Convective Discussion
Isolated thundershowers are occurring near Wabush/Lab City this morning along a frontal boundary that’s sitting across the region. As the boundary slowly progresses east-northeastward today, this activity should continue to progress along that zone. Later today (just south of the front) convection is likely to become more widespread once surface heating is maxed. A weak upper low and associated surface low south of NS will gradually move northeastward today and tonight giving isolated thundershowers to portions of NS and NL.
Technical Discussion
There is a slight risk of severe thunderstorms for extreme western Labrador this afternoon and early evening. Upper air analysis shows a fairly strong jet streak, placing WRN LAB in the right entrance region (though there is no diffluence aloft) There is a weak upper 500 mb trough north of the region but that really doesn’t advect into the region as the day progresses. There is a decent tongue of moisture at 850 analyzed from the Great Lakes into south-central Quebec. The question is how far northeastward will this stretch through the course of the day. The instability is there and 12Z tephis shows about 30-40 knots of shear, in addition the surface boundary being the trigger. Moisture will be the key ingredient to generate strong storms this afternoon. YZV shows good lapse rates in the low-mid levels with drying conditions about 700mb. Adjusting the surface T and Td can generate CAPEs of close to 1000 J/Kg and associated DCAPEs of around 600-800. If cells develop, strong wind gusts (close to 80 km/h), small hail and heavy downpours will be the concern.
The upper level low and associated PVA south of NS will give some isolated thundershowers as it progresses to the northeast (although it will be weakening over time). Precipitable water is quite high so the only concern would be torrential downpours. Even in the presence of embedded TCU, heavy rain can be expected.
Regional Impacts
For Labrador
Possible strong winds, small hail, frequent lightning and heavy downpours for the YWK area. OTWZ isolated thundershowers within the grey zone.
For Nova Scotia and Newfoundland:Isolated thundershowers giving torrential downpours are possible.
For New Brunswick and PEI:
