Some of the weather related events are as follows:
Rain and
flood
Air contains water vapors. When warm air moves up in the sky,
water vapors in it gather to form clouds. If the clouds are big enough and have
abundant water droplets, these droplets bang together and form bigger drops.
When the drops get heavy, they fall because of gravity, and we have a rainfall.
If rain is heavy and it falls for days or there is a lot of
snow and there is a meltdown, it can cause rivers to overflow causing a flood.
Thunderstorm
A
thunderstorm is a storm with lightning and thunder along with the gusty winds,
heavy rain and sometimes hail. A thunderstorm is formed when there is abundant
moisture in the air which causes clouds and precipitation to form and when
there is an uplift of the air. The uplift must be very strong to produce
cumulonimbus cloud that reaches high above in the atmosphere.
An unstable or active air circulation system comes into being
because of a big temperature difference between the cold air of the high
altitude and the warm air on the ground.
Hail is created when small water droplets are caught in the updraft of a thunderstorm. These water droplets are lifted higher and higher into the sky until they freeze into ice. Once they become heavy, they will start to fall. If the smaller hailstones get caught in the updraft again, they will get more water on them and get lifted higher in the sky and get bigger. Once they get lifted again, they freeze and fall. This happens over and over again until the hailstone is too heavy and then falls to the ground.
Tornadoes
A tornado is a very active rotating column of air extending
from a thunderstorm to the ground. The most violent tornadoes can cause
tremendous destruction with wind speeds of up to 500 km/h. They can destroy
large buildings, uproot trees and hurl vehicles A tornado’s damage path can exceed
one kilometer wide to 30 kilometers long. Most tornadoes form from thunderstorms. In North America when warm, moist air from the Gulf of Mexico and cool, dry air from Canada meet, they create instability in the atmosphere. A change in wind direction and an increase in wind speed with increasing altitude create an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the updraft tilts the rotating air from horizontal to vertical. An area of rotation, 4-10 kilometers wide, now extends through much of the storm. Most strong and destructive tornadoes form within this area of strong rotation.
Winter
storms get energized when two air masses of different temperatures and moisture
levels clash. In North America winter storms usually form when an air mass of
cold, dry, Canadian air moves southward and collides with a warm, moist air
mass moving north from the Gulf of Mexico. The point where these two air masses
meet is called a front. If cold air advances and pushes away the warm air, it
forms a cold front. When warm air advances, it rides up over the denser, cold
air mass to form a warm front. If neither air mass advances, it forms a
stationary front.
Classification
of some severe weather events according
to Environment Canada’s website:
Blizzard: A Blizzard warning is issued when winds
of 40 km/hr or greater are expected to cause reduced visibility of 400 meters
or less, due to blowing snow,
or blowing snow in addition to falling snow,
for at least 4 hours.
Blowing
Snow: When blowing snow is caused by winds of at least 30 km/h, is expected
to reduce visibility to 800 meters or
less for at least 3 hours then a blowing snow warning is issued.
Freezing Rain/ Drizzle: When rain or drizzle falls onto below zero ground
and freezes on
contact forming a layer of ice causing slippery roads then a freezing rain
warning is issued.
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