WMOD00288 ‎(2)‎

• Title: Twelve Basin Investigation - Volume I
• Prepared For: Bureau of Reclaimation
• Prepared By: Robert D. Elliot, Jack F. Hannaford, Russell W. Chaffer
• Date: 5/15/1973
• Weather Modification - Doc Type: Report

The a~~ance of available data is reflected in the treatment of missing data.
If any portion of a sounding which is used to calculate a parameter is missing, the
entire sounding is discarded [rom the analysis. Missing precipitatioo observalinns
are, however, carried through the analysis as missing rather than discarded.
The parameters derived from the sonndings and made available for analysis are'
. wind component normal to the massif barrier at the 600 mb level
. stability index (e [500] - e [7001]), where saturation is assumed
e e
. pressure at the nodal surface
. pressure, temperatnre, wind direction and speed at effective cloud top
. temperature at lifted cloud top
. temperature at the base of the effective cloud layer
. average normal wind component in the effective cloud layer
.

.

height of the 500 mb level
normal component of the wind at the height of the barrier crest
mixing ratio at effective cloud base
mixing ratio at effective cloud top

.

.

~,

\,

. difference of the above two quantities
. pressure at the base and top of each eland layer detected in the soundiog
Each sounding is first checked for valid winds. The procedure is to begin at
the height of the valley floor and step upward at even 50 mb increments until a
level is reached at which the component of wind oormal to the barrier is greater thao
V . , an adjustable minimum geoerally set at 2 m sec-l This level is designated to
ml.n
be lhe top of the dead layer. If the dead layer is found to extend above the crest
height, the observation is discarded since no lifting would be indicated. Then the
winds at the levels required for the nodal surface calculation are checked to insure
a positive component normal to the barrier. If the component is negative (ie, winds
blowing the wrong direction over the barrier) or the wind is missing, the sounding
is discarded. Finally, the winds at all levels between the top of the dead layer and
the nodal surface are checked to insure positive components normal to the barrier.
The next step is to identify all cloud layers in the sounding. A layer is de-
fined as being cloudy if the dewpoint d.epression in that layer is less than an
assumed threshold value as described earlier. The thresbold value used is a function
of pressure varying linearly from 2C at 800 mb to 6C at 400 mb. At pressures greater
than 800 mb the threshold is held conslant at 2C; at pressures less than 400 mb the
threshold is held constant at 6C. with all cloud layers defined, it is then necessary
to detennine which layers were effectively participating in the precipitation processes.

1-31

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