22

Trzebiez  during  those  days  varied  from  0.1  to  0.4°C.  On  22  February,  after  an  intrusion  of
cold  Arctic  air  extending  south  as  far  as  Central  and  Southern  Europe,  a  high  formed  there
which  oscillated  between  the  British  Isles,  south-eastern  Europe  and  Scandinavia  until  the  end
of  the  month.  Under  the  prevailing  anticyclonal  conditions,  the  air  cooled  gradually.  Around
Szczecin  Lagoon,  the  daily  means  decreased  to  about  -4°C,  with  minima  ranging  between  -4°
and  -9°.  A  snow  cover  formed  again  which  was  8  cm  thick  on  20-21  February'.  The  water
temperature  in  Trzebiez  fell  to  0°  on  26  February.
March
In  March,  the  situation  was  largely  unchanged  at  first.  The  anticyclone  stabilised  over
Scandinavia  where  it  remained  for  14  days,  causing  frosty  and  dry  air  from  the  north-east  and
east  to  flow  across  the  Baltic  Sea.  With  anticyclonal  conditions,  predominantly  light  winds,
and  radiative  cooling  in  clear  nights,  the  air  temperatures  fell:  daily  means  in  Trzebiez  ranged
between  -5°  and  -10°C,  minimum  temperatures  were  below  -10°C  in  the  majority  of  cases.  In
(Ewinoujoecie  the  grass  minimum  temperature  was  below  -16°C  from  9  to  15  March  (the
lowest  value  recorded  was  -20.3°C).  The  snow  cover  thinned  gradually.  On  15  March,  the  air
flow  changed  to  westerly,  bringing  mild  maritime  polar  air  masses.  Temperatures  around
Szczecin  Lagoon  increased  to  positive,  they  did  not.  however,  exceed  2°C  until  22  March.
Daily  maxima  varied  between  2.5°  and  5°C.  Only  patches  of  snow  cover  remained  in
Swinoujscie.  Water  temperatures  in  Trzebiez  rose  above  0°C  as  early  as  15  March,  and
increased  gradually  to  1°C  on  26  and  4.5°C  on  31  March.  From  23  to  30  March,  daily  means
varied  between  2.5  and  9.6°C.  The  day  of  maximum  temperature  (13.1°C)  was  preceded  by
strong  southerly  and  south-westerly  winds.
April
The  first  15  days  of  April  had  mean  daily  air  temperatures  around  5°C.  Minimum  temperatures
were  positive,  except  on  the  first  day  of  the  month.  On  9  and  10  April,  heavy  rain  was  recorded
at  all  stations  around  Szczecin  Lagoon.  Water  temperatures  increased  gradually,  from  4.6°C  in
the  first  days  of  the  month  to  10°C  on  17  and  15.4°C  on  30  April.
Table  2.7.  Air  temperatures  and  variations  from  the  normal  value  (1961-1990)
in  Szczecin  Lagoon  in  winter  season  1986/87

November

December

January

February

March

mean

max.

min.

mean

max.

min.

mean

max.

min.

mean

max.

min.

mean

max.

min.

Swinoujscie

6.9

13.0

0.9

2.2

11.7

-4.6

-6.2

4.1

-19.0

-0.8

6.3

-9.7

-1.3

12.8

-12.3

divergence

2.2

1.1

-5.6

-0.7

-3.9

Trzebiez

6.5

12.9

-1.2

1.9

11.3

-5.8

-7.9

4.1

-26.2

-1.1

6.9

-11.9

-1.7

13.1

-14.0

divergence

2.2

1.1

-6.9

-0.7

-4.3

Szczecin

6.6

13.4

-3.0

2.0

12.5

-6.6

-7.9

4.4

-30.0

-0.9

7.3

-13.5

-1.0

13.0

-13.7

divergence

2.2

1.2

-6.fi

-0.5

-4.0

Table  2.8.  Water  temperatures  and  variations  from  the  normal  value  (1961-1990)
in  Szczecin  Lagoon  in  winter  season  1986/87

November

December

January

February

March

mean

max.

min.

mean

max.

min.

mean

max.

min.

mean

max.

min.

mean

max.

min.

Mi^dzyzdroje

7.1

8.1

5.3

3.7

5.6

1.3

-0.1

1.6

-0.5

-0.2

0.1

-0.5

0.2

2.1

-0.5

divergence

0.7

1.0

-  1.2

-1.2

-2.2

Trzebiez

6.6

7.8

5.6

2.9

5.8

Ü.2

0.1

0.4

0.0

0.2

0.4

0.0

0.8

4.5

0.0

divergence

1.2

0.8

-1.0

-1.1

-2.6

Szczecin

7.3

8.8

6.6

3.7

7.6

0.3

0.3

1.4

0.0

0.5

1.0

0.2

1.8

5.5

0.1

divergence

1.1

1.1

-  1.2

-  1.3

-2.5