<P> During winter in either hemisphere, the lower altitude of the Sun causes the sunlight to hit that hemisphere at an oblique angle . In regions experiencing winter, the same amount of solar radiation is spread out over a larger area . This effect is compounded by the larger distance that the light must travel through the atmosphere, allowing the atmosphere to dissipate more heat . Compared with these effects, the changes in the distance of the earth from the sun are negligible . </P> <P> The manifestation of the meteorological winter (freezing temperatures) in the northerly snow--prone parallels is highly variable depending on elevation, position versus marine winds and the amount of precipitation . A case in point is Canada, a country normally associated with tough winters . Winnipeg on the Great Plains at a relative distance from large bodies of water has a January high of − 11.3 ° C (11.7 ° F) and a low of − 21.4 ° C (− 6.5 ° F). In comparison, Vancouver on the coast with a marine influence from moderating Pacific winds has a January low of 1.4 ° C (34.5 ° F) with days well above freezing at 6.9 ° C (44.4 ° F). Both areas are on the 49th parallel north and in the same western half of the continent . A similar effect, although with less extreme differentials, is found in Europe where in spite of the northerly latitude of the islands, the British Isles has not a single non-mountain weather station with a below - freezing mean temperature . </P> <P> Meteorological Reckoning is the method of measuring the winter season used by meteorologists based on "sensible weather patterns" for record keeping purposes, so the start of meteorological winter varies with latitude . Winter is often defined by meteorologists to be the three calendar months with the lowest average temperatures . This corresponds to the months of December, January and February in the Northern Hemisphere, and June, July and August in the Southern Hemisphere . The coldest average temperatures of the season are typically experienced in January or February in the Northern Hemisphere and in June, July or August in the Southern Hemisphere . Nighttime predominates in the winter season, and in some regions winter has the highest rate of precipitation as well as prolonged dampness because of permanent snow cover or high precipitation rates coupled with low temperatures, precluding evaporation . Blizzards often develop and cause many transportation delays . Diamond dust, also known as ice needles or ice crystals, forms at temperatures approaching − 40 ° F (− 40 ° C) due to air with slightly higher moisture from aloft mixing with colder, surface based air . They are made of simple ice crystals that are hexagonal in shape . The Swedish meteorological institute (SMHI) define winter as when the daily mean temperatures go below 0 ° C (32 ° F) for five consecutive days . According to the SMHI, winter in Scandinavia is more pronounced when Atlantic low--pressure systems take more southerly and northerly routes, leaving the path open for high--pressure systems to come in and cold temperatures to occur . As a result, the coldest January on record in 1987 was also the sunniest in Stockholm . </P> <P> Accumulations of snow and ice are commonly associated with winter in the Northern Hemisphere, due to the large land masses there . In the Southern Hemisphere, the more maritime climate and the relative lack of land south of 40 ° S makes the winters milder; thus, snow and ice are less common in inhabited regions of the Southern Hemisphere . In this region, snow occurs every year in elevated regions such as the Andes, the Great Dividing Range in Australia, and the mountains of New Zealand, and also occurs in the southerly Patagonia region of South America . Snow occurs year - round in Antarctica . </P>

When does winter occur in the northern hemisphere