Snow

Snow was a form of precipitation; similar to rain, though when the atmospheric temperature was below the freezing point of water, the result was snow. Other than Earth, snow was known to fall on other planets, including Gallifrey, Sto, Ood Sphere and Ribos (during its Icetime season). The Doctor was known to be fond of snow, commenting with glee when he arrived on Ood Sphere "snow, real snow.". (DW: Gridlock, Voyage of the Damned, The Ribos Operation, Planet of the Ood)

Whilst on Earth in many differing time periods the Doctor found himself present during or following it snowing;
 * Upon arriving alone in 1851, London; at Christmas, the Tenth Doctor was very pleased with actual snow. (DW: The Next Doctor)
 * When the Ninth Doctor and Rose Tyler were in Cardiff in in 1869, it snowed prior their arrival and following their departure. (DW: The Unquiet Dead)
 * In 1898 when the Eighth Doctor and Fitz Kreiner were thrust into events at Banquo Manor it and its grounds were covered in snow (EDA: The Banquo Legacy)
 * In 2059, Tenth Doctor was happy to see snow on Earth after bringing the remaining crew of Bowie Base One back from Mars. (DW: The Waters of Mars)

Fake snow
In his tenth incarnation the Doctor, encountered many instances of snow that wasn't snow at all;
 * During Christmas Day, 2006 the "snow" falling on London was in fact ashes from the remnants of the Sycorax space ship that was destroyed by the Torchwood Institute, on Harriet Jones' order. (DW: The Christmas Invasion)
 * During Christmas, 2007 the tenth incarnation of the Doctor used his TARDIS to excite the atmospheric conditions around London to create snow. (DW: The Runaway Bride)
 * On Christmas Day, 2008 the ballast from the spaceship Titanic went through the atmosphere, where reentry resulted in another instance of falling ash that resembled snow. (DW: Voyage of the Damned)

Behind the scenes

 * One of the deleted scenes for The Waters of Mars showed the Doctor expressing his love for snow and Yuri Kerenski telling the him that it's the Carbon Wash cleaning the atmosphere and questioning him because he doesn't know this fact. Whether this fact is still supposed to be seen as part of the episode is unclear and it is also unclear as to whether this is still real snow with a new scientific name or a process which is unknown.

Other appearances

 * DW: Marco Polo
 * DW: The Keys of Marinus
 * DW: The Tenth Planet
 * DW: The Ice Warriors
 * DW: The Seeds of Doom
 * DW: The Ribos Operation
 * DW: The Unquiet Dead
 * BFA: The Magic Mousetrap
 * DWM: A Cold Day in Hell!
 * EDA: The Infinity Doctors
 * MA: Cold Fusion
 * NA: Timewyrm: Revelation
 * PDA: The Wages of Sin
 * PDA: Drift
 * NSA: The Krillitane Storm
 * TN: Time and Relative
 * TVC: A Christmas Story
 * K9TV: Angel of the North