Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Risk of isolated thunderstorms producing downpours and wind gusts over northwestern NB, and northern Gulf of St. Lawrence regions.

Convective Discussion

This morning, the upper ridge at 500mb remains positioned from Hudson Bay to Maine. At the surface, a warm front extends from a low pressure area over northern Ontario to James Bay then southeastward through central Quebec, Maine and western Nova Scotia. Based on this mornings upper air soundings, the most likely areas for convective activity today is northwestern New Brunswick. Surface moisture is increasing over northern Maine and some of this moisture will have to advect over NB in order for convection to initiate.

Modifying the Caribou profile with a surface temperature of 32 and dewpoint of 18 results show:

·         Mixed layer cape values in excess of 1000 J per kg

·         A fair amount of this instability would be situated between 700-450 mb which would suggest a chance of hail (possibly around 1cm)

·         Slow moving storms could produce downpours with precipitable water in order of 30mm

·         And finally wind gusts 40kt or more.

 

On Monday, a non-tropical low pressure system east of the Carolinas will reach Georges Bank and bring isolated showers and thundershowers to the Atlantic coast of Nova Scotia. Further north, afternoon thunderstorms are possible.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

 

Nova Scotia and New Brunswick: A risk of thundershowers this afternoon and early evening.

Newfoundland and Labrador and Prince Edward Island: None

 

Convective Discussion

 

Cape values of 500-1000 J/kg and shear of less than 20 kts will yield the potential for pulse storms along a weak trough over western NB and NS this afternoon and evening. If the convection does occur then the slow moving cells could give local downpours of 25 mm or higher.  The precipital water indicates 25-30 mm. Dry mid-levels will give the potential for some gusty winds if the convection does occur.  

 

Thunderstorm Outlook for Day 2

 

Pulse storms possible for northwestern NB on Sunday giving similar impacts as this afternoon.

 

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

 

Low risk of high based thunderstorms over the higher terrain in northern New Brunswick and western Newfoundland late this afternoon and evening. Convective downdraft gusts are the main concern should anything develop.

 

Convective Discussion

 

A very hot and slightly humid air mass continues to reside over the Maritime provinces today. A trough over southern Labrador into northern Newfoundland will slowly sink southward today and reach northeastern New Brunswick and the Gulf of St. Lawrence tonight.  Temperatures profiles over NB this morning suggest a very dry air mass but with a lot of buoyant potential.  An isolated thunderstorm cannot be ruled out, especially with the help of forcing from hills and where forest and other vegetation may provide the extra moisture and energy needed or with the help of a sea breeze convergence off the Bay of Chaleur. The forecast highs are such that the convective temperature of 37 could even be reached on its own. Given such a dry and warm profile at all levels, there may not be much in the way of precipitation but convective wind gusts could be a concern. There may be a similar situation off the higher terrain in southwestern Newfoundland.

 

 

Thunderstorm Outlook for Day 2

 

Daytime heating air mass type thunderstorms are possible mainly over Maine tomorrow afternoon but with the slight winds aloft from the west, some of these cells could reach into western New Brunswick in the evening. The risk remains very low as mixing in the low levels may inhibit development. A ridge of high pressure  sinks south into Newfoundland and Labrador tomorrow with no convective weather expected.

 

 

 

Roberta McArthur

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Slight risk of a non-severe thunderstorm over southern portions of the interior of Newfoundland later this afternoon.

 

 

Convective Discussion

 

Over Newfoundland, an area of surface based instability is expected to develop later this afternoon over unpopulated interior areas of the island. This is supported by a weak disturbance embedded in the strong northwesterly flow aloft. One condition for the destabilization to occur would be for the current cloud deck to break-up/scatter out which should happen beginning over the west coast during the early afternoon, then later over inland areas.   

Warm and dry conditions will prevail over the Maritimes today.

 

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Hot and somewhat more humid conditions are in store for Friday across the Maritimes. Some of this (modified) airmass will try to push across Cabot Strait into southwest NF. Temperatures profiles over NB are supporting the potential for the development of an isolated thunderstorm, especially with the help of forcing from hills and  where forest and other vegetation may provide the extra moisture and energy needed.

 

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