Map from Google - Mongolia

In Mongolia the climate is strongly continental, with long and frigid winters, and short and warm summers: the temperature range between winter and summer is definitely wide.
Precipitation is scarce, and is concentrated in summer, when the country is partly affected by the Asian monsoon; in winter, when a thermal high pressure system dominates, sky is often clear. Precipitation is more abundant in the north, where it exceeds 300 millimetres (12 inches) per year, while in the south, which is desert, it drops below 200 mm (8 in) per year. During winter, snowfalls are frequent but usually light, so that they create a thin white veil, which can be carried away by the wind; sometimes a light snow can fall even when the sky is clear: when temperatures are very cold, moisture can condense directly.
Much of Mongolia is occupied by a plateau at an altitude between 1,000 and 1,500 metres (3,300 and 4,900 feet), which tempers the summer temperatures. In the plateau, strong winds can blow, especially in spring. Due to the aridity of the climate, these winds can bring dust storms, which are more frequent in the south (where they occur more than 30 days per year), quite frequent in the centre (15 to 30 days per year) and very rare in the north (even less than 10 days). In winter, the wind brought by outbreaks of cold air masses, can amplify the feeling of cold and lead to rapid frostbite to those who are not properly covered: for example, with a temperature of -20 °C (-4 °F), which is normal in Mongolia during the cold months, a wind of 72 kph (45 mph) generates a wind chill (equivalent temperature) of -35 °C (-31 °F), and therefore the risk of freezing. When the temperature plunges below -30 °C (-22 °F), in case of prolonged exposure there's a risk of freezing even in the absence of wind.
The climate in Mongolia is unstable, so from year to year there may be significant variations in temperature and precipitation.

Steppe in Mongolia

The amount of sunshine in Mongolia is good throughout the year, because clear skies are frequent, and it reaches a maximum in spring; in summer the number of cloudy days increases a bit, because of the aforementioned summer Asian monsoon.
The average temperature in January goes from -32 °C (-26 °F) in the coldest areas of the north, to -15 °C (5 °F) in the south. The temperature does not necessarily decrease with altitude, on the contrary, for the phenomenon called temperature inversion, it may even increase with altitude: the coldest areas of the country are the valleys between the mountains of the north. On the contrary, in summer the temperature rises proceeding from north to south and going down in altitude: at 1,500 metres (5,000 feet) above sea level, the daily average in July is around 13 °C (55.5 °F) in the far north, 15 °C (59 °F) in the centre-north and 20 °C (68 °F) in the south, while at 1,000 metres (3,300 feet), it goes from 16 °C (61 °F) in the north to 23 °C (73 °F) in the south. So, only at the lowest altitudes and in the south, the summer can be considered hot. The areas located at the lowest altitudes, around a thousand metres or less, are not very large; so in most of Mongolia the summer has generally cool nights (sometimes even cold) and pleasant days, even though in the whole country, heat waves with peaks of 35/37 °C (95/99 °F) are possible, at least below 1,500 metres (5,000 feet).
The northern part of Mongolia lies in the permafrost area (the southern limit is more or less at the latitude of the capital), in which the ground below a certain depth remains frozen throughout the year, and makes it difficult to build houses and infrastructures, and to dig for extraction of raw materials.

In addition to the plateau, in Mongolia there are mountain ranges: in the west the Altay Mountains, whose highest point is Hüiten Peak, 4,374 metres (14,350 feet) high, in the west-central the Khangai Mountains, which reach 4,000 metres (13,000 ft), and north of the capital the Khentii Mountains, which reach 2,800 metres (9,200 ft). The mountainous areas are those that receive the most abundant rainfall, and they are practically the only ones where you can find forests. Above 3,500 metres (11,500 ft), there are glaciers and snowfields, while at lower altitudes, above 2,000 metres (6,500 feet), sometimes it can snow even in summer.
The Gobi Desert is located in the south, and although it is drier than the north, it receives some rain showers in summer, able to feed some grass and the camels, at least in the eastern part, where 150 to 200 mm (6 to 8 in) of rain per year fall. The most arid area is the south-west, where precipitation drops below 100 mm (4 in) per year, and in some cases below 50 mm (2 in).
Here is the average precipitation of Sainshand, located in the south-east, at 950 metres (3,100 ft) above sea level.
Average precipitation - Sainshand
SainshandJanFebMarAprMayJunJulAugSepOctNovDecYear
SainshandJFMAMJJASONDY
Prec. (mm)1123815303010521111
Prec.(in)000.10.10.30.61.21.20.40.20.104.4
Days00012354211020

In summer, temperatures in this area are high, as we can see from the averages of Sainshand.
Average temperatures - Sainshand
SainshandJanFebMarAprMayJunJulAugSepOctNovDec
SainshandJFMAMJJASOND
Min (°C)-23-20-11-171417158-1-12-20
Max (°C)-12-7314232829282112-1-10
Min (°F)-9-4123045576359463010-4
Max (°F)101937577382848270543014

The main lakes of Mongolia are: Khar-Us, located in the west at 1,150 metres (3,800 feet) above sea level, in a desert area; Uvs in the northwest at 760 metres (2,500 feet), also in a desert area, where the average temperature in July is around 19 °C (66 °F); and finally Khövsgöl, which is located at 1,650 metres (5,400 feet) in the north, in an greener area, and given the high altitude and its size (which makes it able to create a local microclimate), on its banks it's very cool or cold even in summer.

The capital Ulaanbaatar (Ulan Bator) is located in the north, at 1,300 metres (4,250 feet) above sea level, and is relatively rainy, not only for the northern position, but also for its proximity to the mountains (the aforementioned Khentii in the north, and a single mountain, Bogd Khan, in the south), so that it receives about 300 mm (12 in) of rain or snow per year. During winter it's the coldest capital in the world, having a January average of -20 °C (-4 °F). The minimum temperature at night drops easily below -35 °C (-31 °F); on January 2012 it dropped for a consecutive week below -40 °C (-40 °F), with a peak of -44 °C (-47 °F), while in January 2001 it reached -45 °C (-49 °F). The daily average is around 0 °C (32 °F) in April and October. In May and September, lows are around freezing (0 °C or 32 °F), and highs around 15 °C (59 °F), but given the climatic variability, sometimes there can be intense frosts even in these months. During winter, snowfalls occur frequently, but they are light. The sky is often clear, although in the coldest hours, mists may form. Summer is pleasant: highs in July and August are about 22 °C (72 °F), with very cool nights, around 10 °C (50 °F). Occasionally, it can get cold even in summer, while during the day it can get hot: the temperature rarely exceeds 32/33 °C (90/91 °F), but sometimes it can reach 37/38 °C (99/100 °F).
Here are the average temperatures.
Average temperatures - Ulaanbaatar
UlaanbaatarJanFebMarAprMayJunJulAugSepOctNovDec
UlaanbaatarJFMAMJJASOND
Min (°C)-25-22-14-5281082-5-14-22
Max (°C)-14-9-1917212219148-3-12
Min (°F)-13-87233646504636237-8
Max (°F)71630486370726657462710

Summer is also the rainiest season: from June to August, more than 50 mm (2 in) of rain per month fall, usually in the form of showers in the afternoon. Here is the average precipitation.
Average precipitation - Ulaanbaatar
UlaanbaatarJanFebMarAprMayJunJulAugSepOctNovDecYear
UlaanbaatarJFMAMJJASONDY
Prec. (mm)22381550657530853270
Prec.(in)0.10.10.10.30.622.631.20.30.20.110.6
Days01123101114521251

Ulaanbaatar

At higher altitudes, the summer temperatures become cooler, as we can see from the averages of Altay, a city located in the west, at 2,200 metres (7,200 ft) above sea level.
Average temperatures - Altay
AltayJanFebMarAprMayJunJulAugSepOctNovDec
AltayJFMAMJJASOND
Min (°C)-25-23-15-706861-7-16-21
Max (°C)-13-9-1512181818133-3-8
Min (°F)-13-95193243464334193-6
Max (°F)91630415464646455372718


When to go

The best time to visit Mongolia is the summer, from June to August, when the temperature, at least in the plateau and the mountains at low altitude, remains above freezing even at night. Summer is certainly the rainiest period of the year, and during the day it can be hot especially in centre and south and at lower altitudes, but at least you avoid the bitter cold. However, in summer it can also get cold at night, so you have to be ready to cover and uncover, depending on hour and weather conditions, in addition it is advisable to bring a scarf, for wind and dust protection.

What to pack

In the winter: clothing for the big cold, synthetic thermal long underwear, fleece, parka, wind jacket, hat, gloves, warm boots.
In the summer: spring/autumn clothes, T-shirts for hot days, long jacket for the wind, sweater or sweatshirt for the evening and high altitudes, raincoat or umbrella, scarf for the wind-borne dust, hiking shoes, sunscreen, sunglasses. For high mountains, down jacket, hat, gloves, scarf. For overnight stays outdoors, sleeping bag, warm jacket.