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Texas Weather

Material from the Texas Scrapbook
Originally Published in the Texas Almanac of 1872

CLIMATOLOGY OF TEXAS.

BY PROFESSOR C. G FORSHEY, SUPERINTENDENT TEXAS
MILITARY INSTITUTE.
(From Texas Almanac)

1. GEOGRAPHICAL POSITION.

THE State of Texas is bounded on the north by Red River, nearly on the 34th parallel, from the 94th to the 100th meridian; on the east, by the Sabine, nearly along the 94th meridian; on the south, by the Gulf of Mexico, whose coast has a south-western trend, from latitude 29¡ 45′, long. 93¡ 55′, to the 97th meridian, and thence it bears nearly south, from lat. 28¡ to z6¡, where it reaches the 98th meridian. The Rio Grande is the western boundary, hence to lat 32¡, at long. ro6¡ 3o.’

For the purposes of this paper, devoted to Texas climatology, all that portion of the State Iying west of the 100th meridian will be excluded, except when expressly embraced. Further and more exact information is necessary before that region can be described; and a much denser population must be carried thither, before that description will be needed.

11. CLIMATIC DIVISIONS.

The area of Texas presents two distinct climates, with an intermediate region, sharing, in a marked degree, the peculiarities of both. These are bounded by lines, or belts of longitude, rather than of latitude, and are dependent upon hygrometric rather than thermal considerations.

By pursuing and applying the principles announced in the chapter on meteorology; and giving due force to geographic causes, we shall best describe and give bounds to the two climates adverted to, and account for the many discordant phenomena along the neutral area between them.

As shown in the principles of meteorology, if all the water the air can hold at 80¡, were suddenly condensed upon the earth, its depth would not much exceed five inches; and as the air never parts with all its vapor, not indeed much more than half of it, it becomes obvious that the moving atmosphere has to perform the offices of irrigation, by visiting the reservoirs of water, taking up their burden of vapor, and carrying and discharging it over the thirsty earth. The southerly winds alone, in Texas, have such a direction as to bring us water. The Gulf of Mexico is our reservoir. All west winds and north winds are thirsty, and come to drink up and bear away the water our south winds have pumped up from the Gulf of Mexico and sprinkled over us.

Ill. THE SOUTH WlNDS,

I. The winds of spring, summer, and autumn, and a due portion of the winter, blow from the south, across the area of Texas. Along the Gulf coast, from the Sabine to the Brazos, the direction of this wind is from a point east of south; from the Brazos to the Lavaca Bay it is from due south; and from all the Gulf and Mexican bounds of Texas, west of Lavaca, it is believed that the wind has a little westing. This last, however, lacks the testimony of systematic observations.

2. This south wind, starting from near the boundary of the regular trades, and running in a counter direction, has a mean velocity of some five miles per hour, at the coast, and diminishes in force as it progresses interior. On the parallel 34¡, I found it scarcely perceptible, in August, I858. The inhabitants say, it is usually more active. It may have a force of two miles per hour. It comes from the Gulf, charged with vapor, almost to saturation. At every degree interior, it has less and less of this vapor, so that the vigor it imparts to vegetation, even in the most obstinate droughts, within the first seventy miles of its travel from the coast, is greatly lessened, and at 21/2¡ is nearly inappreciable.

3. These remarks, as to the humidity of the south wind, must of course be confined to that portion of Texas Iying northwardly from the Gulf Both theory and experience prove that in all those western portions of the State where the south wind comes not over the Gulf, it can have little or nothing of the humidity that marks the character of the same wind east of long. 97¡, or 98¡ west. For in the travel of such wind as passes from south to north, along meridians west of the Gulf of Mexico, it is obvious they have no opportunity to imbibe humidity, after their passage over the Cordilleras. Those mountains have an average elevation of more than 10,000 feet, or two miles. All winds ascending then from the level of the Pacific, even if saturated in starting, must have their dew-point depressed by near 30¡ in ascending; and in descending to the plains on the side of the mountains, must be very dry winds. Hence the Dry Region of Western Texas.

4. The south wind is a thin stratum. often not exceeding two or three thousand feet while the strata above, often two or more, have different directions, and a very different condition, as to the vapor they bear.

5. At times, and especially during winter, in the interval between northers, a stream of north wind blows briskly over the south wind, for some time before it can break through to the earth, and form the real norther. While this is transpiring, rain is quite impossible, however well supplied with vapor the thin stratum of south wind may be; for, whenever it ascends, in a manner to produce rain, by reduction of temperature, it mingles with the north current, which is so very thirsty as to drink up every particle of vapor.

6. And even when the south wind accumulates considerable thickness- for it grows thicker by continuing long-and extends from the earth’s surface up to the base of the cirrus region, the attempts to produce rain are often defeated by the greedy aridity of that great upper current, which has come over the Cordilleras. Still, rain is more abundant under these circumstances than when there is a north wind interposed between the regular south wind and upper south-west stratum of the air.

7. Hence, for these considerations, the fluctuating character of the seasons between the meridians 96¡ and 98¡ west.

8. The south winds are the source of comfort and positive luxury to the inhabitants of Texas during the hot weather of summer.

The nearer the sea-coast, the cooler and more brisk the current. But the entire area of prairie, and a large portion of the timbered country, feel it as a pleasant, healthful breeze, rendering our highest temperature tolerable.

Causes which produce and direct the South Wind.

9. The sun heats up the air, over the land more than over the sea; and lands not covered by forests radiate more heat than those that are shaded. The air over the prairie portion of Texas, then, has a tendency to rise, and the cooler air from the Gulf flows outward to rep]ace it. This, in its turn, heats up, and rises as it travels onward, calling for still other supplies of refreshing air from the Gulf. As the prairie portion of the State lies chiefly west of Galveston Bay, or meridian 95¡, the south wind comes from points east of south, up to this meridian.

10. This south wind is doubtless supplied, along the border of trades, by a descent of the upper stratum of reflux trades, which current has a motion northward before its descent, and thus adds considerably to the force with which it flows onward.

11. The retardation, mentioned above as noticeable at a distance from the Gulf, is caused by the large admixture of this south wind above with the southwest reflux trades. The latter always moves slowly, and gradually merges this Texan south wind, and bears it off north-eastwardly, between lat. 34¡ and 38¡.

V. TEXAS NORTHERS.

Number and Duration.

1. During seven or eight months of every year, Texas is liable to a class of storms, or winds, styled "northers" from the direction from which they come.

2. In the year 1857, there were twenty-six northers experienced at the Texas Military Institute, in Fayette county. Of these some two or three were gentle or baffled northers. They occupied fifty-seven days, having an average of two and one-fifth days in length. The latest in spring, was May I6, and earliest in autumn, was November 7.

3. In the year I858 there were thirty-seven northers, about thirty-three of which might be classed as well marked, the others being either gentle or baffled northers. These occupied seventy-eight days. The latest in spring was May 9, and the earliest in autumn was October 7.

4. In the first half of I859~ there have been twenty-four northers, of which four may be described as gentle or baffled northers. They have occupied forty-seven days in their transit, and the latest was May 24.

5. It is proper to remark that nearly all the northers of May and October are mild, and rarely do much damage, or produce so low a temperature as to be severely felt. All the other months, November to April inclusive, are liable to northers of considerable severity.

6. It appears then, that in thirty months last past, of which eighteen months are liable to distinct northers, we have experienced eighty northers, not including the feeble ones of May and October. The same period has seventy-seven weeks, very nearly affirming the hypothesis of weekly returns of the norther. An inspection of the table shows a large number of punctual weekly recurrences of this meteor.

7. At this place of observation their duration varies from one to four days.

Area and Boundaries of Norther.

8. The region over which this peculiar storm has its sweep, is not very great, though its precise limits can not be defined: By diligent inquiry from persons of great experience, we submit the following limits: 9. On the north, by the valley of Red River, in the Indian Territory; on the east, by the second tier of counties from the east boundary of Texas, near meridian 95¡ south to the Trinity, and thence southeast to the mouth of the Sabine. On the south they are felt across the Gulf to the coast of South Mexico and Yucatan. On the west they are bounded by the Sierra Madre, up to the mouth of the Pecos, and thence by about the 101st meridian to the sources of Red River.

1O. Within this area there are various degrees of violence, having their axis of intensity between meridians 97¡ and 98¡ *, and increasing in force and duration, the further south. At Red River, on this line, they are usually limited to a day or two; whereas at Corpus Christi and Matamoras, one norther often continues till the next supersedes it; and at Vera Cruz, a twenty-days norther is not remarkable.

West of Fort Belknap, to the Pecos, the northers grow feebler and rarer.

North of Red River, on the route from Fort Washita to Fort Smith, they are rarely felt.

On the east margin they are much modified by the forests of the timbered region. At all points, an open prairie increases their vigor.

Forces and other Phenomena.

11. The norther usually commences with a violence nearly equal to its greatest force, if its initial point be near the observer. If it has traveled some distance, it will be warmed up, and moderated in its violence, at first attack. Its greatest force might be marked 5, in a scale between a gentle breeze at r, and a hurricane at 10. The writer has measured one traveling at about thirty-two miles per hour-but many others at twelve to eighteen miles. The mean progress seems to be about fifteen miles per hour.

12. Just before a norther, two to six hours, the south wind lulls, and the still air becomes very oppressive. A low black cloud rolls up from the north, and when it comes near the zenith, the wind strikes with vigor. Sometimes we have a sudden dash of rain; but generally northers are intensely dry, and soon drink up all the moisture of the surface earth, and of the objects upon it, capable of yielding their humidity.

Great thirst of man, and all other animals, is experienced; an itching sensation over the skin; a highly electric condition of the skin of horses and cats; a wilting and withering of vegetation, even when the temperature would not account for it; a reduction of temperature, usually very sudden, sometimes, though rarely, a degree per minute, for twenty minutes; and in winter commonly a reduction from 70¡ or 75¡, to 30¡ or 40¡. This fall of temperature is the more severely felt from the drying power of the north wind-evaporation from the surface of the skin increasing the severity of the temperature.

Theory of Cause and Mode of Operation.

14. Hypothesis.-Suppose, by any means, a cataract or plunge of air from the great upper current, traveling to the north-east, were poured down upon the earth, about the central or northern portion of the "norther" area, what would be its characteristics, and whither would it tend ?

15. It would be cold and dry. One mile of descent would bring a temperature I7¡ lower, and two miles, a temperature of 33¡, provided the air should retain the temperature of that elevation. Its dew-point would be very low, though its descent should be but one mile; for its elevation in crossing the Cordilleras could not be less than two miles, or I0~000 feet. Whatever its temperature, in descending, it must be intensely dry.

16. The barometer must rise during the cataract, for these two reasons: that the whole column, being dry, would be heavier than if the dew-point were high, and that the downward plunge of the air must raise the barometric column.

17. The direction in which this torrent would flow at the earth’s surface, is determined by the same physical law that occasions water to run down hill. It is heavier than humid air, and must flow into the trades, to supply the demand that causes them. The direction would be south, until the current should reach the trades, and be deflected with them to the west.

18. After the cataract fairly commenced, it would widen and deepen; it would rush by gusts along the ground, until its course was fairly established; it would lift up the humid south wind, now saturated, or nearly so, and would condense its vapor into a thick, black cloud on its margin, and give a shower at the beginning. Its thirstiness, however, would enable it to drink up nearly all the vapor its cold would condense, so as to give but little rain. It would commence later, both in front and in rear of its initial point. It would increase in violence in both directions, but vastly more so in advance, where it would widen, and continue in violence and duration to the tropics.

19. Application.-All these are marked phenomena of the real norther, and hence, for the present, we adopt the hypothesis of a plunge or cataract of air from the upper regions, as the theory of this peculiar storm.

20. The unskilled meteorologist will receive this solution with less reluctance, when he is assured that between latitude 23¡ and 28¡, there is a well-established region of high barometer, in which the reflux trades send down to the surface of the earth a vast flood of air-by gentle descent-to resupply the trades, and to flow in the opposite direction, and form the south and south-west winds which prevail over all the southern half of the temperate zone, on this continent. Our own life-giving south wind is fed by this general descent of air along the border of the tropics.

Phenomena not readily explicable.

2I. When a dry norther commences, the whole air, in an hour or two, curdles and becomes smoky, or rather whitish, and has a distinct smell. Its odor sometimes resembles that which is developed by a flash of lightning, though, at other times, it reminds one of fine straw smoke, in its odor. It is highly probable that this turbidness and odor are due to the ozone set free, by the high electrical excitation, in a dry norther. Experiments instituted to test the matter, last April, were too late in the season.

22. Sirocco.-When the norther has a little westing, it is observed to be more intensely dry, and to be destructive to vegetation, even before the frost which usually follows it. Corn, beans, young foliage, and the grass and weeds of the prairie, bow and wither before it.* (* The citizens of Galveston,, and the southern portions of Texas, will remember the violent north-wester in 1856, which preceded and attended the storm which wrecked the Nautilus. It was, in my judgment, a true sirocco. In like manner the north-west wind that withered the corn-fields in Lamar, Fannin, and Grayson, and the counties south of these, on the 17th day of August, I858, deserve a like name.) A few of these I have called siroccos. They occur as well in summer as in spring or autumn, and differ, in several respects, from the true norther.

23. It is not a little remarkable, that the central violence, as well as the middle region, or axis of the norther, lies along the boundary between the two climates.

24. By way of aiding the observer to recognize this boundary, without knowing his longitude, we would call attention to certain indices in the animal and vegetable kingdom, which are entirely reliable, and are peculiar, or belong chiefly, to a dry climate:

Animals.-Mule-eared rabbit, civet-cat, Mexican hog.

Reptiles-Coachwhip, joint-snake, spreading-adder, Amphis Benae or blind-snake, scorpion, and tarantula.

Birds.-Mexican buzzards, swallow-tailed fly-catcher or scissor-tail, prairie hawk.

Insects.-The cutting-ant and the devouring grasshopper.

Vegetation, Trees.-All of stunted growth, except on streams. The mesquit tree, infallible; cactus plants; Agave Americana, or aloes.

These will not be limited along a definite line, but will not be found far from, or numerous east of, longitude 97¡. The Lower Cross Timbers lie nearly along the limit of all these indices.

VI. GENERAL CONSIDERATIONS. I. This essay will have shown that the climatic divisions of Texas, as alleged in Article II., are founded upon natural, and therefore permanent, laws. Human interest is best consulted in the tracing out and early announcement of these laws, for every district of country. Fortunately for the future wealth and independence of the vast Empire State of Texas, she boasts these phases of climate; for they beckon to enterprise and industry of such varied and mutually dependent kinds, as to warrant a large, a prosperous, and a happy population, on each climatic area.

2. The great staples, the cereals, the flocks, and the vines, these are the departments for investment and industry, which, with a diversified and extremely exuberant soil, shall give an abundant population and unrivaled prosperity to every district of the State, east of the one hundredth meridian.

3. The development of her resources, and the intelligent appropriation of her various soils and climates, each to its fittest purposes, must, in a very few years, render her the most powerful and the most enviable of the sisterhood of States; and must enable her, better than any other member of the Union, should separation ever be her misfortune, to sustain herself alone, and to command the respect of mankind, for her empire of fertile acres, and for the diversity of industry and production that shall give her independence.


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