Altitude and Its Effects on Weather

Most of Thailand is hot and humid all year, but the high mountains of the north and north-east are much cooler. On a cool-season morning, the summit of Doi Inthanon can be close to freezing, while the average January low in Bangkok is 23.4 °C. Knowing how height changes the weather helps you pack the right clothes and choose the right month.

Climate figures in this article are 1991–2020 averages from Thai Meteorological Department (TMD) stations. They describe a typical year, not a forecast.

Why higher places are cooler

Air gets thinner and cooler as you go up a mountain, so the higher you are, the colder it usually is. The difference is small on a low hill but large on Thailand's highest peaks, especially in the early morning during the cool season.

Doi Inthanon in Chiang Mai province shows this clearly. On 27 November 2025, the national park reported these temperatures at different points on the mountain:

It was the fourth morning in a row with hoar frost on the mountain, and the park warned that the summit road could be slippery with frost. For comparison, the average daily low in Chiang Mai city in November is 19.9 °C.

The cities stay much warmer. Bangkok's lowest recorded temperature is 9.9 °C, and Chiang Mai city's is 3.7 °C. Thailand's official record low, −1.4 °C, was measured at Sakon Nakhon on 2 January 1974.

Thailand's cool highlands

Park fees and opening periods below were checked in September 2026. They can change, so confirm them with the park before you go.

Doi Inthanon National Park

Doi Inthanon is about 100 km from Chiang Mai city; the main entrance is about 70 km south-west of the city. Entry costs 300 THB for a foreign adult and 150 THB for a child aged 3 to 14.

• Kew Mae Pan nature trail: closed from June to October every year, reopening on 1 November. A local guide is required, at 220 THB per group of up to 10 people.
• In the rainy season: the summit, the chedis and the waterfalls stay open while the trail is closed.

Phu Kradueng and Phu Ruea (Loei)

Phu Kradueng is a mountain with a plateau on top; its highest point is 1,316 m. The main trail climbs to the rim and continues to the plateau office, a total of 8.7 km. An averagely fit walker takes under 5 hours.

• Entry: 200 THB for a foreign adult, 100 THB for a child.
• Closed: from June to September every year.
• Porters: 30 THB per kg if you do not want to carry your bag up the trail.
• Camping: tent hire costs from 150 THB (2 people) to 400 THB (4 people), plus 60 THB per person for bedding. Bring warm layers for the night.

Phu Ruea National Park, also in Loei, rises to 1,365 m, and frost is possible during cold snaps. Entry for foreign visitors is 200 THB.

Phu Chi Fa

Phu Chi Fa, a forest park in Chiang Rai province, reaches 1,628 m. It is known for its "sea of mist", when the valleys below the viewpoint fill with mist. The season runs from October to February, and the best months are December and January.

Lowlands and coasts: the monsoon matters more

At sea level, height matters less than the monsoon. Bangkok, Pattaya and the islands stay warm all year, and the main difference between months is the rain.

• The Andaman coast (Phuket): the most rain falls from August to October; December to March is the drier period.
• The Gulf coast of the south (Koh Samui): the pattern is almost the opposite. The wettest period is October to December, and TMD expects the 2026 rains on this coast to continue until December.
• Pattaya: drier than Bangkok, with about 1,106 mm of rain a year and the most in October.

When to go up: season by season

Cool season (mid-October to mid-February)

This is the most comfortable time for the highlands. In Chiang Mai city, the average daily low falls to 15.7 °C in January, while the average high is still 30.0 °C, so you need both light clothes and a warm layer. On the high peaks, December and January mornings can bring frost.

Hot season (mid-February to mid-May)

Across Thailand, typical hot-season highs are 35–39 °C, and the hottest days go above 40 °C. Chiang Mai city averages 36.7 °C in April. March and April are also smoke season in the north: on 4 April 2026, Chiang Mai, Lamphun and Phayao provinces were declared disaster zones for air pollution. Check PM2.5 on the free Air4Thai or IQAir AirVisual apps before you plan outdoor days.

Rainy season (mid-May to mid-October)

In 2026, TMD declared the rainy season open on 15 May and expected the rains in upper Thailand to end around mid-October. August is Chiang Mai's wettest month (223.3 mm). Some mountain parks and trails close for part of this season (see the checklist below). Plan sightseeing for the morning and keep the afternoon flexible.

What to pack for each height

High mountains (Doi Inthanon, Phu Kradueng, Phu Ruea, Phu Chi Fa):

• A warm jacket, long trousers and closed shoes for December and January
• A hat and gloves for sunrise viewpoints
• A rain jacket and shoes with a good grip in the rainy season

Beaches and lowlands:

• Light, breathable clothes and sandals
• A hat, sunglasses and sunscreen without oxybenzone: it is banned in marine national parks, with fines of up to 100,000 THB
• A light layer for air-conditioned malls, buses and trains
• A dry bag for your phone and passport on boats and in rainy months

Before you go: a weather checklist

• Check the 7-day forecast, rain radar and heavy-rain warnings on the Thai Meteorological Department website or in TMD's free "Thai Weather" app, which has an English version.
• Check park closures before you book: Phu Kradueng closes from June to September, and the Kew Mae Pan trail from June to October.
• On cool-season mornings, allow extra time on mountain roads: frost can make the Doi Inthanon summit road slippery.

Getting to the mountains

A private car lets you leave early for a sunrise viewpoint and stop where you like on the way. Smile Taxi Service fares are fixed, per vehicle (not per person) and one way, with expressway tolls included.

• Book a sedan from Suvarnabhumi Airport to Chiang Mai.
• Book a sedan from Chiang Mai to Chiang Rai. Phu Chi Fa is in Chiang Rai province.
• For a day in the mountains from Chiang Mai, ask about the Chiang Mai + Doi Tour: a private tour of up to 10 hours for 3,300 THB (sedan), 3,500 THB (SUV), 4,000 THB (van) or 4,500 THB (VIP van). See all tours and day trips.
• For Phu Kradueng or Phu Ruea in Loei, there is no fixed fare. Message us on WhatsApp or LINE for a quote.

Sedans take up to 3 passengers, SUVs up to 5 and vans up to 7. You pay the driver in cash (THB) at the end of the trip; if you can only pay by card, message us for a PayPal payment link (a 5% fee is added). Cancellation is free up to 24 hours before pickup. After that, a cancellation or change costs 25% (less than 24 h), 35% (less than 12 h) or 50% (less than 2 h) of the price, and a no-show 100%, also when you pay the driver in cash (details). See all routes and prices, or read our guides on getting from Bangkok to Chiang Mai and from Bangkok to Chiang Rai.

Useful Thai weather words

Weather and emergency numbers

FAQ

How cold is the top of Doi Inthanon?

It can be near or below freezing at dawn in the cool season. On 27 November 2025, the summit was 2 °C, with −2.3 °C at the coldest point.

Can I hike Phu Kradueng in the rainy season?

Not for most of it. The park is closed from June to September every year. Entry is 200 THB for a foreign adult.

What does Doi Inthanon cost to enter?

300 THB for a foreign adult and 150 THB for a child aged 3 to 14.

Where is the coldest place in Thailand?

High peaks such as Doi Inthanon (2,565 m) get frost in cold spells. The national record low is −1.4 °C, measured at Sakon Nakhon in 1974.

Do I need warm clothes for Thailand?

Only for the north and the mountains, from about November to February. The average low in Chiang Mai city in January is 15.7 °C, and mountain summits can drop below 0 °C.

Planning a trip to the mountains? Message us on WhatsApp or LINE, or book your transfer online.

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