ARCTIC FRONTS.The weather associated
with fronts in the Arctic has much the same cloud
structure as with polar fronts, except that the middle
and high cloud types are generally much lower, and the
precipitation is usually in the form of snow.
Periods of maximum surface wind usually occur
during and just after a frontal passage. This strong wind
flow often creates hazards, such as blowing snow and
turbulence, which make operational flying difficult.
The best flying weather in the Arctic over land
usually occurs in midsummer and midwinter; the worst
(low ceilings and visibility) is during the transitional
characterized by frequent storms and well-defined
frontal passages, but because of the dryness of the air,
cloudiness and precipitation are at a minimum. In the
summer, there are fewer storm passages and fronts are
weaker; however, the increased moisture in the air
results in more widespread clouds and precipitation.
Over the sea areas the summer weather is very foggy,
but winds are of lower speeds than in the winter.
During the transitional periods of spring and fall,
operational flying conditions are usually the worst.
Frontal systems are usually well defined, active, and
turbulent. Icing may extend to high levels.
Temperatures in the Arctic, as one might expect, are
very cold most of the year. But contrary to common
belief, the interior areas of Siberia, northern Canada,
and Alaska have pleasantly warm summers with many
hours of sunshine each day. There are large differences
in temperature between the interior and coastal areas.
temperatures climb to the mid 60s or low 70s and
frequently rise to the high 70s or low 80s, occasionally
even into the 90s. Fort Yukon, Alaska, which is just
north of the Arctic Circle, has recorded an extreme high
temperature of 100°F, while Verkhoyansk in north
central Siberia has recorded 94°F.
During the winter, the interior areas of Siberia,
northern Canada, and Alaska act as a source region for
the cold arctic air that frequently moves southward into
the middle latitudes. The coldest temperatures on
record over the Northern Hemisphere have been
established in Siberia.
In the northern areas of the interior regions,
temperatures are usually well below zero during the
winter months. In fact, during these long periods of
darkness and near darkness, the temperature normally
falls to 20°F or 30°F, and in some isolated areas the
normal daily minimum temperature may drop to 40°F.
In north central Siberia the normal minimum daily
temperature in the winter is between 45°F and 55°F.
The arctic coastal regions, which include the
Canadian Archipelago, are characterized by relatively
cool, short summers. During the summer months the
temperatures normally climb to the 40s or low 50s and
occasionally reach the 60s. There is almost no growing
season along the coasts, and the temperatures may fall
below freezing during all months of the year. At Point
Barrow, Alaska, the minimum temperature rises above
freezing on no more than about 42 days a year.
Over the Arctic Ocean, the temperatures are very
similar to those experienced along the coast; however,
the summer temperatures are somewhat lower. Winter
temperatures along the Arctic coast are very low but not
nearly as low as those observed in certain interior areas.
Only on rare occasions does the temperature climb to
above freezing during the winter months. The coldest
readings for these coastal areas range between 60° and
These figures may seem surprising. At first one
might think that the temperatures near the North Pole
would be lower than those over the northern continental
interiors. Actually the flow of heat from the water under
the ice has a moderating effect upon the air temperature
along the coast.
CLOUDINESS.Cloudiness over the Arctic is at
a minimum during the winter and spring and at a
maximum during the summer and fall, again due to the
low-moisture capacity of cold air. The average number
of cloudy days for the two 6-month periods on climatic
charts shows a general decrease in cloudiness in the
entire arctic area during the winter months. The greatest
seasonal variation is found in the interior, and the least
is found along the coasts.
During the warm summer afternoons in the interior
regions, scattered cumulus form and occasionally
develop into thunderstorms. The thunderstorms are
normally widely scattered and seldom form continuous
lines. Along the arctic coast and over the Arctic Ocean,
thunderstorms occur infrequently. Although tornadoes
have been observed near the Arctic Circle, their
occurrence is extremely rare. In these areas, summers
are quite cloudy, with stratiform clouds predominating.
Seasonal changes in cloudiness take place quite
cloudiness in the coastal regions. These clouds are