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Great Plains Blizzards
North Dakota, March 1966
blizzard: a severe weather
condition characterized by high
winds and reduced visibilities due
to falling or blowing snow. The
NWS definition specifies winds in
excess of 30 kts (35 mph) and
visibility of less than a quarter of
a mile for at least 3 hours.
Typical tracks of cyclones
that form east of the Rockies
Where are blizzards most common?
Where are blizzards most common?
Humans and Blizzards
hypothermia: decrease in the body’s core temperature to a level at
which normal muscular and cerebral functions become impaired
Colorado Cyclones
and Blizzards
Cold, Wind and Snow
Extremely cold air is the first component
of a blizzard.
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Where would this cold air originate?
Why would this air be so cold (-30 to -50˚F)?
What happens to the sea level pressure of
extremely cold airmasses, and what would this
mean for blizzard formation?
What type of front marks the leading edge of
this extremely cold airmass?
A cyclone to provide wind and snow is the
second component of a blizzard.
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What factors contribute to the formation of a
cyclone on the east side of the Rocky
Mountains?
What happens to the extremely cold Canadian
air when it comes in contact with the cyclone?
Where would strong winds form in this
situation?
What is the source of moisture for blizzards
associated with Colorado cyclones?
Figure 7.7
Movement of airmasses and development of
fronts as surface low-pressure center forms
Trough of warm air aloft (trowal)
Snowfall created by the
trowal can exceed 10-12
inches in a 300 mile swath.
Why would the snow created
by the trowal be particularly
susceptible to creating
whiteouts and huge drifts?
Second factor creating snow north of the cyclone center
involves topography
How do the high plains and Rocky Mountains enhance
snowfall in a blizzard?
Hint: how would the temperature of an air parcel cool traveling
westward from St. Louis to Denver (elevation gain 4,500 feet) change?
Alberta Clippers and Blizzards
Upper air conditions
•Jetstream orientation
•Wave in the jetstream
Surface conditions
Why would Alberta Clipper
blizzards tend to produce less
snow than Colorado cyclone
blizzards?
Mature phase of and Alberta Clipper cyclone
Ground Blizzards
a blizzard that is caused solely by blowing snow
(no new snow is falling)
• Under what conditions can a ground blizzard occur?
• How deep is a ground blizzard?
Winter of Blizzards 19961997
Table 14A
Summary of surface data at Fargo, North Dakota, during nine blizzards in the 199697
winter
Date of blizzard
(199697)
Lowest
Temperature
(F)
Highest
Temperature
(F)
Greatest
Hourly
Sustained
Wind (knots)
Fasted
Reported
Wind Gusts
(knots)
Snowfall
(inches)
1617 November
9
26
34
42
13.5
1618 December
-8
22
33
43
7.9
23 December
-14
-8
21

4.9
45 January
0
20
33
40
10.7
911 January
-15
15
24
35
4.8
15 January
-8
12
38
49
1.0
2223 January
-17
24
34

4.9
34 March
-5
31
25

15.5
56 April
9
38
24
56
7.0
Figure 14 B
Schoolhouse Blizzard
Formed:
January 12, 1888
Dissipated: January 13, 1888
Maximum amount:* 6 inches (15 cm)
Lowest pressure: 930 hPa
Damages:
UNKNOWN
Fatalities:
235
Areas affected: Mid-Western US
* Maximum snowfall or ice accretion
Figure 14 C
Figure 14 D