Climatology of snow cover and snow water equivalent based on satellite data

Seasonal variations of SWE

Snow cover starts to form in November and melts in April in the Baltic region. At the beginning of the season SWE values are low (0–20 mm) (Fig. 5) because the snow is fresh and has low density. Later in the season, when average air temperature is negative (in January and February), the snow cover starts to build up and the snowpack becomes denser – SWE values increase to 30–60 mm (Fig. 5). The highest values of SWE are typically recorded in the second half of February, although on some years it may be in March. Exceptions are mild, changeable winters with frequent thaws, when the SWE depends mostly on liquid precipitation events with a negative or close-to-zero air temperature. SWE in the Baltic States follows a meridional distribution and the lowest values are observed in the western coastal areas, while the highest values are found in the continental eastern parts (Fig. 5). At the end of March or at the beginning of April snow cover starts to melt rapidly and SWE values decrease to zero.

Figure 5: Spatial distribution of mean monthly SWE, 2000-2013.

Exercise 12

Choose the correct statements about satellite based SWE climatology.

a) In certain months, when a thin snow layer or wet snow is predominant, availability of SWE derived from satellite data, can be reduced to single days.

b) Satellite based SWE product is influenced by the cloud cover.

c) SWE do not vary much during changeable winters with frequent thaws.

d) Satellite data provides good spatial overview of SWE conditions in the region.

e) A decrease in satellite based SWE indicates snow melt.

f) GlobSnow-2 data has a tendency to overestimate SWE under deep snow conditions.

Correct answers are: a), d), e).