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Storm System To Lift From The Southern U.S. To Great Lakes Over The Next Couple Of Days

A storm will develop, intensify and lift northward from the southern Plains to the Great Lakes over the next two days. The weather hazards of most concern today are severe thunderstorms with damaging winds, isolated large hail and tornadoes and heavy rain with possible flooding in the Lower Mississippi Valley and Mid South. Then on Thursday, a zone of heavy snow may fall in Iowa and Wisconsin. Read More >


Across eastern Washington and north Idaho, thunderstorms can develop by midday and carry on into the evening hours. Threats from thunderstorms can be many, ranging from tornadoes, flooding and lightning. Tornadoes can be the front-page headline in newspapers or the top story on the evening news, but damaging straight-line winds of "tornado force" can also injure and kill animals and humas.


Barn Damage near Lewiston, ID due to straight-line winds 5/29/03.

Downburst winds from a thunderstorms usually results when an area of air within the storm is cooled by chilly raindrops or hailstones, or by evaporation of the raindrops, which quickly cools the air. This pocket of cooled air, heavier than surrounding air, accelerates downward to the ground. As the cool air slams into the ground, it spreads out from the area of impact. The varied terrain in our region can enhance downburst winds.

This process, in extreme cases, can cause winds higher than 100 mph! Weather forecasters call these bursts of wind "microbursts" if they are less than 2 1/2 miles across and "macrobursts" if they are greater than 2 1/2 miles across. These downbursts of air can be very hazardous and even life-threatening to pilots and can cause extensive damage, injuries and fatalities at ground level as well.

Try to get indoors during all thunderstorm activity. High winds can suddenly develop, which can cause things on the ground to become swift moving, airborne missiles, which can injure or kill.



Large hail to 1 1/2 inches near Newport, WA on 7/10/03.

Hail is another thunderstorm threat that often occurrs across the Inland Northwest. Hail forms within thunderstorms. As liquid water freezes in the cold mid and upper levels of the storm, the ice is kept aloft by strong updraft winds for a time. Then when they become too large to be kept aloft by the updrafts, they cascade to the ground.

Hailstones vary from pea-size (about 3/8 of an inch in diameter) to larger than grapefruits (nearly 5 inches in diameter). Hailstones can produce tremendous damage to farm crops, either as large hailstones or as concentrated fall of small hailstones that accumulates to a depth of several inches. Large hail can easily damage vehicles and buildings, and can be life-threatening to animals and people.

Again, try to get indoors during all thunderstorms. A fall of small hail can suddenly change to a fall of very large ice missles, than can injure or even kill.

Remember, tune into NOAA Weather Radio, the Weather Channel, or your local radio or TV stations for further details. At any location you find yourself, plan on how be safe when thunderstorms develop.

For more information on strong winds and hail, visit the National Weather Service Severe Awareness web page.