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

Convective Outlook Valid for Today, Tonight and Tomorrow

 

Regional Impacts

 

Today

NS/PEI/NL…Heavy downpours with rainfall rates of 20 to 40 mm/h with slight risk of embedded convection.

NB…Slight risk of a thundershower over northwestern regions.

 

 

Tonight

NL/LAB…Heavy downpours associated with Ernesto to affect southeastern Newfoundland.

NB…Locally downpours with risk of embedded thunderstorms possible.

 

 

Tomorrow

NB/PEI…Locally downpours with risk of embedded thunderstorms possible.

NS/NL/LAB…None.

 

 

Convective Discussion

The centre of Ernesto is beginning to track into the southern marine waters and northeast towards the Avalon Peninsula of Newfoundland tonight. Some bands of heavy rain with a few embedded thunderstorms have begun to move north into Nova Scotia this morning and southern Newfoundland well ahead of Ernesto. With precipitable water near 55 mm over this area, rainfall rates could be high at times today. As the actual storm moves south of the Avalon tonight, rainfall rates are expected to be high for a short period of time. There is a slight risk of embedded thunderstorms with the passage of this storm as well today and overnight.

 

A shortwave trough over southern Quebec and New England will slowly move eastward to lie over New Brunswick tomorrow then stall across the region. Heavy downpours are possible with this especially over northwestern New Brunswick as this trough slows further.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NL/LAB… Scattered thunderstorms possible across Labrador today with downpours of 15 mm/h.

NS/NB/PEI… None.

 

Tonight

NS…Heavy downpours with risk of embedded thunderstorms possible giving rainfall rates of 20 to 40 mm/h.

 

Tomorrow

NB…Slight risk of a thundershower over northwestern regions.

NL/LAB…Heavy downpours ahead of Ernesto to affect southern Newfoundland.

NS/PEI…Risk of heavy downpours but thunderstorm risk is low at this time.

 

 

Convective Discussion

An upper trough stretches from southern Ontario northeastward into Labrador that is slowly moving eastward but will slow down as it begins to interact with Tropical Storm Ernesto over the next few days as the storm tracks over the southern marine waters. A shortwave trough over southern Ontario has been fairly active with convection yesterday and continued overnight into this morning. This shortwave will slowly drift eastward and weaken somewhat today. A secondary trough south of Ungava Bay this morning will help stretch moisture into western Labrador. MLCAPE values in southern Labrador are forecast to rise upwards of 1000 J/kg today along with mainly linear bulk shear values of 20 to 30 knots. With precipitable water forecast to increase to 30 mm, the main hazard today will be torrential downpours of 15 mm/h but brief strong wind gusts are possible if discrete cells organize into lines.

 

As Hurricane Ernesto continues northward and begins to enter the southern maritime waters early on Monday, an area of heavy downpours is possible well ahead of the circulation that will affect the southern maritime provinces on Monday with a slight risk of embedded thunderstorms mainly for overnight and early Monday with the help of cloud top cooling. Precipitable water is forecast to increase above 55 mm across Nova Scotia then east towards southern Newfoundland by Monday night.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NL… Scattered severe thunderstorms possible across southern Labrador today. Main hazards are strong wind gusts of 70 to 90 km/h, heavy downpours of 25 to 35 mm/h, and 1 to 2 cm hail.

NS/NB/PEI… None.

 

Convective Discussion…

After a busy couple of days in the Maritimes, the focus shifts to southern Labrador today, where an upper trough with some diffluent upper level flow brings the risk for some scattered severe thunderstorms this afternoon. MLCAPE values are forecast to rise upwards of 1500 J/kg today over southeastern Labrador, leaving plenty of fuel for thunderstorms to work with. In addition, bulk shear values of 25 to 35 knots in the same area increases the potential for some of these storms to become severe. Shear is expected to be fairly linear, however some curvature of the low level winds is possible early on in the afternoon. As such, a discrete supercell or two cannot be ruled out early this afternoon, before storms become more linear later on. The main hazards today will be torrential downpours of 25 to 35 mm/h, strong wind gusts of 70 to 90 km/h, and 1 to 2 cm hail.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS… Scattered thunderstorms today with heavy downpours of 20 to 30 mm/h.

NB… Slight chance of an isolated thundershower over northern New Brunswick this afternoon, with downpours of 10 to 20 mm/h.

NL… Slight chance of an isolated thundershower this afternoon over extreme southern Labrador, with downpours of 10 to 20 mm/h.

PEI… None.

 

Convective Discussion…

The upper low that brought severe thunderstorms to parts of the Maritimes yesterday will move east over Nova Scotia today. This once again brings the risk for some scattered thunderstorms that will be capable of producing heavy downpours. MLCAPE values over 1000 J/kg will provide ample instability to get convection going under the upper low this afternoon, weaker bulk shear and lower PWAT values over central mainland NS keeps the risk slightly lower here. Higher PWAT values of 30-35 mm over eastern mainland NS and parts of Cape Breton increase the potential for severe thunderstorms here, with rainfall rates of 20 to 30 mm/h possible. Localized flooding will also be a risk under storms that remain slow moving today.

There also exists a very slight risk for an isolated non-severe thundershower in northern New Brunswick and extreme southern Labrador this afternoon. Smoke aloft over Labrador in addition to a thermal ridge above 700 mb may inhibit convection here today as storms will struggle to get going.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp