Day 1 Convective Outlook for Atlantic Canada Valid for July 25, 2018

 

Convective discussion:

 

There is the risk for non-severe thundershowers over southern Labrador, in the Annapolis valley area of Nova Scotia and over the southwestern marine waters this afternoon and evening.

 

Technical Discussion:

 

A warm front currently over southern Labrador is lying near quasi-stationary today. There is the slight risk of embedded thundershowers along and north of the front today and into the  overnight hours where cloud top cooling may help to destabilize the air mass further. Precipitable water values are ranging between 40-50mm so locally heavy downpours are possible. The area from Goose Bay toward Cartwright is already under a rainfall warning.

 

There is a slight risk of a thundershower over Nova Scotia this afternoon, especially in the Annapolis Valley where clouds are expected to clear, allowing convective temperatures to be reached. There is no real trigger over the area other than ample moisture and moderate instability so anything that develops will not be long lived but given the high precipitable water levels, a locally heavy downpour is possible.

 

On the northwestern edge of the ridge, some thundershowers are occurring over West Scotian Slope and approaching Georges Bank and will likely continue to slowly push northward today.

 

Regional Impacts:

 

Nova Scotia: Slight chance of a thundershower.  

 

Labrador: Chance of thundershowers with local downpours.

 

Southwestern marine waters: Thundershowers this afternoon.

 

New Brunswick, Prince Edward Island and Newfoundland: Nil

 

 

 

Roberta McArthur

 

Day 1 Convective Outlook for Atlantic Canada Valid for July 24, 2018

Convective discussion:

 

Risk of non-severe thundershowers over southern Labrador today and tonight.

 

Technical Discussion:

 

A warm front will move into southern Labrador today. Abundant cloud is associated with the warm front so just a chance of embedded thundershowers near and north of the front are expected. Precipital water is 30-50 mm so local downpours in thundershowers are possible.

 

Regional Impacts:

 

New Brunswick: Nil.  

 

Nova Scotia and Prince Edward Island: Nil

 

Newfoundland: Nil.

 

Labrador: Chance of thundershowers with local downpours.

 

 

 

 

 

 

 

Day 1 Convective Outlook for Atlantic Canada Valid for July 23, 2018

 

Convective discussion:

 

Convective activity will be generally low in Atlantic Canada today due to lack of sunshine throughout much of the Maritimes and Newfoundland. However, isolated t-shwrs are likely in NS where sunshine and high dew points initiate convection. Although Cape Breton is not in the minor threat area on the map, any t-shwr activity in Antigonish County could move into Inverness County.

 

Unlike yesterday, Labrador shouldn’t see any significant convection due the passage of a cold front followed by a ridge of high pressure.

 

Technical Discussion:

 

If convection occurs in the Maritimes and Newfoundland, CAPE will be low due to warm air aloft. Shear is low in NS so t-shwrs that occur would be non-severe. Shear is moderate in NB, PE, and NF so longevity and separation of updrafts and downdrafts could occur if t-shwrs formed.

 

T-shwr activity is unlikely in NB, PE, and NF due to cloud and showers and lack of a trigger other than sunshine which generally is not expected or not expected to persist. Sunshine could be a trigger in NS.

 

Regional Impacts:

 

New Brunswick: very unlikely

 

Nova Scotia: Isolated non-severe thundershowers likely Valley and northern mainland.

 

Newfoundland: Unlikely.

Labrador: Very unlikely

 

 

 

 

 

 

 

 

Day 1 Convective Outlook for Atlantic Canada Valid for July 22, 2018

Convective discussion:

High probability of thunderstorms in western and central Labrador. Heavy rain, gusty winds and possible hail would likely accompany these thunderstorms. There is a slight possibility of severe conditions.

Thundershowers will likely persist south of NS and NF with the southern Avalon remaining in the risk of non-severe thundershowers.

Technical Discussion:

CAPE values could exceed 1000J/kg in western Labrador. In addition, 0-6 km shear would be in the 40-50 knot range. Supercells and squall lines are possible.

Regional Impacts:

New Brunswick: Nil

Nova Scotia and Prince Edward Island: Nil, except a very slight risk northern mainland NS if a period of prolonged sunshine occurs this afternoon.

Newfoundland: Chance of a thundershower on the Avalon.

Labrador: Likely.

Day 1 Convective Outlook for Atlantic Canada Valid for July 21st, 2018

Convective Discussion

Isolated thundershowers are occurring near Wabush/Lab City this morning along a frontal boundary that’s sitting across the region. As the boundary slowly progresses east-northeastward today, this activity should continue to progress along that zone. Later today (just south of the front) convection is likely to become more widespread once surface heating is maxed. A weak upper low and associated surface low south of NS will gradually move northeastward today and tonight giving isolated thundershowers to portions of NS and NL.

Technical Discussion

There is a slight risk of severe thunderstorms for extreme western Labrador this afternoon and early evening. Upper air analysis shows a fairly strong jet streak, placing WRN LAB in the right entrance region (though there is no diffluence aloft) There is a weak upper 500 mb trough north of the region but that really doesn’t advect into the region as the day progresses. There is a decent tongue of moisture at 850 analyzed from the Great Lakes into south-central Quebec. The question is how far northeastward will this stretch through the course of the day. The instability is there and 12Z tephis shows about 30-40 knots of shear, in addition the surface boundary being the trigger. Moisture will be the key ingredient to generate strong storms this afternoon. YZV shows good lapse rates in the low-mid levels with drying conditions about 700mb. Adjusting the surface T and Td can generate CAPEs of close to 1000 J/Kg and associated DCAPEs of around 600-800. If cells develop, strong wind gusts (close to 80 km/h), small hail and heavy downpours will be the concern.

The upper level low and associated PVA south of NS will give some isolated thundershowers as it progresses to the northeast (although it will be weakening over time). Precipitable water is quite high so the only concern would be torrential downpours. Even in the presence of embedded TCU, heavy rain can be expected.

Regional Impacts

For Labrador

Possible strong winds, small hail, frequent lightning and heavy downpours for the YWK area. OTWZ isolated thundershowers within the grey zone.

For Nova Scotia and Newfoundland:
Isolated thundershowers giving torrential downpours are possible.

For New Brunswick and PEI:

Nil.

Jeremy