Weather front areas of precipitation help determine the frontal type and location. There are two different meanings used within meteorology to describe weather around a frontal zone. The term "anafront" describes boundaries which show instability, meaning air rises rapidly along and over the boundary to cause significant weather changes. A "katafront" is weaker, bringing smaller changes in temperature and moisture, as well as limited rainfall. A cold front is located at the leading edge of the temperature drop off, which in an isotherm analysis shows up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface
Third letter of Hernán Cortés to the Emperor Charles V In the first part of the letter, Cortés describes the Battle of Otumba, as well as the reorganisation of the Spanish troops after the defeat of the "Night of Sorrows" at Tlaxcala, with the aim of encircling Tenochtitlán. In reference to this reorganisation, Hernán Cortés relates that it was necessary to create "Military Ordinances" to establish order among the troops and avoid thefts and pillages. Cortés goes on to describe the construction of the brigantines used to enter Tenochtitlán by the canals. These vessels were manufactured in Tlaxcala, as this region was the main source of support for the Spaniards