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.