In the first days of October, 2013 Rossby wavers of the jetstream showed an omega pattern over Europe, a crest with a high pressure system in between two troughswith low pressure vortices. This configuration is very stable and only slowly moving eastwards as a whole wave packet. So the fair weather in the range of crest – golden October in Central Europe – as well as the cloudy and rainy weather in the range of both troughs are persisting for a longer time.
Weather situation October, 3th 2013, 10.00 UTC. Infrared picture. Source: EUMETSAT
Weather situation on October 3th, 2013, 18:00 UTC. Omega has moved a little eastwards. Source: EUMETSAT
Weather situation on October 4th, 2013, 06.00 UTC. Omega has moved a little again. Germany previous days sunny and cloudless now becomes cloudy more and more. Source: EUMETSAT
The jetstream is a strong wind in upper troposphere encircling the whole planet. It is driven by mid-latitude differences in temperatures between cold polar air and warm (sub)tropical air. In jetstream Rossby waves are forming and propagating eastwards. Low pressure systems are located inside wave troughs whereas high pressure systems are located inside wave crests. Both weather systems arise from turbulences in jetstream like white water rapids in a river do.
Jetstream is birthplace of high and low pressure systems and determines their pathways. So jetstream is making the actual weather in all the regions in the range of it’s influence.
Jens Christian Heuer