Don't bank on natural snow in Bansko at Christmas and New Year: at mid-mountain, 1,800 m, there was enough of it for the holidays in only just over one winter in three across 1984/85–2013/14, and even less often towards the end of the period. The last six winters of the series, from 2008/09 to 2013/14, all passed without enough natural snow at Christmas. Holiday skiing in the Pirin relies on two things: the highest runs and snowmaking, with which all 30 Christmases out of 30 come out snowy. For snow at Christmas Bansko beats half of Bulgaria's resorts (50%), but only 23% of the 690 resorts in Europe on the site, and it trails Borovets in the Rila, which manages 16 of 30 at 1,900 m. These figures describe the climate of 30 winters and the models' climate scenarios, not a forecast or a report for the current week; the resort publishes the latest snow depth itself.
Over the holidays the snow holds up high
Bansko's runs on OpenStreetMap descend from 2,516 m to 993 m (34 km, 19 lifts), and the difference in snow is huge. On the highest run, 28 of the 30 Christmases across 1984/85–2013/14 were snowy, with 173 days with at least 30 cm per season. Down at the bottom, 993 m, where the ski road reaches town, just 1 Christmas out of 30 was snowy, and snow of 30 cm or more added up to 6 days a season. Without the guns, skiing down to the bottom over the holidays is nearly impossible, so plan your holiday skiing up top; if the run isn't under snowmaking, take the lift back down.
The two halves of the period show where things are heading: in 1984/85–1998/99, 6 of 15 Christmases were snowy; in 1999/2000–2013/14, 5 of 15; and days with at least 30 cm per season fell to 87 from 98. In total, 19 of 30 Christmases passed without enough natural snow. The EURO-CORDEX models, compared only against their own model reference 1986–2005, give 4.4 Christmas days out of 14 with natural snow of at least 30 cm in that reference, dropping to 2.5 days by 2041–2060 under medium emissions (RCP4.5) and 1.1 under high (RCP8.5). With snowmaking the holidays stay almost entirely snowy, 12.5 and 12.2 days out of 14, but the natural-snow season shrinks to 54 and 39 days against 85 in the reference (methodology).
The best month for skiing in Bansko
In a typical winter of 1984/85–2013/14, continuous natural snow cover of 30 cm or more established itself by 6 January and lasted until 12 April; that happened in 29 of 30 winters. So the best weeks for Bansko run from mid-January into March, and February is the most snow-sure of them: it sits entirely inside the season. With snowmaking the runs are ready from 9 December to 3 May; mid-mountain picks up 92 days with at least 30 cm per season (149 with snowmaking) and 140 days with at least 5 cm. If snow at Christmas is what matters most to you, Borovets or the high resorts from the overall list for Europe are better bets; if your dates are flexible, Bansko in February delivers proper natural snow from the top right down to mid-mountain.