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Last modified
7/28/2009 2:38:01 PM
Creation date
4/16/2008 11:06:54 AM
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Weather Modification
Title
Special Regional Weather Modification Conference Augmentation of Winter Orographic Precipitation in the Western US
Date
11/11/1975
Weather Modification - Doc Type
Report
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<br />The length ahead for which a forecast of suitable cloud tops temperature <br />must be made can be judged from Figure /~. Orders to commence generator opera- <br />tions most frequently fell between 0900 and 1300 (experimental day starts 1100, <br />but generators could be <br />turned on up to 2 hours <br />in advance unless the <br />prior day was an unseeded <br />experimental day). Orders <br />to turn off were sharply <br />peaked at 0900 the next <br />day. Except for the first <br />year, it was not mandatory <br />to issue orders prior to <br />the start of the experi- <br />mental day. The operator <br />could wait until condi- <br />tions were observed to be <br />favorable for seeding. <br />However, he was obliged <br />to forecast that condi- <br />tions would continue <br />substantially in the <br />favorable category during <br />the balance of the day <br />once he had made his <br />meteorological decision. <br />If he missed this fore- <br />cast, the results would <br />be diluted. <br /> <br />3S <br /> <br />I~ <br />,1 <br />,I <br />,I <br />-L <br /> <br />.. <br />" <br />o <br />Z' <br /> <br />... <br />... <br />. <br />Z' <br />g 30 <br />.. <br />c: <br />.. <br />... <br />c: <br />.. <br /> <br />11 <br />r I <br />II <br />I I <br />I I <br />I <br />f\ ~ T:I.a "ff leq..en I <br />, \..- , <br />I <br />.~~ <br /> <br />; <br />.2 1S <br />... <br />IJ <br /> <br />: <br />. <br />. <br />" <br />... <br />: 10 <br /> <br />...----- Time aD Requese <br /> <br />... <br />o <br /> <br />.. <br />.. <br />IJ <br />1 <br /> <br /> <br />S <br /> <br />09 11 13 1S 17 19 21 23 01 03 OS 07 09 11 <br /> <br />TDlE {lIST) <br /> <br />~ 4. FOUR YEAR FREQUENCY BY HOUR OF GEnERATOR TURN-ON AND <br />TURN-OFF ORDERS. <br /> <br />3. EVALUATION BY SIX HOUR INTERVALS <br /> <br />Sounding parameters such as the cloud top temperature, cloud base water <br />content, 700 mb level wind flow, and stability were related to the precipitation <br />falling during that 3 hour period whose first hour included the sounding, by <br />means of multiple regression equations. Certain reliable precipitation stations <br />were grouped together into areas representative of upwind flank, the crest re- <br />gion, the dmrowind flank, and the downwind valley (San Luis Valley). The corre- <br />lations between observed group 3-hour and also 6-hour precipitation values and <br />the regression-predicted values lay mostly in the .50 to .70 range. It was <br />found necessary to organize the 3-hour precipitation values and parameters <br />into six hour blocks to achieve a suitable degree of independence between blocks. <br />This reduced the number of cases by over a half but tests had shown that succes- <br />sive six-hour precipitation blocks had considerable statistical independence, <br />whereas, the three-hour blocks were correlated. The regression predicted values <br />of precipitation were used as an independent variate to reduce any variation <br />due to randomization bias. Such a bias would occur, for example, if by chance <br />the treated sample contained a large number of deep clouds with strong orograph- <br />ic upslope wind relative to the number falling in the control sample; thus <br />leading to a bias favoring a seeding associated excess of precipitation. <br /> <br />The group average seed - no-seed differences in precipitation for the warm <br />cloud top cases are displayed in Figure 5. There were a total of 97 cases <br /> <br />13 <br /> <br />/ <br />
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