Regional Impacts
Today
NB: Risk of severe thunderstorms over northern New Brunswick late this evening capable of producing very strong wind gusts, nickel to quarter size hail, heavy downpours, and the risk of a tornado.
NS: Slight chance of an isolated thundershower over southwestern Nova Scotia early this afternoon.
PEI/NFLD/LAB: None.
Tonight
NS/NB/PEI/NFLD: Risk of severe thunderstorms over the Gulf of St. Lawrence overnight capable of producing strong wind gusts, small hail, and heavy downpours.
LAB : None.
Tomorrow
NB: Risk of severe thunderstorms late in the afternoon and into the evening capable of producing very strong wind gusts, nickel to quarter size hail, and heavy downpours.
NS/PEI: Slight chance of a thunderstorm over western areas in the evening capable of producing strong wind gusts, small hail, and heavy downpours.
NFLD: Chance of some isolated thundershowers in the late morning and early afternoon over central and eastern Newfoundland which could produce some heavy downpours.
LAB: None.
Convective Discussion…
An active few days are in store for the Maritimes, with a very hot and humid airmass that has settled over the region. Today brings the potential for severe thunderstorms over northern New Brunswick associated with some upper troughing over central Quebec. MLCAPE values over the area of interest are forecast to rise upwards of 1500 to 2000 J/kg due to the humid airmass. Strong dynamic forcing will also be advected into the region later today as the upper troughing approaches, with effective shear values reaching 50 to 55 knots this evening over northern New Brunswick. One of the major limiting factors today will be how quickly the capping inversion can erode over New Brunswick. Without the 12Z Caribou sounding, it is difficult to gauge the current state of the atmosphere over the region, however the 12Z Maniwaki and Chibougamau sounding both indicate a strong cap around 850 mb. Due to this and the timing of the upper trough swinging through, storms are not expected to fire until later this evening. All hazards are in play today due to the strong dynamics and high CAPE values. PWATs are expected to rise into the 40 to 50 range leading to the potential for some torrential rainfall rates of 25 to 50 mm per hour in these storms. Nickel to quarter size hail will also be possible with some fairly strong lapse rates, in addition to some very strong wind gusts in the range of 90 to 110 km/h. A tornado cannot be ruled out either, with the 12Z Sept-Iles sounding indicating some strong curvature in the low levels. Model hodographs also support strong low level curvature over northern New Brunswick this evening. There also exists a very small chance for an isolated thundershower over southwestern Nova Scotia early this afternoon due to a shortwave over the Gulf of Maine, as well as over eastern Labrador with an upper trough over the Labrador Sea. These storms are unlikely to produce any severe hazards.
Tonight, the main risk area from today will move out over the Gulf of St. Lawrence with the upper jet likely to sustain these thunderstorms overnight. Storms will likely become elevated as they cross the gulf, reducing the severe hazard potential, but strong wind gusts, small hail, and heavy downpours are all still possible. Tomorrow, this risk area will diminish in severity as it moves out over the Atlantic ocean, but a second approaching upper jet could spark up another round of severe thunderstorms over New Brunswick late in the day with similar MLCAPE (1500 to 2000 J/kg) and effective shear (50 to 55 knots) expected. The risk however is slightly lower than today, due to a stronger cap expected to be in place and possibly some drier mid-level air. If storms do spark up late in the day however, they will likely become severe. The main hazards tomorrow will be similar to today (very strong wind gusts, nickel to quarter size hail, and heavy downpours), however more linear shear is expected so no tornado risk is being forecast at this time.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Forecaster: Copp