As soon as Arlington Park was named site of the Breeders' Cup World Thoroughbred Championships, people began talking about the weather. Well, the 10-forecast issued today by the National Weather Service calls for partly cloudy skies and a high of 58 degrees in Chicago on Oct. 26.Weather patterns make 10-day forecasts a crapshoot, and nowhere does the weather change faster than in Chicago. But after rain early next week, the forecast is for the high 50s next Thursday, Friday, and Saturday.The fact is, of the previous 18 Breeders' Cups, the race day high temperature has been over 60 only 10 times. The high was only 43 two years in a row, 1990 at Belmont Park in New York and 1991 at Churchill Downs in Kentucky.The Breeders' Cup was held in Canada in 1996 and the high that day at Woodbine was 60.The warmest day yet for a Breeders' Cup 1992, when it reached 87 degrees at Gulfstream Park in South Florida.The highest Breeders' Cup attendance was 80,452 at Churchill Downs in 1998. On that day, the high temperature was 54. On the day it was 87 degrees at Gulfstream, attendance was 45,415.