Day 1 Convective Outlook for Atlantic Canada Valid for July 23, 2018

 

Convective discussion:

 

Convective activity will be generally low in Atlantic Canada today due to lack of sunshine throughout much of the Maritimes and Newfoundland. However, isolated t-shwrs are likely in NS where sunshine and high dew points initiate convection. Although Cape Breton is not in the minor threat area on the map, any t-shwr activity in Antigonish County could move into Inverness County.

 

Unlike yesterday, Labrador shouldn’t see any significant convection due the passage of a cold front followed by a ridge of high pressure.

 

Technical Discussion:

 

If convection occurs in the Maritimes and Newfoundland, CAPE will be low due to warm air aloft. Shear is low in NS so t-shwrs that occur would be non-severe. Shear is moderate in NB, PE, and NF so longevity and separation of updrafts and downdrafts could occur if t-shwrs formed.

 

T-shwr activity is unlikely in NB, PE, and NF due to cloud and showers and lack of a trigger other than sunshine which generally is not expected or not expected to persist. Sunshine could be a trigger in NS.

 

Regional Impacts:

 

New Brunswick: very unlikely

 

Nova Scotia: Isolated non-severe thundershowers likely Valley and northern mainland.

 

Newfoundland: Unlikely.

Labrador: Very unlikely

 

 

 

 

 

 

 

 

Day 1 Convective Outlook for Atlantic Canada Valid for July 22, 2018

Convective discussion:

High probability of thunderstorms in western and central Labrador. Heavy rain, gusty winds and possible hail would likely accompany these thunderstorms. There is a slight possibility of severe conditions.

Thundershowers will likely persist south of NS and NF with the southern Avalon remaining in the risk of non-severe thundershowers.

Technical Discussion:

CAPE values could exceed 1000J/kg in western Labrador. In addition, 0-6 km shear would be in the 40-50 knot range. Supercells and squall lines are possible.

Regional Impacts:

New Brunswick: Nil

Nova Scotia and Prince Edward Island: Nil, except a very slight risk northern mainland NS if a period of prolonged sunshine occurs this afternoon.

Newfoundland: Chance of a thundershower on the Avalon.

Labrador: Likely.

Day 1 Convective Outlook for Atlantic Canada Valid for July 21st, 2018

Convective Discussion

Isolated thundershowers are occurring near Wabush/Lab City this morning along a frontal boundary that’s sitting across the region. As the boundary slowly progresses east-northeastward today, this activity should continue to progress along that zone. Later today (just south of the front) convection is likely to become more widespread once surface heating is maxed. A weak upper low and associated surface low south of NS will gradually move northeastward today and tonight giving isolated thundershowers to portions of NS and NL.

Technical Discussion

There is a slight risk of severe thunderstorms for extreme western Labrador this afternoon and early evening. Upper air analysis shows a fairly strong jet streak, placing WRN LAB in the right entrance region (though there is no diffluence aloft) There is a weak upper 500 mb trough north of the region but that really doesn’t advect into the region as the day progresses. There is a decent tongue of moisture at 850 analyzed from the Great Lakes into south-central Quebec. The question is how far northeastward will this stretch through the course of the day. The instability is there and 12Z tephis shows about 30-40 knots of shear, in addition the surface boundary being the trigger. Moisture will be the key ingredient to generate strong storms this afternoon. YZV shows good lapse rates in the low-mid levels with drying conditions about 700mb. Adjusting the surface T and Td can generate CAPEs of close to 1000 J/Kg and associated DCAPEs of around 600-800. If cells develop, strong wind gusts (close to 80 km/h), small hail and heavy downpours will be the concern.

The upper level low and associated PVA south of NS will give some isolated thundershowers as it progresses to the northeast (although it will be weakening over time). Precipitable water is quite high so the only concern would be torrential downpours. Even in the presence of embedded TCU, heavy rain can be expected.

Regional Impacts

For Labrador

Possible strong winds, small hail, frequent lightning and heavy downpours for the YWK area. OTWZ isolated thundershowers within the grey zone.

For Nova Scotia and Newfoundland:
Isolated thundershowers giving torrential downpours are possible.

For New Brunswick and PEI:

Nil.

Jeremy

Day 1 Convective Outlook for Atlantic Canada Valid for July 20th, 2018r

 

Convective Discussion

 

Isolated thundershowers are occurring west of Labrador (halfway to James Bay) again this morning. This activity should slowly move eastward during the day. Cumulus clouds are becoming more widespread over central and eastern Labrador. Isolated thunderstorms will likely develop especially over higher terrain.

 

Technical Discussion

 

The cold pool associated with the upper low northeast of Labrador will continue to support convective clouds today. The main focus will be over southeastern regions where surface temperatures will reach 25. Convection will be enhanced by higher terrain especially south of Lake Melville. Moisture in this airmass is limited so the main threat would be brief high winds (gusts around 70km/h or even a little more are possible).

To the west, a low over northern Ontario with a warm front extending eastward continues to support some elevated convection with a help a weak (80kt) anticyclonic upper jet. Some of this dynamic might approach western Lab late in the day but the prime area for surface-based convection will likely remain south of the frontal feature (and out of Lab) where higher wind gusts appear to be the main threat.

 

Regional Impacts

 

New Brunswick, Prince Edward Island, Nova Scotia and Newfoundland

Nil.

 

For Labrador

Lightning and possible gusts for eastern Labrador.

 

 

 

Jean-Marc Couturier

 

Day 1 Convective Outlook for Atlantic Canada Valid for Month Day, Year

 

Convective Discussion

 

Isolated thundershowers are occurring over northern Quebec this morning. Smaller cumulus clouds are widespread across Labrador. Also, Radar is currently detecting an area of rain over southeastern Newfoundland.

 

Technical Discussion

 

A surface low and its associated frontal wave east of Hudson Bay will advance over northern Quebec today. A 20 knot southwesterly low-level jet is supplying ample moisture and instability to support thunderstorms southeast of the low. Temperatures in the 20-24 degree range and dewpoints approaching 15 should be enough to fuel isolated thundershowers with CAPE values in excess of 500 J/kg west of Labrador this afternoon. Some of these storms could propagate over Western Lab with some help from a 40-50 knot westerly upper jet.

 

A frontal band continues to maintain a very moist air mass over southeastern Newfoundland. The sounding from St John’s West indicates a moist profile from the surface up to 850mb and again from 500mb and up, with precipitable water of 47mm! A series of vorticity centres will support isolated thundershowers along the frontal band throughout the day.

 

Regional Impacts

 

New Brunswick, Prince Edward Island and Nova Scotia

Nil.

 

For Newfoundland

Heavy downpours for the southeast.

 

For Labrador

Lightning and possible gusts for western Labrador.

 

 

Jean-Marc Couturier