Atlantic Canada Weather Blog: Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today: there is a risk of severe thunderstorms this afternoon across the northern half of NB today giving strong winds, small hail and torrential downpours. There is slight risk of thundershowers this evening over the north LAB coast near the Nain area.

Tonight, into Friday morning: a risk of thundershowers across southern NB, PEI and NS.

Friday afternoon: isolated afternoon thunderstorms possible for western mainland NS, west of Halifax.

Convective Discussion

We have the ingredients for a potentially active afternoon across a good chunk of NB as a cold frontal trough slowly approaches from the west. Tds are now on the rise, and so too is the PWATs, which will get into the low 40’s by mid to late afternoon. As mentioned yesterday the instability is nothing to write home about but sufficient to aid in the development of strong cells. The shear does seem a little weaker on model guidance compared to 00z and 12Z yesterday, but still maxes out to about 40 knots as the day progresses. And of course, our trigger is the frontal trough. The Albany 12Z sounding might be the best to use to sample the upstream airmass, and it looks quite prime for a convective day. There is a strong inversion though at about 750 mb that will have to be broken but given the large area of cloud-free skies with little in the way of smoke aloft that should be breached as we reach the convective temperature of about 30 degrees. Lapse rates are not great so I don’t expect large hail as CAPE, overall, will be skinny. It should be noted the new criteria for significant hail is 2.5 cm (which is quarter-sized). Strong wind gusts of 90-100 km/h and intense rainfall rates over a short period of time are the main concerns in the stronger cells.

A severe thunderstorm watch will most likely be issued for the northern half of New Brunswick sometime over the lunch hour.

Thunderstorm Outlook for Today