On Wed, 10 Feb 2016 22:16:15 -0000, "JohnD" wrote:

Does anyone know whether there's any sort of standard rule for defining
whether the wind is veering or backing? Definitions for pressure trends seem
quite well established, steady, rising, rising rapidly etc). But are there
any equivalent rules for direction?

Presumably one needs to compare the current eg 2-min or 10-min mean
direction with the equivalent value eg 30 or 60 minutes ago. But are there
rules for the time period to use, and when steady becomes backing/veering
and then the threshold for 'rapidly'?

Time doesn't really come into it. What matters is that the wind is changing
direction with time. If the wind is changing direction in a clockwise direction
(when viewed from above) it is veering. If it is changing direction in an
ant-clockwise direction it is backing. These changes may take place at a point
over many hours due to the gradual movement of broadscale pressure systems. At
the other end of the spectrum they may take place almost instantaneously on the
pasaage of a front, for example. Terms like 'gradually backing' or 'a sharp veer
on the front' are appropriate to use.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
http://peakdistrictweather.org