High-pressure weather system (11)
I believe the answer is:
anticyclone
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">high-pressure weather system</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for anticyclone that I've seen before include "Swirl in the atmosphere" , "Circulating weather system" , "High-pressure weather system" .)