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Negative  Surges  in  the  Southern  Baltic  Sea

5.  Most  severe  negative
surges  on  the  southern
Baltic  Sea  coast
5.1.  November  1956
Meteorological  situation
On  24  November  1956,  while  the  Baltic  Sea  still
was  under  the  influence  of  a  weak  high-pressure
ridge,  a  wide  low-pressure  trough  over  the
Norwegian  Sea  travelled  southeast,  crossing  the
western  part  of  Scandinavia.  The  southern  Baltic
Sea  coasts  were  governed  by  an  initially  weak,
later  moderate  westerly  air  flow  which  backed
SW  in  the  late  evening,  increasing  gradually  to
7  Bft.  On  25  November,  the  trough  -  still  tracking
eastward  -  deepened  considerably.  The  SW-S
storm  reached  8-10  Bft  in  the  whole  Baltic  Sea
region.  As  the  cold  front  tracked  across  the
western  and  central  parts  of  the  southern  Baltic
coasts  in  the  late  hours  of  this  day,  the  8-9  Bft
storm  veered  W-NW,  slowly  abating  later.

Hydrological  response  of  sea  level
Sea  levels  remained  just  under  500  cm  until  the
afternoon  of  24  November.  In  the  late  hours  of
24  November,  the  trough  reached  the  Baltic  Sea
and  the  southern  coasts  came  under  the  influence ­
  of  increasing  westerly  winds,  which  gradually ­
  veered  SW  and  S,  causing  sea  levels  to  fall
until  they  reached  their  minimum  values  in  the
late  hours  of  25  November.  The  minima  occurred
nearly  simultaneously  along  the  entire  southern
Baltic  coast.  Minimum  values  of  342,  365  and
383  cm  were  recorded  in  Wismar,  Warnemünde
and  Sassnitz,  respectively,  at  18  UTC,  and  in
Swinoujscie  and  Kotobrzeg  at  20  UTC,  with
values  of  401  and  393  cm,  respectively.
In  the  night  of  26  November,  when  the  storm
front  had  passed,  the  stormy  winds  backed  west,
later  northwest.  Sea  levels  responded  immediately ­
  and  began  to  rise,  reaching  values  close  to
or  slightly  above  500  cm  as  early  as  the  morning
of  26  November.

Fig.  5.1.  a  Pressure  pattern  and  wind  field  over  the  Baltic  Sea  on  25  November  1956  at  12  UTC