On Dec 12, 10:52*am, Nick wrote:
Interesting to try and define the diagnostic features of a "cold
westerly" as opposed to the (sadly too common in past 20 years) humid
rPm airmasses with temps barely below that of Tm.

Round here (Southampton) I would say the following:

- A ground frost on all mornings with no frontal activity overnight.
Happened this morning and, most notably, Saturday.
- Clear skies overland with shower activity visible out to see.
Generally stays relatively free of showers here due to on-shore wind,
though the occasional one seems to get through (Bristol Channel/
Cheshire Gap?) rPm, by contrast, tends to be a lot more overcast
generally due to the onshore wind. In the summer the reverse is true:
"cold westerlies" often give quite thundery days, whereas rPm days are
frequently fairly sunny and warm.
- Fresh feel to air.

All evident at the moment.

Nick

That sounds about right; if you use the term "cold westerly type", or
a dynamical cold westerly, instead of the simple use of two words
"cold westerly". Semantics, I know, but it's important - semantics are
especially importantin this newsgroup! A cold westerly in itself does
need two basic elements:

a) it is colder than average;

b) it is a westerly.

We had close to one this morning. *))