Convective Discussion
No severe impacts expected. Highest chance for convection for Labrador from the west to the Mid Labrador coast. A slight chance for Newfoundland this afternoon, and a chance for a thundershower to move into westernmost New Brunswick.
For Labrador a trough extending from Hudson Bay to the Mid Labrador Coast, combined with an upper jet over northern Labrador, with a right entrance near the trough axis, will give some support for lift. As the upper jet moves east this afternoon, so will the instability . Moisture isn’t great, with precipitable water in the 15-25 mm range. CAPEs are on the low, with the highest expected less than 500 J/kg, with the highest amounts at the southern edge of the threat zone. Also shear is marginal at about 30 kts. Expect a few thundershowers with some moderate wind gusts. The freezing level is near 9000ft, so small hail is possible.
For Newfoundland there is little dynamic forcing. The there is a weak upper trough moving through, followed by weak ridging from mid-levels up, and an associated weak upper jet. The main forcing mechanism will be daytime heating, and some moisture. The 12Z tephigram from Stephenville was less stable than model guidance, and with a forecast high near 25 C and a dewpoint near 13 C, a parcel lift gave a CAPE around 300-400 J/kg. Based on this there is a chance for isolated thundershowers this afternoon, with some gusty winds.
Regional Impacts
Labrador: Occasional non severe thundershowers with some gusty winds and a chance for small hail.
Newfoundland: a possibility for isolated thundershowers this afternoon.
New Brunswick: a slight chance for thundershowers this afternoon in the extreme northwest, but only if the cloud breaks up today.
Doug Mercer