Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

Newfoundland: embedded TCus and Isolated thunderstorms giving mainly high rainfall amounts, exceeding 50 mm, combined with synoptic rainfall.

Southern Labrador: isolated to scattered thundershowers

Marine for southern Gulf of St. Lawrence, Cabot Strait and southern Gulf – Port au Port: Slight chance of waterspouts late this afternoon into this evening with gusts to gales possible.

 

Convective Discussion

A low over southern Labrador has a frontal trough extending southeast  to western Newfoundland. Ahead of the trough a strong southerly  jet extending from near the surface to midlevels is advecting significant moisture. While the tephi profiles are marginal at best, with low level capping,  lower level lift and moderate PVA, combined with some orographic forcing along the southern coast of the island, will give some enhance embedded TCus  and isolated CBs to enhance rainfall amounts. Winds will be brisk just with the synoptic forcing, and freezing levels are probably too high for anything significant.  For Labrador the situation is similar, but without the moisture feed. Almost moist adiabatic profiles with drying above 700 mb, with PWAT between `15-25 mm and southerly shear around 25 kts, argues  for isolated to scattered thundershowers with some gusty winds. With freezing levels near 5000 feet, small hail is definitely possible.

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB and PEI: for this afternoon numerous clusters of strong thunderstorms producing heavy downpours 25+mm, hail 1cm, and gusts between 60-90 km/h.

Newfoundland&Labrador: Very moist airmass with isolated embedded thunderstorms spreading throughout the province - producing rainfall amounts in excess of 50 mm.

 

Convective Discussion

Surface Low pressure over Lower Quebec North Shore with cold front extending southwestwards along the St. Lawrence Valley. A southerly low level jet is spreading moisture from the Gulf of Maine across NB to Western Labrador. While steady rain is expected over northern regions, multi-cellular thunderstorms will continue to develop ahead of the advancing cold front. The threat of these storms becoming severe is reduced over areas where showers and thunderstorms have already developed during the morning. The focus will now be over southernmost NB and PEI for the most robust storms, and the main threat will remain the possibility of EF0-1 wind damage.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

This afternoon until early evening: Isolated thundershowers over southern Labrador and central and eastern Newfoundland. Brief moderate showers with wind gusts between 50-70 km/h are possible.

Tonight: A few thundershowers over western and southern New Brunswick and western Nova Scotia. Brief heavier showers.

 

Convective Discussion

A number of weather features stand out this morning. The 500mb upper trough extends from the Labrador Sea to Northeastern Gulf of St. Lawrence, and a weakly cyclonic upper jet stretches from the Quebec North Shore to Southeastern Newfoundland. The cold air aloft more than makes up the limited surface heating and so a few cumulonimbus will develop this afternoon despite CAPE values between 250-500 J/kg. The airmass is drying nicely as open cellular pattern forming over the region. Weak downdraft could produce wind gusts between 30-40 kt.

 

A warm front will advance over the Maritimes tonight, but it will be quickly followed by a cold front advancing from Quebec Tuesday. Along the warm front some embedded non-severe thundershowers may touch westernmost areas.

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Newfoundland and Labrador: Slight risk for an isolated thundershower this afternoon over southeastern Labrador and northern regions of Newfoundland. Slight risk of embedded thundershowers overnight over the Gulf of St. Lawrence and southwestern Newfoundland.

 

Convective Discussion

 

An upper level feature over Labrador with a cold 500 mb trough slowly moving eastward will provide some instability in TCUs and showers for much of Labrador and northern Newfoundland today. Some brief heavy downpours are possible with cells that develop given freezing levels around 7000 ft and precipitable water of around 20 mm. A quick moving short-wave trough currently over central Quebec will swoop though northern Gulf of St. Lawrence overnight and over Newfoundland by Monday morning. There may be a slight risk for embedded convection in the morning hours.

 

Some TCUs in showers are expected this afternoon over northern New Brunswick. The 12Z Caribou sounding shows a sharp warm nose from 650 to 500mb and the convective temperature today is likely not going to be high enough to break that cap, thus no thundershowers are expected. A second short wave trough over southern Quebec this evening is expected to slide southeastward and some overnight convection along the warm front may clip western parts of the maritime marine district Monday morning.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Labrador: Isolated non-severe thundershowers this afternoon. Locally heavy downpours and small hail will be the main threats.

 

Nova Scotia: Isolated non-severe thundershowers this afternoon mainly along the spine and towards the Atlantic coast this afternoon. Locally heavy downpours and moderate wind gusts will be the main threats.

 

 

Convective Discussion

 

An upper level low over the Labrador Sea with a trough extending southwestward into southeastern Labrador and the Lower North Shore Quebec will initiate some convection this afternoon and evening. There is some slight cooling aloft with orographic lift to aid in thunderstorm development. Southeastern Labrador could see CAPE values of around 400 J/kg with precipitable water around 20 mm. 0-6km shear is however quite low so cells that do develop could give some brief heavy downpours but would not last long. With freezing levels of around 7000ft, small hail is possible.  TCUs in showers are expected further west into western Labrador throughout the day where some slight warming aloft is expected to cap and further development.

 

A second trough extends from the Avalon Peninsula towards the Atlantic coast of Nova Scotia this morning. Some initiation is possible behind the trough given the daytime heating in clearing skies with the possible help of a sea breeze along the spine of Nova Scotia. The upper dynamics are not as favourable, however, with a warm nose at 700 mb to overcome and drier air moving in behind the trough. If cells initiate they should move in a west/northwest direction toward the Atlantic coast and fizzle by the evening. Precipitable water is in the mid 20s and some moderate mainly uni-directional 0-6km wind shear near 40KT could keep cells that initiate going with some locally heavy downpours and moderate wind gusts possible. As this trough continues further south into the Maritime slope waters, the warmer surface temperatures as well as any convective cloud top cooling could initiate overnight convection for tomorrow morning. CAPE values in excess of 1000 J/kg and moderate 0-6km shear will help in organization of a possible organized line over East Scotian Slope and Laurentian Fan.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Instability associated with a cold pool dropping in from Hudson Bay and low pressure over Labrador could initiate some convection over central Labrador and into northern Newfoundland tomorrow. A short-wave trough will be moving into the Maritimes from southern Quebec tomorrow which could have some embedded convection associated with it as it tracks across southern New Brunswick into Nova Scotia overnight into Monday morning.