Convective Outlook Valid for July 30th 2019

Convective Discussion

 

An upper ridge moving over the Maritimes will suppress the convection somewhat and may inhibit convective initiation till late in the day. Overall the CAPE values are quite favorable being greater than 1000 j/kg for most of the Region. 0 – 6 km Wind shear values are of 35-40 knots over NW NB and for Newfoundland this will increase the potential for organized convection over these areas. Over Newfoundland if convection occurs it will likely begin early this afternoon while the thermodynamics still remain strong. Over New Brunswick the probability of severe weather is low but it is possible that severe thunderstorms could advect from Maine late in the day.

 

Regional Impacts

 

New Brunswick…

A general risk of thunderstorms for most areas with a heightened risk of severe storms for northwest areas, local rain of 25mm. If severe thunderstorms develop they will be very late in the day as dynamics gradually become more favorable.

Nova Scotia…

A low risk of thunderstorms that could produce local rainfall amounts near 20mm. A slight risk of that multiple thunderstorms could move over the same area causing further amounts.  

 

Prince Edward Island…

A low risk of thunderstorms that could produce local rainfall amounts near 20mm.

 

Newfoundland…

A low risk of thunderstorms that could produce local rainfall amounts near 25mm and wind gusts of 50-70 km/hr. A slight risk of that multiple thunderstorms could move over the same area causing further amounts.  

 

Labrador…

There is a chance of thunderstorms embedded in the trough that is approaching from Quebec.

 

 

Mel Lemmon

 

 

 

 

Day 1 Convective Outlook for Atlantic Canada Valid for July 29th, 2019

Convective Discussion:


Convective activity expected today over much of the Atlantic Canada with small chance of some convection becoming severe.

Lots of low level moisture and solar insolation will kick off some thundershowers across much of the Maritimes today. Shear is around the 25 – 35 kt mark and there are no substantial synoptic features to kick start and/or organize things. There is also a mid level warm nose which should cap off some but not all convective activity. So generally speaking, thundershowers over the Maritimes should be non severe but over area with shear near 35 kts, there is a chance of longer lived thundershowers that could become organized and become severe. There is also a possibility of tstorm formation over or along the Annapolis valley that could become quasi-stationary and extend out towards Antigonish county. The main threat if severe thunderstorms develop is heavy rainfall but hail and winds near criteria are also possible.

An area of low pressure over Labrador and an associated trough will kick off mid level tstorms over the area. Generally speaking, these thundershowers are expected to be non severe but a line currently over then Northeast Gulf could bring down some heavy downpours over parts of western Newfoundland.

Regional Impacts:
Maritimes: Slight chance of heavy rainfall reaching 25mm/hr.

Newfoundland: Slight chance of heavy rainfall reaching 25mm/hr over parts of western Newfoundland.

Labrador: Severe thunderstorms not expected.

Marine areas: Heavy rainfall over northeast gulf. Winds possibly reaching ~35 kts in thunderstorms.

Barrie MacKinnon

Convective Outlook Valid for July 26 2019

Convective Discussion:


Thunderstorms are unlikely over Atlantic Canada today due to very dry conditions and subsidence in the mid levels over the Maritimes and Newfoundland. The subsidence inversion in the 700 to 600 mb layer should suppress any convection exceeding that layer. These conditions are the result of a large surface high over southern areas and an approaching upper level ridge today and tonight. Showers are likely later today over southeastern and central Newfoundland. However, the dry air and subsidence aloft should prevent any TCu’s that form from obtaining sufficient height to become CB’s.


Over Labrador, relatively warm air aloft and cool air in the low levels will give a profile too stable for deep convection. In addition, mid-level cloud and moisture will suppress solar insolation.


Regional Impacts:

Maritimes: none.

Newfoundland: Scattered showers, thundershowers unlikely.

Labrador: none.

Marine areas: none. 

Convective Outlook Valid for July 25 2019r

Convective Discussion:

A slight chance of thundershowers over northern Labrador and for the southern border between Labrador and the Quebec border. Over southernmost sections of the Scotian Shelf and the southern Grand Banks occasional thundershowers.

Today a broad trough will be moving into Labrador from the west as a trigger, with some associated cooling aloft and weak destabilisation. The main inhibitor is again a lack of moisture. From 850 mb and higher there is precious little moisture, and at the surface the dew points are near 10 C or less.  PWATs over and upstream of Labrador are only near 17 mm. Now there is some low to mid level cloud moving in , which may supply the necessary moisture. Topographic forcing may help a little north and south, as previously mentioned. Impacts will be mainly some gusty winds , followed by  some brief heavy showers,  Freezing levels are again below 9000 ft, so there is a slight chance for small hail.

For the Maritimes there is little upper forcing, low shear near 20-25 kts, PWAT less than 20 mm, and low to moderate dew points. For Newfoundland the shear is higher as is the PWAT in the southeast, but upper forcing  is again limited. Finally , Stephenville and St. John’s tephis, show a moderate cap in the west and a strong cap in the east.

For offshore waters, high SSTs near the North Wall of the Gulf Stream will trigger some thunderstorms, further north isolated embedded convection is possible,

Regional Impacts:

Maritimes and Newfoundland: none.

Labrador: low chance for non-severe convection for northern Labrador and the southern border.

Marine areas: occasional non-severe thunderstorms over the southern Scotian Shelf, as well as the southern Grand Banks.

Doug Mercer

Convective Outlook Valid for July 24 2019

Convective discussion:

Non-severe thunderstorms possible for Labrador, western New Brunswick, and most southern offshore waters. Severe is likely near Geroges Bank, where squall warnings are in effect.

Currently there is a trough extending over southwestern forecast waters, which currently have SSTs above 26 C.  This is giving CAPEs near 2500-3000 J/kg, and wind gusts in excess of 40 kts are likely. PWAT is in the 50 mm range. But 0-6 km Shear is low, near 20 kts. So these are multicells organised along the weak trough moving though. While SST’s drop gradually farther east, there are still SSTs near 20 C  for  southernmost parts of Laurentian Fan and the Grand Banks

For western New Brunswick the main limiting factor is moisture. PWAT is near 20 mm, at 850  mb dew points are near or less than 8 C, and surface dew points are less than 16 C. While there is a strong  upper jet over the province, it is not well placed for any significant lift. There is a weak trough over the southern part of the province, and some low level moisture is advecting in from southern Maine. Conditions are clear with come Cu setting up. Based on this there is a chance for isolated thundershowers this afternoon and ending this evening, with the highest chance in the south.

For Labrador there is a QS low near Ungava bay with a trough extending south crossing western areas moving towards the coast, giving weak lift enhanced a bit near the trough. A slowly approaching deep thermal trough from the west will help destabilise things,  and the aforementioned upper jet is over southernmost Labrador. The left exist is a bit too far east, but may enhance things along the border range in the south, and maybe south of Lake Melville near the coast. Limiting factors are again low PWAT amounts near 20 mm, and  low dew points. Excpect non severe thundershowers with some moderate wind gusts. With freezing levels generally below 8500 feet, small hail is possible.

Regional Impacts:

Labrador: non-severe thundershowers are expected this afternoon into this evening. These’s a chance of near severe cells near the southern border of Labrador.

Western New Brunswick: slight chance of thundershowers this afternoon.

Slope waters  extending to south of the Avalon Peninsula: For western slope waters just south of the main discussion area, squalls are likely for western areas. Elsewhere non-severe embedded thundershowers are expected.

Doug Mercer