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.

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Some weak thunderstorms are likely to develop late today over northern New Brunswick. This evening and tonight the risk will spread through the gulf impacting western Newfoundland by the morning..

 

Convective Discussion

 

The atmosphere will continue to destabilize later today and through tonight as a cold upper trough makes its way through the region. Overall the amount of moisture has diminished over the last few days but steepening lase rate should be sufficient to generate stronger updrafts overnight and tomorrow morning for the eastern gulf waters and tomorrow afternoon for parts of Newfoundland.

 

For tomorrow deep shear and CAPE will continue to increase as the upper trough approaches, with ~40 knots of 0-6km shear and ~1000 j/kg. Organised convection is possible with a low probability of supercell formation. Strong wind gusts, 25mm + rain and small hail is possible.

 

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

For New Brunswick… local downpours of 20mm are possible for northwestern areas, however should organized thunderstorms develop possibly more.

 

For Northern Nova Scotia and southern Newfoundland… embedded thundstorms with weaker updrafts possible, some locally heavier rainfall could occur.

 

Convective Discussion

 

Today the vertical velocities should not be overly strong but despite this there is still a decent amount of moisture available with 30 + mm of precipitable water from the Sept-Iles and Caribou soundings. For today some locally heavy downpours and training of thunderstorms is possible and stronger returns are already showing up in Maine this morning. With daytime heating this should intensify further for western areas of New Brunswick into the afternoon.

 

Thunderstorm Outlook for Day 1

 

 

 

For tomorrow falling heights and increasing shear along with lowering freezing levels could lead to a larger hail potential and gusty surface winds.

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

No impacts due to thunderstorms are expected today.

 

Convective Discussion

 

Most of the deep convection today will remain to the west and to the south as an upper thermal ridge will suppress the deeper thunderstorm for the Atlantic Region. Solar insolation will kick in over new Brunswick and TCUs will quickly develop but the storms should not be deep enough to generate thunderstorm activity, although intense showers may be possible. Over the marine area large, heavy rain producing storms can be expected, with respectable deep shear of about 30 knots and CAPE values > 1000 j/kg some organised storms could develop.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2