Met office surface pressure chart

[Phil Burgess]

Have a look at a met office surface pressure chart like this one: http://www.metoffice.gov.uk/weather/eur ... ssure.html

Can anyone tell me what the feint red dashed lines with numbers on them signify?

[Noel Howard]

I think the very faint lines are longitude and latitude lines.

The dotted lines are defined in the Key as follows:

Thickness lines
Pressure decreases with altitude, and thickness measures the difference in height between two standard pressure levels in the atmosphere. It is proportional to the mean temperature of this layer of air, so is a useful way of describing the temperature of an airmass.
Weather charts commonly show contour lines of 1,000-500 hPa thickness, which represent the depth (in decametres, where 1 dam = 10 m) of the layer between the 1,000 hPa and 500 hPa pressure levels. Cold, polar air has low thickness, and values of 528 dam or less frequently bring snow to the UK. Conversely, warm, tropical air has high thickness, and values in excess of 564 dam across the UK often indicate a heatwave.


Noel

[Phil Burgess]

Thanks Noel, I'll sleep better now!