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

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

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

NB… Isolated thunderstorms possible this afternoon with heavy downpours of 15 to 25 mm/h.

PEI/NL… None

 

Convective Discussion

Today, an upper low sits stalled over the central Maritimes with two thunderstorm risk areas existing today with this feature; the first located over Nova Scotia, and the second over northwestern New Brunswick. MLCAPE values of 1000 J/kg are similar over both areas of interest, however better dynamics (35 to 40 kts of bulk shear) can be found over northwestern New Brunswick, so a few discrete thunderstorms are possible here this afternoon. These storms will have the potential to produce locally heavy downpours of 15 to 25 mm/h. In Nova Scotia, similar to yesterday, storms are expected to be more stationary leading to an increased risk of higher rainfall accumulations over localized areas today. Some of these storm may have the potential to produce rainfall rates of 20 to 30 mm/h, with higher accumulations possible under stationary cells.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB… Isolated thunderstorms giving some heavy downpours, mainly for western areas.

PEI… Isolated thunderstorms giving some heavy downpours, a chance of a funnel cloud east or potentially a waterspout over eastern marine areas.

NS.. Some thunderstorms, some potential for locally amounts over 25mm. A chance of a funnel or possible waterspout west of Cape Breton.

 

Convective Discussion

Yesterday back building thunderstorms tended to produce more local rain than expected, while not as likely there is still a chance that we may have more of these weak, slow moving, storms that seem to reform over areas of convergence/terrain and linger longer than would normally be expected with these types of thunderstorms. For the most part the airmass is fairly similar to yesterday with CAPE values ~ 1000 J/kg and surface Td’s in the mid teens. Rainfall rates could once again exceed 30mm/hr, if storms end up back building once again local amounts could be more than that rate. No doubt the slow moving upper trough over the gulf will aid in the instability through the day as storms are expected to slow intensify. A lack of solar insolation may slow things down somewhat when compared to yesterday but some areas will no doubt clear up a bit during the day.

 

There is a slight chance that a funnel cloud or possibly a water spout could form in the vicinity of the upper low over eastern gulf waters today and possibly into tomorrow. These should pose little risk to non marine areas but it is possible that they could impact some coastline if they occur. Marine waterspout watches have already been issued, and the funnel cloud sign on the outlook is for that possibility.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon