Regional Impacts
Today:
NS: Embedded thunderstorms this evening west of Halifax, heavy downpours of 30-60 mm.
NB: Risk of embedded thunderstorms along the Fundy coast this evening, heavy downpours of 30-60 mm. Chance for an isolated thunderstorm in extreme NW NB this evening, locally heavy downpours of 25-50 mm.
PEI: Chance for embedded thundershowers to move into PEI before midnight, locally heavy downpours of 10-15 mm.
NL: None.
Tonight:
NS: Embedded thunderstorms along the Atlantic coast between Halifax and Cape Breton Island overnight, heavy downpours of 25-50 mm.
NB & PEI: Slight chance for embedded thundershowers overnight, locally heavy downpours of 10-15 mm.
NL: None.
Convective Discussion…
An upper low over southern Ontario this morning will slowly move east, interacting with a stream of tropical moisture off the eastern seaboard today. Embedded thunderstorms have been observed over New England and to the southeast of Cape Cod this morning. These storms will move northeast today, reaching the southwestern shores of the Maritimes by this evening. Ample jet support wrapping around the aforementioned upper low will aid in sustaining this convection as it approaches the Maritimes, and is expected to persist along the Atlantic coast of NS tonight. The 12Z Yarmouth sounding this morning indicated precipitable water values of 50 mm, with this number expected to build to 60-65 mm over much of NS this evening. With a high volume of moisture in the atmosphere, any significant instability could lead to torrential downpours in the area of interest. Currently, MUCAPE values are forecast to build upwards of 500-750 J/kg by this evening along the Atlantic coast. With these numbers in mind, torrential downpours will be the main threat, with 30-60 mm and rainfall rates upwards of 25 mm/h possible. These amounts may end up being higher if the mid-level instability increases, depending on how much upper and mid-level cold air wraps around the upper low over Ontario, so this will be something to closely monitor.
A second smaller area of interest closer to the upper low exists in extreme NW NB. Here, an isolated thunderstorm may develop over Maine where stronger dynamics are present, however significant instability may be a challenge to reach. Thus, there is only a slight risk for severe weather, with the main threat being locally heavy downpours of 25-50 mm.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Copp