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UKMO

(or UKMetO) United Kingdom Meteorological Office. The HQ, (and central computing / NWP facility) was formerly located at Bracknell, Berkshire, UK., but since late summer of 2003 is now in Exeter, Devon [ together with the Hadley Centre for Climate Prediction and Research]. (NB: they now like to be called 'the Met Office'). Visit the web site at:- http://www.metoffice.gov.uk/

Undercut

See Cold undercut

Unstable air

An air parcel will continue to move away (rise or fall) from its original location when the initial force exerted on it is removed. [ see the FAQ entry on stable and unstable air masses.

Upper Air

Normally taken to be the levels between 850 mbar (about 5000 ft), and 200 mbar (39000 ft). The most common heights used being 500 mbar (18000 ft) and 300 mbar (30000 ft).

Upper fronts

It has long been recognised that the simple 'Norwegian model' (q.v.) of a frontal zone extending with a defined slope from the surface to the top of the troposphere did not often fit the observed weather experienced on the ground or by aircraft in flight. Often, bands of precipitation which were not ideally tied to the classical front were observed, and with the coming of satellite imagery, structures could be detected which are now classified as upper fronts. On actual/prognostic charts issued by meteorological centres (strictly these are surface charts), such features are shown using the classical symbology, but the triangles (cold fronts) and 'bobbles' (warm fronts) are not filled in, and are termed upper cold and upper warm fronts respectively.

Upper Ridge

A ridge on an upper air chart - evidence of warm air in depth through the troposphere.

Upper Trough

A trough on an upper air chart - evidence of cold air in depth through the troposphere.