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File No. 880-42 APPENDIX

Report of the weather conditions near Miles City on the morning of May 12, 1942 as taken from the weather map at the Minneapolis, Minnesota, Airport Station and prepared by the Board's Air Safety Specialist in Meteorology.

SYNOPTIC SITUATION

A polar continental air mass covered Nebraska, North Dakota, South Dakota, Montana, and Wyoming. Unstable, tropical maritime air moving northeastward, from the Gulf of Mexico, covered Kansas and Missouri. Dry superior air covered Colorado. The main frontal system between the polar and tropical air was centered in a low pressure system in southeastern Wyoming with a warm front extending eastward through southern Nebraska and a cold front extending from the center through Western Colorado.

There was strong evidence of an upper cold front extending northward from the center and along this upper front thunderstorms were occurring. Overrunning was producing precipitation to the north of the center one to two hundred miles in advance of the upper cold front and behind the upper front over most of Montana.

The pressure gradient was weak over the Dakotas, but was producing winds of eight to twelve miles per hour from the east and southeast over eastern Montana. A pressure trough extended along the upper cold front and winds were from the north or west over the area two hundred miles west of the trough line. The trough line and attendant precipitation area were moving eastward at fifteen to twenty miles per hour.

Ceilings were unlimited from Minneapolis to Jamestown, N. D. and Dickinson, N. D. and Golva, N. D. reported twelve to thirteen hundred with visibility above ten. Custer, Montana reported thunderstorm with moderate rain with visibility three miles. Light rain had started at Miles City, Montana where the ceiling was reported as fifty-five hundred and visibility above ten.

By 8:30 a.m. EWT the pressure trough associated with the upper cold front had moved into extreme eastern Montana with precipitation continuing to the west of the trough and for about one hundred miles in advance of the upper front.

Ceilings were lowering to six to nine hundred feet between Dickinson, N. D. and Custer, Mont. with light rain and light fog reducing the visibility to three to four miles. The pressure center moved eastward and at 8:30 a.m. was located on the Wyoming–Nebraska border. The warm front of the system moved northward into southern Nebraska.