As a powerful low pressure system explodes across the northern High Plains on Wednesday, an outbreak of dangerous severe thunderstorms, including tornadoes, will erupt from southern Alberta into southern Saskatchewan and much of Montana.
Some of the cities and towns most at risk include Calgary, Lethbridge and Medicine Hat, Alberta; Swift Current, Saskatchewan; Great Falls, Mont.; Glasgow, Mont.; Williston, N.D.; Billings, Mont.; Helena, Mont. and Miles City, Mont., to name a few.
The greatest impacts from these thunderstorms will be large and potentially destructive hail up to the size of baseballs, or even softballs.
These storms will also have the ability to produce damaging gusts of winds over 60 mph and a few tornadoes, one or two of which could be long-lived and violent.
Baseball and softball-sized hail can be very destructive to crops, vehicles and even roofs on homes, as shingles are easily damaged. This size hail can also seriously injure or even kill exposed livestock. Any people caught without shelter can also be quite seriously injured.
While some scattered thunderstorms will be around to start off the morning, the main outbreak will not begin until the late afternoon or evening hours.
Initially, the storms will be more spread apart, and have ample opportunity to tap into significant twisting in the lower part of the atmosphere. This means the highest tornado threat will be found in central and northern Montana.
The storms will then congeal into a line that takes on more and more of a bowing, or backward 'C' shape, as it accelerates across the Canadian border.
Once this happens, the storms will still have the ability to produce large hail and tornadoes, but the biggest impacts will come in the form of damaging gusts of wind.
Though severe thunderstorms are not frequent across Montana and the Prairies of southern Canada in June, this is the best time of year for them to occur as jet stream energy shifts north for the summer. Still, this will be a particularly widespread and dangerous situation, the kind that usually happens only once or twice a year.
If you will be out and about across southern Alberta into southern Saskatchewan and much of Montana, you will need to pay special attention to the weather.
Once thunderstorms develop this afternoon, they will strengthen quickly, and dangerous conditions could follow soon after.
One added concern across the region will be very heavy, potentially flooding rain. This storm system will have the ability to produce a large area of 1-3 inches (25-75 mm) from Calgary into Edmonton, Alberta.; and Regina, Saskatchewan.
Current technology has advanced enough over recent years to provide ample alert of the potential for severe weather and the approach of localized severe storms. Be sure to understand the difference between a watch and a warning. A watch means that an area is being monitored for dangerous weather. A warning means that dangerous weather is imminent. When a warning is issued, there may be too little time to travel across town or across a county to escape the storm. The time to have a plan of action and move to the general vicinity of a storm shelter or safe area is when a watch is issued.
Keep in mind that lightning is one of Mother Nature's most dangerous killers. If you can hear thunder, you are close enough to the storm to be struck by lightning, even if the sun is still shining.
The same storm another round of flooding to Morocco has brought flooding issues to Portugal, setting its sights on more of southern Europe this weekend.
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O'Fallon, MD (1990)
Strong downburst from a thunderstorm caused an apartment to collapse, injuring 25 people.
New England Coast (1898)
Famous "Portland" storm formed off Cape Cod with loss of 200 lives. Many others were lost to the raging sea in 50 small vessels. A total of 27 inches of snow in New London, CT; 15 inches at Waterbury, CT. Peak wind was 72 mph in Boston. Boston received more than a foot of snow.
Second heavy snowfall in three days hits the region with 12 inches on the ground in NJ; 14 inches in NY; greatest November snow in New England since 1898.