who are its member states?
British Caribbean Territories (joint meteorological organization and membership), French Polynesia, Hong Kong, Macau, Curaçao and Sint Maarten and New Caledonia.
World Meteorological Organization
The six WMO Member Territories are the British Caribbean Territories (joint meteorological organization and membership), French Polynesia, Hong Kong, Macau, Curaçao and Sint Maarten (joint meteorological service and membership) and New Caledonia. (List of all members with admission dates.)
what time of year is hail most likely In North America it occurs between  March and October,with the bulk of the occurrences from May through September. what does it refers to? Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet") what are the factors favoring it? Movement of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. what cases of it are recorded? Megacryometeors, large rocks of ice that are not associated with thunderstorms, are not officially recognized by the World Meteorological Organization as "hail," which are aggregations of ice associated with thunderstorms, and therefore records of extreme characteristics of megacryometeors are not given as hail records where is this mentioned organization based? UNANSWERABLE who governs it? Convention of the World Meteorological Organization
wiki:19672204
World Meteorological Organization [SEP] Membership
As of May 2019, WMO Members include a total of 187 Member States and 6 Member Territories. Ten United Nations member states are not members of WMO: Equatorial Guinea, Grenada, Liechtenstein, Marshall Islands, Palau, Saint Kitts and Nevis, Saint Vincent and the Grenadines and San Marino. Cook Islands and Niue are WMO Members but non-members of the United Nations. Vatican City and State of Palestine and the states with limited recognition are not members of either organization. The six WMO Member Territories are the British Caribbean Territories (joint meteorological organization and membership), French Polynesia, Hong Kong, Macau, Curaçao and Sint Maarten (joint meteorological service and membership) and New Caledonia.