Day 1 Convective Outlook for Atlantic Canada Valid for July 5, 2018 - Resent for missing valid date

 

Convective discussion:

 

Some isolated thunderstorms are possible this afternoon and evening associated with a warm front extending from central Quebec to the Gulf of St. Lawrence pushing northeastward as well as within the warm sector over New Brunswick and Prince Edward Island.

 

Technical Discussion:

 

A low pressure system over Hudson Bay will slide eastward today. Showers with embedded thundershowers are occurring this morning over Quebec extending southeastward towards northern New Brunswick and will continue to push to the northeast In the afternoon and evening, these showers with the risk of thundershowers are possible as the front moves into southwestern Labrador stretching southeastward into the Gulf of St. Lawrence. The cold front will quickly approach southwestern Labrador by midnight tonight and will reach northwestern New Brunswick by early Friday morning. Heavy downpours are possible with this cold frontal passage but as it is moving through the area in the overnight hours, the severe potential is less.

 

The Maritimes remain in a hot and humid air mass today.  Conditions will be unstable this afternoon with interior temperatures expected to be in the low 30s. The adjusted KCAR sounding is showing CAPE values between 1500 and 2000 J/kg,  however conditions remain fairly dry in the low levels and there is a lack of sufficient low level wind shear and upward forcing for there to be any severe potential... A sea breeze is expected to set up this afternoon which will likely be the main enhancement to help start up convection over eastern New Brunswick. Precipital water values of 35mm are the area, so heavy downpours are possible should convection initiate.

 

Regional Impacts:

 

New Brunswick and Prince Edward Island PEI: brief heavy downpours and gusty winds in isolated cells.

 

Nova Scotia: Brief showers mainly along the spine.

 

Labrador: Heavy downpours and gusty winds, especially along the cold front overnight for southwestern Labrador.

 

Newfoundland: Nil.

 

 

Roberta McArthur

 

 

 

 

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

 

Convective discussion:

 

Some isolated thunderstorms are possible this afternoon and evening associated with a warm front extending from central Quebec to the Gulf of St. Lawrence pushing northeastward as well as within the warm sector over New Brunswick and Prince Edward Island.

 

Technical Discussion:

 

A low pressure system over Hudson Bay will slide eastward today. Showers with embedded thundershowers are occurring this morning over Quebec extending southeastward towards northern New Brunswick and will continue to push to the northeast In the afternoon and evening, these showers with the risk of thundershowers are possible as the front moves into southwestern Labrador stretching southeastward into the Gulf of St. Lawrence. The cold front will quickly approach southwestern Labrador by midnight tonight and will reach northwestern New Brunswick by early Friday morning. Heavy downpours are possible with this cold frontal passage but as it is moving through the area in the overnight hours, the severe potential is less.

 

The Maritimes remain in a hot and humid air mass today.  Conditions will be unstable this afternoon with interior temperatures expected to be in the low 30s. The adjusted KCAR sounding is showing CAPE values between 1500 and 2000 J/kg,  however conditions remain fairly dry in the low levels and there is a lack of sufficient low level wind shear and upward forcing for there to be any severe potential... A sea breeze is expected to set up this afternoon which will likely be the main enhancement to help start up convection over eastern New Brunswick. Precipital water values of 35mm are the area, so heavy downpours are possible should convection initiate.

 

Regional Impacts:

 

New Brunswick and Prince Edward Island PEI: brief heavy downpours and gusty winds in isolated cells.

 

Nova Scotia: Brief showers mainly along the spine.

 

Labrador: Heavy downpours and gusty winds, especially along the cold front overnight for southwestern Labrador.

 

Newfoundland: Nil.

 

 

Roberta McArthur

 

Convective discussion:

 

Some isolated thunderstorms are possible this afternoon and evening associated with a warm front extending from central Quebec to the Gulf of St. Lawrence pushing northeastward as well as within the warm sector over New Brunswick and Prince Edward Island.

 

Technical Discussion:

 

A low pressure system over Hudson Bay will slide eastward today. Showers with embedded thundershowers are occurring this morning over Quebec extending southeastward towards northern New Brunswick and will continue to push to the northeast In the afternoon and evening, these showers with the risk of thundershowers are possible as the front moves into southwestern Labrador stretching southeastward into the Gulf of St. Lawrence. The cold front will quickly approach southwestern Labrador by midnight tonight and will reach northwestern New Brunswick by early Friday morning. Heavy downpours are possible with this cold frontal passage but as it is moving through the area in the overnight hours, the severe potential is less.

 

The Maritimes remain in a hot and humid air mass today.  Conditions will be unstable this afternoon with interior temperatures expected to be in the low 30s. The adjusted KCAR sounding is showing CAPE values between 1500 and 2000 J/kg,  however conditions remain fairly dry in the low levels and there is a lack of sufficient low level wind shear and upward forcing for there to be any severe potential... A sea breeze is expected to set up this afternoon which will likely be the main enhancement to help start up convection over eastern New Brunswick. Precipital water values of 35mm are the area, so heavy downpours are possible should convection initiate.

 

Regional Impacts:

 

New Brunswick and Prince Edward Island PEI: brief heavy downpours and gusty winds in isolated cells.

 

Nova Scotia: Brief showers mainly along the spine.

 

Labrador: Heavy downpours and gusty winds, especially along the cold front overnight for southwestern Labrador.

 

Newfoundland: Nil.

 

 

Roberta McArthur

 

 

 

 

Day 1 Convective Outlook for Atlantic Canada Valid for July 4, 2018

Convective discussion:

Some isolated thunderstorms expected today associated with a frontal trough south of Nova Scotia and southeast of Newfoundland.

Some isolated thunderstorms possible for New Brunswick, PEI, northern NS and Cape Breton later today and tonight as a weak warm front moves into the region.

Technical Discussion:

A weak trough south of the Maritimes and Newfoundland will continue to push off to the southeast today. Meanwhile a weak warm front will move into New Brunswick today then across northern Nova Scotia, PEI and Cape Breton tonight.

There have been some elevated thunderstorms this morning across southern marine waters south of NS and over the Grand Banks. This will continue today as the trough slides southeastward. Meanwhile a warm front now over southeastern QC will move into the Maritimes today. KCAR tephi shows about 40 knots of wind shear, but extremely dry in the low levels…same for WMW. Just a slight risk of a thunderstorm later today and tonight for some areas given the weak upper support. OTWZ nil sig weather expected.

Regional Impacts:

New Brunswick, northern Nova Scotia (including Cape Breton) and PEI: brief heavy downpours and gusty winds in isolated cells.

Newfoundland and Labrador: nil.

Jeremy

Day 1 Convective Outlook for Atlantic Canada Valid for July 3, 2018

Convective discussion:

Some isolated thunderstorms expected today and tonight associated with a weakening cold frontal trough that’s slowly crossing the Maritimes and Newfoundland.

Isolated thunderstorms possible for southeastern Labrador this afternoon and evening associated with a fairly strong short wave trough with some PVA.

Technical Discussion:

A weakening cold frontal trough will cross southern New Brunswick and western Newfoundland today to lie from Nova Scotia to southeastern Newfoundland this evening.

Isolated morning convection is occurring along the aforementioned frontal trough and this will likely occur at anytime today and tonight in its vicinity. KGYX 12Z tephi shows about 35 knots of shear with decent low-mid level lapse rates, as well as deep low level moisture. Modifying the profile generates between 500 and 800 CAPE, however the instability is marginal given the weakening state of the front…so just garden-variety pop up cells are expected with a very low threat of severe weather. Locally heavy downpours and some gusty winds can be expected. Freezing levels are quite high posing very little chance for hail.

In behind the front (southeastern Labrador) there is a considerable increase in wind shear, falling 500 mb atmospheric heights, drying at the mid levels, a short wave trough (and associated PVA) and a favorable left exit 250 mb jet. However, what’s lacking is the low-level moisture and instability. Isolated non-severe thunderstorms will possibly develop towards the mid afternoon today.

Regional Impacts:

New Brunswick, northern Nova Scotia (including Cape Breton), PEI and Newfoundland: locally heavy downpours and gusty winds.

Southeastern Labrador: Gusty winds.


Jeremy

Day 1 Convective Outlook for Atlantic Canada Valid for July 2, 2018

 

 

Convective discussion:

Possible severe thunderstorms  for this  afternoon into the evening, with a slight chance for supercells, for New Brunswick.

Some isolated to scattered thunderstorms possible for western Labrador. Isolated thundershowers over the Southern Grand Banks.

 

Technical Discussion:

A low pressure system near  James Bay will move to lie over Ungava Bay tonight.

 

For New Brunswick there will be increasing low level moisture and warm advection in the warm sector, along with increasing shear as the cold front from the low approaches. Current model tephis show an almost classic shotgun setup, with the inversion breaking between 15-21Z. Currently CAPES are forecast in excess of 1000 J/kg, and precipitable water about 30-40 mm. Surface and low level dewpoints are also good, with 20 C likely this afternoon at the surface, and a couple of degrees lower at 850 mb. It gets dry near and above 700 mb, which will support downdrafts. The shear starts a bit light at 25 kts, but increases into the evening to 35 kts. Finally Storm Relative Helicity is in the 150-250 m^2/s^2.

 

If a supercell does develop later this evening, strong downdrafts are likely with DCAPES in the 1200 J/kg range  based on KBUF, KGYX, and WMW upstream. There will likely be heavy downpours, and nickel sized hail is also possible.

 

On the other hand the steering flow winds will be west to southwesterly, so it could skim by to the north, and the trailing front will also be mainly in the north. Also, the Bulk Richardson Number indicates CAPE dominating shear, so it may be more of a multicell scenario than supercells, and in fact the guidance is hinting at a prefrontal line. In that case, the downdrafts and rain is still likely, but freezing levels of 15,000 ft, make hail unlikely.

 

For Labrador the warm front will pass through western Labrador early this afternoon, quickly followed by the cold front. In the  west, if the system passes a little farther north, there may be some convection with heavy rainfall.

 

For the Southern Grand Banks, a low slowly moving away will five isolated thundershowers until the system passes east overnight tonight.

 

Regional Impacts:

 

New Brunswick: heavy downpours, gusty winds, maybe small hail, and maybe a supercell. Wind will be an issue if a prefrontal squall line forms.

 

Labrador: Possibly heavy downpours.

 

Southern Grand Banks: Wind gusts and local heavy showers ending overnight.

 

Nova Scotia/Prince Edward Island/Newfoundland/Iles de la Madeleine: nothing significant.

 

Doug Mercer

 

Lead Meteorologist, Meteorological Service of Canada

Environment Canada / Government of Canada

doug.mercer@ec.gc.ca / Tel:902-426-9200

 

Météorologue principal, Service météorologique du Canada

Environnement Canada / Gouvernement du Canada

doug.mercer@ec.gc.ca / Tél: 902-426-9200