Abstract
A high-impact freezing rain event affected parts of southeastern Romania on 24–26 January 2019. The freezing rain caused extensive damages in Bucharest, the capital city of Romania. The meteorological analysis highlighted the presence of a particular synoptic pattern involving a high-pressure system advecting cold air mass at low levels, while at mid-levels a warm and humid intrusion was associated with a low-pressure system of Mediterranean origin. At Bucharest, the vertical profiles from ERA5 and radiosondes emphasized the presence of a thick warm layer between 1000–1400 m above the re-freezing layer close to the surface. A climatology of freezing rain events in Bucharest was built to understand the frequency and intensity of this phenomenon. On average, there were approximately 5 observations of freezing rain in Bucharest per year between 1980–2018. The number of consecutive freezing rain days was used as a proxy for the event severity. Moderate-duration events (2 consecutive days) represented 16 periods of all 59 non-overlapping freezing rain periods in Bucharest and long-duration events (3 consecutive days) represented 3 periods. The monthly distribution showed that freezing rain occurs more frequently between December–February with a maximum in December. The moderate and long-duration freezing rain events were associated with two main sub-synoptic patterns related to the Carpathians lee cyclogenesis.
Highlights
Freezing rain—“rain that falls in liquid form but freezes upon impact to form a coating of glaze upon the ground and on exposed objects” [1]—is a meteorological phenomena more frequently observed in Europe during the winter months (i.e., December–February) [2,3]
Freezing rain events associated with a small accumulation of ice or those that occur over a short period can result in transportation difficulties and an increase in the number of accidents [8]
The results showed that freezing rain events were primarily driven by warm advection and their frequency was influenced by topographic features, water bodies and the dominant storm tracks during winter
Summary
Freezing rain—“rain that falls in liquid form but freezes upon impact to form a coating of glaze upon the ground and on exposed objects” [1]—is a meteorological phenomena more frequently observed in Europe during the winter months (i.e., December–February) [2,3]. In a study based on 10 years of observations from weather stations in the continental United States, 25% of all freezing rain cases occurred without a warm layer [20]. For those cases, freezing precipitations were associated with the upward motion in a shallow saturated layer situated close to the surface. January–4 February over the Balkan Peninsula resulted in 10 cm accumulation of ice in Slovenia and damages estimated at EUR 400 million [29,30] Despite these major events, few studies were devoted to the climatology and synoptic-scale and local influences on freezing precipitation events.
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