Newfoundland has a Humid Continental climate (Köppen climate classification Dfb) influenced by coastal currents and icebergs. Summers are usually pleasant but brief. July mean temperatures remain cool along the southern and eastern coast, especially, with mean daily temperatures in the low to mid teens Centigrade. However, the interior enjoys warmer mean temperatures slightly above 15°C. In July, the maximum temperature can even occasionally rise to as high as 30°C in the interior! In winter, the Gulf of St. Lawrence, and the North Atlantic Ocean waters prevent temperatures in Newfoundland from dropping too far. Mean January temperatures range from -9°C to -7°C in the interior, to around -4°C, on the southern coastal areas.

The Gulfstream flows from the North American continent to the north central Atlantic Ocean and further towards western Europe and passes to the south of Newfoundland. Depending on propagation and distance from shore, this flow may directly influence the weather in Newfoundland by its warm water transport and resultant climatic change effects. In winter a more northerly coast-proximal propagation may result in humid air being transported into the region, with the resultant land-sea interaction leading to snow and precipitation. In Winter a more southerly Gulfstream flow may result in a greater outreach from the Labrador flow reaching Newfoundland, resulting in cold temperatures, fog in the north, clear skies in the south, In summer a more northerly propagation may result in warmer but more conditionally unstable situation, whereas a more southerly propagation may result in a more cooler and stable, yet perhaps hazier, stable situation.

Coastal fog is very frequent in the spring, on the east coast, because of the icebergs off shore. In the summer, when warm air flows from the south quadrant over the cold waters surrounding Newfoundland, fog engulfs the southwestern and southern coast … occasionally for days!

The entire island receives an abundant amount of precipitation, usually peaking in November, and reaching a minimum in April. Winter snowfall is normally in excess of 250cm everywhere, with amounts exceeding 400cm in parts of the western interior.

Spring rains often fall on still frozen ground and objects. Thus, ice storms are frequent in southern Newfoundland.

Shipping traffic in the St. Lawrence Seaway may affect smog in the area direct proportionally: eg. more shipping, more smog. This, however, is dependent on the airflow in and around the Newfoundland areas.

Airports

The following aerodromes across Newfoundland and St Pierre et Michelon are listed on SKYbrary

Climatic and Weather Phenomena Affecting Aviation in Newfoundland

• Fog - Fog, often persistent, affects airports in Newfoundland in spring and summer.
• Snowfall - although airports in the region are comparatively well prepared for winter weather, heavy snowfall can seriously affect operations and runway availability (see articles on Landing on Contaminated Runways and Runway Surface Friction). Pilots should also take care to ensure clearance from snow banks while taxying.
• Ice Storms - Freezing Rain is a significant hazard between February and May.
• Low Temperatures - Although the Atlantic waters moderate the temperatures during the winter months, care should be taken to apply Altimeter Temperature Error Correction when the aerodrome temperature is 0°C or colder.