| In January | 11 |
| „ February | 11 |
| „ March | 13 |
| „ April | 13 |
| „ May | 20 |
| „ June | 20 |
| „ July | 21 |
| „ August | 19 |
| „ September | 22 |
| „ October | 14 |
| „ November | 9 |
| „ December | 9 |
Therefore one can count that two-thirds of all the days from May to September have rain or snow-falls. In the winter time, on the other hand, only one-third of the days have downpours.
Fog—the flyer’s worst enemy—also collects during the summer half of the year. Foggy days on an average were:
| In January | 0 |
| „ February | 0 |
| „ March | 2 |
| „ April | 1 |
| „ May | 2 |
| „ June | 10 |
| „ July | 20 |
| „ August | 16 |
| „ September | 10 |
| „ October | 4 |
| „ November | 1 |
| „ December | 0 |
One is therefore pretty sure to be without fog until May, but from June to September it is general. First, in October the fog begins to get less and then disappears altogether in the middle of winter.
It appears quite clearly from the “Fram” observations that only the dark period of the year has somewhat stable weather conditions, with a clear sky. During the light period of the year the weather is gray and thick.
These conditions are as unfavorable as possible for all flying expeditions towards the Pole. The good weather during the winter—October to March—cannot be taken advantage of on account of the darkness, and it is necessary to be satisfied with the much more unfavorable weather during the lighter period of the year.
Luckily there is, however, an intermediate condition of weather, when the light is still there, but the summer’s gray weather has not yet set in properly. April with its eight clear weather days, seventeen days without downpours, and only one foggy day ought to offer the best conditions for flying. Only one has to remember that when flying over a longer distance the chances of getting into ugly weather are much greater than one would imagine from the impression given by the figures. In a distance of an extent equaling that from Spitzbergen to the Pole, during a good month such as April, one will in most cases have to pass through a bad and good weather-zone. In April, too, one has to reckon with severe cold. “Fram” had a temperature as low as -38° 4 c. in the month of April and even at the end of that month it can go down to -29° c. If it is, therefore, one’s intention to fly on a day of good weather, it is necessary to be well protected against the severe cold.
In 1925 the polar flight could not be undertaken as early as April. Notwithstanding the fact that the journey from Norway was undertaken before the real opening of the shipping season, and that the preparations in King’s Bay proceeded quickly and according to program, our machines were not ready to start until the beginning of May. An earlier start might well have been possible if the previous winter had been spent in Spitzbergen.
It was the business of the meteorologists to determine which was the best day in the month of May for the start. With “Fram’s” experiences before us the prospects of finding a good starting day were not very rosy. In May, 1896, when “Fram” was about halfway between Spitzbergen and the Pole, there were twenty-five days with rainfall, and only three days at the beginning of the month had clear weather. Should May, 1925, turn out just as bad as May, 1896, the polar flight would take place under very risky meteorological conditions.