The climate of Denmark is cold in winter and mild in summer; being influenced by the ocean, it's less cold than one might think. In fact, clouds, humidity, rain and wind are predominant. The country is small and flat, so there are little climatic differences between the areas, however, the western coasts and the small islands are windier and more temperate than the mainland and the biggest islands.
Here are the average temperatures of the capital, Copenhagen, which is located in the east, a short distance from Sweden.
Copenhagen - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)-1-114812141411741
Max (°C)3461116192222181384
Min (°F)303034394654575752453934
Max (°F)373943526166727264554639

Precipitation in Denmark is not abundant, but it's frequent and well distributed throughout the year, because Atlantic depressions occur in all seasons. In Copenhagen, 525 mm (20.5 in) of rain (or snow) per year fall.
Here is the average precipitation in Copenhagen.
Copenhagen - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)352535354050505060505045525
Prec.(in)1.411.41.41.62222.4221.820.7
Days151114121112121214141515157

Winter in Denmark is cold, with an average temperature of January and February just above freezing (zero degrees Celsius or 32 degrees Fahrenheit) in Copenhagen. The days are very short (in December the sun sets at three in the afternoon), and temperature fluctuations between day and night are little. In the western coast and in the small islands, winter is a little milder, with minimum temperatures around freezing, but with a lot of wind, especially in the north. Apart from that, temperatures are fairly uniform across the country.
During winter, the amount of sunshine is poor, in fact the sky is often overcast; wind can be intense, and precipitation is quite frequent, although usually not abundant. Anyway, in this season the weather conditions vary greatly depending on the situation. When the westerlies prevail, temperatures can remain a few degrees above freezing even at night, and it rains even in winter. But when the country is reached by eastern currents brought by the Siberian High, the temperature suddenly drops, and may plunge several degrees below freezing, down to about -20 °C (-4 °F) in the worst moments. These cold periods may last for a few days, usually less than in Sweden or Finland.

Spring is initially cold, and remains cool still in May: the maximum temperature in Copenhagen is on average about 11 °C (53 °F) in April and 17 °C (62 °F) in May. However, spring is the relatively least rainy season of the year.

Summer has usually pleasant temperatures: highs in July and August are about 22 °C (72 °F) in Copenhagen and in other major cities, while they are a bit lower, around 20 °C (68 °F) in the western coasts bordering the North Sea. Night temperatures are pretty cool, being around 13/15 °C (55/59 °F). In practice, summer in Denmark is similar to the first half of May in New York.
During summer, every now and then the southern currents can bring some hot days, which usually do not last more than two or three days: the temperature rarely reaches 30 °C (86 °F), and the highest recorded temperatures are about 32 °C (90 °F).

In autumn, the weather is dull and rainy, and at times windy. In November, the sunshine amount is minimal as in winter. In Copenhagen, in September the maximum temperature is already about 18°C (64 °F), and it drops to 13 °C (55 °F) in October and 8 °C (46 °F) in November.

Copenhagen

The sun in Denmark is rarely seen from November to February, while from May to August it shines for about half the time (the days are very long, so the total sunshine is not low).
Copenhagen - Sunshine
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Hours124688885321

The temperature of the Baltic Sea is close to freezing in winter, while in summer it is a bit cold for swimming, reaching 17 °C (63 °F) in July and August.
Copenhagen - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)222510141717151284
Temp (°F)363636415057636359544639

To the west, the temperature of the North Sea is milder than that of the Baltic, being a bit higher in winter, and similar or slightly lower in summer.
Esbjerg - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)6556101316161512107
Temp (°F)434141435055616159545045

When to go



The best time to visit Denmark is the summer, from June to August. Temperatures are mild or warm during the day, while they are cool or even slightly cold at night; the rains are quite frequent, but they are not heavy and generally do not last long. June is cooler, but slightly less rainy than July and August, and it's also the month with the longest days (but they are nonetheless very long throughout summer).
In the first half of September, the temperature is still acceptable, and besides, forests shine with their bright autumn colours.

What to pack



In winter: warm clothes, fleece, down jacket, hat, gloves, scarf, wind jacket, raincoat or umbrella.
In summer: clothes for spring and autumn, being ready to add or remove the outer layer, t-shirt, but also long pants, jacket and sweatshirt; raincoat or umbrella.