WMOD00297

• Title: Hygroscopic Seeding in Oklahoma
• Date: 10/31/1971
• State: OK
• Weather Modification - Doc Type: Report

In the second area, about 5 mi. W' of Fairview, a precipitation echo
appeared at 1620, reaching intensity 2, covering an area of 2x3 miles.
and diminishing to intensity 1 by 1647. 0-1 seeded this ceU system
beginning about 1649, concentrating at the S\V edge. By 1659 the radar
echo had returned to intensity 2, with the growth at the SW end. At 1708
,the echo began weakening, and disappeared by 1720. The observations are'
consistent with the hygroscopic seeding having aided in the resuscitation
of the precipitatio? from the cell system.

The third area was 5-8 mi NW of Fairview. Us base appeared better than
others in the area. A radar echo appeared at 1656. 0-2 seeded with AgI
twice in this cell system, at 1650 and at 1652. Radar intensity 4 was
reached at 1704, and a size of 4x6 miles. 0-1 seeded ~he general area
beginning about 1701. The storm began weakening at 1708, and disappeared
from radar at 1736. Visually, we noted that the precipitation was intense
and that the decay of the system seemed especially rapid. A very long
continuing cirrus feather could be seen grov{ing out of its top at 1733 and
extending far E or SE - - a symptom of the localized glaciation from _l\gI
flares. We had observed the first glaciation, in several areas, at 1658.
Lightning occurred at 1711. The evidence suggests that the initial cloud
growth, glaciation, and precipitation development was natural. The AgI
should have increased the convective development, and both types of seeding
likely aided in the extracting of precipitation during the last half of the storm.

This was the last development in the area, and the area decayed rapidly.
0-1 seeded later (1750-1830) in a'convergence region S of Altus which had
been yielding steady light precipitation, but this region also was dissipating
and no effect could be expected.

The August 23 case was too close to NSSL and too complex to permit any
brief evaluation to be useful.

For August 28 a brief look at the radar showed a N\V-SE line-up of the
precipitation area near and over Lake Altus that related rather well to the
orientation of the seeding. However, the seeding is tailored to the best
conditions, and so even if there is a correlation there is no strong evidence
for a particular cause and effect relationship.

The seeding on August 30 was in marginal clouds west of Altus. The
precipitation was enough to have economic value. The area is probably too
far from the NSSL radar site to justify evaluation.

On September 2, a very weak cloud system was seeded briefly east of Altus.
There were possible effects, but not any of economic significance.

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