WMOD00312 ‎(2)‎

• Title: Cloud Seeding Feasibility for the Shasta-Trinity Watershed
• Date: 12/1/1993
• Weather Modification - Doc Type: Report

the highest terrain, in modest concentrations of 0.1 to 0.2 g m-3, and at temperatures between
o and -10 oC. The radiometer is unable to estimate the vertical distribution of SLW. Upper-
air measurements provided vertical profiles of temperature and humidity from which the
probable vertical distribution of the SLW was inferred.

During the winters of 1983-84 through 1986-87, 26 storm systems having complete liquid
water data were observed. A total of 584 h of SL W occurred; 343 of these hours had
measurable precipitation at BLU. These numbers translate to 170 pet more hours of SLW
than precipitation on average per storm. This increase was especially true for the more zonal
or west to east moving storms. Colder storms moving out of the Gulf of Alaska in northerly
flow tended to have SLW periods of the same length or slightly shorter than the
accompanying precipitation periods.

The highest concentrations of liquid water in a given storm were observed during lighter
periods of precipitation. This relationship is typical of radiometer observations of winter
storms in other locations in the intermountain west (Rauber et al., 1986; Boe and Super,
1986; Super et aI., 1989; Long, 1987; Huggins, 1990). SLW developed in similar quantities
in both storms producing large quantities of precipitation (usually during a lull in the
precipitation), and in fairly weak precipitation producers (SLW tended to be observed
throughout the lifetime of the storm).

Figure 3.2 shows amounts are low. More than 80 pet of SLW hourly averages are below 0.2
mm (for a cloud of 1-km depth, this amount equates to less than 0.2 g m-3). This distribution
is consistent with SLW observations taken in other parts of the intermountain west.

100
90
Q.)
C)
co 80
....
c
Q.) 70
0
...
Q.)
a.. 60
Q.)
> 50
....
co
:J 40
E
:J
0 30
20
10
0

'\.

85% < .2mm

A Utah Long (1987)
. Colorado Boe and Super (1986)
. California Heggll & Rauber (1988)

o .10 .20 .30 .40 .50 .60 .70 .80 .901.001.101.201.301.40
I I I I I I I I I I I I I I I
.10 .20.30.40.50.60.70.80.901.001.101.201.301.401.50

Integrated Liquid Water (mm)

Figure 3.2. - Cumulative distribution of integrated SLW as measured by a vertically pointing microwave radiometer at
various field site locations. Averaging interval varied from 15 min (Utah) to 1 h (Colorado and California).

6