Diurnal climatology of thunderstorms, precipitation spell and visibility over Uttarakhand

In this study, a detailed diurnal climatology of thunderstorms, precipitation spell and visibility are prepared using the hourly thunderstorm, precipitation spell and surface visibility data from four stations, viz., Mukteshwar and Tehri stations in hills and Dehradun and Pantnagar stations in plains of Uttarakhand. The charts, thus prepared, containing the hourly mean monthly frequency of occurrence (FO) and the hourly diurnal probability of occurrence (PO) of these three weather events can be utilised to identify the most or least probable day and hour of a day for the occurrence of these weather events over a specific region in Uttarakhand. The FO of thunderstorms is found to be higher over the hills of Uttarakhand during pre-monsoon season and plains during monsoon season. The analysis of the temporal characteristics of thunderstorms reveals higher PO during morning and afternoon/evening hours over plains and afternoon/evening hours over hills of Uttarakhand. The precipitation over Uttarakhand, as rain and drizzle, starts increasing in June, with peak FO of precipitation spells in July and August months. The FO of rain is substantially larger than the FO of drizzle throughout the year in stations of the Garhwal region, whereas over the Kumaun region, the difference in FO of rain and drizzle is not large. The study results show that the occurrence of fog over hills is more often during daytime in the monsoon season, whereas the PO of fog is higher during morning and late-night hours from the second fortnight of December till February over plains of Uttarakhand.