Convective Outlook Valid for July 5, 2019

Convective Discussion

Near severe thundershowers  possible for  northern New Brunswick, with non-severe thundershowers possible for much of the Maritimes. Thundershowers possible for western Labrador and the Maritimes.

Maritimes: These will be mostly air mass driven by daytime heating up to the low thirties and dew points near 15-20 C . A deep ridge will move though New Brunswick this afternoon and over eastern Nova Scotia by this evening, having generally sunny conditions. CAPEs near or possibly exceeding  500 J/kg range are reasonable for the Maritimes provinces, with New Brunswick possibly in the 500-1000 J/kg range, and possibly higher central and north. The highest risk are for heavy downpours and high wind gusts. The main factors against these cells developing is a lack of moisture aloft, as well as a lack of upper support. 0-6 km shear is near 30 kts, and will diminish a bit this afternoon. Freezing levels near 13 to 15 thousand feet make significant hail unlikely.

Labrador: For western Labrador  there are two factors that may spawn some weak cells this afternoon, that may become healthier into early this evening. . Near or just east of Churchill falls there is a  north-south trough with some sunny breaks to the west. Farther west there is a weak diffluent upper jet approaching from Quebec.  These, combined with daytime heating may produce some cells with CAPEs up to 500 J/kg, with PWAT near 33 mm, and dew points near 14 C in the west. Wind shear is near 25 kts and will increase from the west into this evening to near 35-40 kts.

Regional Impacts

New Brunswick: : Near severe thundershowers possible this afternoon into this evening with heavy downpours and gusty winds possible.  Highest risk for severe in the north this afternoon.

Nova Scotia: Non-severe thundershowers possible this afternoon into this evening with heavy downpours and gusty winds possible.

Prince Edward Island: Non-severe thundershowers possible this afternoon with gusty winds and occasional heavy downpours.

Labrador: Non-severe thundershowers giving occasional downpours. A slight chance for small hail.

Newfoundland: None

Doug Mercer

Convective Outlook for Atlantic Canada valid for July 4th, 2019

Convective Discussion

 

Thunderstorms expected over eastern New Brunswick and parts of eastern Nova Scotia as well as western Labrador today.

 

The thunderstorms over the Maritimes will be primarily thermodynamically driven.  Lots of solar insolation today combined with good low level moisture will generate moderate CAPE values of around 500 J/kg however the lack of a triggering mechanism should restrain convective development to coastal areas where it will be influenced by a sea breeze and coastal convergence which should act as the kicker.  If thunderstorms develop along the coast, they will likely be slow moving so heavy local downpours will be the main threat.  Looking at satellite this morning, there seems to be a lot of forest fire smoke in the upper atmosphere.  This could impede convection as it will reduce solar insolation. 

For western Labrador, good low level moisture and solar insolation combined with cool temperatures aloft will bring CAPE values of around 500 J/kg.  There is a small possibility of severe thunderstorms being initiated; however, wind shear is quite insignificant, therefore thunderstorms cell will have difficulty maintaining themselves.

 

Regional Impacts

 

New Brunswick

 

Slow moving thunderstorms along the coast which could bring local heavy downpours.  Small hail and moderate winds also possible.

 

Nova Scotia

Slow moving thunderstorms which could bring local heavy downpours.  Small hail and moderate winds also possible.

 

PEI

None

 

Newfoundland & Labrador

For western Labrador,  local heavy downpours and moderate winds with a small chance of cells producing damaging winds. No impacts elsewhere.

 

 

Barrie MacKinnon

 

Convective Outlook for Atlantic Canada valid for July 3rd, 2019

Convective Discussion

 

Risk of thundershowers over western New Brunswick this afternoon and early this evening with no convective activity expected elsewhere.

 

Clearing skies over western New Brunswick will increase solar insolation which may be enough to trigger a few non severe thundershowers.  An approaching ridge  from the west brings subsidence to the area, so any convection that could get triggered should be  moderated due to the mid level stability.  Anywhere from 100 to 500 J/Kg can be expected over the area but, again, positive buoyancy should be limited to mid levels which should limit CB development.

 

Regional Impacts

 

New Brunswick

 

Scattered thundershowers possible over western NB but severe thunderstorms not expected.

 

Nova Scotia

None

 

PEI

None

 

Newfoundland & Labrador

None

 

 

Barrie MacKinnon

 

Convective Outlook for Atlantic Canada Valid for July 2nd, 2019

Convective Discussion

 

The main area of focus will be over Maine with surface based convection having already begun, this convection will spill into New Brunswick this afternoon. Overall dynamics for severe thunderstorms are not overly favorable however there weak surface trough with moderate amount of CAPE > 1000J/kg and high moisture. The main concern will be heavy downpours possibly exceeding 25mm hour and with the low freezing levels 2-3 cm hail is also possible. It is unlikely but some of this convection could move across weather Nova Scotia this evening.

 

Over Newfoundland some embedded CB’s ahead of the surface low pressure system will generate locally heave rainfall amounts.

 

Regional Impacts

 

Nova Scotia

Locally heavy downpours, 15 - 20 mm possible if thunderstorms move into Southwestern parts of the province this evening.

 

New Brunswick

Main concern will be over western regions with heavy downpours 20-25mm and moderate sized hail possible.

 

Newfoundland

Embedded thunderstorms ahead of the surface low could give locally heavier rainfall of 15 – 20mm. Over western Labrador very low topped thunderstorms could develop with some rain and small hail.

 

PEI

None

 

 

Convective Outlook Valid for July 1st, 2019

 

Convective Discussion

 

There are a few areas of convective potential for today into tomorrow morning. A slow moving upper low currently near Sable Island will continue to track eastward and stall just east of Cape Breton by this evening. Meanwhile, a trough currently over Hudson Bay will track eastward towards central Quebec and western Labrador this evening and reach northwestern New Brunswick by tomorrow morning.

 

Under the upper level feature south of Nova Scotia, most of the convection should remain over eastern coastal regions of Nova Scotia, Eastern Shore, Sable and marine waters farther east this afternoon and evening near the vicinity of the low centre. Due to the slow nature of this system, some areas are expected to get locally heavy downpours. A rainfall warning is in effect for Victoria county due to upslope enhancement in easterly winds. Precipitable water values remain in the 30-35mm range looking at the Yarmouth and Sable Island morning soundings. Winds should remain quite stable over the marine waters but any convection that makes it onshore may see brief wind gusts reaching 30kts. Rain could be heavy at times over southern Newfoundland today as the low continues to drift closer but the threat of convection is low.

 

Areas of western Labrador will see an increasingly unstable air mass this afternoon as weak troughing moves into the area and convective temperatures are expected to be reached to initiate surface based convection, especially over areas that have cleared out of the stratus early this morning. CAPE values could reach the 500-700 J/kg range but with weak shear this morning, generally pulse type storms are expected. Into late afternoon, however, the 0-6KM shear is forecast to increase from 20 to 30KT which may allow some thunderstorms could be maintained or possibly organize into small squall lines. This along with fairy low freezing levels may produce small hail, brief heavy downpours and strong gusts. Conditions are not expected to reach severe warning criteria.  The upper flow may hinder initially some of the surface based convection as well due to warming aloft as a warm front approaches the region from central Quebec. An extension of this trough will also make its way farther south toward Maine and northwestern New Brunswick by early tomorrow morning.

 

 

Regional Impacts

 

Nova Scotia…

Locally heavy downpours over eastern mainland Nova Scotia and Cape Breton

 

New Brunswick…

Isolated thunderstorms may affect northwestern New Brunswick early tomorrow morning.

 

Labrador…

Small hail, strong winds and locally heavy downpours are possible for western and central Labrador late this afternoon and overnight.

 

 

HAPPY CANADA DAY!

 

Roberta McArthur