WMOD00315 ‎(2)‎

• Title: Colorado River Augmentation Demonstration Program - Technical Report January 1983 - March 1985
• Date: 4/1/1986
• Weather Modification - Doc Type: Report

over the Mesa in a more direct fashion. Similar effects were
observed on the north side of the Mesa, with northwest
winds; the lower winds became perpendicular to the Mesa
as they approached it. Even southwest flow entering the
"convergence notch" between the arms of the Mesa probably
crosses the Mesa and descends on the north side relatively
quickly. This rapid transit and descent may pose a targeting
problem, as the time available for newly nucleated crystals
to grow in a SLW-rich environment will be relatively short,
about 30 minutes, given an average cross-barrier wind com-
ponent of 10 m/s.

None of the aircraft LWC data were collected during any of
the 23 previously-identified episodes of heavy SL W, although
2 flight~ were made in conditions that later developed into
major episodes. Most of the heavy SLW episodes occurred
with GJT 70-kPa winds from more southerly directions than
cases sampled by the aircraft. Significant icing did occur on
several occasions, and in one instance a flight was terminated
due to heavy airframe icing, which suggests that some re-

search aircraft may not be able to remain on station during
the heaviest SLW episodes.

2.4.2 Radar Measurements. - Hourly averages of cloud tops
measured by a Ka-band radar at the Island Lake Site were
plotted against SLW for January through March 1985 (fig.
2-5). Echoes were subjectively classified as either stratiform
or convective based on the appearance of the facsimile trace
produced by the radar. Those echoes classified as convective
were primarily embedded convection.

With only two exceptions, SLW amounts greater than
0.5 mm were observed during convective periods, and were
associated with cloud tops between 4 and 6 km m.s.!. Few
tops higher than 6 km were observed.

A least-squares fit to figure 2-5 produced a correlation coef-
ficient of 0.22 and a slope of + 1.08, showing only a weak
(though positive) relationship between cloud top height and
SLW.

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· Convective 12641
HOURLY AVERAGES 0 Stratiform 14611

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Figure 2-5. - Hourly averages of Ka-band cloud tops plotted against SLW. The greatest amounts of SLW were observed during convective
periods. Few cloud tops higher than 6 km m.s.l. were observed.

9