WMOD00091

• Applicant: Western Weather Consultants
• Project Name: Procedure for Determining Seeding Rate
• Date: 11/1/1984
• Weather Modification - Doc Type: Report

" t.-r-~
Inl"!'""\:~~~",--,
',''---':-'''-'~''~ '..:\ ,~
.-t .1" - .", ", " : c'_'",! n'
I:'::> '.'ro.!} II
;' 01",'1';\/;', n<'" .! i,
: ;.; 11"" \.! ,1"1.'iJ ., I'
c..;l.'.\._ ,". ';LJ I
. .-----__ f')
DIJ'.' '.;,.., "" _.~/---
f1.1t1i'l'''''1 Ur I, 'j 'Ii.... . ',..".. 1
" u '-l:..rlQ'Ul.sj~;VfS yze
seeding area.

WESTERN WEATHER CONSULTANTS. INC.

PROCEDURE FOR DETER1>\I~niG SEEDING RATE

)

appropriate raohs to determine the cloud picture over the
Determine the following cloud characteristics and values:

Clo~d De~ - Determine actual or if sounding is saturated down to near
the surface use 8000 ft. N.S.I.. as a minumum base value. Next use a cloud
top value of IS,OOO ft. M.S.L. for pre-trough clouds if actual clouds are
deeper or the actual evaluated cloud top value if lower than 18,000 ft.
M.S.L. and the top is determinable from the sounding. For post-trough
cloud tops use tIle actual cloud top as determined from the sounding.
~ext, determine the cloud depth in thousands of feet (example: 4800 ft.
cloud depth = 4.8 for cloud depth).

**Note - the minimum cloud depth that we will consider seedable is 1900
ft. = 1.9.

To determine ttt2 Cloud De.pth Va~ue. for the seeding equation, subtract the
minimum cloud deDth value of 1.9 from the actual cloud depth expressed in
thousands of feet (From our example: 4.8 Qinus 1.9 = 2.9 is the Cloud
Depth Value).

Cloud Base Water Content - Fco8 the sounding, determine the forecast
(based on the observed) cloud base water content. The minimum cloud base
water value that we will consider seedable is 1.6 gm/Kg. To dete~,ine
the Cloud Base Hater ~,.ralue for the seeding equation, subtract the winimu::l
cloud base water value from the actual or forecast value determined from
the sounding (example: Observed value of 3.7 go/Kg minus 1.6 ~ 2.1 value).

-
~.
.

Cloud Temoerature - For pre-trough clouds, the cloud temperature is deter-
mined at the 500 mb level. With the synoptic motions in these types of
cloud systems and the region of moisture that essentially is responsible
for the clouds precipitation mechanism, the 500 mb level is a consistent
and ~easonable level to monitor as the ice crystal region for that cloud's
precipitation mechanism. The formula for determining "the cloud tem~eraturc
value is as follows:

(pre-trough) T500 = 15 - ( IT5001 - 12)

Where the warmest seedahle cloud temperature at either 500 mb or cloud top
is - 120c. And the coldest 500 mb temoerature that is considered is
--
- 270 c.

For post-trough clouds (usually orographic in nature), the cloud top
is the level considered as indicative of the cloud temperature. The down-
wind synoptic motion in the vicinity of thecloud top produces somewhat at
a lid on the upper motion of the cloud top are usually in the precipitation
mechanism portion of this type of cloud system. The Formula for determining
..~
the cloud temperature value is as follows:

5oi;tl, 5(./;'O/" [(post-trough) Tct = 18-( I Tctl - 12)

of Where the warmest seedable cloud temperature at either the cloud too or
.",., .,.~ 500 mb level is - 120c. P'Q C()l.dest cloud to!) temperature that we will
consider seedable is - 30o~.

,

For post-trough in the !\'orch Sector, eg thE Ce:1.tr-1.1 Program area, the
coldest cloud ton temperature that ~e ~ill ccnsidcr is _27GC.

(post-trough) TCe = 15-( Ircc! - 1.2)