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<br />, <br /> <br />However. these results do not stand out clearly abo~~ the background variability <br />in precipitation. <br />4) During some hours on expericental days. blocking type flow prevented <br />the nucleant from the ground generator network from ascending over the target <br />area (5.3% of the sIx-hour blocks). There was total or partial blocking of <br />effective entrainment of nuclei in 12.6% of the six-hour blocks. Under the5e <br /> <br />conditions th~ nucleant was carried well to the west or northwest of " the FargeL <br />~rea. ~~~n the .following day,was a not-seeded experimental day, i~ was often <br />contam1.n.a.ted by ~u:clei return!n.& from the west .~ol1owing the breakup of the <br />"bloCking fl~ r~g~ (7.6% of the "thtee-hour blocks). <br /> <br />i <br /> <br />j) Extra-area effects of seeding app~ar to have occurred over a broad area <br />lying up to 160 km from the generator sites. Much of this effect occurred as <br />expected. downwind of the target area. during yithin-bounds vind conditions. <br />", Some of the effect ,occurred. not as expected. well to the vest of the target area <br />- a8 a result of the seeding under blocking flow conditions. 'Over "the dmmuind <br />free (e.g.. San Lu~s Valley) apparent net increases in precipitation are s~all <br />in absolute value. ,No net effect appeared at the abundant stations in the area <br />to the Yest of the target instrumented as part of the original target area. <br />6) Insufficient data were available in the stable clpu4 category to <br />'establish empirically where the warm side l~ito(cloud" top temp~ra~ure) ~f the <br />" posi~lve effect S~ed_ing vindoV lay~ In the unstable' ~ategory the sounding <br />derived cloud top did.POt rep~esent. the'true top. .The true tops developed <br />fo1:1ov1ng the release of 'instabUi.ty over the upwind slopes of the barrier: <br />hence. no assessment of a varm side limit could be "investigated for this category. <br />7)" See~1ng dur~ng a frontal passage had no effect other than that accounted <br />-forby the f~ta~~!., ~ssociated _d":-stribu~ion of stability and wln~.. " '-- <br />- ' -08) The overaIl"potentia"r' for precipitation enhancement was assessed -in this". - <br />evaluation study at around 10%. taking into account randomization bias. This <br />translates into an overall streamflow enhancemenc potential of around 19%. This <br />potential was not realized in the seeded 24-hour experimental days for several <br />'reasons: a) the opportunities lost with late starts in the fall season. b) sus- <br />pensions, c) missed forecnsts of suitable days. d) losses in the accounting for <br />experimental day precltation vhen strong blocking flov existed and seeding was <br />ineffective in the target ~ren, e) excess accounting in not-seeded days when <br />conta~ination-o~c~rred" O~ a not-se~deri experimental day folloving a seeded block- <br />~ng flaY day, f) losses when cold top stable orographic clouds were seeded under <br />strong vind - deep cloud conditions, and g) possible moderate seeding-produced <br />losses on the upwind slopes ~hen strong convection was seeded. <br /> <br />-22- <br /> <br />. <br /> <br />. <br />-.r <br /> <br />A-1l-6 <br />