Synoptic conditions of snow occurrence in Budapest

Daily circulation patterns responsible for snow occurrence in Budapest were analysed. Three types of circulation patterns were distinguished, using a Principal Component Analysis and clustering technique, for days with snowfalls and snow cover persistence. Low pressure systems located over the Italian Peninsula (southwest of Budapest) are characteristic for days with snowfalls. Such lows coming from the west generate warm fronts and are a source of humidity necessary for the snowfalls. At the same time, higher pressure extends north or east of the Carpathian Basin and brings polar continental air masses and consequently low temperature. Snow persistence also requires temperature below zero. This condition is fulfilled at the airflow direction from the east (or south east) which brings frosty air from the interior of the continent. A winter high pressure system extending over the Carpathian Basin also generates low temperature, mainly due to the noctumal radiation conditioned by a clear sky.