Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NL/LAB… Isolated thundershowers with be locally heavy downpours of 10 to 20 mm/h and small hail of 1 cm or less. There is also the possibility of cold core funnels.

 

Tomorrow

NB/LAB…Isolated thundershowers giving locally heavy downpours of 10 to 20 mm/h.

 

Convective Discussion

A rather cold upper low continues eastward this morning over Newfoundland and into the Labrador Sea with a risk of some isolated thundershowers in northern and central Newfoundland and southeastern Labrador today. This area has a history of waterspouts over the Gulf of St. Lawrence and with continued cold air aloft, relatively warm surface land and water and topographic influences will aid in the potential of cold air funnels today over Newfoundland as this low continues eastward.  With MLCAPE values around 800 J/kg, and weakening strait line bulk shear of 15KT, any thundershowers that develop are unlikely to become severe. Nonetheless, some brief heavy downpours of 10 to 20 mm/h will be possible and with lower freezing levels given the cold air aloft, there is a risk of small hail.

 

Another weak low is expected to move towards western New Brunswick and Labrador from Quebec tomorrow. Daytime heating and some instability will allow for pop-up convection ahead and near the centre of this low is where the risk of thunderstorms will be. There is little shear but moderate precipitable water so some locally heavy downpours are possible.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

 

Roberta McArthur

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NB/NS/PEI/NL… Slight chance for some isolated thundershowers today across central Atlantic Canada. Main hazard will be locally heavy downpours of 10 to 20 mm/h.

 

Convective Discussion…

An upper low moving northeast into the Gulf of St. Lawrence this morning brings the risk for some isolated thundershowers across central Atlantic Canada today. Convection will be focused near the center of the upper low, though better bulk shear values (40 to 50 knots) to the east, closer to the Cabot Strait, may allow for some thundershowers to develop over Cape Breton and western Newfoundland later this afternoon. MLCAPE values are quite low across the region today, less than 750 J/kg, so thundershowers are unlikely to become severe. Nonetheless, some brief heavy downpours of 10 to 20 mm/h will be possible.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NB… Slight chance for some isolated thundershowers this afternoon and evening. Main threat is locally heavy downpours of 10 to 20 mm/h.

NS/PEI/NL… None.

 

Convective Discussion…

An upper low currently sitting over the St. Lawrence Valley will be the main trigger for convection today. The low will slowly begin to move east this afternoon, with convection expected to fire in Maine before crossing the border as the low moves into western New Brunswick. Instability is expected to be quite limited today, with only up to 500 J/kg of MLCAPE forecast this afternoon. Modest bulk shear of 15 to 25 knots should inhibit most storms from becoming too organized, so severe weather is not expected today. Nonetheless, the upper low should be enough to fire a few weak thunderstorms later this afternoon in western New Brunswick once convective temperatures (20 C) are reached, with locally heavy downpours of 10 to 20 mm/h being the main risk.

 

This low will continue to move east tonight, to lie over Anticosti Island by tomorrow afternoon. As such, most of the convection will be centred over the Gulf of St. Lawrence tomorrow. As the low moves into the Gulf early tomorrow morning, relatively warm waters of 18 to 20 C in the area of interest, and the cold upper low, should provide enough instability and vorticity for convection. With this, there exists a slight chance for a waterspout off the Acadian coast of New Brunswick in the morning hours.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Maritimes… Isolated thunderstorms giving 15-30mm, some potential for torrential downpours today. Some stronger wind gusts possible.

Newfoundland… Isolated thunderstorms giving 15-30mm, some potential for torrential downpours today. Some stronger wind gusts possible. Heavier downpours along south coast possible overnight.

 

Convective Discussion

Most of the region will remain under this moist airmass for today and into tomorrow for Newfoundland. The most probable areas for isolated severe storms have been highlighted but it should be noted that intense rainfall could set up in various locations today and warnings ,if required, would be very short fused. There are a few areas that lend themselves to a slightly higher potential due to severe thunderstorms, including interior Newfoundland and central parts of the Maritimes. The break up of the cloud is already happening in these areas and along with the solar heating there are potential triggers for convective initiation in these areas. Surface based CAPE is likely to exceed 1000 j/kg in these areas and with the approaching upper trough at 500 there is ample shear of >50 kts for longer lived thunderstorms. Despite some of these values, updrafts are still somewhat weak with thin CAPE that could be sheared off initially, possibly impeding the deeper convection somewhat.

 

The other area of interest will be likely be along the south coast of Newfoundland tonight as the atmospheric river sets ups just over the eastern part of the island, the instability may be high enough to bring rainfall rates over 40mm/hr, radar rainfall estimates and convection will have to be closely monitored through the evening and overnight.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow