Organized precipitation and associated large-scale circulation patterns over the Kingdom of Saudi Arabia

The Kingdom of Saudi Arabia (KSA) is characterized by a desert climate, with rainfall mainly occurring during the cooler months (November–April) and sometimes in conjunction with intense extratropical systems that can cause serious damage and casualties. Given the vast size of KSA, there are gaps in understanding the association between large-scale atmospheric circulations and local organized rainfall events, and in characterizing the diversity of this association. To address these gaps, we analyse an in-house 5-km horizontal grid spacing regional atmospheric reanalysis that has been specifically generated for the Arabian Peninsula to explore the mechanisms behind the organized rainfall events over KSA. Nine major regions with distinct climate regimes were objectively selected to represent KSA rainfall climatology. The results demonstrate that organized thunderstorms over KSA only occur under sufficient moisture and environmental instabilities. Mesoscale convective systems responsible for organized rainfall generally develop and propagate with low-level moisture flow from the nearby seas (the Red Sea to the west and Arabian Gulf to the east) toward the desert. In the central part of KSA, the most frequent physical mechanism responsible for rainfall is winter extratropical influence, followed by spring extratropical–tropical interactions, and spring tropical influence. The east coast is characterized by two rainfall modes: a continuous southwest–northeast rain corridor and concentrated southwestern rain. Large-scale organized convection following three physically distinct mechanisms (extratropical, transition and tropical) is revealed along the west coast. 

precipitation Saudi Arabia weather pattern classification Moisture Storms Tropics