During extreme weather conditions the following organisations will provide up to date warnings:
British Isles

UK – Met Office / Warnings

Ireland – Met Éireann / Warnings
Europe

France – Meteo France / Warnings

Germany – Deutscher Wetterdienst (DWD) / Warnings
Scandinavia
Norway – The Norwegian Meteorological Institute / Warnings
Sweden – Swedish Meteorological and Hydrological Institute (SMHI) / Warnings
Iceland – Icelandic Met Office (IMO) / Warnings

Denmark – Danish Meteorological Institute / Warnings /Sea Ice
Finland – Finnish Meteorological Institute / Warnings
North America
Canada – Environment Canada / Warnings

USA – National Weather Service (Warnings found on home page)
Australasia

Australia – Bureau of Meteorology (BOM) / Warnings
New Zealand – MetService / Warnings
Asia
Japan – Japan Meteorological Agency (JMA) / Warnings
India – India Meteorological Department / Warnings / Monsoon