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Rainfall
Snowflakes are formed from water vapor, at or below 0° Celsius
(32° F), without passing through the liquid water state.
As a general rule, 1 mm of rain equals 1 cm of snow.
December
(Note: The value 0,0 is either that no rain had fallen or that the amount
of rainfall in the rainfall gauge was below 0,05 mm )
Click this to see the mentioned locations in
the Reference Map
As can be seen, the rainfall during December was not high. E.g.
if counting only days, during which the rainfall was 2.0 mm (resulting
roughly as 2 cm of snow) or higher, then the number of days in Sortavala
was 2, Helsinki 7, Viipuri 3, Kajaani 7, Kuusamo 3 and in other
locations, not visible in the chart above: Oulu 7, Sodankylä
1 and none in Utsjoki none.
Most rainfall during a single day in locations not visible in the
above chart were: Kuopio on 6 Dec 8 mm, Oulu on 21 Dec 5 mm, Sodankylä
on 21 Dec 2 mm and Utsjoki on 19 Dec 2 mm.
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January
(Note: The value 0,0 is either that no rain had fallen or that the amount
of rainfall in the rainfall gauge was below 0,05 mm )
Click this to see the mentioned locations in
the Reference Map
Depending on location, the rainfall in January was either more
or less than that during December. If again counting only days during
which the rainfall was 2.0 mm (resulting roughly as 2 cm of snow)
or higher, then the number of days in Helsinki was 5, Kajaani 7,
Kuusamo 3 and in other locations, not visible in the chart above:
Kuopio 3, Oulu 4, Sodankylä 6 and 6 in Utsjoki.
Most rainfall during a single day in locations not visible in the
above chart were: Kuopio 11 Jan 8 mm, Oulu 2 Jan 9 mm, Sodankylä
10 Jan 5 mm and Utsjoki 13 Jan 5 mm.
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February
(Note: The value 0,0 is either that no rain had fallen or that the amount
of rainfall in the rainfall gauge was below 0,05 mm )
Click this to see the mentioned locations in
the Reference Map
February had, in general, less rainfall than January. Days during
which the rainfall was 2.0 mm (resulting roughly as 2 cm of snow)
or higher, then the number of days in Helsinki was 3, Kajaani 2,
Kuusamo 4 and in other locations, not visible in the chart above:
Kuopio 6, Oulu 4, Sodankylä 4 and 2 in Utsjoki.
Most rainfall during a single day in locations not visible in the
above chart were: Kuopio 24 Feb 7 mm, Oulu 27 Feb 18 mm, Sodankylä
15 Feb 9 mm and Utsjoki 18 Feb 5 mm.
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March
(Note: The value 0,0 is either that no rain had fallen or that the amount
of rainfall in the rainfall gauge was below 0,05 mm )
Click this to see the mentioned locations in
the Reference Map
As can be seen from the chart above, the rainfall during March
1940 fell mainly in the second half of the month. Days during which
the rainfall was 2.0 mm (resulting roughly as 2 cm of snow) or higher,
before 13 March, then the number of days in Helsinki was 2, Kajaani
0, Kuusamo 0
Still, locations during which most rainfall during a single day
occurred before 14 March, and which are not visible in the above
chart were: Oulu 3 March 12 mm, Sodankylä 3 March 6 mm and
Utsjoki 4 March 2 mm.
Back to Top !
Monthly
rainfall, winter 1939 - 1940
Click this to see the mentioned locations in
the Reference Map
This chart shows the rainfall in different locations in Finland,
during the months of the Winter War. Unfortunately, the information
of Sortavala after December was not available.
Back to Top !
The
long time average rainfall
The Finnish information is from the
years 1901-1930
The Russian information is from a longer time periods, see the notes below
the figure
* = The source for the average temperatures of
the named Russian cities is from www.worldclimate.com
The Moscow data is derived from months between 1820 and 1989
The Kursk data is derived from months between 1891 and 1988
The Volgograd (Stalingrad) data is derived from months between 1918
and 1988
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Snow cover
Newly fallen snow undergoes many alterations on the ground. As the
snowmass on the ground packs and becomes denser, the snowflakes consolidate
and the entrapped air is expelled. These changes are caused by effects
of temperature, humidity, sunlight and wind. In general, the lower
the temperature, the drier the snow and the less consolidation. As
the temperature rises, the snow tends to compact more readily. Temperatures
above freezing cause wet snow conditions. Lowered night temperatures
may refreeze wet snow and form an icy crust on the surface.
Also wind packs snow. Wind-packed snow may become so hard that even
walking on it is possible without any special equipment. Warm wind
followed by freezing temperatures may create an icy, unbreakable crust
on the snow. Another effect of wind is that of drifting the snow.
The higher the wind velocity and the lighter the snow, the greater
the tendency to drift. Drifting snow can seriously hamper troop movements
(if e.g. the wind keeps pushing snow to a plowed road), depending
of the wind direction and velocity. In addition, as the wind increases
the effect of extreme cold (windchill effect)
on the body, it too may slow down or temporarily stop movement, forcing
troops to take shelter. The snowdrifts created by wind usually make
the snow surface wavy.
Snow cover, together with the freezing of waterways and swampy areas,
changes the terrain noticeably. Generally, the snow covers minor irregularities
of the ground. Many obstacles such as rocks, ditches, and fences are
eliminated or reduced. Lakes, streams, impassable during the summer,
often afford the best routes of travel in the winter when they are
frozen and snow-covered.
All in all, as time passes, slowly accumulated snow cover is not
as deep to a foot man as a snow cover which has fallen in a short
time period due to the aforementioned consolidation. Even if the top
layer of snow is dry, and thus light and a man sinks in it easily,
the lower layers of snow have often been packed hard, increasing the
carrying capacity of the snow. Therefore one should not automatically
assume that a man, trying to cross a field with a snow cover of 50
cm, is indeed up to his hip in snow.
If comparing the information on the chart below with the "Monthly
rainfall, winter 1939 - 1940" chart or the monthly rainfall
charts, you can see the effect of snow consolidation. E.g. the accumulated
rainfall in Kuusamo between 6 and 30 December was 17
mm. Still, the snow cover increased, in the same time frame, only
3 cm, from 16 cm to 19 cm.
Back to Top !
Reported
snow depths
Click this to see the mentioned locations in
the Reference Map
Other examples of the thickness of
the snow cover in locations not visible in the previous chart
|
Month
|
Nov
|
December
|
January
|
February
|
March
|
|
Day
|
30
|
5
|
15
|
25
|
31
|
5
|
15
|
25
|
31
|
5
|
15
|
25
|
29
|
5
|
15
|
| Valamo (island) |
3 cm
|
3 cm
|
3 cm
|
9 cm
|
10 cm
|
28 cm
|
35 cm
|
36 cm
|
34 cm
|
38 cm
|
45 cm
|
55 cm
|
55 cm
|
?
|
?
|
| Konevitsa (coastal fort, island) |
7 cm
|
5 cm
|
6 cm
|
12 cm
|
11 cm
|
21 cm
|
25 cm
|
26 cm
|
24 cm
|
24 cm
|
29 cm
|
37 cm
|
36 cm
|
?
|
?
|
| Rankki (coastal fort near Kotka) |
?
|
?
|
?
|
?
|
?
|
8 cm
|
16 cm
|
25 cm
|
24 cm
|
25 cm
|
27 cm
|
34 cm
|
34 cm
|
34 cm
|
49 cm
|
Back to Top !
The thickness
of the snow cover in some locations during the Winter War
compared to a 30 year average
Click this to see the mentioned locations
in the Reference Map
Back to Top !
Snow cover
in mid- and southern Finland on 15 March 1940
 |
In the map on the left, the snow thickness is represented in
centimeters.
The green numbers show the thickness of the snow cover in forests
and are positioned in their correct places. The black numbers,
adjacent to the green numbers, show the thickness in open areas
of that same place where the green number is.
There are few exception, e.g. the figure showing the snow thickness
(10 cm) in the open areas in the Turku archipelago.
Source:"Suomen meteorologinen vuosikirja
1940, osa 2", p.56 - 57
|
Back to Top !
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Wind
Wind can have a dramatic effect on personnel operating outdoors in
subzero temperatures.
In general, the wind speeds in Finland during the Winter War were
quite low, depending of course of the location, the wind blowing harder
in the coastal areas than inland. In December, e.g. In Sortavala,
on the northern coast of Lake Ladoga, the highest measured wind speed
was in the morning of 22 December, at 07:00 AM, 14 m/s (direction
ESE). However, the wind died quickly, being 5 m/s (direction W) at
15:00 PM.
The monthly average wind speeds in Sortavala, during December 1939,
were 4.5 m/s at 07:00 AM, 3.9 m/s at 15:00 PM and 3.9 m/s
As an other example, in Sodankylä, the monthly average wind
speeds at
07:00 AM, 15:00 PM and 21:00 PM were
1.6 m/s, 2.1 m/s and 2.2 m/s in December 1939
1.4 m/s, 1.5 m/s and 1.9 m/s in January 1940
1.8 m/s, 2.5 m/s and 2.9 m/s in February 1940
1.5 m/s, 3.1 m/s and 1.6 m/s in March 1940
(Generally speaking, wind with a speed of 2 m/s or less, is considered
"calm")
From the summaries in The Meteorology
Yearbook of Finland:
|
Location
|
December 1939
|
January 1940
|
February 1940
|
March 1940
|
|
direction*
|
# of days**
|
direction
|
# of days
|
direction
|
# of days
|
direction
|
# of days
|
| Helsinki |
E
|
4
|
NE
|
10
|
NE
|
8
|
NE
|
8
|
| Viipuri |
SW
|
5
|
NE
|
6
|
?
|
?
|
?
|
?
|
| Sortavala |
NW
|
11
|
?
|
?
|
?
|
?
|
?
|
?
|
| Kuopio |
W
|
8
|
W
|
6
|
W
|
5
|
NW
|
7
|
| Kajaani |
NW
|
6
|
E
|
6
|
E
|
8
|
E
|
7
|
| Sodankylä |
NW
|
5
|
SE
|
6
|
N
|
5
|
SE
|
4
|
* = The most common direction (from where the wind blows, e.g. "W"
is a wind blowing from the west).
** = The number of days which could be considered "windy".
Back to Top !
Windchill
In low temperatures, the human body is continually losing heat. This
heat dissipation happens mainly from bare (exposed) skin into air.
The dissipation is increased by moving air (i.e. wind, if walking,
running, on top of a moving vehicle etc.). If there is wind, it increases
the heat loss and thus also person's perception of cold (which is
also affected by many other factors, like mental and physical condition,
amount clothing, quality of clothing etc.). The effect of the wind
combined with low temperatures can be dangerous to personnel operating
outside. The effect of these two elements occurring together is called
windchill. For the windchill to take effect is that the wind penetrates
the layer of insulating warm air to expose body tissue (or the wind
gets in direct contact with exposed body parts, usually the face and/or
hands). The sensation of cold is mainly a result of high heat dissipation
and its effect on the surface circulation of the flesh.
While individuals from different backgrounds will sense cold with
different standards, the threshold values, based on human physiology,
are as follows:
1 000 W/m² or more heat loss is generally sensed as cold
1 300 W/m² or more is very cold (proper precautions should be
taken or risk frostbite injuries)
1 600 W/m² or more is dangerously cold (frostbite is likely to
occur within minutes without precautions)
In the formula that I received from the Finnish Meteorological Institute
(many thanks for Timo Laine for sending it to me), the heat
loss from bare skin (W/m²) can be calculated in combination with
wind speed and temperature.
H = is the "Heat turnover" ("konvektiivinen lämmönvaihto",
Fin)
V = is the wind speed (meters per second, m/s)
T = is the temperature (in Celsius)
S = is the warming effect of the sun (depends geographic location,
season and overall cloudiness, 0 - 200 W/m², the normative value
in Finland is 150 W/m² = equals about +5 degrees Celsius)
H = (10.47 + 12.68 Ö
V - 1.163 x V ) x (33 - T) - 112.5 - S
The above formula applies only in cold temperatures. The number 112.5
in the formula represents the heat produced by metabolism. It should
be noted that while humidity is a factor in above freezing temperatures,
in cold (sub zero) weather it ceases to have a notable impact.
(In case your browser doesn't display
the following symbol correctly, "Ö"
= "square root" )
As an example. The temperature is - 5 C°, but the wind is blowing
quite hard, 8 meters per second (I'm leaving the warming effect of
the sun out of this intentionally, as it's not included in the chart
above)
The heat turnover, from exposed skin is:
(10.47 + 12.68 x Ö8 - 1.163 x 8) x
(33 - -5) - 112.5 = 1 294.66 W/m²
In most cases, a person would say that its very cold (the result is
very close to the threshold value of 1 300 W/m² )
Even though the above formula is not, due to varying conditions and
factors, capable of giving a exact result, it still serves as a guideline
for calculating the windchill effect and gives a good idea of the
tremendous impact of wind in sub zero temperatures.
Go back to Part
I
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