDT

A severe tropical cyclone brewing north of Western Australia has intensified more rapidly than expected, reaching a category four severity and prompting warnings of heavy rainfall, damaging winds and a destructive storm surge along coastal areas.