Tahran hava durumu: ay ay

Tehran forum threads describe January as genuinely cold, typically hovering somewhere between -1 and 5C with real possibility of rain or snow, and posters comparing it to a winter in Denver, Colorado - cold, but not as harsh as a European winter further north. A recurring theme across threads: the Alborz mountains ringing the city to the north trap traffic smog in the valley, and posters flagged December and January as when that smog problem is worst. The consistent travel tip was that while Tehran itself runs cold this time of year, heading south to cities like Shiraz delivers noticeably milder weather within the same trip, making a north-to-south winter itinerary a common recommendation.

March here is dominated by Nowruz, which starts about the 21st and empties this city while filling every road, train and hotel in the country. Regulars are specific: book transport a month ahead, expect closures in the first days, and if you can, shift your visit to the second week of the holiday when things reopen and the crowds thin. The weather is still winter's end - 17.3C by day reading as 16C, 7.2C nights that feel like 4C, and 9.7cm in our snow column, most of which belongs to the mountain edge of the city rather than the south. Rain is 57.7mm across 9.9 days. The record: humidity 58 percent, 9.9 hours of sun and AQI 78.

Asked about late April, posters answer "high 20s to low 30s I expect. Won't be cold for sure," and advise skipping a jacket — "the weather by the time you arrive will be pretty mild and warm, just bring a sweatshirt in case it rains." Read that with one caveat the thread doesn't make: the question spanned Shiraz, Yazd, Isfahan and Kashan, and nobody separated the cities. Tehran sits higher and further north than all of them, and our record puts its April at 21.2°C days and 8.4°C nights — mild by day, genuinely cool after dark, so the sweatshirt is doing more work here than the thread implies. Only 7 rain days and 11.4 hours of sun. The non-weather constraint travellers raise for April is beds: hotels book out, so reserve early.

Iran-forum threads on May weather (a woman traveler specifically asking if it runs too hot) land on warm, not brutal: high 20s Celsius by day, breathable cotton and light layers doing the job, with a scarf as a headcover rather than heavy fabric. The recurring practical note for anyone: pack a light layer for air-conditioned buses and cooler evenings even on a hot day, plus sunglasses and sunscreen for the strong daytime sun. Some rain is possible but described as light and occasional, not a planning concern. The record: 29.3C days feeling like 28C, 18.1C nights, just 21mm of rain across 5.4 days, 12.3 hours of sun and humidity a dry 37 percent - properly warm, properly dry, comfortable in the shade.

September opens the autumn half of the year travellers here recommend, running to November, and the phrase used for Tehran is hot but not humid. Our columns make that concrete in a way a board cannot: 26 percent humidity and a dew point of 1.9C under a 31.9C afternoon, which is why the feels-like comes in at 30C rather than above the reading. Nights fall to 21.4C. Rain is essentially absent, 5.4mm on a single day. The month starts with the first autumn winds, and the south of the country stays hot well after the capital has turned - so a September itinerary that runs from here to Yazd or Kerman is travelling back into summer. The record: 11.1 hours of sun and AQI 70.

Iran's forum rates October as the second-best travel window after spring — mild, comfortable temperatures with the summer heat gone, and noticeably fewer tourists than peak season. Regulars' one consistent note: Tehran itself runs a bit cooler than the cities further south, so a light jacket is worth having even midday.

Regulars are consistent this counts as one of the better months to be in the city specifically, mild and pleasant by day even as the far cooler, wetter north of the country deals with near-daily autumn rain by this point. Our row backs that mild, dry-for-autumn read, 15.8C over 7.9C nights feeling 5C, with just 30.3mm of rain across 6.2 days and a first trace of mountain snow, 5.3cm, visible on the peaks ringing the city rather than falling downtown. Regulars are specific that evenings turn genuinely chilly once the sun goes down, so a real jacket matters even though daytime layers can stay light. This remains within the broader autumn window regulars call the best overall stretch for pairing Tehran with Isfahan, Shiraz and Yazd. The record: humidity 55 percent, 8.6 hours of sun, a 7.8 kph wind and AQI 93.