Climate

Air temperature

Depending on the latitude, the average annual temperature in Šumava varies, ranging from 6.0 °C (750 m above sea level) up to 3.0 °C (1300 m above sea level). . These are mainly the valley of the River Vltava from Horní Vltavice up to Lipno and the enclaves in the area of Pláně (Lake Moor, Horská Kvilda and the moors SW of Modrava). In the extreme conditions of Lake Moor, the summer months are on average 2 °C and the winter months 4 °C colder than peaks with the same altitude in other locations. The more enclosed parts of the valley, for example around the Otava River, are also relatively cold, although not as much as the above mentioned sites.

The warmest month is July; the coldest is January. The annual temperature amplitude is more pronounced in the valley than in the highlands. Daily temperatures reach their maximum around 14.00 and the minimum temperature around sunrise. The amplitude is again highest in the valleys and forest enclaves and in the extreme locations; the temperature is on average 5 °C higher than in the open locations. Vyšší Brod 36.0 °C; Lenora 35.2 °C; Kašperské Hory 36.8 °C).

The absolute minimum temperatures are substantially lower in the inverse locations than on the peaks, so the terrain configuration is more significant than the altitude. Extreme temperature values - see table Climate min.


Table Climate min.: Selected extremely low temperatures from 1961 - 1990

Location min. temperature Date
Churáňov - 24,2 °C 12. 1. 1987
Kašperské Hory - 25,6 °C 7. 1. 1985
Lenora - 33,0 °C 7. 1. 1985
Nová Pec - 29,0 °C 7. 1. 1985
Vyšší Brod - 32,3 °C 7. 1. 1985
Jezerní slať (Lake Moor) - 41,6 °C 30.1. 1987
Horská Kvilda - 34,9 °C 30.1. 1987
Hliniště - 36,5°C 30.1. 1987


The temperature characteristics are illustrated by the number of icy days (Tmax <0 ° C), of which there are around 70 a year at an altitude of about 1200 m and 40 at altitudes of 700 m. There are about 170, or in fact around 140 frosty days (Tmin <0 ° C) a year, but here again the influence of the relief applies more so in high-altitude locations where these days account on average at 250 per year.


Icy days mainly occur in winter, only at the highest altitudes, i.e. 1200 m above sea level from mid September up to early May. Frosty days occur in most of the territory throughout the year except in July and August, however in the above mentioned inverse locations frost occurs even during the summer months. The number of summer days (tmax > 25 °C), depends on the altitude. This is about 5 days in locations with an altitude of 1 200 m and 25 days in locations with an altitude of 700 m.



Humidity

Annual average relative humidity is around 80% in most of the area. However, the northeast outskirts at lower altitudes record slightly lower humidity. Annual variation is relatively small; the maximum is accounted for in December. Minimum humidity is recorded in May and July. Daily fluctuations are much stronger than annually, especially in the concave terrain spots. The maximum usually occurs in the second middle of the night before sunrise, a minimum of around 14 to 15 hours. Maximum 100 % absolute air humidity is reached very often, especially at high altitudes (in dense fog, in precipitation). The absolute minimums fall below 10% during winter inversions in the higher open altitudes.

Wind

The direction and speed of the wind are greatly influenced by the rugged relief of the Šumava landscape. Generally, the highest average speed of the wind is recorded in the free (treeless) convex areas, which is from 5-8 m / s. On the other hand, in the enclosed deep valleys the speed of the wind falls to 1-2 m / s. The open areas are generally affected by prevailing west to southwest air currents, the least common are the north and southeast currents. In the valley, the current is channelled along the main axis of the valley, on the mountain ridge; the frequency of perpendicular directions towards the edge axis slightly increased. Similarly, the wind direction is distorted in the terrain gaps.

In some places the local weather circulation appears during clear weather conditions: Descending cold air at night and in the early morning hours in the valley downwards (most notably in the wake of the Vltava River) and the anabatic daily current down the slopes and up the valleys (most notably on the north-eastern slopes, which is due to the overall orientation of the main Šumava massif).


Daily wind speed with the maximum in the afternoon and the minimum at night is more pronounced at lower altitude areas; the average wind speed during the day and night is virtually the same on the peaks and mountain ridges. The annual wind speed is less pronounced, the maximum falls in the winter months (particularly at lower altitudes), and the minimum in the second half of the summer. The west to southwest direction prevails throughout the year, its predominance is more pronounced in winter and summer, while in spring it is the north and in autumn it is the south directions of the wind that are more frequent.


Precipitations

The lowest average annual rainfall is recorded in the north-eastern borders at 800 - 900 mm. Toward the main border ridge the rainfall values rapidly increase and reach the highest levels at the state border - the area south of Březník 1600 mm and more, elsewhere around 1 400-1 500 mm but fall in the area between Strážný and Nové Údolí to 1 200 - 1100 mm per year. This division is due to the orographic effects of the prevailing western current, i.e. a significant windward on the Bavarian side and along the state border and leeward on the north-eastern slopes. Regarding the annual rainfall, the rain in the windward and most humid zone is evenly distributed throughout the year, the main maximum falls in June and July, supplementary to December, mainly associated with the increased frequency of the western currents. In the lower, drier zone, the only major value is the summer maximum, while the period from October to March has fairly balanced, relatively low totals. The maximum monthly rainfall totals correspond with this; i.e. in the border zone for the winter, while in the lower areas in the summer.

Short-term extreme rainfalls can be observed in the maximum level of rain in 24 hours. More often this rain has the character of a storm and sometimes reaches levels over 100 mm. According to the statistics, 100 mm and more rainfall can be expected once every 5 years. The absolute maximum was recorded in Srní-Schatzův forest on 30.5. 1940, i.e. 189.1 mm. On the same day Zhůří reported 155.6 mm, Kašperské Hory 163.0 mm, Churáňov 132.5 mm, Javorník 145.2 mm etc. The last big floodwater had its eye at the edge of Šumava NP on 1.8.1991 (Špičák174.6 mm, 165.3 mm, Železná Ruda 148.5 mm).

The average number of days with precipitation has a similar spatial and time distribution as the rainfall totals. It runs from 170 - 180 days in the wettest and 150 days in the driest locations. The locations with the highest altitude have about 80 - 100 i.e. about half, of solid precipitation (snow) and the lowest altitude locations have an average number of days with snowfall of around 50 per year.


The average number of days with storms (regardless of rainfall) in the whole area is 30 to 35. Thunderstorms commonly appear from April to September, the majority in June and July.



Snow cover

The locations with the highest altitude along the state border, especially the areas between Debrník and Černá Mountain and between Třístoličník and Smrčina receive most of the snowfall. The least amount of snow falls at the lowest altitudes on the north-east edge of the described area. Continuous snow cover occurs on average 90 to 100 days a year in the lowest altitudes and for more than 200 days at the highest altitudes. This period with continuous snow cover is particularly in the lowest altitudes, punctuated by periods of several days without snow. The first day of snow falls in the lowest altitudes at the end of October and in the highest altitudes at the beginning of October; however in these areas, the snow cover can exceptionally appear as early as September. The last day of snow cover in the lowest altitudes usually falls to the end of April and in the highest altitudes to mid-May, although the discontinuous snow cover can last in this area up to the end of May, exceptionally until mid-June.

The thickest snow cover is usually in the lower altitudes in February and in the highest parts of Šumava in March. The average maximum snow cover ranges from 40 cm in the lowest and 150 cm or more in the highest altitudes. The absolute maximum in the lowest altitudes is around 80 - 100 cm; in the highest altitudes, given the total lack of data from earlier and later periods, it can be estimated at around 300 - 400 cm.

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