Good question. The year is 576 CY, so well before the Greyhawk Wars. All the information in the original Greyhawk folio is current. Let's set the starting month as Planting (the Oerth equivalent of April) for reference. The weather in the Bandit Kingdoms is fairly treacherous year round. It's dry, hot and sunny most of the time. Winters can be harsh and cold with little precipitation, but the occasional blizzard that does blow through is violent and merciless. Planting is probably one of the relatively nicest times of the year.