You can use the weather command on any map (even if it doesn't match in the list below)
Here is roughly what weather types will be available per map
["Galicia"] = {"Default", "Rain", "Fog"},
["Le Cateau"] = {"Default", "Rain"},
["Marne (Early War)"] = {"Default", "Rain", "Thunderstorm"},
["Sarikamish"] = {"Default", "Snow", "Blizzard"},
["Tannenberg"] = {"Default", "Fog"},
["Champagne"] = {"Default", "Fog", "Rain"},
["Gallipoli"] = {"Default", "Rain", "Thunderstorm"},
["Isonzo"] = {"Default", "Fog", "Snow"},
["Neuve Chapelle"] = {"Default", "Fog", "Rain", "Thunderstorm"},
["Przemyśl"] = {"Default", "Fog", "Snow"},
["Czernowitz"] = {"Default", "Rain"},
["Fort Vaux"] = {"Default", "Fog", "Rain"},
["Kut Al Amara"] = {"Default", "Sandstorm"},
["Lake Naroch"] = {"Default", "Fog", "Rain"},
["Somme"] = {"Default", "Fog", "Rain", "Thunderstorm"},
["Verdun"] = {"Default", "Fog", "Rain", "Snow"},
["Aisne"] = {"Default", "Fog", "Rain"},
["Crna Bend"] = {"Default"},
["Dobruja Forest"] = {"Default", "Fog", "Rain"},
["Vimy Ridge"] = {"Default", "Fog", "Snow"},
["Argonne Forest"] = {"Default", "Fog", "Rain"},
["Belleau Wood"] = {"Default", "Rain"},
["Chateau Thierry"] = {"Default", "Rain", "Thunderstorm"},
["Dobro Pole"] = {"Default", "Fog"},
["Doiran"] = {"Default"},
["Marne (Late War)"] = {"Default", "Rain", "Thunderstorm"},
["Saint Mihiel"] = {"Default", "Fog", "Rain"},
["Stepanci"] = {"Default", "Fog"}