Weather conditions in Helsinki in October.
The main factor influencing Finland's climate is the country's geographical position between the 60th and 70th northern parallels in the Eurasian continent's coastal zone, which shows characteristics of both a maritime and a continental climate, depending on the direction of air flow. The mean temperature in Finland is several degrees (as much as 10°C in winter) higher than that of other areas in these latitudes, e.g. Siberia and south Greenland. The temperature is raised by the Baltic Sea, inland waters and, above all, by airflows from the Atlantic, which are warmed by the Gulf Stream.
For more information visit the website of the Finnish Meteorological Institute http://www.ilmatieteenlaitos.fi/en/index.html
On the site http://www.ilmatieteenlaitos.fi/weather/climate_6.html You'll find climatological statistics for the normal period 1971-2000, wchich will give You a rough idea about the climate in Helsinki.
On the site http://www.ilmatieteenlaitos.fi/weather/climate.html is a link if You want to ask for more information about the climate in Finland.