Convective Outlook Valid for Augut 17 2019

Convective Discussion

No severe impacts expected. Highest chance for convection for Labrador from the west to the  Mid Labrador coast. A slight chance for Newfoundland this afternoon, and a chance for a thundershower to move into westernmost New Brunswick.

For Labrador a trough extending from Hudson Bay to the Mid Labrador Coast, combined with an upper jet over northern Labrador, with a right entrance near the trough axis, will give some support for lift. As the upper jet moves east this afternoon, so will the instability . Moisture isn’t great, with precipitable water in the 15-25 mm range. CAPEs are on the low, with the highest expected less than 500 J/kg,  with the highest amounts at the southern edge of the threat zone. Also shear is marginal at about 30 kts. Expect a few thundershowers with some moderate wind gusts. The freezing level is near 9000ft, so small hail is possible.

For Newfoundland there is little dynamic forcing. The there is a weak upper trough moving through, followed by weak ridging from mid-levels up, and an associated weak upper jet. The main forcing mechanism will be daytime heating, and some moisture. The 12Z tephigram from Stephenville was less stable than model guidance, and with a forecast high near 25 C and a dewpoint near 13 C, a parcel lift gave a CAPE around  300-400 J/kg. Based on this there is a chance for isolated thundershowers this afternoon, with some gusty winds.

Regional Impacts

Labrador: Occasional non severe thundershowers with some gusty winds and a chance for small hail.

Newfoundland: a possibility for isolated  thundershowers this afternoon.

New Brunswick: a slight chance for thundershowers this afternoon in the extreme northwest, but only if the cloud breaks up today.

Doug Mercer

Convective Outlook Valid for August 16th, 2019

Convective Discussion

 

A weakening short wave trough with an area of light to moderate rain over Maine this morning is expected to break up into scattered showers this afternoon as it pushes into western New Brunswick. The risk for thundershower activity this afternoon should remain over Maine into southern Quebec where dynamics are more favourable.

 

Meanwhile, there is a low pressure system over Ungava Bay slowly tracking eastward with a cold front extending south and westward toward northern Labrador and Quebec. Ahead of this cold front, there may be enough upslope lift over the Torngat Mountains combined with an approaching 30KT 850mb jet to initiate some elevated convection this afternoon. Central Labrador remains in an unstable southwesterly flow and temperatures may be close to reaching their convective temperature needed to initiate thunderstorms this afternoon but there is a lack of a real trigger and with moisture dropping this afternoon and a warm layer at 700mb, there is less of a risk other than scattered TCUs in showers.

 

Regional Impacts

 

Labrador

Possibility of isolated thundershowers over the Torngat Mountains ahead of the cold front this afternoon. TCU in showers for central Labrador.

 

New Brunswick

Showers with possible local heavy downpours this afternoon over western sections.

 

Newfoundland, Nova Scotia and Prince Edward Island

None expected

 

 

 

Roberta McArthur

 

Convective Outlook Valid for August 15th, 2019

Convective Discussion

 

Atlantic Canada is mainly under the influence of a ridge of high pressure today which will suppress convection over the Maritimes. Sea breeze convergence will provide some lift and isolated showers are possible for Newfoundland this afternoon and evening. There is a weak upper level trough over North Shore Quebec moving eastward towards southern Labrador today which will provide further instability with some cooling aloft. In addition, some coastal convergence and upslope flow will help to produce some isolated thundershowers this afternoon over central and southeastern Labrador. Given only weak shear, locally heavy downpours will be the main threat. With CAPE values of around 250 J/kg and freezing levels near 8,000ft in the area, there is also a slight risk of small hail.

 

Regional Impacts

 

Labrador

South central and eastern Labrador – Risk of thunderstorms with heavy downpours and a slight risk for small hail. 

 

Maritimes and Newfoundland

None expected

 

 

 

Roberta McArthur

 

Convective Outlook Valid for August 14th, 2019

Convective Discussion

 

A quiet day across Atlantic Canada as a low pulls away northeast of Newfoundland and high pressure moves in.  No convective activity expected.

 

Regional Impacts

 

Atlantic Canada

None

 

 

Barrie MacKinnon

 

Convective Outlook Valid for August 13th, 2019

Convective Discussion

 

The focus will be over Newfoundland today where thunderstorms are expected.   A very healthy strengthening jet over the area brings 0-6 km wind shear values near 40 kts which is expected to increase to near 60 kts later this afternoon for some areas.  At the current forecasted temperatures highs, 500 J/kg can be expected with higher amounts possible if highs reach a few degrees above forecasted temps.  A trough over the Maritimes will help kick start convective activity and low freezing levels of around 8500 ft could make hail a possibility under some of these storms.   Areas that stay cloud covered throughout the day should see reduced convective activity.  It is possible that some of the cells that develop may become severe.  Heavy rainfall and hail are the main threat if  severe thunderstorms develop.  The increasing wind shear later today could actually help to limit convection as t-storms development could be sheared off.

 

Regional Impacts

 

New Brunswick

Non expected

 

Nova Scotia and PEI

None expected

 

Newfoundland

Thunderstorms of which a few severe thunderstorms are possible.  Heavy rainfall and large hail are possible. 

 

Labrador

Southernmost coastal Labrador – Risk of thunderstorms with slight chance of severe tstorms.  Heavy rainfall and large hail possible. 

 

 

 

Barrie MacKinnon