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1.7 Meteorological Information
The 2200 surface weather chart prepared by the National Meteorological Center showed a quasi-stationary front extending southeastward across Lake Michigan from near Milwaukee, Wisconsin to near South Bend, Indiana.
The weather at O'Hare, reported at 2120, was an estimated ceiling of broken clouds at l0,000 feet, visibility seven miles, temperature 72°F, dew point 68°F, wind from 120 degrees at four knots, and the altimeter setting was 29.9h inches of mercury At 2100 the Glenview Naval Air Station, Glenview, Illinois, reported the weather to be an estimated ceiling of broken clouds at l0,000 feet, visibility 10 miles, temperature 74°F, dew point 70°F, and a wind from 090° at 6 knots. Thunderstorms were observed by weather radar located at the Chicago Weather Bureau forecast center but none were in the area where the accident occurred. There is no evidence available to indicate that UAL 389 flew in any thunderstorms.
The 1834 Peoria radiosonde ascent showed that the air below 23,000 feet contained alternate layers of stable and conditionally unstable air which was relatively moist at all levels. The freezing level was near 14,000 feet m.s.l.
The crew of a B-707 was flying approximately 30 miles behind UAL 389 at FL 280 as they approached Lake Michigan. The captain of the B-707 stated that the descent over the lake was made on instruments from FL 280 until they descended to 8,000-l0,000 feet where they broke out of the clouds 15-20 miles off shore. Light turbulence and areas of precipitation were encountered during the descent. The B-707 crew could see only the lights on shore when they broke out of the clouds and the captain stated that visibility was "fuzzy and unclear." The first officer said he could see the water clearly, it was hazy, and the lights on the shoreline were visible.
