Poles go to the polls this weekend and the two candidates for the presidency are literally neck and neck ,with less than a point between them. The outcome is far too close to call so that tiny random factors could play a decisive role – even the weather.

The latest weather forecast for Sunday, June 1, is not good. It indicates mostly unsettled conditions, with a higher likelihood of rain and thunderstorms, particularly in the south and east, according to the Institute of Meteorology and Water Management (IMGW) and other regional meteorological services.

Western and northern Poland (including Poznań and Gdańsk) expect partly cloudy to overcast skies, with scattered showers, but also some dry intervals during the day. In the central regions (including Warsaw) the forecasts suggest cloudy weather with possible rain showers, especially in the afternoon.

But in the southern and eastern regions (including Kraków and Lublin) the outlook is for rain, and even locally intense thunderstorms, in the late afternoon and evening.

That is bad news for the radical populist right-winger Karol Nawrocki and good news for his opponent, the liberal Mayor of Warsaw Rafał Trzaskowski.

The last Ipsos poll before the vote by state broadcaster TVP  showed Trzaskowski leading Nawrocki  48% to 47%. The outcome now largely hinges on the almost 40% of voters who supported other candidates in the first round,  and especially the 5% of the population that remain undecided, according to Ipsos. One per cent of the Polish electorate is 295,000, but the race is so close that the result could be decided by a few tens of thousands of people.

As a bne IntelliNews drill down into the first-round voting patterns showed, supporters of the two candidates are sharply divided along geographic lines (map) with most of Nawrocki’s supporters living in the east and southeast of the country in smaller settlements – where it is expected to rain the most this weekend. Trzaskowski has more support from well educated people and women living in cities in the north and west of the country.

And the thunderstorm warning by the Institute of Meteorology and Water Management is currently at level 1 (on a scale of 1-3) for exactly the regions where Nawrocki has the bulk of his supporters, except in a block in the centre of the country. (map)

If the rain in the southeast is heavy this weekend and those thunderstorms appear, that may persuade enough Nawrocki supporters to stay home and tip the balance of voting in Trzaskowski’s favour.