WMOD00277

• Contract/Permit #: 14-06-D-6467
• Title: An Operational Adaptation Program for the Colorado River Basin
• Prepared By: Lewis O. Grant, Chappell, Crow, Mielke Jr., Rasmussen, Shobe, Stockwell, Wykstra
• Date: 10/1/1969
• State: CO
• Country: United States
• Weather Modification - Doc Type: Report

8

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OF OCCURRENCE

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W
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CL

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PERCedAGE

OF TOTAL S/l()WFALL

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W I
2:: /
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2

o 04 08 12 16 18 '14
HOUR OF DAY
(24 HOUR CLOCK)

Figure 29. --Distribution of snowfall at Climax,
Colorado, as a function of the hour of day, November
through May, 1964-67.

8

Clima.x 2NW during storm periods with
coincident ppt. :'it one or more otherstation.

lJ')
IJJ 60
~
U4
o
z 20

3 5 7 9
A,M.

5 7 9 II
P.M.

Climax 2NW during storm periods without
coincident ppt. at another station. -

50
30
10

Hot Sulphur Springs 2SW during storm periods
with coincid nt ppt. at one or more other station.

Grand Lake 6SSW during sotrm periods with

~~

Allenspark during storm period with coincident
60 ppt. a.t one or more other statio~

:o~ ':

Figure 30. --Six month diurnal frequency pattern of
hourly precipitation, November - April for three
I seasons, at four stations in or near the Upper
Colorado River area above Kremmling.

marked peak in the occurrence of
snow occurs at around 0300 Mountain
Standard Time. A pronounced mini-
mum in occurrence exists from 0700
to 1100 MST, followed by smaller
secondary peaks during the afternoon
and evening. The probability of
precipitation at 0300 MST at Climax
is almost three times that for the
period from 0700 to 11 00 MST. It
can also be seen from Figure 29
(Curve B) that the percentage of total
snowfall follows very much the same
diurnal variation. Hourly intensities
are slightly lower between 0200 and
0400 MST and somewhat higher
between 1600 and 2100.

Consideration of hourly snowfall for
Climax, Colorado, yields many
interesting facts that are typical of
many reporting stations in the
Colorado Rockies. The marked
peak in frequency during the early
morning hours followed by the dip in
the forenoon hours is typical of most
central and northern Colorado
stations. This can be seen from
Figure 30 which shows the number
of cases of coincident precipitation
at Climax, Hot Sulphur Springs,
Grand Lake 6SSW, and Allenspark.

The broad minimum in precipitation
activity between 0700 and 1100 MST
provides an excellent starting time
for an experimental day since this
represents the bottom in a pronounced
diurnal cycle. New meteorological
data required for deciSion-making
arrives during this same time interval
and the combination of the two factors
suggests that this interval provides
an excellent opportunity for the start
of a 24-hour experimental unit. It
also provides for observation periods
relatively free from the complications
of falling snow contributing to the
collection of better data. It is essen-
tial that the experimental unit used
for research programs in the northern
Colorado Rockies take this diurnal
variation into account, since the 300%
variation in precipitation over a day
can far exceed results expected from
modification efforts. A very slight
imbalance in the sample size as a
function of the time of day for an
experimental unit of only a few hours
could substantially override seeding
results.

The large diurnal maxima in the
frequency of precipitation during the
early morning hours at. Climax is
also apparent (Figure 31) for the
precipitation stations at Ouray and
Wagonwheel Gap in the San Juan

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