SOME THOUGHTS ON THE SERVICE RENDERED BY THE UNITED STATES WEATHER BUREAU 1

By C. E. GRUNSKY, Eng. D. (Consulting Engineer, San Francisco, Calif.)

PUBLICATION OF WEATHER BUREAU ning with September. This should OBSERVATIONS prove acceptable throughout the en- tire United States. It has become an established prac- tice to publish the Weather Bureau Publication of the rain record by observations from month to month by calendar years gives an incorrect and calendar years. In the matter of pre- misleading picture of what occurs in cipitation this gives an incorrect pic- some localities such as the Pacific ture of the range of the amount of Coast. Here there is a period from the rain and snow which produces the May 1st to October 30th in which stream flow from one low water rain in sufficient quantity to produce period to the next. material runoff rarely falls. It is in such circumstances unfortunate, to The low water period of the rivers say the least, to have the rain in the of the United States occurs in the fall last months of a wet season as for ex- of the year. This fact being taken ample January to April, 1862, com- into account has led to the publication bined with the rain in the early of stream flow as measured by the months of the following dry season Water Resources Branch of the October to December, 1863. This can United States Geological Survey in give no one a correct picture; it does periods of twelve months begining not even supply a basis of compari- October first. son with seasonal rainfall elsewhere. Rainfall should in like manner be It is a deplorable source of misin- published for twelve month periods formation. preferably beginning on September THE MONTHLY WEATHER REPORT first. The rainfall or seasonal year might begin, so far as the Pacific A glance at any page of the daily Coast is concerned, any time from rainfall record for a winter month in July 1st to September 1st. In the California as published in Climatolog- Middle West, South, and East, how- ical Data will show a succession of ever, where rainfall is heaviest in periods, 7 to 10 days apart as a rule, summer months the seasonal year in which there was some rain some- should commence not earlier than where in the state. with September. The figures on such a page may appear almost as a shaded area. Ex- Because the September rain may amination thereof discloses that many affect the October flow materially and of the rainstorms extend from north- the seasonal river flow year begins ern portions of the state as far south with October the suggestion is made as San Francisco others as far as that the publication of the rainfall be Bakersfield, others still farther south. for the twelve months period begin- If now instead of arranging the 1 American Meteorological Society, Pullman, various stations alphabetically (as is Wash., meeting, June, 1932. The second half of this paper, on evaporation measurement now customary) they were arranged was published in the Mo. Weather Rev., Jan., (for California) geographically from 1932, 60:2-6, 2 figs. Comments by C. F. Marvin. North to South, that is, according to

Unauthenticated | Downloaded 09/25/21 03:28 PM UTC latitude, the picture presented by the annual normal precipitation which is figures recording the amount of rain expected in a year of normal rainfall would at once indicate on the print- from the beginning of the rain season ed page the extent of the storm. The (September 1st) to any date. page would then show at a glance There should then be prepared for how far south the low which passes each such region a diagram in the over Canada, over Washington, or form of a mass curve on a time scale over Oregon and at the same time base, which will show in percentage how far to the north the storms of the normal annual rain the aggre- which course across Mexico have gate amount of rain which is expected brought rain. to any date in a theoretical year of

In some other states geographical normal rainfall. Such a percentage listing from North to South or from to any date of any station normal East to West might be similarly in- in the region to which the curve ap- formative. plies will then give in inches (or mil- The following would be a useful limeters) the season normal at that service that could be conveniently ren- station to date. There is frequent dered by the Weather Bureau. demand for information relating to The whole country should be sub- the normal rainfall to some particular divided into regions according to sim- date for comparison with actual rain- ilar rainfall characteristics not based fal. A single mass curve of normal on the annual amount of rain, but rainfall will ordinarily serve a mul- based on the proportional part of the tiplicity of stations—all of the sta-

Unauthenticated | Downloaded 09/25/21 03:28 PM UTC tions in fact in any region of similar 1931-32 to date. These diagrams seasonal rainfall characteristics. Such should be issued with the weather map diagrams should be available for gen- at least once each week, thereby keep- eral distribution. ing the public informed at a glance A sample diagram of the character not alone of the current year's rain- referred to is herewith presented. fall in relation to the normal, but also On this sample diagram there is of the seasonal regional rain history also shown the mass curve of the to the date of issue. rainfall at San Francisco, California On the sample herewith submitted in 1861-1862, this being California's the rain at San Francisco to March great flood year with 223 per cent of 26th for the seasonal year 1931-32 ap- normal rain at San Francisco. The pears at 90.6 per cent of the annual record of daily rainfall at San Fran- normal, 22.0 inches, or 19.93 inches. cisco was used in preparing this spe- The normal curve at the same date cial curve. shows 85.0 per cent, or 18.70 inches. The annual normals of all points of Every Weather Bureau station importance to which a diagram ap- should prepare such a diagram for plies should, for convenience, be noted office use and for the convenience of on the diagram. The final diagram those who desire to make compari- issued at the end of the seasonal year sons. covering the twelve months from At stations with long time records, September 1st to August 31st would frequent revision of such a diagram be in a convenient form for perman- would not be necessary even though ent preservation. the station's annual normal may pass The value of a record of this type through a considerable range. in graphic form is obvious. It would As each rain season progresses the be particularly valuable to have such rainfall should be platted (in percent- diagrammatic records, based upon the age of the annual normal) on such a daily rainfall, when the influence of diagram in the form of a mass curve a rain storm or a sequence of storms —substantially as shown on the upon maximum stream flow is under sample diagram for San Francisco study.

JUNE TEMPERATURE INDICATES CORN MATURITY IN IOWA* By CHARLES D. REED Weather Bureau, Des Moines, Iowa Whether or not the average tem- September has much more to do with perature of June is above or below the amount of corn that escapes frost 67 ° F. largely determines the extent of damage than does the earliness or late- autumn frost damage to corn in Iowa. ness of the first killing frost in au- In former papers, it was shown1 tumn. Not until recently was it real- that June temperature is a good indi- ized that the average temperature cator of the temperature of the next of June is a better early indicator of three months; and 2 that the average corn maturity than any other of the temperature of June, July, August and several weather elements that might be thought important. This is due to * Atlantic City Meeting, Am. Met'l. Soc., Dec. 27-28, 1932. the good start given to the corn plants 1 Monthly Weather Review, June, 1925, 53: 249-251. by a warm June and to the favorable 2 Monthly Weather Review, November, 1927, 55: 485-488. weather for maturity during seasons

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