Finishing The Dry Conveyor Belt

#2047 "New Beginning Sunrise" Pixels Link 

The conveyor belt conceptual model of the wind patterns found with a mid-latitude low pressure area, is fundamental to the understanding of cloud patterns. Note that the term “cyclone” is frequently used to replace “low pressure area”. The idealized conveyor belts are in the atmospheric frame of reference relative to the low.

The Conveyor Belt Conceptual Model 

The dry conveyor belt (DCB - Orange Arrow) is the contrasting dance partner for the warm conveyor belt in the weather ballet. The DCB originates from high levels and follows the constant energy isentropic surfaces downward as it plows toward the south on the western flank of the warm conveyor belt (WCB). The dry air is relatively dry to start with and becomes drier and warmer as it descends. There are minimal cloud tracers and the atmosphere uses invisible ink to write this part story in the storm. The water vapour is key to diagnosing the DCB as described in the previous post “Reading Water Vapour Patterns“. The croquet hoop and smoke ring analogies can still be used but without cloud or smoke, one must use your imagination to visualize the circulation.

Descending Smoke Ring to Croquet Hoop Analogy

The leading edge of the DCB is also a bowed shaped deformation zone. The anticyclonic branch of the DCB tends to penetrate further south and lower in the atmosphere. This anticyclonic companion flow is drier, lower and warmer that its cyclonic companion across the DCB flow. The cyclonic companion typically turns back northward and rises on the sloped isentropic surfaces. These DCB circulations help to define the character of the cyclonic companion of the warm conveyor belt and the associated cold front.

 The katabatic or inactive portion of the cold front is typically associated with the anticyclonic branch. The warm air above any katabatic cold front is actually descending. Any cloud associated with a katabatic front tends to be well ahead of the surface wind shift and cold front.

The cyclonic branch does not descend as far and tends to wrap around the cyclonic circulation which is the low pressure area for the mid-latitude storm. The anabatic or active portion of the cold front is typically associated with the cyclonic branch. The warm air any anabatic cold front is ascending and thus promoting the development of cloud and precipitation – most of which occurs behind the surface wind shift and cold front.

The col in the bow of the DCB deformation zone separate the weather regimes and the anabatic and katabatic portions of the cold front.

The Water Vapour from June 1st 2020
The area of thew DCB is clear on the
corresponding visible imagery

Flows in the atmosphere are rarely as smooth as flowchart arrows. The dry conveyor belt (DCB) tends to be segmented into pulses associated with local wind maxima that move along the jet stream axis and energize the cyclone. These are called jet streaks and they will be another subject for a blog entry – jet streaks are that important too. This cross section is perpendicular to the WCB flow and shows how multiple DCB bursts might interact. Secondary lines of cloud can be expected where these DCB pulses collide with the cyclonic companion of the warm conveyor belt.  Water vapour imagery is essential to analyzing these DCB pulses. Each pulse will bring a burst of stronger winds toward the ground.

Every line in the water vapour imagery has a story to tell and the conceptual models are your keys to unlocking and understanding the wonder of weather. Meteorologists typically analyze the first pulse of dry air. The other pulses are invisible without the aid of the WV imagery. The movement of dry air is every bit as important as the circulations of clouds.

Here is a weather information site created and maintained by my friends in Boulder, Colorado. I think you will find it very useful.

http://weather.rap.ucar.edu/satellite/ and select  Water Vapor (mid)

That's enough for today... much more to come.
Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick