NOVEMBER, 1983. MONTHLY WEATHER REVIEW. 567
in August alone. The seasonal distribution in the average case parallels the course of mean maximum temperatures, though fires tend to 1% behind temperature. This great seasonal concentration of fires, of course, tends to make suppression difficult, because so many fires occur at one time. The most striking evidence of the difficulty of successfully handling lightning fires is found in the fact that mceptional storms have set in a single day as many as 340 fires. I have classified storms into four eneral groups, those causing less than 50 fires,
250 fires, and those with over 350 fires. In handling fires resulting from storms of the first t h e e dasses we have been uniformly successful in holding the size of the average fire to about 35 acres, the figures for esch class being 49, 39, and 34. In other words, though many fires result from these generall local storms, our pro- tection organization is equip e z t o handle the situation.
250 fires, the situation is, however, radically different. Fires from these storms attained an average size of 312
acres, over eight times as great a.s from storms of the other classes. The 1ar est fires known in northern
In practice, a general electrical storni, such as these, results in what may be regarded as an overload of busi- ness. We are not equipped to handle all fires promptly, and must rely on cooperative help, which is not always satisfactory. One of the most important contributions that could be made to organized fire protection in Cali- fornia, and, indeed, throughout the West, would be prediction, even a few hours in advance of the occurrence of these great general storms. We could then do muc.h of the emergency organization work, which must now wait until fires are actuall set.
perhaps the most severe test that fire protection forces must meet. During the past decade, on the average,
42 per cent of the entire crop of lightning fires for an entire season have occurred in a single sto?, further evidence of the extreme concentrat,ion of this form of fire business. I have s oken briefly of the when and how of lightning fires, and f should now like to speak of the where. We have plotted on a State map the point of origin of each fire for a period of 10 years. Even the most casual study shows that as a matter of recorded experience there are both well-marked lightning centers, and what may, I think, be fairly regarded as lightning zones. It seems evident :
1. That from north to south in the Coast Range, the belt generally decreases in width.
2. The same general trend is apparent in the Sierra Region.
those wit f from 51 to 150 fires, those with from 151 to
For the three great gener 9 storms which have set over
California resulted from t % ese catastrophes.
fires indivi B ually are generally not par- ticularly Lighi% d cult to handle, but in bunches they represent
3. In southern California the zona are genetrally narrower than elsewhere. In intensity, or number of fires per unit of area, there is a general, though by no means regular, decrease from north to south. 
This analysis of the place of occurrence 01 liihtning fires has proved of great value in he1 ing us to most sffectively place our men, to organize Betection service, etc. On the map there are many blank spots for which no explanation can now be offered. Whether they are purely accidental and will be filled in as more data accumulate is open to question. They may concsivably be out of the pmcipal storm tracks.
When we mal ze the great storms, we find that they cover retty
t,he limit of souther1 estension, for exam le, haa been
south are subject to intense s t o m , but so far have not participated in the most extensive storms. This it seems is a point worthy of cooperative study. This, then, is the situation in regard to lightning fires in the forests of California. Obviousl enough, the
f e the ability to predict the occurrence, particular1 of the great general storms. It is probably true that dese storms are intimately related to the general weather condition and can be predicted, given suflicient study of the problem. The more local convectional storms are also worthy of attention. Undoubtedly 1 htn centers exist, where storms form repea ti3 y an YStOrm from which the travel. One such center is certainl the
Sllasta. For three years now the Forest Service has been utilizing its fire lookout men as recorders of the occurrenw and movements of storms. Hundreds of observations have been made, and an anal is of this mass of data will
forming in a particular center tend to travel in a given direction, it will be possible to phone ahead of the storm, and thus to make redictions a t least a few hours in advance. Similar sata have been secured for the ast two seasons in Idaho, Montana, Washington, and b e on, as well as in California, and suggestive leads
More study, I believe, is needed o the occurrence of lightning storms in relation to general weather conditions. Cooperative study of this phase of the problem should certainly be of value. In general, the securin of field
come in realizing our goal of prediction of 1 htning storms. It seems to me not beyond the possible %at the field men of the Forest Service, articularly our lookouta,
This is the lightning fire zone in general.
muc i the same region. Thi? is not true in deta& but
about the same for a K three. The national f orests to the
reatest contribution to better handling o s them would
Sierra Va 5 ey, another is the region around &o u t
doubtless prove of value. s f it is found that storms
for 5 urther investigation have dread been uncovered.
data is probably the most serious difficulty to b e over-
may prove to be ideally situate B for that purpose.
9
HOW WEATHER FORECASTINO CAN AID IN FOREST FIRE CONTROL.
By HOWARD R. FLINT.
The title subject given above is one so little discussed by those most concerned that one mi
to believe that it had been forbidden of the drastic forest laws of the time quest or by the merry days of Robin Hood, when an eye or a nght forefinger and thumb of the skilled but unhappy archer was the price paid for a minor trans- gremon of the laws of the kin s forest. Of course no such taboo bas actually existei, but natural Conserva-
1 Presented at W i n g of American Meteorological society, Loa Angel=, Calif., Sept.
tism and inertia have ever been about as effective as written legislation in retardin inevitable progress. The result has been a failure on $0 part of the aver
use to him.
have dismissed the subject with the .ironic remark that anyone could tell when he was going to have a fke by
the absence of rainfall for a fortnight, mid that knowing
19, 1923.
ester to make full use of a tool which may be o T gmct for-
-Ten years ago the average forester would probably 
568
in advance when fires would occur woi~ld be of little ns-
sistance in any event, since they must be met and put out whenever and wherever they occurred. To-day we find practical foresters, tshe men who must form the fire-protection organization and build up the fire-suppression machines, consulting daily weather fore- casts and, to some extent at least, permitting their udg- ment to be influenced by what. used t.0 be termed the
 weather mans guess. These forest,ers have guessed the weather t,hemselves and are learning by experience that the weather mans guess with its present, scien- tific foundation is correct a large and an increasing percentage of the. t.ime. They are learning that it is n
tool the possibilities of which have only begun to be de-
veloped. Telephone, telegraph, ant1 radio communication, sup- ported by real organization and the spirit. of helpful co-
operation, make it possible to put the words of t,he weather forecaster in Chicago or San Francisco in the most remote and isolat-ecl ranger headquarters in the northern Rocky Mountains within an hour or two of the time the forecast was formulated. T1~1l-y this is magic, and with its aid the niatt.er of fact forester can hope, not to beat Nature at her own game, but to sit in at a game with Nature aided by cards st,acked in advance and with better than an even chance winning of a hard contest. In order that there mwy be left in the minds of those present no lurking shade of doubt- concerning the mag- nitude and practical iniport.ance of the forest-fire proh- lem, it seems advisable to quote a few stat,ist.ics borrowed from the official records of the northern Rocky Moun- tain district of the United St,ates Forest Service. This is one of the several im ortnnt forest, regions of t.he United States. land better adapted to the growth of forest trees than any other known crop. It is naturally a re ion well en-
travels and researches of foresters have revealed no other region in which forest fires art! of more fre uent occur-
destructive. This condition is due chiefly to the peculiar climatic and vegetative conditions wliicli will be tlis- cussed later. Mouutnin region 25,000,000
rather complete and detailed fire resetdies have been kept for this vast area.. There have occurred in that timo
18,169 fires of record. llteg have covered a tot,al area of 4,400,000 acres, some of which, however, has burne.cl over twice, and a little of i t three times during the period. More than ten and a half billion feet, of merchantable timber has been killed, only a t.rifling amount. of which has been or can be salvaged. The nctud money value of the losses has been conservatively estimated at
$27,000,000, a staggering sum, and the cost of fighting fires has been over h e and a half million dollars. These figures axe for national forest lands alone. The losses on private lands in the region have been fully ns great, probably greater in proportion to the acreage involved. 88 er cent of all the loss occurred in two sea.sons, 1910
pression, was ma e in these two seasons in a period of about 90 days each. The climate in most of this region is of the Pacific coast type, with the extremes accen- tuated by the altitude and distance from the ocean. The summers are characterized by extremely low pre- cipitation in June, July, and August, desiccating south- west winds from the semidesert region along the Colum- bia and Snake Rivers, and very low relative humidities.
It induces Q about 40,000,000 acres of
dowed for the production of wood, but at t 5 is time the
rence or in which they are more intensive anc Y completely
acres are in the national 9 orests. For the pust 15 years Of the northern Bock
fl
an f 1919, and 53 er cent of the espenditurrs for fire sup-
During July and August storms frequently pass over this region witsh little or no recipibation, but accom anied
an unusual1 bad one in that respect, 1,381 fires of record
were set in tlie nation forests of nortshern Idaho in a single day. The dominant forest growth of the re ion is
usually in thick stands and having rather dense crowns; folia e tlint, carries a high content of inflammable resins;
From the st,andpoint. of forest-fire prot.ect,ion t-he com- bination forms a. most, diificult condition and tlie dest.ructc ible resources at. stake are d u e t 1 at. $140,000,000 in c1irec.t t,angible values, not to mention other values which
can not well be calculated at resent,.
might be placed and held in this re ion a t all times
situation which might arise. It is a parent that the
would be useful for that purpose only three months of each year and would necessarily be forced to seek other occupation during the balance of the year. At this t,ime it does not seem possible to justify the cost of an orgunizn.t.ion of bhat kind. I t would soon absorb the entire value of the resources at stake. The alternative, and the policy which is now in effect, is t.0 maintain E
skelet.on organization which ctin readily meet the more common situations and swell this organization in. time of fire enier ency by t,he employment of a sufficiently
specially trained and prepared organization. It! is apparent that the success or failure of this scheme will depend Fery largely on the prompl and accurate recognition of emer ency conditions in time to permit of
is true in the infhitesmal and in the large, for minutes count in getting action on a fire, and it takes about a
century to grow a forest. A single fire, due to a slight error in judgment or the ela se of a few precious minutes
jud ment of a century. 6 t h the aid of the facta outlined aboveh should be ee, or a t least to imagine,
mi ht be of great value in fire-control work.
50 begin with, the forester who has going fires in his district could obtain more effective results ar.yl make material savings in cash if lie knew in advance mth a fan- degree of certainty just what the weather held in store for him during the next few hours. Will the wind remain t-he same or will it swell to a gale? Will the relative huniidit drop to 10 per c.ent to-morrow afternoon, or
presage rain within 24 hours, or will it spread ruin in the
shape of a score of new li htning fires over the far-fluy dry hills of the district P these are burning questions. O m the weather forecaster answer in advance any or all of theml It should be an ins iration to know that in a
answered them in advance, though seldom in the
has there been the organization or the faith to ully utiliie the information. Lightning is the greatest single-cause of forest h s in the region we have been discussmg. In these dags of rapid transportation and instantaneous co.mmunicat1on a few hours warning of the approach of a violent electncal
hg violent electrical disc R arges. In the season o 9 1920
9
mere cause B by lightnin alone. More than 200 of these
made up of coniferous trees-pines, firs, and ot a ers-
and % ark and wood t.hzit, burns freely when ignited.
It. is conceivable that a su I cient,ly large furce of men
during the summer to cope effective K y with any fire
cost of such an organization would r: e enormous. It
hrge force o 7 temporary emergency help directed by the
the mn.rshalin of t a e emergency forces. It can truth- fully be said o K forestry,  time is essence thereof. This
in getting action, may un 2 o the good work and sound
[ow really dependable and T c etailed weather forecasts ossible to visualize in some d
will it g e above 50 per cent? Does the distant cloud
number of cases that have Yl een checked up he has
fast
NOVEMBER, 1923. MONTHLY WEATHER REV113W. 569
storm might be of material value. A single fire oft.en costs thousands of dollars. Is it not ossible that a
ralio and telephone instruments during and just before electrical storms And the researches of one or two eminent nieteorologists all suggest an affirmative answer. Again, the forest officer must decide, often in the absence of any unusual number of going fires, whether the time is ripe for the expansion of his forces, to t,he limit., to a moderate degree, or not a.t all. Past experi- ence is t.he only t.rue ba.sis for judgment.. Accurate and readil available weather records should
dollars. Can the meteorologist redict a week or a 1iiont.h
The researches of Huntin ton, Doughs, Ricarcl, and
bilities in this line. Casual local observations in icate
de endable warning could be given? J he behavior of
roba i ly I should say supplant, gasis for a judgment which
in advance t.he probable genera P trend of the season ?
d
ot,hers lkt least suggest. that. t. a ere a.re undeveloped )ossi-
that there may possibly be 8 very intimate relation hetween local slimmer rainfall and the de th of snow on the higher ranges during t,he months of h a y and June. Briefly, in sununarizing the idea set forth in the title of this paper, it) niay be said that there is a t least some warrant for the belief t,lint weather forecasting can aid forest-fire control in at least three different ways, naniel -
1. I!& warning through t,he usual 36-hOur forecasts
of a.n a.pproachiug change in the weather which will influence the behavior of possible or goin
2 . By iiiems of special forecast,s w ich will give warning sis or more hours in advance of the occurrence of lightning in any iven locality.
on suns ot or other phenomena, o the approach of
1910, mid 1919 in the northern Rocky Mountain region.
Pres.
9
3. By warnings t 7 Irough long-ran e forecasts, based
n.bnormn P seasons comparable to the seasons of 1889,
METEOROLOGICAL FACTORS AND FOREST FIRES.'
By J. V. HOFMANN.
A gathering of foresters with, m t l at the invita.tim of,
meteorologists ma.rks the realization of t.he long-fel t. need of a close correlation of t,hese nat.ura1 sciences. This accomplishment leaws behind t.lic rry of the insist.- ent few who were ever urging unity of purpose and coop- eration and o ens the door to a new era of ilevelopm~nt that will appr all of the scientific facts to the exist,ing conditions. deteorological factors and forest develop- ment are inse arable in nature, and rogress in the es-
the extent that these factors are macle inse arable in
ological factors needs no discussion at this meeting, con- sequently this pa er is confined to the individual or col-
Although all of the climatic factors are related to thc development of the forest, those direct1 related t,o the
trol of the fire situation is the greatest question in tho conservation of the timber sup ly. The study of t.he
tinued for two years by the Wind River Experiment. Station. These studies hare included the effect of all of the meteorolo ical factors on forest fire conditions ns
oration, wind and other factors influence the fire hazard, but the relative humidity was found to be the most im- portant factor in the development of a dangerous fire period as well as the most usable factor in act.ual firo
control. * * * the Wind River Forest Esperi-
fires showed that fires did not spread when t! e relative humidity was above 60 per cent. That they spread very slowly and only in very favorable material when the humidity was between 50 and 60 per cent. When tho humidity was between 40 and 50 per cent fires picked up, varying from a few running fires to fires that merely smoked up and did not spread. With a humidit of 30
rapidly spreading fires occurred. A humidity below 30
per cent caused all fires that were in niaterial that would
tablishment o f a forestry practice wi P 1 be measured by
the study of the sciences. The correlation of t R e meteor-
lective relation o P these factors to the forest conditions.
forest fire problems are most important $; ecause the con-
influence of climatic factors on R re hazard hns been con-
well as on the be a avior of the fire. Temperature, evap-
Studies c.onducted b
g
ment Station of the e d ect of relative humidit on forest
to 40 per cent fires gained some headway an ;Y some
dlow spread nt all bo gain headway, or s read beyond control. Crown fires occurred when t R e humidity dro pcd to 35 er cent or lower. * * * 3ncpestions t! ly one of tlie main causes of our enor- mous fire losses 1ia.s been due to the failure to realize how very suddenly forest materials may chan e from a. low dewee of inflammability to a.n estremely a igh degree of inhnimlibility and convert in a few hours fires which have been smoldering harmlessly for da-ys into raging conflitgrations. A realization of this situation can lead to only one con- clusion, that the smoldering fires must be put out im-
Temperature has been the whole t,he relative short periods or days, However, a low period of humii ity during the first days of September caused the most serious fire period of the year which resulted in many fires that s rend rapidly and were be ond the control
the relatire uiniciity remainecl hi h again. * * *
forest fire hazard that has been discussed in this paper emphasizes t,he iniportance of the relative humidity and shows tliat4 it is the principal factor that can be used as an index of the fire conditions as well as its direct use in
of the fire {fliting forces until Septem i! er 8 and 9 when
The corre1at.ion of the meteor0 f: ogical factors and the
fire control. With this fac.t established it. is evident that the greatest need in forest fire prevention and control is a hGwledge of changes in relative humidity as far in advance as possible. Recognizing t.his point, the Wind River Experiment Station is now conducting studies to determine the rela- tion between relative humidity and static electricity. This study has progressed far enough to demonstrate a definite relation, and furthermore that static can be used as a basis for the prediction of changes in humidity.
1 Excerpts ofpaperread at moetlng of Americsu Heteorologieal Scciety at La Ailgelcs, Calif., Septcmbcr, 1923.