HASTINGS COLLEGE FACULTY LECTURES:
“NEBRASKA WEATHER AND RAINFALL”
(An Account of the Means of Predicting the Weather in the late 1930s)
By W. J. Kent
To be valid, the study of the weather, that is, the “climate” of any given location must be made in connection with a study of its surrounding territory for the following reasons: The movements of the air masses which bring to us our daily weather changes are widespread in area — in fact, they consist of great whirling movements of air covering several states, coming from the West and traveling eastward, crossing the continent in a few days and in a general way giving the same kinds of weather all along their paths. At the same time, however, there are fluctuations everywhere along the way. Thus, the climate of Colorado or of Iowa differs somewhat from that of Nebraska, and likewise, that of Minnesota from that of Ohio. And so it is that a study of the climate of any one of our states must be made with reference to its geographical location. The area’s distance from the coast, its longitude, and its latitude, are also important factors. The importance of the question of distance from the sea will be noted at once when one observes that all desert regions lie in the interiors of great continents: for example, the deserts of Africa, of Asia, of Australia, and of North America are centrally located in these continental areas.
Since all our moisture, falling in rain or in snow, is brought to us from the sea, it follows that the farther a region lies from the seacoast, the less precipitation it will receive. However, this general rule must be qualified: many factors of a secondary nature enter here, so that some parts of the interior of the United States enjoy rather abundant amounts of precipitation while others, Nebraska included, are regions of deficient rainfall.
In some parts of the world, changes in wind directions, which are seasonal, bring wet and dry periods. This phenomenon can be observed on our own west coast, while in North India, a rainfall of as much as 470 inches per year has been recorded. This amazing situation is brought on by the rising masses of moist air which pass over the Himalayan Mountains, while Death Valley in our own California may not have had a single drop of rain in twelve years. Thus, the rainfall at Scottsbluff, Nebraska, averages about 14 inches per year, while that in Omaha averages 30 or more inches per year.
For many reasons, the climate and weather of all of the states of our union have peculiarities of their own. The climate of Nebraska is thus quite unlike that of Michigan, while the Michigan climate differs from that of Florida. Furthermore, for many of these “characteristics” we have to consider the local environment. It is from this point of view that we will take up a consideration of the climate and weather conditions of our own state at this time.
In Nebraska, the weather with all of its changes is due to barometric movements, west to east. One will naturally question from where these movements of high and low pressure come and why it is necessary to take into consideration all of these matters when trying to understand the weather. For one thing, although weather maps usually show these movements only over the U. S., they come to us from the Pacific Ocean where they have had their origin.
To explain how they originate goes deep into the science of climatology, nonetheless they are well understood among climatologists. The accepted explanations at the present time are partly theories. Yet, many actually correct principles of operation are involved. In the first place, due to higher temperatures in the tropics to the south of us, there is an elevation of barometric surfaces with a downward slope toward the poles both north and south. These masses of air rising at the equator have a tendency to flow off to the north down the incline barometric surfaces. To fill in the vacant spaces to the south which they leave, there is a flow near the surface of the earth in the opposite direction. This causes what is known in science as “the general circulation of the atmosphere.” Just how this works is explained by what is called the “Counter-Current Theory.” That is, these currents of air flowing above in one direction and below in the opposite way give rise to the creation of great masses of air, which move in a rotary-type motion. Sometimes the movement takes place in a clockwise direction, and at other times the movement is employed in a counter clockwise direction. In the high-pressure areas, there is also, at the center, a flow down from above and outward, below, which rises at the center. The circulation in the one flow is the exact reverse of that of the other.
A fact peculiar to our region is that these highs and lows have a more or less definite place of origin over the Pacific Ocean. They approach our western coast and enter our country at certain places, which are more or less fixed points. Their southern entrance is near the borderline between Mexico and California. There is a second entrance farther north, between the borderline between California and Oregon. A third entrance lies near Puget Sound, and a fourth one is located still farther north in British Columbia.
The line of directions in all cases is eastward but not without variation. The path from the southwest goes to the northeast, while that of the northwest flows to the southeast. The centers of these air movements sometimes fluctuate, giving the outer boundaries almost unlimited extent. Thus, the air movement may cover several states or almost the entire country. These eastward movements may proceed at fast or slow strides, varying from a few miles, to as many as 50 miles an hour. Also, they sometimes remain stationary for some days at a time. However, the direction of their movement never changes. Whatever we receive in the way of weather is brought to us by these areas of high and low barometric pressure. This is an absolute fact which occurs without exception. From studies of daily weather maps all predictions or forecasts are currently prepared. Present day science knows no other way of telling in advance what changes in weather conditions are likely to occur. So, although at times they may harbor doubts, scientific men make a study of a weather map and then issue statements on what to expect for the next day or so in the way of weather conditions. This scientific way of studying the weather is new — of such a recent date in fact — that we still have with us the individual who wants to know what kind of a winter to expect; whether or not the dry summers are over; and whether the next cycle period is to be wet or dry. What ails this gentleman is a faulty memory. He is prone to forget that the days of the weather prophet are gone. The weather prophet with his long-range predictions has departed, and the scientific weather forecaster who has taken his place presumes no knowledge of conditions not outlined before him on his weather map.
With these brief introductory statements we will hurry on to a study of Nebraska’s weather and climate in connection with the weather and climate of its neighboring states, since their conditions cannot be left out of our consideration. For the same storm tracks which pass over Nebraska also cross the entire United States. However, the storm tracks which affect us most are two: the one from the northwest and the one from the southwest. Especially is this true in western Nebraska. In the eastern part of the state, the other track, originating from the northwest and pushing down from the north, is also sometimes important.
The fact that eastern Nebraska has so much more rain than does the western part of the state is quite generally understood. The average yearly rainfall at Scottsbluff is about fourteen inches, while in Omaha it is more than thirty inches, and at Hastings it is about twenty-two inches. But this pattern does fluctuate from year to year. Why these differences from one year to the next? What are these cycles which we frequently read about? Why is our state getting dryer in recent years? The questions are numerous and well founded.
Two atmospheric conditions are essential for the production of rain: First of all, the humidity percentage must be high; secondly, the temperature must be right. When this combination of conditions occurs, precipitation will follow. A shower of rain or a snowstorm, then, is the result of favorable conditions in the atmosphere. These may be brought about in a variety of ways: An ascending current of warm moist air, cooling as it rises, may result in multiple clouds or even in thunderstorms. In Nebraska, our summer clouds called “snow banks” are formed in this way. If this condition were to take place in New Jersey, where there is much more humidity in the air, these same snow bands would frequently grow darker and sometimes before evening a shower of rain would occur. Not so, here in Nebraska, because our humidity remains so low. We have summer thunderstorms in Nebraska, but they are very seldom of this type. Local rains which originate in the same place as they fall are common in some parts of the U. S., but not with us here. The moisture which comes to our state is brought to us by those areas of low barometric pressure and is the result of evaporation over the surface of the Pacific Ocean. One exception must be noted, although it is usually of little importance: Easterly winds blowing in from localities of higher humidity will have a tendency to increase the rainfall in the eastern end of our state. But as was previously indicated, this is not a factor of much importance.
What is of importance to understand is what is moving into the area – to understand the whirling movements of the air in the area of high pressure, the air moves clockwise and outward, causing a down-flow at the center. All the while the air descending is warming up and expanding. The percentage of relative humidity is becoming less and less good, and there is always the tendency toward the lack of any cloudiness.
In the area of low pressure, the winds are meanwhile moving around counterclockwise, rising currents of air at the center are cooling, and as a result there is a condensation of moisture and a tendency towards cloudiness. With the approach of these regions of high barometric pressure, one can hope for fair weather, but in the region of low pressure, cloudy or stormy weather is to be expected.
There follow from the facts just mentioned several well defined laws of the winds. When a region of high pressure approaches from some westerly direction, the winds come from the same quarter; but when a “low” approaches, the winds come from the opposite direction. We sometimes express this situation by saying “the winds come with the highs and blow against the lows.” To put this a little more clearly, we may say that when high pressure comes from the northwest we have a wind from the northwest and when a high comes in from the southwest we have a southwest wind. But when a low approaches from the northwest then the winds are from the direction just opposite or southeast, and when a low comes up from the southwest then the winds are from the northeast. The storm always comes up against the wind, while fair weather comes with the wind. Insofar as winds from the north and south, are concerned, they mostly cause temperature changes.
The matter of winds is complicated by yet another factor. There is another type of wind (very common here in Nebraska) known as “local wind.” It is important to distinguish this kind of wind from that of the barometric type. Usually, such a distinction is a simple matter: the local winds come up with the sun in the morning and go down with the sun at night. They are usually caused by differences in temperature between places not far distant from each other. However, the barometric winds do not stop with the setting of the sun, but continue through the night. Also, the barometric winds are with us in the early mornings, while the local winds come later in the morning with the rising of temperatures. The barometric winds are caused by changes in air pressure. While Nebraska’s most common winds are “local,” all its very bad winds are of the barometric variety.
With this general introduction to the causes of weather changes in mind, let us consider Nebraska weather in particular. Our location to the east of the mountains is of special note. Millions of years ago, the folding of the crust of earth caused the rising of the mountain ranges to our west. We are located on the “leeward side” of all of these mountains. That is, the side opposite from which our prevailing winds come. We might also say that every desert region in the world is similarly located: the great desert of North Africa is on the northern side of the Sudanese Mountains and the winds there are from the south; the desert of central Asia is on the northern side of the Himalayan Mountains and the prevailing winds there are from the south; Nebraska is on the east side of the Rockies and the prevailing winds are the “westerlies.”
When the regions of low pressure move in from the west they must rise to pass over the Rocky Mountains. As they rise, there is a fall in temperature and a condensation of moisture, and precipitation occurs. Usually it is in the form of snow because of the fact that very high altitudes produce very low temperatures. In passing over the mountains these air masses lose much of their moisture and, therefore, descend on the eastern slope in a state of very low humidity. One of the two essential conditions for rain is, thus, lacking. Rising temperatures, occurring at the lower altitude, and the expansion of air volume also tend to lower the percent of relative humidity and, thus, further lessen the probability of rain.
Climate-wise, the state of Nebraska is, unfortunately, poorly located. Ever since the Rocky Mountains rose from the sea and cut off the moisture content of the air this has been a relatively dry locality — a locality lacking in precipitation. The tops of the mountains to its west, with a covering of snow many feet deep, are responsible for Nebraska’s lack of moisture. However, some years are dryer than others. And so the question at once comes up — why so? Considered from a scientific point of view, this question is readily answered.
As you will recall, the air movements which originate over the Pacific Ocean will normally control our weather. But at times abnormal weather conditions prevail over the sea. When this happens, a change follows at once in the procession of highs and lows coming in from the sea and proceeding across the country. If this change is such that more lows than highs develop, we get more rain, but if more highs than lows come, our weather will be fair and dry. Strange as it may seem, it is a fact that these somewhat frequently occurring abnormal conditions out over the Pacific Ocean are responsible for our shifts from fair to stormy weather. Characteristic of our climate, they are probably more noticeable in Nebraska than in some other places because of our universal lack of sufficient moisture. Only once in 25 years of record keeping at Hastings have we had an exception to this rule. In 1915 we recorded 38 inches of rain at the College weather recorder. There were actually complaints that year that we received more rain than needed. With this one exception, we have had insufficient rain for the entire past twenty-five year period.
Our average here over a long term of years has been about 22 to 23 inches of rain per year. There have been, of course, annual fluctuations. There were 22 ½ inches in 1933, 14 ¾ in 1934, 27 ½ in 1935, and 15 inches in 1936. In none of the years just mentioned have we had sufficient rain, while in two of them we have experienced a very bad drought. Showers of rain seem never to be properly distributed and when precipitation is not in abundance, farm crops are certain to suffer.
This leads back, of course, to a consideration of the causes of the unusual weather conditions over the Pacific Ocean, which disturb the regular storm or air movements of the atmosphere. The difference between fair and stormy weather is primarily a change in the circulatory motion of certain air masses. If the winds circulate left to right (clockwise), the result is fair weather. When they circulate right to left (counter-clockwise), the result is cloudiness or showers.
We have already mentioned the compound cause of these conditions: First of all, is the elevation of the barometric surfaces in the tropics due to high temperatures, with the ensuing flow of warm air down the incline surface toward the poles above, together with a current below flowing to the south. The flow of these currents plus that of the currents to the north and south is the principal cause of the circulating masses of air moving eastward. Under ordinary conditions, they mostly flow from the right to left direction due to the higher temperatures. Farther south, in warmer latitudes, they mostly flow from the right to left direction due to the higher temperatures. Farther north, usually one flowing right to left is followed by one flowing in the opposite direction, or left to right.
Now the question comes up as to what causes a change in the regular movements of air with their circulating winds? The answer to this is the fact that local conditions are largely responsible. We have already mentioned the case of the effects of local winds on the land. The same situation operates over the seas – actually, in a far more pronounced fashion. On land, there are always obstructions and wind breaks, but over sea, there are vast expanses of water-surface – hundreds, or even thousands, of miles in extent, where there is absolutely nothing to stop a local wind once it gets started. In general, what we describe under the term “local weather conditions” is far more definitive over sea, than over land.
To demonstrate just how this works, let us take as one illustration the case of a local wind hovering from the north. First of all, this will cause a drop in temperature; then the elevation of the isobaric surface will drop, and the velocity of the upper air currents will be lessened, while that of the lower currents increases. Following this, there will be a change in the relative velocities of counter currents (largely the cause of the whirling air movements). Next, the velocity of the local wind (from whatever direction it may come) may be sufficient to cause a change in the returning current – the lower of these two, mentioned before. At this stage the regular course of events is sometimes interrupted. When an unusual number of counter-clockwise whirls pass over, the result is a spell of rainy weather. However, this seldom happens. What we usually experience is just the opposite: the occurrence of more of the clockwise whirls, all of which bring fair and dry weather. This condition is not very noticeable in winter, but in summer it is disastrous to the growing of farm crops. We commonly refer to a situation of this kind as “a drought.”
The description just put forth summarizes what is presently known about droughts, which are not at all a new thing in Nebraska. Droughts have always been with us. Our location on the leeward side of the mountains gives us very little rainfall. Thus, we almost always need more rain. Whenever a dry period comes on, we in Nebraska suffer severely. Other parts of the country may also suffer for the same reasons we do, but usually their suffering is not so great as ours. When there is much rain, a great reservoir of water is stored up in the soil. This phenomenon is commonly called “sub-soil moisture.” Because of capillary attraction this water is in a constant state of returning to the surface, thus, furnishing growing plants a constant water supply. When a dry period comes in summer, a growing crop may suffer and may even turn out as a poor crop, but a total crop failure seldom, if ever, occurs. However, in Nebraska where there is little or no subsoil moisture, the production of good crops is entirely dependent on regular rain showers. When rains fail to come, growing crops wither and die at once.
Our simplified explanation of the causes of rainfall leaves no room for anything such as the so-called “periodic cycles of wet and dry years.” Actually, the cycle theory for explaining the occurrences of drought needs but little explanation. There has been much discussion of it at times, and we still hear it mentioned by men whose official scientific work gives support to the theory that our wet and dry weathers come to us in cycles of however many years. That is, today we have a wet cycle followed by a dry one, etc. However, records of rainfall as kept at various stations in this part of the country do not show anything more than yearly variations in the amount of rain fallen. Our own records kept here in Hastings for a period of 25 years show wet years and dry years, but no other periodic changes. Also, records kept elsewhere for longer periods of time show only these same yearly changes with no other phenomenon.
The evolution of the “cycle theory” is interesting. First of all when we hear about seven-year cycles, all of this reminds one of Joseph’s interpretations of the Pharaoh’s dream: seven fat years and seven lean years! The idea of the seven-year cycle period was followed by the concept of an eleven-year cycle, bound in some mysterious way to certain changes in the appearance of the sun, known as “sun spots.” However, records of rainfall did not substantiate either of these suppositions. Then some scientific speculators advanced the time of the cycle to twenty-three years – that is, to a period of about double the length of the eleven-year period. And last summer, a man connected with the Smithsonian Institution and another man from the U.S. Weather Bureau advanced a new idea of a forty-year cyclic period. The short period records of rainfall kept by various weather observers have readily discounted cycles. Not so, with the long period cycles. It will, of course, require record keeping for hundreds of years to either prove or disprove the forty-year cycle theory, but it may prove to be accurate.
While we can pass off the rainfall question by saying there is little change except for yearly fluctuations in regard to the actual amount of rainfall, there are other changes of considerable importance. One of these is that of wind velocities. This is a very serious question directly connected with the problem of soil erosion. In fact, in Nebraska, soil erosion may well be our most serious problem at the present time. This problem has arisen since the early settler began to dig up the virgin sod, the grass covered earth that originally blanketed this part of the state. With increasing cultivation of the soil, the erosion has become progressively more serious. In years of drought the erosion increases because of the lack of a grassy covering for all the land. In recent years, much land has been left unoccupied for the purpose of decreasing crop production and thus raising selling prices. Some persons have quite recently coined a name, “the dust bowl” to describe that part of the country to our southwest. We are not placed exactly in this so-called “dust bowl,” but we are close to its eastern border. Certainly there can be little doubt that our dust storms have increased during the last few years. We have, of course, experienced them only since our farmers began to break up the original prairie sod. However, they have grown steadily worse and threaten to destroy much of the fertility of our land. We are confronted here with a most serious situation – and one which continues to grow steadily worse.
Concerning other questions of changing climatic conditions, the historical facts (where it is possible to consult records) show little or no change. Of course, at first it would seem as if our rains were diminishing, and it does look as if our part of the country is actually drying up. To disprove this seeming change, we have records of rainfall, all carefully and scientifically kept since the early days (more than sixty years) as well as records being available in Lincoln and several other places in the state. Furthermore, our wind velocities probably are no greater than formerly experienced, but are now more heavily loaded with dust particles – a situation brought about, as we mentioned before, with the cultivation of the prairie sod.
Of course we do have an increase in hot winds from the southwest in late summer. This condition has grown worse in recent years – a situation explained by the kind of farm crops now being cultivated in western Kansas, almost exclusively wheat. Wheat fields are always very warm in summer because of their propensity for creating reflected heat. When the winds come up from the south and west they pass above these fields – every one of which is a true “hot spot” that seems to increase the high temperatures. So it happens quite frequently that we harvest our wheat and then burn up our corn. These hot southwest winds which are so destructive to our cornfields represent a condition which has become much worse since western Kansas has been devoted almost entirely to the growing of wheat.
I am quite aware that my statements about the rather “fixed, unchanging” conditions of our climate run counter to general public opinion. Just about every one who has lived long in the state of Nebraska talks about how the climate of Nebraska has changed over the years. However, if one stops to consider all things more carefully he will, I believe, conclude that most of these so-called “changes” are more apparent than real. Actually, the average rainfall has not lessened. We have plowed up the buffalo sod that once held back the water and sent it to low ground. Now, when the rain comes, it sinks at once into the dry cultivated soil. The run off of water after a shower is now practically nothing, where in years back, it was very large.
I would like to close with a brief mention of some facts about the science of meteorology as it stands today: this science is sometimes called “climatology” – a more nearly correct nomenclature. In one way, it is the oldest of all sciences. Since in the very earliest times of which there is any record, people have, by various signs, interpreted changes in the weather. Among the clay tablets which formed the extensive library in the ancient city of Babylon, there is one which says “when there is a ring around the moon, it will rain.” This attempt to foretell weather by natural signs has not yet ceased to be. Many people still have their favorite signs by which they speculate on weather changes to come.
Following the millennia (when such commonly held signs were the only means of weather prediction), came the almanac. Some of you may not be familiar with this small booklet, which usually advertised some kinds of patent medicines and incidentally presumed to predict the weather for an entire year in advance! The almanac we still have with us, but its generally accepted usefulness is a thing of the past.
One interesting phase of the new weather science is closely associated with the early history of Nebraska. The situation came about largely through the early settlement of the state, having been by men who had served in the Civil War. During this conflict it sometimes, perhaps frequently, happened that a great battle (which usually lasted for several days) was followed by showers of rain. Thus, the idea became quite common among the soldiers that these showers were caused by the disturbances of the air occurring through the explosion of gunpowder. It was, of course, an entirely wrong assumption. The part of the United States where most of the Civil War battles were fought took place where showers are of frequent occurrence. In these areas rains could be expected at intervals of every few days or so. Military commanders would thus wait for “fair weather” before starting a new campaign, and by the time the campaign was over several days later it would be time for another shower of rain. Thus, the rains which frequently followed one of these battles were the result of natural causes – not gunfire. However, the idea that cannon fire would produce rain was brought into the thinking of early Nebraskans by the Civil War veterans. This led to the appearance of the professional “rainmaker,” with his small cannon. The idea here was to shoot charges of gunpowder into the air and so to produce rain. This concept, which lasted for some years in Nebraska, is still being mentioned in some places.
Directly after the close of the Civil War (that is, in the early eighteen seventies), the keeping of weather condition records began. Out of this grew the gradual development of the Weather Bureau, with its regular forecasting of “the weather.” The Weather Bureau has now advanced from its crude beginnings to the present high standards of excellence. The latest development of this science can be seen in the present day Weather Maps from which the weather calculations are made, and which are widely distributed by means of the daily newspapers.