Weather charts: troughs

[Mak]

Hello all,

Some weather charts such the ones in http://ows.public.sembach.af.mil/wxcharts/wxcharts.htm show, in addition to the usual fronts and isobars, also "troughs". These seem to be positioned more or less perpendicular to the isobars.

Can you explain me what the significance of these troughs is?

Cheers.

Mak

[Mark 1]

Troughs can display a lot of the characteristics of a front (rain, low cloud etc), without there being a defined change of air mass.

[High Wing Drifter]

Hi Mak,

As Mark more succinctly says, they mean bad weather. My understanding is that the trough is a line of depression, which is basically convective air. Without the lines they can be seen in the isobars by a sudden sharp deviation left (as they are in a low pressure system). Expect cloud, turbulence and marked change of wind direction, very possibly to the extent of windshear.

The height of the cloud base depends on the OAT and Wet Bulb temp. I think the calc is something like Cloud Base = (OAT- WetBulbTemp)/1.2*1000.

The opposite is for a high pressure zone and is called the "ridge", with the same appearance on the isobars. Effectively this is subsiding air so clear skies, low viz and an inversion layer with possible windshear at the inversion.

Apologies if I over answered, but its good for me to blow the cobwebs off this stuff everynow and again.