un

Between the Stikine Mountains and the Coast Mountains
the plateau experiences the great cold of northeastern
British Columbia, but is more frequently visited by short
intervals of mild weather. North of the Lesser Slave

Lake to Teslin line lies a territory with winters of

great
severity.

The chief distinction between the Yukon and Mackenzie
winters is the greater variability in the Yukon over a
period of years. It is true that unexpectedly mild winter
| months can be found in the records. For instance, a mild
spell which set in on February 20, 1938, produced tem-

» peratures of 40 to over 50 degrees F., daily, until March 2s

while the month of March averaged six

or seven degrees
above normal.

To offset this was a period from about
January 10 of that year to February 20 when temperatures
of 30 to 50 degrees F. below zero occurred on many days.
Also, in January, 1909, there was-a steady flow of air from
northern Siberia across the Beaufort Sea into the Yukon,
producing temperatures of 50 and 60 degrees F. below zero
on many days and scarcely any relief from intense cold.
Descriptions of beautiful winter weather in the Yukon
have been transcribed from one book to another

and have
created a false impression.

One should not be misled.
The settler in this region must be prepared for more certain

and more intense cold than the dweller on the Saskatchewan
prairies:

The summer months in northwestern Canada are
distinctly different from the same months in northeastern
Canada. The source-region for very cold air is restricted
to the Arctic Ocean and air flowing out from this source
crosses land which is strongly heated during the periods of
clear or very lightly clouded skies which accompany Arctic
outflow. The very long insolational period of each summer
day makes this surface-heating very effective in raising the
temperature of the lower levels of the Arctic outburst.
Where the outflow of Arctic Ocean air crosses the extensive
water-areas of the Gulf of Boothia, Foxe Basin, Hudson
Strait, and Hudson Bay, its lower layers remain cool.
Therefore, an Arctic outburst is soon modified in the
Mackenzie Valley, but is able to retain Arctic characteristics
at the surface during considerably longer travel toward the
south and southeast. Hence the far northeast has a very

_ cool summer and the principal outflow of cold air appears

to take place in that direction. At the same time that
Foxe Basin and Lancaster Sound are discharging ice and
icy waters, the sea-surface off the Alaska-British Columbia
Coast is rapidly gaining temperature. By August the waters
off Cape Nome have reached 48 degrees F., the waters
between the Aleutians and the Alaska Panhandle 51 to
58 degrees F. Even the southern reaches of the Bering
Sea average 46 to 49 degrees F. in July and 49 to 51 degrees F.
in August. Airmasses moving over this region with polar
characteristics are, therefore, more rapidly modified than
cold volumes of air crossing into the Hudson Bay region.
Following are examples of polar outflows in July, 1945:

Temperature, Water-Vapour
Elevation Degrees F. (Grains per Pound Dry Air)
Above — = =
Sea Arctic | Norman] Fort Arctic }Norman] Fort
Bay Wells | Nelson Bay Wells | Nelson
Ground. .... 41 60 58 a4 38 43
0-5 km.. +... 32 52 56 26 35 39
1-Okm..... 25 42 49 22 30 24
TiSakmn pe sey 19 36 44 15 29 24
2:O)km 13 32 38 14 24 21
2-5 km a. 7 26 31 12 14 20
3-Okm..... 2 21 24 10 20 18
4-Okm..... =: 6 11 15 6 14 14
5:0: kmi.. —19 0) Ti 4 11 9
6:0:kme ee —31 —12 —"4. 1 6 6
Sc Oikmieee —40 —41 SA Allo ass tance | Cesena 1 pol | eee ees
10-0 km..... =e Op, Sa ibe Wee Cains) he cae eee eee
12-0 km...:. =a7 —54 ee teoreon al ieieg Seem eae

Warm air from the southwest raises the temperature
rapidly in northeastern British Columbia and in the Mac-
kenzie Valley but seldom reaches the eastern Arctic.
However, air warmed in mid-continent may flow north to
the polar archipelago. Following are examples of a warm
flow on the western side of an anticyclone moving across
the Rockies on July 13, 1945. This air scarcely affected
Arctic Bay, but on the 29th of the same month mid-continent
ait produced at Arctic Bay the figures given.

Temperature, Water-Vapour
Elevation Degrees F. (Grains per Pound Dry Air)
Above =
Sea Arctic | Norman] Fort Arctic | Norman} Fort
Bay Wells | Nelson Bay Wells | Nelson
Ground. .... 46 76 70 49 34 80
Sakmann 46 67 71 44 37 77
1-Okm..... 45 58 71 39 33 63
TO: km 40 51 67 35 25 47
2°Oikm’. . 5. 35 44 60 32 20 39
DeoSskimeese ee 30 35 53 2 22 33
Se OR pre 26 28 47 23 18 28
4-Okm..... 15 17 36 10 15 20
S-O:km™= =... 1 9 23 10 10 14
6-Okm..... aly ae 13 13 6 9
S-Okmee see —40 =a) —10 Gael labia eee lane eae
10-Okm..... —67 —56 een erm eee eg ricaceeal lies ee
12 Olkmn ee =a 5 = 10) Remeron hs eau kee

It should be noted that the water-vapour-content |
remains quite low at Norman Wells with both types of |
airmass. The selective effect of the Mackenzie Mountains
and other chains to the west apparently prevented much
vapour from the southwest from crossing the r At
this time the radiosondes on the Pacific Coast indicated
70 to 85 grains per pound of dry air at the surface, dimin-
ishing to 35 grains at 2 kilometres. Therefore, it appears
that mostly the air above 6,000 feet above sea crossed the
Mackenzie Mountains, producing a chinook effect at Norman
Wells upon descent when temperatures reached 80 degrees F.
or higher at the ground. This Paucity of water-vapour is |
characteristic of the northwestern region and may be
compared with an average of all days in the lower lake

anges.

[ 149 }