Day 1 Convective Outlook for Atlantic Canada Valid for July 15, 2018

 

Convective discussion:

 

Risk of non-severe thundershowers over southeastern Nfld. and much of New Brunswick.

 

Technical Discussion:

 

In New Brunswick cape values of up to 750 J/kg however very low shear values (ie. No high or low level  jets in the proximity). High freezing level of 12K feet will reduce any hail size.

A convective temperature of 24 degrees is required however there is currently considerable low level cloud in NW New Brunswick  limiting solar heating. No real trigger to initiate convection either. If/when convection is realized the main threat is localized rainfall due to the light flow. Precipital water is 30-40 mm.

 

Regional Impacts:

 

New Brunswick: Possible thundershowers. Possible high local rainfall amounts in heavier showers.  

 

Nova Scotia and Prince Edward Island: Nil

 

Newfoundland: Chance of a thundershower.

 

Labrador: Nil.

 

 

 

 

 

 

 

Day 2 Convective Outlook for Atlantic Canada Valid for July 14, 2018

Convective Discussion

Slight risk for convection later in the day Saturday over northwestern Labrador as a trough moves in from the west. Meanwhile a slow moving trough south of Nova Scotia may generate conditions favourable for thunderstorms over most southern waters of the maritime marine district and possibly into the Newfoundland’s southwestern Grand Banks.

Technical Discussion

An upper trough moving toward Labrador has a history of producing thunderstorms in its wake over northern Quebec. The timing for the passage of this feature over western Newfoundland is not that great and the risk for severe convection during the outlook period for western Labrador is low.  Over the southern Maritime Marine district similar instability remains and upper level triggered thunderstorms are possible with primary threats being wind gusts of 35 knots or slightly more if they form. Of course the mixing of these winds would be subject to the in-situ stability over the marine areas.

Regional Impacts

Newfoundland, Labrador, New Brunswick, PEI, Nova Scotia, and Labrador Marine: No severe convection expected.

Maritime and Newfoundland Marine: Slight risk of thunderstorms around the through over southern waters. Primary thunderstorm threats should they form would be wind gusts near gale force.

Marshall Hawkins

Day 1 Convective Outlook for Atlantic Canada Valid for July 13, 2018

Convective Discussion

No severe convection is expected across Atlantic Canada today with the exception of and increased risk for severe convection over  the southern Maritime  and Newfoundland marine districts.

Technical Discussion

Multiple capping inversions across the region resulting from an upper ridge to the west and a slow moving upper trough over the region will not provide conditions favourable for the development of severe convection over the majority of Atlantic Canada. For the southern Maritime/Newfoundland marine districts, persisting upper level divergence associated ahead of the upper trough will assist in the continued development of convection throughout the period. Aside from lightning,  the primary risks with these cells would be wind gusts near 35-40 knots. The threat of wind is the largest where water temperatures are warmest in the shaded area above.

Regional Impacts

New Brunswick, Nova Scotia, PEI, Newfoundland, Labrador: No severe convection expected.

Labrador Marine: No severe convection expected.

Maritime Marine/Newfoundland Marine: Thunderstorm risk is largest over the southern waters. Primary threat – wind gusts near or exceeding 35 knots (stability dependent w.r.t sea surface temperatures), otherwise, no severe convection expected.

Marshall Hawkins

Day 1 Convective Outlook for Atlantic Canada Valid for July 12, 2018

Convective Discussion

Other than the embedded convection associated with  Post-Tropical Storm Chris, no severe convection is expected across Atlantic Canada today. For details regarding the impacts of Chris, please refer to official forecasts from the Canadian Hurricane Centre, Newfoundland and Labrador Weather Office, and the Atlantic Storm Prediction Centre.

Technical Discussion

Primary threat for severe convection is in the developing frontal regions of Post-Tropical Storm Chris encompassed by the grey area above. The effects generated by these thunderstorms would likely not be a severe departure from the already predicted synoptic conditions. As the warm front develops toward the end of the period, cloud top cooling may begin to play a roll over the Northern Grand banks for the generation of nocturnal thunderstorms.  Otherwise, no significant weather is expected over the remaining regions in Atlantic Canada.

Regional Impacts

Newfoundland:  Heavy embedded showers and isolated thunderstorms associated with the rain bands of Chris.  The impacts driven from synoptic scale processes are more likely to be an issue than an individual embedded thunderstorm cell. Primary threats with these thunderstorms would be wind gusts and downpours, both factors are not likely to be a significant departure from the prevailing weather conditions produced by Chris.

Newfoundland Marine: Heavy embedded showers and isolated thunderstorms expected with the passage of Chris. During the latter hours of this outlook, once the warm front is more developed, the risk of thunderstorms extends northward to the Northern Grand Banks. Primary threat with these thunderstorms would be wind gusts and these gusts are not likely to be a significant departure from the weather synoptic conditions produced by Chris.

Maritime Marine: Heavy embedded showers and isolated CBs over eastern regions associated with the passage of the developing fronts. Primary threat with these thunderstorms would be wind gusts and these gusts are not likely to be a significant departure from the prevailing weather conditions produced by Chris.

Nova Scotia: Moderate to at times heavy embedded showers expected over eastern Cape Breton associated with the passage of Chris otherwise no significant convection expected.

Labrador: Isolated TCU possible over southeastern regions this afternoon. No significant convection expected.

New Brunswick, PEI: No significant convection is expected.

Marshall Hawkins

Day 1 Convective Outlook for Atlantic Canada Valid for July 11, 2018

Convective Discussion

A trough swings through the region and then begins to interact at the mid levels with Hurricane Chris towards the end of the period. Shower or thundershower activity is possible for parts of the Nova Scotia Spine and possibly further up to Cape Breton. Less of a threat of thundershowers moving into central Newfoundland. The most active region, or potential threat, for severe convection is over the southern Nova Scotian Marine district which will be more impacted by the northeastward track currently forecast by the Canadian Hurricane Center.

Technical Discussion

A well structured upper trough moving over the region will pass over Nova Scotia and western Newfoundland during the outlook period. CAPE Values remain low across all the region and can only be modified to produce CAPE values less than 500 J/kg through significant  mechanical lift (via upper level trigger) or unphysical autoconvection temperature for the regions in the slight risk zones. Freezing levels remain above 10k feet for the maritimes with a decrease expected post trough passage, significant hail is not expected and shear values are marginal ahead of the trough.

There is uncertainty as to how this trough will interact with Hurricane Chris toward the end of the outlook period. It will likely begin to undergo deformation during the later half of the period which increases the uncertainty involved with the northward transport of moisture content. This primarily effects the likelihood of stronger convection over the southern Nova Scotia marine district.

Regional Impacts

Newfoundland: Slight chance of a thundershower ahead of the trough later this afternoon mainly confined to the interior. Increased mid level moisture transport ahead of the trough may supply sufficient fuel; however it depends on how much drying occurs as the air mass with more moisture crosses the land. Mid level lapse rates (NWP) are only favourable should moisture increase prior to the trough passage. No severe convection is expected.

Labrador: Southeast of the trough occasional TCU activing with dry gusts possible. Risk of a thundershower is low, isolated CB possible. No severe convection is expected. Northwest of the trough although vorticity remains near the upper low, only TCU generation is expected( and maybe an isolated CB) as there is insufficient moisture for severe convection. Slight risk of a thundershower here. No severe convection is expected.

Nova Scotia: Showers and/or thundershowers possible from the interior of southwestern Nova Scotia northeastward along the spine to and including the highlands of Cape Breton. The chance of severe convection is low; however, thundershowers are possible which would include moderate to heavy downpours. Rates and downpour accumulations are currently expected to remain below warning thresholds. Freezing levels are near 12,000 ft and are expected to drop in the wake of the feature, significant hail is not expected.

New Brunswick & PEI: No significant severe weather is expected. Isolated TCU activity over eastern PEI possible later this afternoon.

Marshall Hawkins