Spatiotemporal variability in cloud base height and cloud fraction across the Virginia Blue Ridge Mountains

Clouds are currently poorly represented within climate models, thus acting as one of the biggest remaining uncertainties in climate forecasts. To mitigate the paucity of understanding and to improve the accuracy of current and future climate models, it is necessary to develop detailed accounts of cloudiness parameters on the mesoscale domain. In the present study, we investigate local differences in low-level cloud base height from June 2013 to May 2014 and the role that complex terrain and surface meteorology plays in these observed differences over two sites east and west of the Virginia Blue Ridge Mountains (BRM), USA. Low-level cloud ceiling is significantly higher over the drier valley (west of the BRM) for the full period of record (p<0.01), and during the summer (JJA) and spring (MAM) months (p<0.01). These differences are attributed to the relative dryness of the Page/Shenandoah valley (west) compared with that of the Virginia Piedmont region, and the resultant differences in diurnal temperature range. Cloud fraction was highest during the summer months (JJA) and lowest during the winter months (DJF) over both sites. This study illustrates the necessity to consider cloudiness on the mesoscale, as cloudiness can vary significantly between adjacent localities, particularly over complex terrain.