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<br />.' . ... <br /> <br />SECTION 2..0 <br /> <br />FORECASTING TECHNIQUES DEVELOPMENT <br /> <br />A number of special studies are underway for the purpose of improv- <br />ing and objectivizing the forecasting of events of seeding opportunity <br />and avalanche hazard. Due to the delay in award of the contract, <br />most of these Phase I studies are still in the data reduction stage. <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />An extensive study of the variation of area precipitation patterns in <br />relation to synoptic scale 700mb wind is ready for preliminary <br />interpretation (Section 2. 1. 1). This, along with the practice fore- <br />casting results, forms the basis for improving the quantitative precip- <br />itation forecasting over the target area. <br /> <br />/' <br /> <br />2. 1 <br /> <br />Area Precipitation Studies <br /> <br />2. 1. 1 <br /> <br />Wind Direction Dependence of Area Precipitation <br />Patterns <br /> <br />Ridge/valley winter precipitation ratios range between 2 and 5 to 1 <br />over the Coiorado Rockies. Both ridge and valley areas are simul- <br />taneously uilder similar large scale meteorological influences. It <br />is therefore obviQUS that the forced mechanical (orographic) lifting <br />of m.oist air as it approaches the ridges strongly dominates over the <br />large scale vertical motions field in establishing the area precipitation <br />pattern. <br /> <br />The magnitude of the orographic lifting is roughly determined by <br /> <br />w ; v. (::)i <br /> <br />, <br /> <br />where <br /> <br />........ dx ~ .!!l~ <br />V=-l + dtJ. <br />. dt <br /> <br />- - <br />x = direction of the fall-line and i~. j = o. <br /> <br />This, coupled with the fact that the largest concentration of condensate <br />is possible in the warmer, lower layers logically leads to the import- <br />ance of the degree of alignment of low level winds with the terrain <br />slope in setting the mesoscale precipitation patterns (and the variations <br />thereof). Superposition of contrasting effects from multiple ridges <br />with differing slope vectors, however, complicates the problem. . <br /> <br />2 <br />