the storm until it grew into a Category 5. As it moved through the Gulf, the mayor of the
historic city of New Orleans ordered a mandatory evacuation of the city. Not everyone was
willing or able to comply.
Figure 16.34: Hurricane Katrina nears its peak strength as it travels across the Gulf of
Mexico. ( 24 )
When Hurricane Katrina reached the Gulf Coast, it had weakened to a Category 4 storm.
Even so, it was the third strongest hurricane to ever hit the United States. The eye of the
storm struck a bit east of New Orleans, buffeting the area around Biloxi, Mississippi with
the worst direct damage. The initial reports were that New Orleans had been spared. But
as water began to rise in the lowest lying portions of the city, officials realized that the storm
surge had caused the levee system to breach. Eventually 80% of the city was underwater
(Figure16.35). Bytheendofthathorribleperiod, around2,500peopleweredeadormissing
from the Gulf Coast, most of them from New Orleans. Over two hundred thousand of people
left New Orleans as a result of the hurricane, and many have not returned due to loss of
their homes and livelihood.
Blizzards and Lake Effect Snow
A blizzard is distinguished by certain conditions (Figure16.36):
- Temperatures below –7oC (20oF); –12oC (10oF) for a severe blizzard.
- Winds greater than 56 kmh (35 mph); 72 kmh (45 mph) for a severe blizzard.
- Snow so heavy that visibility is 2/5 km (1/4 mile) or less for at least three hours; near
zero visibility for a severe blizzard.
Blizzards happen across the middle latitudes and toward the poles. They usually develop on
the northwest side of a mid-latitude cyclone. Blizzards are most common in winter, when