Monday, July 17, 2023
Regional Impacts
Today
NB: Isolated thunderstorms possible producing gusty winds.
LAB: Isolated lightning
Tonight
NB: Isolated lightning
Tuesday
NB: Thunderstorms with downpours with rainfall rates of 15-25mm/h
LAB: isolated lightning
Convective Discussion
A broad area of ascent driven by a surface trough, vorticity advections and favourable upper jet dynamics will drive isolated storms later this afternoon across parts of northwestern Labrador.
In the Maritimes today a trough will continue to advect eastward throughout the day. Elevated instability exists near and east of the trough, with high PWATs thin MUCAPE profiles of 200-300 J/KG, however due to the proximity of a mid tropospheric thermal ridge very high freezing levels exist. As a result, buoyancy looks to be limited through the ICN, thereby limiting charge separating and lightning. Regardless downpours may produce rainfall rates of 15-25mm/hr, despite no lightning being expected along this feature.
Behind the trough in NW NB, clearing and residual moisture in the PBL will yield MLCAPEs near 1000 J/Kg, with moderate shear profiles. However beyond surface heating there is a lack of a dynamic triggering mechanism which should temporarily delay initiation and limit the number of storms that do develop. The Mid to upper troposphere does dry significantly by the late afternoon and early evening, supported by observations upstream (12z Maniwaki UA). This favours a wind hazard for storms (DCAPEs 700-1000 J/Kg), while limiting the risk for heavy downpours. Storms will weaken late this evening, but may exist just after midnight before dissipating.
On Tuesday deep moisture rebuilds ahead of an shortwave moving eastward from Southern Quebec, this will yield a downpour threat for NW NB. Despite lower CAPEs, this synoptic trigger should allow for a greater prevalence of storms and lightning compared to today.
Cool air aloft and differential heating in the terrain in northern Labrador may also produce some localized lightning.
Overnight Tuesday into Wednesday this deep moisture will move eastwards along a trough and any storms that develop will bring the risk of heavy downpours.
Thunderstorm Outlook for Today
Thunderstorm Outlook for tonight:
Thunderstorm Outlook for Tuesday:
Thunderstorm Outlook for Wednesday:
Allen