Salt Lake Telegram | 1932-10-25 | Page 4 | Analysis of Lightning Storms Shows Which Are Fire Menaces to Forests

Analysis of Lightning Storms Shows vs Which Are Fire Menaces to Forests WASHINGTON Oct 25 es S. S S. S S. A A Afew few minutes of rain often is all that marks the difference between a lightning lightning light light- ning storm that will start a forest fire lire and a safe storm that will not This is one of at the fire weather facts appearing from a study of weather and forest fire records in the northern north north- em ern Rocky mountains compiled by H H. T. T Gisborne of the northern Rocky mountain forest experiment station and reported to the U. U S. S weather bu reau Mr Gisborne undertook his statistical statis stalls research in order to provide forest for for- est cst administrators and especially firefighters firefighters fire fire- fighters with data that will wUl enable them more efficiently to meet the late lata summer menace of at lightning caused d fires In the northern RockI and andin andin andin in many other parts of at the west lightning lightning light light- ning is a by far the largest single source of ot forest fires exceeding even careless careless care care- less Jess campers and spark scattering lumbermen's engines Mr Gisborne's study was made on ona a year five record complied compiled of ot data gathered by observers on over mountain peaks in three states He found that the average number of thunderstorms per summer 88 was three or four times as large as had previously been thought to be the case based on observations from lowland lowland low low- land Jand stations He also found that the danger from a storm bore a direct re relation relation relation re- re lation to the duration of at rainfall both before and after the lightning began to flash as well as to the number o of lightning strokes that reached the ground Lightning storms that caused fires averaged 87 minutes of ot rainfall before before be be- fore the lightning began whereas storms that did not start fires had minutes of rain before the thc light light- ning Fire causing storms toll followed owed the lightning with only minutes of ot ofrain rain ram on the tho average while safe sate storms kept up the rainfall for an average of 44 minutes These figures figures fig fig- ures tires ar are arc re regarded as quite significant for the rain wets the dry litter Utter on the tho ground it if it falls long enough while the rain If It sufficient will put out fires ires which the lightning has started One assumption though logical was shattered by Mr study This was that tho the dry thunderstorm thunderstorm thunder thunder- storm which sends little or no rain to the ground beneath is especially dangerous Figures showed that these storms are ue comparatively rare and that when they do occur they start no more fires in proportion to their numbers than do rain bringing thun thun- This is because the lightning light ning in dry storms passes mostly from cloud to cloud cl u not many flashes striking the earth It is usually possible for an observer observer ob ob- ob server on a mountain top to tell even at a considerable distance whether a lightning flash leaps from cloud to cloud or whether it strikes the earth This is a matter of at considerable practical practical practical importance Mr Mi- Gisborne's study Indicates for or in the starting storms 76 per r cent of ot all flashes were of ot the cloud to cloud variety where whereas as the storms that started fires sent 44 H per cent of their lightning flashes to the earth