Large scale weather patterns working against the Maritimes as drought worsens

CTV Atlantic meteorologist Kalin Mitchell analyzes the weather patterns that continue to keep the Maritimes in a prolonged stretch of abnormally dry conditions.

In the latest update from Agriculture and Agri-Food Canada, areas of the Maritimes have now been analyzed as being in extreme drought. The larger scale weather patterns that have contributed to the extended stretch of dry weather continue as we approach mid-September.

Drought worsens in Maritimes

According to the latest report from the Canada Drought Monitor, the drought in the Maritimes worsened through August.

The report cites a top-five driest August on record for a number of locations, including parts of the Annapolis Valley, N.S., having the driest August on record with less than 15 mm of rain. Fredericton (fifth), Moncton (fifth), Saint John (third), Charlottetown (fourth) and Summerside (fifth) all landed in the top-five for driest August as well.

Areas that had been in severe drought deteriorated into extreme drought conditions. The report goes on to say surface water conditions are stressed. More municipalities have issued mandatory water conservation orders and “crop losses have been reported as irrigation ponds and wells dry up.”

Extreme drought is now impacting parts of the northeast and south of New Brunswick, Prince Edward Island, Annapolis Valley, northern areas of mainland Nova Scotia and Cape Breton.

Jet stream pattern not helping

We have a huge source of very moist air right next door: the Atlantic Ocean.

A large amount of precipitable moisture is produced by the sub-tropical Atlantic. That is moisture that would be available for low-pressure systems to convert into rain. It is the source of our version of “atmospheric rivers” narrow bands of moisture laden air that can feed into rain events producing higher totals.

Through much of the summer and now continuing towards mid-September, the pattern of the jet stream near Atlantic Canada hasn’t been directed enough south-to-north to really tap into that moisture source for a meaningful period of time. Instead it has been directing the moisture mostly towards the northeast of the region, towards the North Atlantic.

Likewise persistent ridging of the jet stream over western Canada has worked to prevent periods of moisture from the Pacific from working more directly west-to-east. Hence less rain events from that direction as well.

High pressure dominates

Even if moisture from the sub-tropical Atlantic was directed into the Maritimes, it is only one needed ingredient. You need a weather system to concentrate and lift that moisture up in the atmosphere to wring the rain out of it.

Much of this summer has seen persistent high-pressure systems in place over or close to the Maritimes. High-pressure systems produce subsidence or a sinking of the air in the atmosphere around them. That prevents the rising motion needed to produce cloud cover and precipitation.

The same jet stream pattern that has worked to steer moisture away from the region also has worked to steer low-pressure systems away as well. Frustratingly, there is a low-pressure system that will pass just far enough east of Nova Scotia Wednesday night into Thursday morning that the region will miss out on most of the rain with it.