Modifying the 12Z Caribou sounding to the convective temperature of 24 deg gives 830 J/kg of CAPE. There is 35 knots of 0-6 km shear. The shear is unidirectional and is all above 3 km. At Caribou, the shear from 0-3 km is very low so based on this sounding, squall lines are unlikely. There is a strong 80 knot jet in the upper levels over the southern Maritimes as indicated by the 12Z sounding at Yarmouth. However, over NS and PEI, CAPEs are low so severity is not expected. The prog sounding for 18Z over western Labrador indicates that with daytime heating to the forecast high of 19 deg, convective initiation would give up to 800 J/kg of CAPE. Shear over western Labrador is low, so only pulse storms are expected if they form.
As is often the case, the challenge today is the amount of sunshine this afternoon to trigger the convection. At 11 am there is still a lot of cloud cover over the areas outlined as potential for convection. For NB where there is a slight risk of conditions approaching or meeting severity, the most likely scenario is for strong storms to form over srn QC and then advecting late this afternoon or this evening over the province.
Risk of thundershowers over most of NB, mainland NS, slight risk PEI. Possible wind gusts and small hail over NB
Newfoundland and Labrador…
Risk western Labrador.
Stephen Hatt
Forecaster
ASPC