The Boy with the U. S. Weather Men Part 28

"That comes after the cyclone," explained Anton. "A 'low' means that the pressure of the atmosphere is less than usual, and, consequently, doesn't press the mercury up so far in the barometer. The air weighs less, that shows that it must be expanding. The winds in front blowing into a 'low' are generally warm winds. When a 'low' is traveling fast, with a 'high' or 'anti-cyclone' behind, the colder winds come rus.h.i.+ng forward to take the place of the rising warm air and they bring colder weather with them. The freeze comes during the early clearing weather of a 'high,' before the anti-cyclonic winds--which blow in the opposite direction, the way of the hands of a clock--have had a chance to steady down."

"Then," said the farmer shrewdly, "if you get reports of wind and of barometer from points to the west and northwest, you can tell when a cold wave in on the way. Is that it?"

"Exactly," the Forecaster replied. "We cannot always tell, of course, when the weather is going to be a little colder or a little warmer, but a cold wave, serious enough to damage crops and property, can always be foretold. Remember your storm tracks again. In this county, in the State of Mississippi, we are very unlikely to get a freeze, unless there is a rapidly moving 'low' pa.s.sing up towards the Ohio and St. Lawrence Valleys followed by an equally energetic 'high' plunging down from the Canadian Northwest."

"And can you always tell what the weather is like, all over the country?"

"Yes, indeed," the Forecaster answered. "There are two hundred official stations scattered all over the United States and the West Indies, each one carefully selected because its site is a key station to weather changes. Twice a day, exactly at eight o'clock in the morning and eight o'clock in the evening, the observations are taken at each station."

"And have they all got rain gauges like mine?" asked Anton.

"Yes, all of them."

"And wind-measurers, like my anemometer?" queried Tom.

"Yes," the Forecaster agreed with a smile, "and some of them have devices that make a continuous record of wind velocity."

"And barometers like mine?" put in one of the younger boys, not to be outdone.

"Various forms of barometers, and barographs, and thermographs, and suns.h.i.+ne recorders and all sorts of things. Some of them even have seismographs, which tell of every tiny little earthquake, that may be going on all over the world. You know, boys, there's hardly an hour of the day that there isn't a small earthquake, somewhere, and there are really quite sizeable earthquakes at least once a month. A well-equipped weather office is quite a complicated affair, and it takes well-trained men to conduct the observations and interpret them properly."

"All those observations are sent to Was.h.i.+ngton, aren't they, sir?"

queried Anton. "Just as I send mine every night to Bob, for him to transmit by wireless."

"Just the same way," the Forecaster answered, "except that they're all sent in cipher, of course. Once in a while the cipher results in some queer combinations. The regular routine requires that an observer send the temperature, the barometric pressure of the atmosphere, the amount of rain or snow, the direction and force of the wind, the state of the weather, the types of clouds and the highest and lowest temperature since the last observation. I remember once, while at the Milwaukee station, we got the following message from La Crosse, Wisconsin:

"'Cross All My Ink Frozen'

"It so happened that we had Charlie Cross working at that station at that time, but the message did not apply to him, nor, for that matter, to his ink. On second consideration and reading, the message read very differently. 'Cross' was the code name of the station; 'All' meant that his barometer read 30.02 and that his morning temperature was zero; 'My'

conveyed the information that his sky was clear, the wind from the south and that his minimum temperature for the night was zero; 'Ink' informed us that the wind velocity at the station was six miles an hour and that he could not add the usual height of the water in the Mississippi as the river was 'frozen.' Similar code messages are sent in twice a day from each of the two hundred stations.

"So you see, Mr. Tighe, if all these various observations combine to describe a certain weather type, if we can check up the accuracy by comparison with stations to the north, south, east and west, and if all these combine to produce a certain definite picture, our weather forecast can be made with tolerable certainty. As an absolute matter of fact, during the past six years, the exact percentage of accurate forecasts is eighty-two per cent, and of the eighteen per cent remaining, eleven were partly right. That leaves a very small proportion of mistakes in weather forecasting. Now, let us take in detail the cold wave which Fred, quite rightly, said was on its way here.

"Here is the Weather Map of the day before yesterday." He placed it on the table in front of the old farmer. "You will notice two sets of curved lines, solid lines and dotted lines. The solid lines are called 'isobars' and they follow the course of places which have the same barometric pressure. The dotted lines are called 'isotherms' and they follow the lines of places having the same temperature. These maps are never twice the same. The Weather Bureau does not possess on its books the record of any two days when the weather was duplicated over the United States."

"You mean that every day's weather map is different?"

"As different as every human face," the Forecaster replied, "and to those of us who have done much forecasting, it is as easy to see from the map when the weather is going to be peaceful or stormy as it is to tell whether a man is smiling or scowling. But let us look at these three charts closely, and you will see just why Fred was right.

"At eight o'clock in the morning, the day before yesterday, there was a well-defined 'low' with a barometer of 29.8 just east of Salt Lake City, driving warmer weather before it. Issaquena County was just recovering from the effects of a 'high,' which, as you can see on the map, was disappearing by its favorite route, the St. Lawrence Valley. What was your temperature here the day before yesterday, Anton?"

"Thirty-six degrees, sir," the crippled lad answered, rapidly consulting his week's record, which was hanging on the wall.

"Fairly cold, you see. And the wind, Tom?"

Tom pulled out a note-book from his pocket.

"North-east, sir," he said.

"Very good. Now, Mr. Tighe, you can see from the map that the barometric pressure, the isobar, running through this part of the country shows a barometric pressure of 30.30. From what Anton told you, it is easy to see that, the day before yesterday, Issaquena County was still in the grip of the tail end of a 'high,' with a high barometric pressure--five points above the low in Salt Lake City--with a cold temperature, and with a wind blowing outwards from the 'high' or anti-cyclone. Is that clear?"

"Clear as well water," the farmer declared.

"Now," said the Forecaster, "let us look at yesterday's map for eight o'clock in the morning. Here, just over the Canadian border, right at Medicine Hat--as though to make good the old proverb--is a vigorous 'high,' with a barometer of 30.50, with a temperature of 20 below zero and with the winds blowing outward from the centre. The 'low,' which the day before yesterday was central over Salt Lake City, yesterday was central over Oklahoma City. It has, therefore, traveled over five hundred miles in the day. On all sides of the 'low' there is rain, and you remember how it rained here, yesterday morning, early?"

"Indeed I do," said Jed Tighe. "I didn't get out on the land until nearly eleven o'clock."

"Now what was the temperature here yesterday morning, Anton?" the Forecaster queried.

"Forty-six degrees," answered Anton promptly, for he had been expecting the question.

"Ten degrees warmer, you see, Mr. Tighe, as the 'low' came nearer. And what was the wind, Tom?"

"South-south-east," the lad answered, his note-book in hand.

"Showing," the Forecaster explained, "that during the twenty-four hours, Issaquena County had lost the effect of the 'high,' which has disappeared from the map, and was fully in the grip of the oncoming 'low.' Now, if you look at the map, Mr. Tighe, you'll see that the isobar for this region shows a barometer pressure of 29.50, a terrific drop of four points in twenty-four hours. No wonder it rained!"

The farmer bent over the map, his eyes glued on the lines which suddenly seemed to spring into life before him.

"Down over the country comes this 'low,' at the rate of five hundred miles a day, with rain and moist winds accompanying it, and sharp on its heels, racing from the north, comes the cold 'high' which we have just seen forming at Medicine Hat. The cold wave is fully organized and is on its way."

He laid the third map on the table.

"Here is the situation at eight o'clock this morning," he said. "The 'low' or storm, has swung at right angles, following the preferred Ohio and St. Lawrence Valley Route. It left Toledo early this morning and at eight o'clock was raging over the Great Lakes, with its centre north of Buffalo. It is speeding up, you see, having traveled eight hundred miles since yesterday. The cold wave 'high' from Medicine Hat has traveled along its usual track and is now central over Kansas, with clear skies and a drop of thirty degrees in temperature. There was a severe freeze in Kansas last night, with zero temperatures, and freezing point was touched on the Mexican border."

"Whew," whistled the farmer, "and is that on its way here?"

"It is," the Forecaster answered. "Your temperature?" he continued, turning to the boy.

"Thirty-seven," Anton answered.

"Going down rapidly, you see. The wind, Tom?"

"Northwest."

"Blowing outwards from the rapidly approaching 'high.'"

"What's the barometer?" asked the farmer, who was quickly grasping the manner of reading a weather map.

"It has gone up again to 30.02. The cold wave is coming fast. Since Dodge City, Kansas, is about five hundred miles from here, and since the 'high' is traveling at about seven hundred miles a day, and as, moreover, there is generally a slight slowing up as it makes the turn, the centre of the 'high' ought to strike us here about six o'clock tomorrow morning. The cold wave, however, is in advance of the centre, so Mr. Tighe, you need to be prepared for a cold wave tonight.

"If you s.h.i.+p your potatoes this afternoon, as you planned to do, they would meet severe weather and might get frozen. If you s.h.i.+p them tomorrow, you might be safe, but you couldn't be sure, because the 'high' is turning northwards and therefore its eastward distance is not so great. If you s.h.i.+p them on Monday you would be safe, but even then you could not s.h.i.+p them to New York, for a fast train might overtake the tail of the cold wave. On Tuesday you can safely s.h.i.+p them to any part of the United States."

The farmer stepped back from the table and his eye roved over the boys.

"And was that the way that you lads figured out that my fruit was likely to be frozen?" he asked.

"Yes, sir," said Anton, "that was how."