A potent upper-air pattern will create extreme instability across the Southwestern Prairies Thursday. A surface trough will slice through the summer air offering a trigger for explosive thunderstorm development in the unstable atmosphere.
Winds at the surface out of the southeast and upper-level winds from the southwest suggest a well-sheared warm sector. The strongest surface heating will remain just south of the border. In spite of that, ample moisture delivery, temperatures falling aloft, effective shear, and plenty of energy will provide a breeding grounding for severe thunderstorms Thursday.
Thunderstorms will develop across Southern Alberta and Northern Montana around 2 pm. Trans-versing northeastwards throughout the afternoon and evening, Initial storm develop may feature discrete cells and bowing segments; a threat for large hail, damaging winds, and an isolated tornado is possible. As progression into the evening continues, a powerful nocturnal complex of thunderstorms known as a Mesoscale Convective Complex (MCS), may develop. These convective weather systems are notorious producers of damaging winds, intense frequent lightning, large hail, and localized flooding in torrential downpours. Moreover, these systems are known to persist well into the pre-dawn hours.
HAZARDS: 90-110km/h wind gusts, 2-5cm hail, torrential rainfall, frequent lightning, and an isolated tornado.
We will be monitoring the thunderstorms throughout Saskatchewan and Alberta attentively on Thursday. Be sure to closely monitor watches and warnings throughout the afternoon, evening and overnight. We will be issuing another forecast for severe thunderstorm risk in Saskatchewan, Friday. The risk depends greatly on the evolution of thunderstorms Thursday into pre-dawn Friday.
HEAVY RAINFALL CONTINUES WEST OF EDMONTON
Much of the focus is rightfully centered around substantial thunderstorm risk further south, but appreciable rainfall amounts along the Highway 16 & 40 corridor is worth mentioning. This region has already seen very-heavy rainfall over the last several days. Another 50-75mm is on tap between Hinton and Edmonton, through Friday.