Regional Impacts
Today
NB: Risk of Severe thunderstorms with heavy downpours, small to moderate sized hail, strong wind gusts. Risk of a tornado over Northwestern sections.
PEI/NS: Risk of a thundershower.
NL: Risk of a thundershower over southeastern sections of the island.
LAB: Nil.
Tonight
Lab: Risk of a thundershower over central sections.
NL: Risk of a thundershower over Southern and Southeastern sections of the island.
NB/PEI/NS : Nil
Tomorrow
NS/PEI/NL /Lab : Risk of a thundershower.
NB: Nil.
Convective Discussion
A frontal system near the Hudson Bay is progressing east and is the initiation forcing for the convection expected today. Currently, we have significant moisture across the Maritimes, along with curved jets moving through the US Eastern Seaboard. The frontal system, paired with these jets and ample moisture, with a cooler/drying airmass behind the cold front, is allowing for there to be a risk for severe thunderstorms in Northwestern NB, with the risk of a tornado today. This setup is giving Mixed Layer CAPE (MLCAPE) values near 1500 J/kg with Most Unstable CAPE (MUCAPE) exceeding 2,000 J/kg along the NB/Maine boarder. Additionally with this amount of instability, and the jet structure previously mentioned, we have a significant amount of Shear and Helicity. Looking at Convective model soundings we are seeing a Cloud Layer shear near 70 Knots, with Storm Relative Helicity (SRH) within the Surface to 3km nearing 140 m2s2. All of these properties do give rise to the possibility of supercells in Northwestern New Brunswick. As such when considering supercells the bunkers right movement seems the most reasonable, which is also fairly aligned with the mean wind direction (generally a Northeast direction).
As the frontal system progresses through Atlantic Canada tonight, we are expected to see a slight weakening in the jet structure and frontal boundaries. As such, there remains a risk for thunderstorms through central Labrador and near the Atlantic Coast. Model guidance does want to push convection onshore but the problem becomes that with the weakening forcings, making the land-sea transition during the overnight hours will be a struggle.
Tomorrow, the synoptic setup becomes more difficult for model guidance to capture the thunderstorm risk; as such, the regions in grey are likely to change as we move closer to the valid timeframe. The synoptic setup is that the low progressing through Atlantic Canada today has the possibility of getting stalled over Labrador with a building ridge over the continental US, and the Azores high. This setup has models indicating a potential Atmospheric river coming from the Gulf of Mexico into Atlantic Canada. As this setup requires several conditions, some of which there is low to moderate confidence in occurring, this is the justification for the grey region not having more details.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Forecaster: Lambert