An inversion is a stable situation which may trap smoke or fog in the lower layers of the atmosphere. Stable conditions are not favorable for turbulent surface winds or erratic fire behavior. Sinking air usually found around high pressure areas. Strong subsidence leads to very dry, warm air often appearing at high elevations first. It may arrive at day or night.
Humidity staying low at high elevations is a sign of strong subsidence.
The change in temperature over a given period of time, generally the period between late evening and a few hours after dark. Windy or cloudy conditions will tend to produce slow temperature recovery while clear and calm weather can cause rapid recovery. A low pressure trough caused by very warm air, both.at the surface and in the lower layers of the atmosphere. In a stagnate situation the thermal trough will remain stationary. However, if a relatively strong disturbance in the upper atmosphere moves across the northwestern portion of the country, it will force the thermal trough eastward through the district.