178 TRANSACTIONS OF THE ILLINOIS 



noted storms was borne to us by west or southwest winds. This 

 storm is, therefore, noted, not so much for its intense severity in 

 Indiana as for its having penetrated the extreme south as it did." 



The atmospheric conditions that precede a blizzard — indeed 

 constitute the preliminary features of it — are a low barometer, 

 centered well south and moving northeasternly. As a rule, we 

 have from six to ten low pressure movements during a month. 

 Almost without exception these pass out of the territory of the 

 United States through the lower St. Lawrence valley. Just why 

 this is so need Dot now be considered. Usually these centers' of 

 low pressure arise in the Rocky Mountain regions of the United 

 States, or enter our territory from Manitoba, and, passing through 

 or near the great lakes, follow the St. Lawrence to the north- 

 east. Conditions of this kind may bring us, in the Central Mis- 

 sissippi Valley, thunder storms, heavy rains or snow, wind, and 

 even tornadoes, but will not give us a genuine blizzard in all its 

 fury with a resultant temperature of from ten to thirty degrees 

 below zero. If, however, an area of low barometer enters the 

 territory of the United States from Mexico or the Gulf of Mexico 

 and passes northeasterly toward the mouth of the St. Lawrence, 

 and if this be during the winter months, we may have a severe 

 cold wave extending far into the south and borne to us in the 

 latitude of Indiana and southeasterly, by winds from the west or 

 •even the southwest. 



In some particulars, the storm under consideration excelled 

 any on record. This is especially true in regard to its extent 

 and unusual severity in the extreme south. When we refer 

 to the record of the Signal Service we ascertain the causes 

 of the unusual distribution of cold. As stated above, certain 

 barometric conditions are the prelude to such storms. 



In this case (and this is but the type of all such storms) a low 

 barometer of unusual energy came within the range of obser- 

 vation near Las Animas, Cal., at '6 o'clock, p. m., Washington, 

 time, on Jan. 6, 1886, from which place it moved southward into 

 the Gulf of Mexico, where it was central at 3 o'clock, p. m., of 

 the 7th. From there it was deflected to the left, being noted 

 eight hours later over the mouth of the Mississippi river, and 

 thence passing northeasterly, following the Gulf and the Atlan- 

 tic coasts, it reached the mouth of the St. Lawrence at 7 a. m. 

 of the 10th. 



An area of low barometer may be illustrated by, if not com- 

 pared to, a vigorous blaze, as a burning building, which creates 

 a rarified condition of the air and a consequent rush of surround- 

 ing atmosphere to fill the void. In the northwestern portion of 

 our continent, in the elevated regions of the Rocky Mountain 

 chain, we have a comparatively constant high barometer. When 

 a low starts up, a corresponding high, from this region of con- 

 stant high, flows in to fill the vacuum. 



