WMOD00196

• Contract/Permit #: 2003-01
• Sponsor Name: Gunnison County, City of Gunnison, Crested Butte
• Project Name: WM Evaluation Report
• Title: The Development, Conduct and Evaluation of a Cloud Seeding Program for the Gunnison River Basin, CO During the 2003-04 Season
• Date: 8/1/2004
• County: Gunnison
• State: CO
• Weather Modification - Doc Type: Reports

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the soundings. March and April had the greatest variety in wind directions, but even
then, when upslope storms are common on the Front Range, the Gunnison project area
rarely received amounts over 0.4" from easterly-type events. November - February
events were almost exclusively from a westerly direction. Many of the soundings were
dry below 650 or 700 mb. Some showed only a 100- or 200-mb thick moist layer,
usually found between 500 and 700 mb. The clouds that were formed in these situations
over the proposed target area were no doubt thicker than these numbers would indicate,
due to the forced lifting of the air mass by the mountain barriers.

Of the soundings examined, the 700-mb temperature was -5 oC or below slightly
less than half of the time, with the average being -4.1 oc. However, the 700-mb
temperature was -2 oc or colder approximately 80% of the time. Figure 2.9 provides a
plot of the mean storm 700-mb temperature averaged by month. As expected, these
average temperatures drop during the heart of the winter season. Although a -5 oc
temperature is commonly used as a maximum threshold for wintertime seeding projects,
much ofthe Gunnison project area is at elevations higher (colder) than the 700-mb level,
with some peaks rising to near 600mb. Thus the seeding material can be expected to rise
significantly higher than 700mb if targeted correctly. This means that seeding is likely to
be effective even when the 700-mb temperature is as warm as -2 oC, in which case the
vast majority of these events are cold enough to be seeded.

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