It almost never rains in the Netherlands
At hetregentbijnanooit.nl (it almost never rains dot nl) avid cyclist Gerard Poels from Grave near Nijmegen keeps track of how many of his bicycle commutes get rained on.
In the past five years it rained during an average of 9.4% of Poels’ rides, each of which took 40 minutes each way. Poels counts every little shower even if it rains for just a few minutes. He claims it happens only 4 or 5 times each year that it rains during the entire ride. During those five years Poels rode his bike to and from work 1,482 times.
Poels set up his site to counter the excuse “I am not going to take the bike to work because it always rains [in the Netherlands]”.
Eamelje.net points out that Peter Siegmund of the Dutch meteorological office (KNMI) calculated the probability that you will get wet if you stay outdoors (PDF). If you stay outdoors for an hour in the Netherlands, there is a 12% chance that you will get rained on. If you stay out for four hours, that probability increases to about 25%, and you will have to stay out for at least a fortnight to be absolutely sure to get wet. Siegmund adds that fans of camping are most likely to stay dry in June. Even then the probability of rain during a single week is still 91%.