Convective Outlook Valid for Today and Tomorrow

Regional Impacts

isolated non-severe thunderstorm over western Labrador this afternoon.

 

Convective Discussion

Aloft this morning there is an east-west oriented ridge over the Great Lakes and the Maritimes. To the north, a frontal band extends from Labrador westward to northern Ontario and the eastern Prairies. At the surface, rain continues fall along  a warm front which is moving towards the Labrador coast and the Great Northern Peninsula of NF. Moist and somewhat unstable airmass will prevail over the rest of Labrador this afternoon and into the evening. Based on the soundings from YZV and LG4, the expected daytime high (low to mid-twenties) should be enough to produce an isolated cell, especially over southernmost areas. Very strong winds aloft may not permit much vertical development, but considering the amounts of moisture brief moderate showers are a good possibility along with winds mixing to the surface and giving gusts between 50-70 km/h.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

Slight risk of a thundershower over Southeastern Labrador

 

Convective Discussion

The tail of a weak departing trough currently over the south Labrador coast could provide enough forcing for showers and a weak thundershower to develop until mid-afternoon. This region is on the southern periphery of pool of cold air aloft. Forecast guidance is suggesting a small area of surface-base CAPE in the 100-200 J/kg range, and the lighting guidance is also indicating a chance of lightning over the same area.    

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts:

 

Labrador: a chance of thundershowers this afternoon into this evening with gusty winds (weak dry microburst)

 

Offshore waters south of  Nova Scotia and Newfoindland: embedded convection with heavy downpours.

 

Convective Discussion

A deep cold trough is moving into western Labrador with some associated PVA and a left exit region from the upper jet west of the trough. There’s also a little cold advection. Near the surface there is a capping inversion that will weaken this afternoon. The main limiter here is moisture and CAPE. PWAT is only 15 mm, dew points are pretty low, and if the upper lift is strong enough you might get 200 J/kg. There’s moderate deep layer shear as well. There’s a chance for a weak dry microburst, which will probably be the major impact. Conditions will improve overnight.

 

For the offshore waters, it’s a continuation of the rationale from yesterday, with an inverted trough as the trigger for a saturated moist adiabatic profile. Shear is moderate near the trough, but mainly less than 35 kts. So mainly rain and some gustry winds.

 

 

 

 

Thunderstorm Outlook for Day 2

 

 

There may be some convection overnight and into Tuesday morning just south of Labrador, but there’s only a slight chance of it reaching towards the Strait.

Convective Outlook Valid for Today and Tomorrow

 

Thunderstorm Outlook for Day 1

 

Regional Impacts: None for land areas of the Atlantic Provinces. A chance of embedded convection with occasional heavy showers for Nova Scotia slope waters spreading northeast towards Sable later today and approaching southeastern Newfoundland overnight.

 

Convective Discussion

There is a ridge extending from the Great Lakes ENE into  the South Labrador Sea, with a second ridge southeast of Newfoundland into the mid Atlantic. Between these two features is a northeast-southwest trough over Newfoundland.  Above the western ridge is a nearly stationary upper trough extending from Lake Erie along the St. Lawrence river towards southern Labrador. Southwest of Newfoundland the surface trough is intensifying as an inverted trough slowly moving toward the Avalon Peninsula tonight and  on Monday.

 

The basic story is that near and under both ridges things are stable under subsidence inversions around 700 to 850 mb, with very little precipitable water and near zero CAPEs, and with wind shears around 40 kts over the Maritimes, and for western Newfoundland approaching 70 kts. So little water, negligible CAPE, and high shear should kill any chance of thunderstorms.

 

For the Scotian Slope and approaching southern Newfoundland things are a bit less definitive. The aforementioned inverted trough is forecast to intensify and extend towards the Avalan. There’s deep moistire and PWs  in the 35-45 mm range, an almost tropical moist adiabatic profile. And the trough as a possible trigger. Shear is weak near and south of the trough, but just north it increases to the 30-40 kt range. My best guess is elevated weak convection with some heavy showers, extending to south of Newfoundland overnight, and maybe brushing the southern Burin or Avalon on Monday.

 

 

 

Thunderstorm Outlook for Day 2

See above.

Convective Outlook Valid for Today and Tomorrow

 

Thunderstorm Outlook for Day 1

 

Regional Impacts: no severe weather expected.

 

Convective Discussion: There is a large ridge centred north of Lake Superior and another large ridge east of the Grand Banks, with a weakening trough over the Atlantic Provinces between them. There is some dynamic support, but the ridging from the west is resulting in a fairly strong subsidence inversion capping convection for the Maritimes and western and northern Labrador.  For southeastern Labrador there is a frontal trough, but increasing cloud and low precipitable  water,  as well as a higher inversion at about 700 mb, argues for a few moderate to heavy showers at worst.

 

Over Newfoundland the story is similar with the riding inversion being weaker, but still there between 850 and 700 mb, and without the trough in Labrador. Precipitable water is a bit higher, especially in the southeast, and deep layer shear is okay, but the inversion and relatively low dewpoints for most of the island are consistent with no CAPE likely in the guidance.

 

 

Thunderstorm Outlook for Day 2: no severe weather expected.