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The weather

During the Winter War

Part II

 

The main sources:
"Suomen meteorologinen vuosikirja 1939, osa 1 ja 2", by Ilmatieteellinen keskuslaitos, Helsinki 1953
(The Meteorology Yearbook of Finland 1939, vol. 1 and 2)

"Suomen meteorologinen vuosikirja 1940, osa 1 ja 2", by Ilmatieteellinen keskuslaitos, Helsinki 1955
(The Meteorology Yearbook of Finland 1940, vol. 1 and 2)

Nowadays the "Ilmatieteellinen keskuslaitos" is the "Ilmatieteen laitos" or "Finnish Meteorological Institute". http://www.fmi.fi
The Yearbook's are available for public at the Institute's library, in Helsinki.

All graphic charts are based on the records of the above-mentioned publications, unless noted otherwise.

As additional sources, I've used the article "Pakkastalven kourissa" by Jyri Paulaharju in the "Talvisodan Pikkujättiläinen", p. 289 - 298
and an article by Professor J.Keränen titled "Säät sotatalvena 1939 - 1940", of which I received a copy by a clerk in the FMI's library.

 

Part I

  • Foreword
  • Celsius-Fahrenheit conversion tool
  • Reference Map
  • The weather during the Winter War on a weekly basis (in general)
  • Temperatures
        The 5-day average temperatures
        The average temperatures during the Winter 1939 - 1940
        The long time average temperatures
        Daily temperatures in Sortavala, December 1939
  • Effects on troops & equipment

 

Part II

 

 

Celsius-Fahrenheit conversion tool

All temperatures on this page are in Celsius.
The below thermometer can serve as a quick conversion tool into Fahrenheit


If you want an exact, from Celsius to Fahrenheit conversion, use the below formula (The "C" is the temperature in Celsius):
(9 / 5) x C + 32

 

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Reference Map

Due to the war, nearly all records from the weather stations at or near the border are unavailable (lost in the war, station evacuated or some other similar reason). As an effort to get a good overall picture, I've tried to use information from several stations around Finland, mainly in the North-South axis. The towns on the right are the towns named in the figures below.

In most cases, the towns mentioned in the figures are sorted "from South to North", i.e. starting from Helsinki and ending in Sodankylä or Utsjoki.

The towns, which are mentioned in this article

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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.

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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.

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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.

 

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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

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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

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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

 

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Daylight

 

While not directly linked to the weather, I thought to add the information of the sunrise-sunset times from three locations in Finland.

Date
1939-1940
Helsinki
Joensuu
Sodankylä
Sunrise
Sunset
Sunrise
Sunset
Sunrise
Sunset
1 Dec
8:56
15:23
8:59
14:41
10:28
13:37
15 Dec
9:19
15:12
9:26
14:26
11:38
12:39
1 Jan
9:25
15:22
9:32
14:37
11:35
13:00
15 Jan
9:12
15:48
9:14
15:07
10:38
14:09
1 Feb
8:38
16:31
8:34
15:57
9:29
15:27
15 Feb
8:03
17:08
7:53
16:39
8:33
16:25
1 March
7:20
17:47
7:06
17:23
7:32
17:22

Note that the "twilight" (during which there is some light), lasted about an hour before and after the sunrise and sunset. E.g. the "civil twilight", before the sunrise in Helsinki on 1 December began at 8:01 and the civil twilight after the sunset ended at 16:17.
Source: http://aa.usno.navy.mil/data/docs/RS_OneDay.html

Greyout is a phenomenon which occurs during twilight conditions or when the sun is close to the horizon, over a snow covered surface. There is an overall greyness to the surroundings (which gives the phenomenon its name) and if the sky is overcast with dense cloud the shadows are absent resulting in a loss of depth perception. The effect is increased if person is fatigued. As this phenomenon makes it hard to distinguish the road from the ditch or even from the snowbanks along the roadside, it of course increases the hazard while driving a vehicle along a road. The same phenomenon can also be a hazard when skiing or even when walking.

 

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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".

 

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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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