-12'C on April 26th!!!
Though Surgut is almost on the same parallel as Helsinki, weather in Surgut is not very pleasant. First time I was there in December 1994 and -29'C did not seem something strange for me. Moreover air was dry and it was less cold than in Moscow with -10.
But my last trip in April 2004 showed that Surgut is really in Siberia. It was -12'C on April 26th!!! snowdrifts everywhere and not a single evidence of spring ;(
Locals told me that this happens in 20% of time. If winter is relatively warm - spring could start in late May.