26

If  the  first  essential  cold  period  appears  already  in  November  or  early  December,  the  water
gets  indeed  rapidly  cooled,  but  it  is  often  not  enough  for  significant  ice  formation.  If  this
period  is  interrupted  by  a  long  period  with  positive  air  temperatures,  or  there  are  several  cold
periods  in  the  winter,  but  of  small  strength,  then  the  sum  of  coldness  is  relatively  large,  the  ice
production  keeps  at  the  level  of  mild  ice  winters.
Differences  of  the  behaviour  of  average  ice  parameters  in  mild,  moderate  and  strong  ice
winters  are  shown  in  Figures  2.8.  -2.10.

Pomeranian  Bay  first  ice  Pomeranian  Bay  last  ice
Szczecin  Lagoon  first  ice  —■—Szczecin  Lagoon  last  ice

Mild  Moderate  Strong

Figure  2.8.  Average  dates  of  first  and  last  ice  in  Szczecin  Lagoon  and  Pomeranian  Bay
in  different  ice  winter  classes

Pomeranian  Bay  days  —±—  Pomeranian  Bay  duration
Szczecin  Lagoon  days  —■—  Szczecin  Lagoon  duration

Mild  Moderate  Strong

Figure  2.9.  Average  number  of  days  with  ice  and  duration  of  the  ice  season  in  Szczecin
Lagoon  and  Pomeranian  Bay  in  different  ice  winter  classes