Clustering possibilities of weather patterns associated with winter cold and warm spells in Hungary

In this rapidly changing climate weather extremes get even more attention since they are occurring more frequently around the world. Even when global temperatures are rising, both extremely cold and warm periods impact our economy, agriculture, and our daily life. Using weather station data from Hungary we found that cold and warm spells (CSPs and WSPs) are more intense and have greater variability in the winter months compared to events in the transition or summer months. We also experienced that temperature extremes have recently become more frequent in March, so we used this month additionally to the three winter months in this research. Our results show that various weather patterns may be associated with CSPs/WSPs, so we investigate the macro-synoptic circulation in the background of these events over a 30-year timespan (1991-2020) using the ERA-5 reanalysis database. This will give us a picture of the weather patterns causing both cold and warm extremes in this part of Europe. In this research, we investigate CSPs/WSPs for each month separately and for the whole winter period combined to gather more information about the meteorological background of these extremes. Our main goal is to group events with similar synoptic background, combining wind, temperature, pressure, and geopotential fields (and anomalies) at various pressure levels during the start, peak and end of the events. Then we analyse these clusters more closely, associating them with well-known synoptic situations in Europe. Furthermore, we would like to increase our investigated timespan to weekly anomalies in the future, as it is easier to compare these anomalies with operational long-range forecasts.