C a s e

H i s t o r i e s

60

54

48

42

36

30

24

18

12

6

0

360

315

270

225

180

135

90

45

0

time (hours)

Figure 4. Wind record from CDOT/CAIC weather tower located immediately above the Over the Rainbow path.

occurred during one 19-hour period on January 30: winds
averaged14.3 m/s from 262 degrees. Peakgusts duringthis
period averaged 26.4 m/s.
Heavy blowing snowwas observed in the days before
the avalanche. Due to a small ridge along the west flank of
the avalanchepaththe westerly winds cross-load the start-
ing zone with snow. These winds createdhard slab condi-

tions but added little additional snow in the upperstart-
ingzone.However,lowerinthe startingzone and track
where a narrow but relatively thick stand of conifers bor-
dersthe path,thestrongwinds likelyaddedsignificant
snow to the pack.
Temperatures were rather unremarkable priorto the ava-

0

-2

-4

-6

-8

-10

-12

-14

-16

-18

-20

100

90

80

70

60

50

40

30

20

10

0

time (hours)

Figure 5. Hourly maximum and minimum temperatures and relative humidity from the CDOT/CAIC weather tower.

259