明天，北京局地有小雪，下周有点儿冷

Group 1 - The winter solstice marks the day with the longest night in the Northern Hemisphere, as the sun is nearly directly overhead at the Tropic of Capricorn [1] - The start of the "Nine Cold Days" is officially recognized today, indicating a period of colder weather ahead [1] - Daytime temperatures are expected to reach a high of 4°C with significant wind chill effects due to strong southerly gusts [1] Group 2 - On the afternoon of the 21st, clear skies are forecasted with a maximum temperature of 4°C in plains and 0-3°C in mountainous areas, alongside a minimum relative humidity of 15% [3] - Nighttime temperatures on the 21st are expected to drop to -6°C in plains and -11 to -8°C in mountainous regions, with a maximum relative humidity of 60% [3] - The weather on the 22nd is predicted to transition from cloudy to overcast with light snow in mountainous areas, with daytime highs of 3°C in plains and 0-4°C in mountains [3]