Orographically induced flows contributing to convective storm initiation: A review

Mountainous regions worldwide are seasonal hotspots for convective storms. Orographic deep convection is integral to local hydrologic cycles yet poses distinctive natural hazards and remains difficult to forecast, with impacts often extending into adjacent lowlands and densely populated areas. This review synthesizes the current understanding of how terrain-atmosphere interactions and orographically influenced mesoscale flows affect convection initiation (CI) over inland midlatitude complex terrain. The discussion is organized around thermally and mechanically driven processes that control the regional distribution of the three basic CI ingredients, moisture, instability, and lift, with lift being the ingredient most directly modified by mountainous terrain. Under weak synoptic forcing, elevated terrain typically generates thermally driven circulations, whereas stronger background flow forces air to ascend over or divert around topographic barriers. In both regimes, orographic ascent can facilitate CI, especially when combined with terrain-induced modifications of the prestorm thermodynamic environment that enhance low-level moisture and instability. However, convection may be suppressed by shallow cool or stable near-surface layers, persistent intermountain inversions, leeside drying, and mixing by downslope winds, or large-scale warm, dry elevated layers. Orography also exerts a broader regional influence because sufficiently high ranges can modify surface-atmosphere exchange and flow regimes far from the terrain, increasing CI frequency, the propensity for severe weather, and forecast uncertainty. The paper highlights the need for future meso- and microscale research in mountain environments to improve the understanding of CI distributions and their associated societal impacts.