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.

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Newfoundland: Isolated thundershowers for western Newfoundland stretching eastward during the evening across the Island.

Labrador: Slight risk for an isolated thundershower over southeastern coastal regions.

New Brunswick: Isolated non-severe thunderstorms today for southern and western regions.

 

 

Convective Discussion

 

A slow moving upper level low resides over eastern Labrador stretching into the Labrador Sea. Some convection may ignite near the low centre today over southeastern coastal areas of Labrador today. A trough extending from Anticosti southwest towards the eastern townships in Quebec will move eastward today to lie over western Newfoundland towards southern New Brunswick this evening.

 

Areas of western Newfoundland could see some enhanced dynamics with the left exit of an upper level jet, combined with an approaching 500mb cold pool to help destabilize the environment ahead of the trough for late this afternoon into the evening and overnight hours. There is not much moisture with around 15 mm of precipitable water but decent uni-directional shear of 35KT could maintain convection with CAPE values between 200 and 500 J/kg. Some cloud-top cooling could maintain what may develop as it moves over western Newfoundland towards the east overnight.

 

Due to the quite cool area aloft over the Gulf of St. Lawrence, and decent uni-directional shear, there could again be a very slight risk of a waterspout develop over areas of eastern Anticosti, Gulf-Port-Au-Port, and Northeast Gulf marine areas this afternoon and evening.

 

Areas of southern Maine extending into southwestern New Brunswick will benefit from some enhanced upper level dynamics being in the area of the right entrance of an upper-level jet. A cold 500mb trough extending over central Maine combined with some warming at 850mb will help to overall destabilize the atmosphere. The only issue is the amount of rain and cloud moving through the area this morning, prohibiting much in the way of surface-based heating and areas over northern New Brunswick will likely not be able to break the warm cap at 700mb. Precipitable water values of 25-30mm over Caribou would suggest that some decent downpours are possible, but with strong 0-6km shear at 55KT a relatively strong flow aloft, cells would not likely see high rainfall rates for long. CAPE values also remain fairly weak at less than 250 J/kg. Some drier air between 700 and 500mb could mean some medium to strong downdrafts are possible and this will be the main concern with convection that develops this afternoon.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

 

Southeastern Labrador: Isolated non-severe thundershowers.

Eastern Gulf of St. Lawrence: Gusty winds and possible waterspouts this afternoon into this evening.

Newfoundland: Generally isolated to scattered non-severe thundershowers. For northeastern regions possible wind gusts to 90 km/h and rainfall amounts reaching 25 mm/h locally.

 

Convective Discussion

A trough crossing the Gulf towards Newfoundland, with a cold trough at 700 mb giving some enhanced instability, along with la left exit region currently east of Deer Lake eastwards towards Ganer, will give some strong updrafts. Moisture is modest with PWAT around 20-25 mm, but shear is in the 25-30 kt range. Profiles and the upper air analysis shows fairly dry air from 850 mm and up, combined with the destabilisation associated with the approaching upper cold trough, and should give some healthy downdrafts. Rainfall amounts under individual cells have a slight possibility to reach 25 mm/h with the fairly brisk speed of the individual cells, but some training may boost the amounts to warning levels.

 

The same cold upper trough over waters in the eastern Gulf near or exceeding 20 C, with a unidirectional strong flow up to or exceeding 850 mb, may give waterspouts this afternoon into this evening. For the Newfoundland coast SSTs are slightly cooler, especially north of Corner Brook and Gros Morne, but have more potential offshore for southern Gulf – Port au Port.

 

 

 

 

Thunderstorm Outlook for Day 2

 

A weak east-west trough dropping south over New Brunswick may produce some thundershowers with a possibility for high wind gusts late in the day. For Newfoundland there is a possiblilty for non-severe isolated thundershowers for the middle of the west coast east to the Baie Verte Peninsula.