Alpine Inversions Setting Up

An interesting alpine winter pattern is shaping up on Thursday over most of British Columbia as a massive ridge of high pressure builds over the region. 

Under such a ridge air descends very slowly but persistently from high up in the atmosphere towards the surface level. During its descent the air is being compressed (due to the higher air pressure at lower levels) and warms by almost one degree C for every 100 metres (dry adiabatic lapse rate: 0.98 deg C / 100m), which is significantly more than the average lapse rate of the atmosphere (0.65 degrees C / 100 metres) that would otherwise prevail. 

This descent gradually turns to horizontal movement as air parcels approach the surface and warming diminishes at those very low levels. As a result the maximum warming due to this process is felt at the high alpine elevations while lower level valleys remain cooler. In your AFX meteograms you can see how alpine inversions form and freezing levels vary wildly from overnight (when the surface is below zero overnight) to afternoon (when the surface warms to above zero during the day and the actual freezing level is above the inversion). 

While this pattern is certainly not unusual, the scenario on Thursday is more intense than is commonly observed - perfect for an alpine Apres Ski!