Munich, where it lies

In Munich, capital of the state of Bavaria, located in south-eastern Germany, 500 metres (1,600 feet) above sea level, the climate is continental, with cold winters, and mild or pleasantly warm summers. Due to its location far from the sea and close to the Alps, the city is exposed to cold waves, so it is often the coldest city in the entire Germany, while in summer it is subject to thunderstorms. The city is also subject to the Föhn, a warm and dry wind that descends from the mountains (the Bavarian Alps in the south, which become clearly visible when this wind blows, because of the clearness of the air), and is capable of causing a rapid increase in temperature and a decrease in relative humidity; this wind is most common in autumn (but it can also blow in winter and spring).
The average temperature of January is 0 °C (32 °F), that of July is 18.5 °C (65.5 °F).
Here are the average temperatures.
Munich - Average temperatures
Min (°C)-3-3148111313951-2
Max (°C)3491419222424191474
Min (°F)272734394652555548413428
Max (°F)373948576672757566574539

Precipitation is quite abundant, close to 1,000 millimetres (40 inches) per year, mainly due to the May-August period, when it exceeds 100 mm (4 in) per month, because of afternoon thunderstorms; for this reason the rainiest season is summer, while the least rainy is winter. In the other seasons the rain often falls in the form of short showers (sometimes even of snow), of drizzle or light snow.
Here is the average precipitation.
Munich - Average precipitation

Winter, from December to February, is cold: the temperature is on average a few degrees above freezing (0 °C or 32 °F) during the day, and a few degrees below at night.
However, different weather situations can occur.
When the westerlies blow, the temperature remains above freezing during the day, and around freezing at night; rain can fall during the day, and maybe light snow in the coldest hours.
When the Föhn blows, the temperature can exceed 10 °C (50 °F), and it can sometimes be mild even at night.
On anticyclonic periods, the weather is cold, the sky is gray and fog can form, and sometimes the temperature remains below freezing even during the day. Fog is more frequent in the northern part of the city.
On the other hand, when the city is reached by cold air masses from Russia, the temperature drops below freezing, for longer or shorter periods, even during the day. Minimum temperatures around -15 °C (5 °F) are not so rare, and in the coldest winters, which in the past were more frequent, they can drop below -20 °C (-4 °F); here are some values recorded in the past: February 1929: -31.5 °C (-24.5 °F), March 1929: -20 °C (-4 °F), February 1940: -24 °C (-11 °F); January 1942: -30 °C (-22 °F); January 1947: -27.5 °C (-17.5 °F); February 1956: -28 °C (-18 °F); January 1985: -27.5 °C (-17.5 °F); February 1986: -23 °C (-9 °F); December 1996: -20 °C (-4 °F); February 2012: -22 °C (-8 °F).
Snowfalls in Munich are frequent, and often occur in the form of sleet or light snow, but sometimes they can be abundant.

Spring, from March to May, is initially cold, then it gradually becomes milder, however, with the possible return of cold weather, and late snowfalls and frosts, still in April. Some cold days, with highs around 10 °C (50 °F) and lows around freezing, can occur also in May, especially in the first half of the month. On sunny days, in April and May the temperature during the day can become mild, or even warm, but the daily temperature range is often considerable, so that nights can remain a bit cold.
Typically, in the second half of May the temperature becomes permanently acceptable, and there can be the first pleasantly warm days, with highs around 25 °C (77 °F) or even above.

Summer, from June to August, is pleasantly warm during the day, though with clear skies nights can be cool, and sometimes even a little cold. Atlantic disturbances may still pass in this season, bringing cool and rainy days, though less frequently than in northern Germany. There can also be some hot and sunny days, in which the temperature can reach 28/32 °C (82/90 °F), however, with some risk of afternoon thunderstorms, sometimes intense and accompanied by hail. More rarely, the temperature can exceed even 35 °C (95 °F).

Autumn, from September to November, is initially pleasant, ie in the first half of September, then it gradually becomes more cold, dull and wet. The first night frosts usually occur in November, but sometimes also in October. During calm nights, fog can form, while the Föhn can bring mild and clear days.
During the Oktoberfest, which is held in the last two weekends of September and the first of October, you can expect minimum temperatures around 5/8 °C (41/46 °F) and maximum temperatures around 15/18 °C (59/64 °F). When the Föhn blows, highs can reach 25 °C (77 °F), while sometimes, especially on early October, it can be colder, with highs about 10 °C (50 °F), hence already with an almost winter-like weather. You can check the weather forecast just before leaving, or you can bring spring/autumn clothes, with some warmer clothes (warm jacket, sweater), for the evening and for colder days.

Munich, Marienplatz

The amount of sunshine in Munich is not high in autumn and winter: the sun rarely shines from November to February, while it goes a bit better in summer: there are on average 7/8 hours of sunshine per day from May to August: for a German city, it's no small thing.
Munich - Sunshine

When to go

The best time to visit Munich runs from mid-May to mid-September, being the mildest of the year. July and August are the warmest months; however, it's better to bring a sweatshirt or sweater, a light jacket and an umbrella, for cool and rainy days, or a raincoat, which can be useful for sudden thunderstorms.