Convective Discussion
A cold front approaching Labrador from the west may give a few thundershowers to westernmost regions this evening. There may be some gusts and small hail. Over most other areas a QS ridge will inhibit significant convection. For slope waters, there will be scattered thundershowers for much of the day and tonight.
Technical Discussion
The cold front will start becoming unstable in western Labrador in the evening (with a slight possibility for late afternoon). PVA will be strongest near 00Z, and some weak lift from the left entrance of the 250 mb jet will help. An associated thermal trough from 700 mb up will give some slight cooling to midlevels as well, but not enough to give significant CAPE. Shear will be on the high side, at 40+ knots, especially relative to low CAPE values expected. However, if cooling aloft is stronger than predicted, the CAPEs may be high enough for a few hundred Joules/kg, giving some local and brief heavy showers of 5-15 mm, and some gusts to 70 kph. Rainfall estmates are based on a fast moving cell and 30 mm of precipitable water. Freezing levels will be about 9500 AGL (11500 ASL), giving a possibility of small hail.
For slope waters, there’s an area of weak embedded convection mainly south of forecast waters, but occasionally creeping into our region. There is low to moderate shear, and about 20-30 mm of precipitable water. The main trigger is weak troughing south of the ridge. Isolated to scattered thundershowers are expected, but, no hail, and wind gusts are inhibited by a warm nose near 850 mb.
Regional Impacts
Labrador: Isolated thundershowers possible mainly this evening west of Churchill Falls and from near Wabush to the north. Possible wind gusts to 70 kph, and a small chance of small hail.
Slope waters of the Scotian Shelf and Southern Grand Banks: Isolated to scattered thundershowers. No severe impacts expected.
Elsewhere: no thundershowers expected.
Doug Mercer