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The plots below shows analyses of z500 and t850 for the period 2-9 January.
The plot above shows backward trajectories based on 850 hPa winds, starting on 1 January and ending on 9 January around Sofia. Under assumption of no vertical motion, the air parcels originated from north-eastern Russia.
The plots below show EFI and SOT for 2-metre temperature day 1 as a proxy for analysis of how extreme the temperature were from 2 to 9 January.
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