Alberta Thunderstorm Forecast

July 27 ***A risk of severe thunderstorms will exist over much of westcentral Alberta on Thursday, with significant severe hail and damaging wind gusts possible in the late afternoon and early evening*** Discussion: Moderate to strong SW flow aloft will exist over the province on Thursday, with subtle height falls ahead of a somewhat weak shortwave trough that passes through during the evening. At the surface, a weak lead wave that tracks over northern Alberta brings a weak cold front to the Elbow that slides southeast and stalls along the central foothills in the afternoon. Further to the south, a lee low develops northwest of Calgary, with hot, dry downslope flow across southern Alberta. As of Wednesday evening, a pool of mid-teen dewpoints exists over parts of westcentral and northcentral Alberta, with the 00Z WSE RAOB revealing somewhat of a skin layer of richer moisture – however, the depth of low level moisture sampled overall isn’t insignificant. The associat...

July 23 ***Severe thunderstorms will be possible across parts of southcentral, central, and eastcentral Alberta on Sunday. A conditional tornado threat may also develop early in the evening over southcentral sections - however, this will be highly dependent on the quality of moisture return into the region*** Discussion: An upper low off the Alaskan panhandle as of Saturday evening pushes a strong shortwave trough across the BC interior during the day Sunday, which digs south as it rotates through flow aloft. Heights will slowly fall over Alberta as ascent downstream of the trough helps to steepen mid-level lapse rates. As cross-barrier flow strengthens during the day, lee troughing develops along the central and southern foothills – and combined with local terrain circulations, low level moisture should begin to pool into the foothills during the morning. The manner in which Sunday’s severe thunderstorm potential plays out across central Alberta will depend perhaps ...

July 20 Falling heights and cooling temperatures aloft over Alberta accompany an approaching upper low across the BC interior during the day Thursday. As the main forcing associated with the upper trough overspreads western Alberta, thunderstorm initiation is likely near the foothills. MLCAPE values may approach 1000-1500J/kg over much of westcentral Alberta, however, thick smoke will likely reduce insolation - especially away from the foothills - which will ultimately determine how much instability builds with daytime heating. H5 flow is near 20 knots, yielding 0-6km shear values near 30 knots. Strong forcing should yield the development of a discontinuous line of thunderstorms comprising the main outer "spiral band" of the upper low, with mainly strong multicells - however, a few brief supercells are likely near the foothills, bringing a risk of severe hail and wind gusts. Further to the west, a more favourable alignment of shear vectors with the axis of forcing ...

July 13 Another well-timed upper disturbance interacts with a moist, unstable boundary layer, especially near a surface trough through northcentral Alberta Thursday afternoon and evening. Combined upper support from the shortwave trough with favourable positioning beneath the left exit region of an H25 jet streak will lead to the development of moderate to strong instability with daytime heating. MLCAPE values of 1000-2000J/kg are common across much of Alberta especially from the Yellowhead north (excluding the far north) –   with pockets of up to 3000J/kg possible in near the richer low level moisture in the surface trough. This will result in vigourous deep convection during the afternoon and evening, in an environment of deep layer shear capable of organizing storms into strong multicells and a few supercells. Large hail and damaging winds will be the main threats – with the strongest storms bringing a risk of very large hail. Activity should more or less progress ...