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

Regional Impacts

Today: Isolated severe supercell structure is possible along colliding boundaries across western NB this afternoon. There is an elevated risk of rotation within these cells. Damaging winds, heavy rain, and hail are also NB hazards today. Across NS, storms are also likely to fire along “the spin” of eastern mainland. These cells are capable of producing moderate rainfall.

Tonight: With a tropical push of moisture and enhanced lift, scattered-numerous strong thunderstorms are forecast across mainland NS during the overnight hours. These storms bring a significant rainfall risk. A special weather statement has been issued to provide the public with advance notice of this event.

Tuesday: As the forcing pulls away over the marine district, embedded thunderstorms are still possible midday. The hazards are diminishing at this time.

Convective Discussion

--Potentially Impactful Next 24hrs-- There are 2 events that are shaping up to affect the Maritimes district. (Nfld and Labrador are quiet for this forecast period.)

1. Supercell development is possible in western NB this afternoon driven by high moisture and high shear. Pwats support deep convection, and there is a 65kt Jet supporting the activity. Effective shear is over 55kts at max daytime heating today. Sig tor and EHI flag tornadic potential, similar to yesterday but with stronger signals. This poses a wind risk, hail risk, and heavy rain risk. The yellow area on today’s outlook conveys this message. Alerts may be required. The dynamics upstream in Maine are being closely monitored at the typing of this report. Organized storms are also possible across inland NS – but these storms don’t have the same enhanced shear dynamics to work with. Mositure across NS is impressive this morning, dewpoints over 20, with fog patches.

2. Tonight brings even more moisture into the equation, from the remnants of what was once Tropical Storm Chantal interacting with a longwave nearly-stationary trof. This stream of juicy air is entering our AOR this evening. As such, Pwats soar over 65 in places, and columns are fully saturated by midnight. The main hazard tonight is heavy rainfall. The yellow area on tonight’s graphic depicts this risk area. KF Rainrate products are depicting hourly rainfall rates of 60 mm/hr. This seems potentially too high. But it cannot be fully ruled out. The system has tropical influence and a history of producing locally very heavy downpours. If storms are training or slow moving, then higher precip amounts are possible. Forecasters will be paying close attention to this tonight.

Thunderstorm Outlook for Today