The Children’s Blizzard, by David Laskin
Chapter Five: Cold Front
(p.117) Of course, Lieutenant Woodruff, and E. J. Hobbs in Helena, and Sergeant Glenn in Huron, knew what a cold front on the prairie felt like, the sudden shift in wind direction, the burst of rain or snow, the crystalline, head-clearing blast of cold air from the northwest. Woodruff even used the term “the front of the wave” in “Cold Waves and Their Progress” to describe how cold waves tend to track the paths of lows from northwest to southeast across the country.
But it wasn’t until after World War I that a team of Norwegian meteorologists, led by the physicist Vilhelm Bjerknes and his son Jacob, zeroed in on the importance of cold and warm fronts in the structure of weather systems, and devised a way of graphically representing their location and direction on weather maps. The insight of Vilhelm and Jacob Bjerknes nudged the fledgling science of meteorology one large step closer to maturity.
The Bjerkneses borrowed the term “front” from the vocabulary (p.118) of the war that had just decimated Europe, and brought neutral Norway to the brink of mass starvation. In World War I, the fronts were the long, wavering lines where the two opposing armies met, dug in, fought, and advanced or retreated after terrific violence. The analogy, the Bjerkneses realized, fit weather exactly. Air masses at a front come together too rapidly to mix.
Instead, at a cold front, an advancing mass of dense cold air shoves itself under warm air, forcing the warm air to rise rapidly along a steep incline, and condense out its moisture: The speed and abruptness of the ascent typically results in short-lived bursts of heavy rain or snow, often accompanied by lightning. Warm fronts, in which warm air advances up and over cold air, progress more gradually, and tend to bring lighter, but steadier and longer-lasting precipitation, to a wider area.
Fronts are the seams in the atmosphere that extend from the ground to the tops of clouds, long, rippling, fragile seams that get ripped apart by storms. A colleague of the Bjerkneses in Bergen later came up with the idea of representing fronts on maps as lines of sawteeth, triangular barbs for cold fronts, and soft semicircular pips for warm fronts. Today it’s hard to imagine the weather map without the warm and cold fronts snaking across it, but this elegant bit of shorthand has only been around since the 1920s. There were no fronts on the maps Lieutenant Woodruff drew and distributed every morning to the eager citizens of Saint Paul.
An evil genius could not have devised a more perfect battleground for clashing weather fronts than the prairies of North America. When conditions are right, which they frequently are, vigorous fronts unleash the worst weather in the world over this region, super-cell thunderstorms spawning tornadoes in late spring, huge globes of hail falling from anvil-topped cumulonimbus clouds in summer, blizzards in winter.
On the prairie, cold fronts can come (p.119) through so rapidly that standing water ices up in ridges, small animals literally freeze to their tracks, people whose clothing is wet find themselves encased in ice. When a strong cold front is accompanied by the blowing icedust of a blizzard, the punishment inflicted on human and beast is unimaginable.
While the slip of tissue paper with Lieutenant Woodruff’s indications for January 12, 1888, sat on a countertop at the Saint Paul Western Union at 113 East Fourth Street, waiting to be translated into Morse code,
and sent out along the wires to newspapers and Signal Corps offices, one of these ferocious cold fronts was dropping southeast through Montana at around 45 miles an hour. With the advance of the cold front, all of the elements of the storm suddenly began to feed off each other, bloating up hugely with every bite.
As the contrasting air masses slammed together, they caused the upper-level winds to strengthen, which served to strengthen the low. As the low deepened, the surface winds increased, causing the temperature differences between the air masses to spike. The greater the temperature difference, the faster the low deepened. The deeper the low, the stronger the front. It was a self-reinforcing and accelerating cycle.
When a storm becomes organized gradually, high wispy cirrus clouds usually appear a day or two ahead of the cold front, followed by a solid low bank of stratus cloud stealing across the sky. But by the first hours of January 12, this storm was spinning up so quickly that there was no time for an atmospheric herald. The cold front was now so strong, and so well defined, that it was like a curtain of ice separating two radically different climates, a curtain that was hurtling in two directions simultaneously, down from the sky, and horizontally across the surface of the earth.
At the same time that the curtain swept down from the north, a warm spongy mass of air was ascending from the opposite direction. The intensifying low forced the two air masses to converge with ever increasing speeds. When they collided, the atmosphere erupted. (p.120) The warm air slid up and over the curtain, rising about three feet every second. As soon as it hit an altitude of about 5,000 to 7,000 feet, the air instantly surrendered its vapor into infinitesimal droplets of supercooled water, liquid specks colder than freezing, but prevented from turning to ice by the surface tension of their “skin.”
As many as a billion cloud droplets swarmed around every cubic meter inside the ballooning clouds. Even smaller particles of airborne debris roiled alongside the cloud droplets, pollen, dust, salt crystals, shredded spiderwebs, and these particles, in their billions, served as the nuclei around which the supercooled cloud droplets coalesced and turned to ice.
The instant the cloud droplets froze, they began to grow exponentially by fixing other droplets onto their crystalline facets. Behind the front, where the air was much colder, ice production inside the clouds happened at significantly lower altitudes, as low as 3,000 feet, and the condensing vapor spat out a different kind of crystal. It was too cold to form the lacy star-patterned crystals known as dendrites, the pretty snowflakes of Christmas cards. Too cold for the little pellets of graupel that accrete as ice crystals glue on layer after layer of supercooled droplets.
Instead, what was being manufactured inside these frigid clouds was a myriad of nearly microscopic hexagonal plates and hollow columns and needles, hard slick-surfaced crystals that bounced off each other as they swirled around. The snow that fell when these plates and columns grew heavy enough was hard as rock and fine as dust. Actually “fell” gives the wrong idea. The plates and needles and columns billowed out of the bases of the clouds in huge streaming horizontal veils, as if the bank of icy clouds had descended to earth and burst apart in the gale.
The newly manufactured snow crystals, smashed and ground into infinitesimal fragments within seconds of their creation, mixed with older crystals that had settled at the surface after previous storms. In the gale, the crystals of different vintages became indistinguishable. (p.121) New snow is not necessary to boost a winter storm into the category of blizzard. All that’s required is wind of at least 35 miles an hour, airborne crystals, and temperatures of 20 degrees or colder (the National Weather Service recently dropped the temperature requirement). The January 12 storm qualified easily.
The disturbance rippled southeast on precisely the path Woodruff had expected, the path taken by 54.14 percent of the cold waves he had studied. By midnight, the leading edge of cold air had reached Poplar River in northeastern Montana. By 2 A.M., it had engulfed Medora in western Dakota, where Teddy Roosevelt had lost so many cattle to blizzards the previous winter.
By 4 A.M., January 12, the cold front was poised just west of Bismarck. At six o’clock in the morning Central time, when the telegrams bearing Lieutenant Woodruff’s midnight indications began to arrive on the desks of weather observers and newspaper editors, the temperature at North Platte, Nebraska, stood at 28, fully 30 degrees warmer than the previous day; while in Helena, 670 miles to the northwest, observer E. J. Hobbs, who had stayed up all night, noted that the mercury had fallen 49.5 degrees in the past four and a half hours, from 40.5 above to 9 below zero.
Omaha was 23 above, and so was Yankton in southern Dakota. The report from Huron, northwest of Yankton, was late, but eventually this bit of data got entered on the map: 19 above at 6 A.M. Central time, nearly 40 degrees warmer than the previous day. More fuel for the approaching storm.
Of course, nobody in Nebraska or Dakota saw it that way. The tragedy of that day was that the fuel came disguised as welcome relief from the weeks of bitter cold, as a spell of softness and relative ease in lives that had too little of either, as an invitation to get outside, (p.122) and work or walk, or simply breathe before the weather closed in again.
In the event, word reached the settlements of southern Dakota not from the Signal Office, but from telegrams sent over the railroad lines. In Codington County in eastern Dakota, just two hundred miles west of Saint Paul, a station agent named Brown received a telegram from Bismarck around 8 A.M., reporting “rapidly falling temperatures and an arctic gale which was steadily increasing in violence.” There was a schoolhouse near his station, and when Brown saw the children walking past, he rushed out at them and stood in the middle of the crossing. He shouted at the kids that “the worst blizzard of the season would be there in two hours.” Many children went back home. All of those who continued on to school regretted it.
End of Chapter Five