May started with a low coming down from the north and staying northwest of SHEBA ship from 1-7 May. A second low came north across the Beaufort Sea on May 4 and joined with the other low on May 5. Surface and upper air winds were westerly to southwesterly through this period. Some snow fell every day until 14 May.
A high moved north through the Beaufort Sea from 8-10 May. Surface winds moved from southwesterly to easterly as the high advanced northward while upper level winds were generally southerly. Cloud cover persisted over SHEBA ship.
A weak low moved northward across the Beaufort Sea from 11-14 May. Surface winds shifted from easterly before the low to southwesterly after it passed to the north.
From 16-27 May a high was present north of SHEBA ship. It moved from northwest of the ship, eastward into the northern part of the Beaufort Sea. A large low occupied the Bering Straight to the south and occasionally wandered eastward into Alaska. This high-low combination produced fairly strong easterly winds at SHEBA ship. No precipitation fell. Fog was minimal and clear periods occurred on 14-15 May. Upper level winds were easterly to southeasterly and very light through this period because the upper level high was usually centered over SHEBA ship, south of the surface high. However, winds along the flight track were fairly strong from the east or southeast.
The first drizzle (non-snow) precipitation was reported on 28 May as a freezing rain. The Beaufort high had slid eastward into Canada while a weak low move north from Siberia. Winds were southerly to southwesterly at all levels. Temperatures above freezing were first recorded on 29 May.
Surface trajectories show the dominance of the high in the Beaufort Sea. Most trajectories trace back east of SHEBA ship and curve in the Beaufort Sea remaining in this high.
A second group of low level trajectories trace to the south and southwest. These occurred when the High was in the southeast Beaufort Sea and some weak troughing occurred in Siberia.
Upper air trajectories, 3-9 km, also appear to have two modes. Those that circle north of SHEBA ship were part of the dominant high pressure system. The upper air high was displaced west of the surface high. The second mode are the trajectories that trace to the south acrossed the Bering Straight and western Alaska. They occurred when a southerly upper air flow dominated the area.
Cross-sections of the trajectories were inspected. An east-west cross-section at 1.0 km was plotted. No ascent or descent of the air can be seen indicating that the flow around the high was at a nearly constant level. The north-south cross- section of upper air trajectories (3-6 km) show some slight ascent in the 3.0 km air coming from Alaska. It is weaker than the previous month, April, and the highest trajectories, 9.0 km, don't reveal any change in height at all.
