With clear skies expected across the prairies on Saturday, daytime heating will to lead to severe weather developing overnight and into Sunday. Strong damaging winds and heavy rain with flash flooding are the main concerns. The situation may in fact become a "derecho" type event.
(A derecho (pronounced similar to "deh-REY-cho" in English, or pronounced phonetically as " ") is a widespread, long-lived wind storm. Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems.) Source:
http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm
Along the international border, storms are expected to be strongest and move east at a minimum of 80km/hr. It will move so fast that the storm system will start up in Montana Saturday night and end up in northern Ontario on Sunday morning. Since these powerful type of systems can cause widespread damage with gusts of between 100 and 120km/hr, areas near or around the main storm system will be affected. Heavy rains with supercell thunderstorms will precede the damaging wind event. Tornadoes and large hail are also possible ahead of the squall line.
Here is the latest graphic from the GFS storm model showing midnight Saturday's Supercell Composite Index:
As you can see in this second snip, the strongest areas of strength move all the way into northern Ontario by noon Sunday, only 12 hours after the first graphic, seen above.
Our preliminary risk map, outlining the area of most concern for Saturday night:
This map may be updated as needed later this afternoon.
Photos and tweets from yesterday's amazing hail storms in the southern Alberta foothills:
