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

that any increase in precipitation that might
result from the increased condensate associated
with warmer equivalent potential temperatu.res
is negated by an increase in the inefficiency of
the cloud system to convert the added condensate
to precipitation. This may be due to a growing
lack of effective ice nuclei in the warmer cloud
systems below that which is required to utilize
the additional cloud wat er produced.

Figure 43 shows the distribution of
snowfall and daily snowfall occurrences as a
function of the 700 mb equivalent potential
temperature computed using 40 K class intervals.
The frequency curve indicates a broad maximum
in occurrence between 301. 50 K and 309. 50 K
with snowfall occurrences noted over a range
extending from about 2830 K to 3210 K.

An interesting bi-modal distribution
is apparent in the snowfall curve. The major
snowfall occurs coincident with the occurrence
maximum between 301. 50 K and 309.50 K.
However, a second peak is noted from 313.50 K
to 317. 50 K indicating the presence of a separate
population of relatively infrequent but quite heavy
daily snowfalls. This bi-modal distribution in
snowfall is similar to that observed at Climax
although the peaks occur at somewhat warmer
temperatures.

, Mean daily snowfalls average about
O. 2 inch water equivalent for equivalent
potential temperatures up to about 301. 50 K. A
gradual increase in mean daily snowfall is
observed up to 311. 50 K followed by an abrupt
increase thereafter. This abrupt upward swing
in the mean daily snowfall again appears to reflect
a favorab Ie combination of factors since it ,::annot

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be totally explained by the variation of the equiva-
lent potential temperature.

(5) Daily snowfall related to stability
The vertical variation of equivalent
potential temperature may be used to define a
stability for moist processes. An index is
derived by subtracting the equivalent potential
temperature at 700 mb from the value at 500 mb.
Figure 49 shows the distributions of snowfall -
occurrence and snowfall at Climax as a function
of this moist stability index computed for 20 K
class intervals.

It is seen that only 4. 2% of the total
snowfall occurs under unstable conditions and
67% with an index between 0 and +6.

The mean daily snowfall reaches a
peak in the class interval from +2 to +4.

Figure 50 shows the distributions of
snowfall occurrence and snowfall as a function
of this index computed using 20 K class intervals.

About 70% of snowfall occurrences
producing over 77% of the total snowfall occurs
with values of the stability index between +0. 5
and +6. 5. Less than 7% of the total occurrence
are aS8'Ociated with unstable conditions and
these produce less than 5% .of the total snowfalL

The mean daily snowfall reaches a
peak in the class from +2. 5 to +4. 5 similar to
that observed at Climax.

(6) Summary
Orographic influences at Climax
result in greater amounts of snowfall with
northwest flow and a dampmg at snowfall
activity when southwest flow is present. The

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, Figure 49. --(a) Mean Daily Snowfall at Climax as a function of
a moist stability index. (b) Distribution of total snowfall and
total occurrences as a function of a moist stability index
computed over a 2-degree class interval.

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