Weather Tidbits: The Norlun Trough

This Weather Tidbits will discuss about the weather feature known as the norlun trough. This is an axis of shifting winds that occur on the northwest side of a low pressure center. This forces air at the surface to converge and rise, resulting in precipitation. Norlun troughs tend to produce a narrow axis of heavy snow. This creates what is essentially a very localized snowstorm. A few ingredients that enhance the development of a norlun trough is a bit of instability with colder air over relatively warmer air and the passage of an upper level disturbance (aka a “shortwave”). Because strong rising air must balance out with strong sinking air elsewhere, a tight gradient in snow totals is very common with a norlun trough. While we can gauge a general idea of where a norlun trough may set up, these are notoriously hard to forecast the exact placement.

A norlun trough is also known as an inverted trough. This is because the isobars (lines of equal air pressure) invert away from the low pressure center when viewed on a surface map.