Stuck with clouds, drizzle, fog each spring? Here’s why

Each spring season it seems without fail there is a period of dull, dreary weather in Atlantic Canada.

I’m not talking about those April showers, but days of clouds, rain showers – sometimes flurries, and drizzle. It’s often coined RDF – rain, drizzle, and fog.

Mark Peters, who lives in St. John’s, N.L., reached out noting spring weather in eastern Newfoundland is historically bad and is often blamed on north and east winds. He wanted to know what allows that to happen each season.

Several factors determine the placement and movement of our weather systems, but a large factor is atmospheric blocking that can be linked to phases in teleconnections such as the North Atlantic Oscillation – an index based on the surface sea-level pressure difference between the Subtropical Azores high and the Subpolar low.

A positive phase indicates below-normal pressure at high latitudes in the North Atlantic and above-normal pressure in the central North Atlantic.

It’s the opposite for a negative phase – above-normal pressure at high latitudes in the North Atlantic, and below-normal pressure in the central Atlantic. It’s that above normal pressure in the high latitudes that leads to atmospheric blocking causing low-pressure stall and retrograde near our region.

The strength and position of blocking high-pressure determines just how it influences the weather, but this can lead to days of damp, dreary weather. In addition to low-pressure, the northerly flow wrapping around both the blocking high and stalled low over the cold ocean waters causes the air to cool and condense to form rain, drizzle, and clouds.

It’s often northeastern Newfoundland that experiences the worst weather under this pattern, but it happens elsewhere in our region including this week in northern and eastern Nova Scotia, and Prince Edward Island.

On the other end, locations father south and west in Newfoundland and Labrador, Nova Scotia, and New Brunswick can experience more sunshine and warmth as the air dries out.

We might not like it, but as common as fog and the North Atlantic breeze, springtime RDF is embedded in the fabric of Atlantic Canada’s weather.