Final answer:
The states of Nevada, Idaho, and southern Oregon are probably under a high-pressure system, demonstrated by less cloud cover and dry conditions due to the rain shadow effect of mountain ranges like the Cascades and the Sierra Nevada.
Step-by-step explanation:
Based on cloud cover and other influences, it is likely that the location in question, along with the surrounding states of Nevada, Idaho, and southern Oregon, is experiencing the effects of a high pressure system. This high pressure is typically associated with clearer skies and less cloud cover due to the descending air inhibiting cloud formation. The rain shadow effect caused by the western mountain ranges, such as the Cascades and the Sierra Nevada, further contributes to this condition. As air masses ascend these mountain ranges, they cool and release moisture on the windward side, leading to arid conditions on the leeward side. This phenomenon is described in the mention of the Cascade ranges cutting off moisture and creating semi-arid conditions.
Meteorologists use weather maps to describe and predict weather patterns, which include areas of high ('H' in blue) and low pressure ('L' in red), along with isobars—the curved grey lines illustrating constant pressure. These maps, in conjunction with satellite photos, help in modeling the path and impact of weather systems, such as hurricanes.
In the context provided, the reference to a surface pressure of 90 bars and overcast conditions similar to Earth implies extreme weather systems that are not relevant to the initial question about pressure systems over the specified U.S. states.