As Bob says, propagation is a fickle thing at the best of times...
As a general rule of thumb though. Sporadic-E is mainly a Sumertime mode and can happen at almost any time of day or night through the summer months.
Autumn often produces some good Tropospheric propagation and, if you have a sea path, then ducting can occur when it's foggy, but not always and sometimes it doesn't need to be foggy where you are.
You might even want to try meteor scatter and possibly use the WSJT software system for transmitting data.
There's a propagation prediction site called 'Hepburns' at http://www.dxinfocentre.com/tropo_eur.html
This is like a 'weather forecast' in that it's only a prediction, it may, or may not, actually happen...
Other useful VHF/UHF propagation sites are http://dl1dbc.net/Meteorscatter/
for meteor scatter
for non-ducting tropospheric propagation
for all sorts of VHF propagation, but especially Field Aligned Irregularity (FAI)
You could try logging into the ON4KST 'chat' system. There is an area for 50/70MHz and you will be able to arrange skeds to try to work people on 4M. The URL to log in is http://www.on4kst.com/