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Beijing has a monsoon-influenced continental climate with hot, humid summers and cold, dry winters. The best time to visit is in September and October, during the "Golden Autumn" (金秋). In spring, dust storms from the Gobi Desert can turn the sky yellow and significantly reduce air quality. Masks are advisable during these events. Summer can be oppressively hot and the tourist crowds tend to be the largest as well. Winter is cold and dry, with infrequent, but beautiful, snow. Temperatures can easily fall below −10 °C in winter and or just as readily rise above 35 °C in summer as well.

Beijing forum threads describe January as genuinely cold, with nights dropping to around -10C and daytime highs sometimes reaching a sunny +5C, and posters consistently flagged the dry, almost humidity-free cold as very different from a damp winter elsewhere. It's windy and the occasional light snow does fall, but skies were described as reliably sunny between cold snaps. Since most major sights - the Great Wall, the Forbidden City's courtyards - are outdoors, the standard advice was heavy layering, a proper down jacket, hat and gloves, and building in regular breaks to warm up indoors, with several posters noting fewer crowds and a genuinely different, quieter view of the attractions in winter.

Regulars are reassuring on the sandstorm question specifically: they're rare, don't happen every year, and are more a risk in April than March - and even on the rare day one does roll through, sleeping past nine or ten usually means missing it entirely. Our row backs a dry, sunny-leaning month overall, 16C reading as 12C over a real -4C-feeling low, with just 10.1mm of rain across 2.9 days and a trace of leftover snow, 1cm. Regulars note that on the handful of days it does rain, the air actually clears a bit rather than getting worse - a useful exception to the column's AQI figure of 139, since a rainy March day is one of the better-air days rather than a worse one. The record: humidity 47 percent, 9.7 hours of sun and a 14.7 kph wind.

Beijing forum regulars rate April among the year's best months — “one of the most ideally temperate/moderate months...for most people,” with mid-month readings around 10-20°C, mornings and evenings on the cooler side and afternoons genuinely comfortable. The one real caveat: wind, and with it the chance of a dust or sand storm blowing in from the north — not guaranteed on any given trip, but frequent enough that regulars mention it unprompted. Crowds are lighter than summer, flowers are blooming, and the general packing advice is a sweatshirt rather than a heavy coat. Our record: 21.1°C days, 7.1°C nights, only 2 rain days and an AQI of 122 — mild and dry, though that AQI number is the one thing the “ideal month” framing tends to leave out.

May is one of the two months - October is the other - that Beijing regulars name as the year's best: the muggy summer has not arrived, and they give a range of about 12 to 28C, which our row's 13.3C nights and 29C days match almost exactly. The cautions are seasonal rather than daily. Sandstorms, smog, haze and the occasional burst of real heat are all things May sometimes does, and our row's AQI 127 is the standing version of that. The dates to plan around are the Labour Day holiday, roughly the 1st to the 5th, when regulars say to keep away from the sights altogether; mid to late May is the quieter half, though the end of the month is normally busy. The record: 23.2mm across 4.2 days, humidity 42 percent and 10.8 hours of sun.

Regulars are consistent this is warm but clearly a step below the real peak, July and especially early August, and specifically call this dry-climate heat more manageable than the humid version found further south in China. Our row backs the intense but dry heat, 33.3C reading as a real 33C, over 19.3C nights, with 44.5mm of rain across 6.4 days and humidity down to 47 percent. Regulars are clear rain here, even in the wetter summer months, essentially never means continuous days-long rain the way it might elsewhere - more chance of a shower, never a washout. This month sits inside the wider window, alongside September and October, that regulars call the best overall stretch to visit, avoiding the big domestic holiday crowds. The record: 11.1 hours of sun, a 14.6 kph wind and AQI 122.

September is one of the two months regulars recommend here and the weather half is unarguable: 28.2C days over 15.8C nights, 53.6mm of rain across 5.3 days, and the crowds thinner once schools go back - though the first week of October is a national holiday and should be avoided. On air they say September is not bad compared with winter and that October is better still. Our column only half agrees: 155 this month, the same in October, against 122 in April and June. Winter is certainly worse at 183 in December, but the cleanest air here belongs to spring. They are right that it changes day to day. The record: humidity 64 percent, 9.6 hours of sun and an 11.5 kph wind.

Beijing's October threads make the case for roughly 10 October to early November: mild days near 20°C falling to about 7 overnight, and — the forum's main argument — the city's winter heating has not been switched on yet. Two honest qualifications. The first eight days are National Day "Golden Week", which regulars say to avoid outright for crowds; and towards the end of October farmers outside the city begin burning straw, which pushes the air back down. Air quality here tracks wind and rain far more than season, and October's monthly average is mid-pack rather than the year's cleanest — April and June both score better.