The Art and Science of Phil the Forecaster: Weather Watching Guide for Everyone…

#2057 "Deformation Cirrus" Pixels Link

Know your cloud… know your country.

It may sound like a reality entertainment series but you too can be a “Cloud Tracker”. This guide is intended to be a short introduction to understanding the clouds and their dynamics. The guide is designed to assist you in understanding the current weather situation. There are multiple excellent and thorough resources for the multitude of cloud types and their specific characterisitics. That information is terrific but not required for this short “Weather Watching Guide”.

The basic premise is that the cloud lines and shapes will allow the curious observer using their right hand, to determine their relative location within a mid-latitude storm and thus the weather. The Conveyor Belt Conceptual Model which was described in all of its detail in the previous 26 Blogs, describes everything you need to know. It is important to try to deduce the wind in the atmospheric frame of reference even though our observation is tied to the earth.

How high is the Cloud? The Outstretched Hand Guide. Convective cloud elements are all about the same size. They appear different just because of their height - how far away they are. If your outstretched hand can fully cover a cumulus cloud, then that cloud is certainly in the low etage and below 6500 hundred feet above the ground. If the thumb of your outstretched hand covers the convective element, then it is high enough to be altocumulus - between 6500 and 20,000 feet above the earth surface which is in the mid etage. If the tip of your outstretched pinky finger covers the convective element then you are looking at cirrocumulus in the high etage above 20,000 feet.

Clouds in the low etage interact with the earth's surface. Any cloud above that is in the free atmosphere. The winds moving and shaping clouds in the free atmosphere are the winds you will want to understand for the Conveyor Belt Conceptual Model.

Oceanic Langmuir Streaks

Are the clouds Parallel to the Wind? Langmuir streaks of cloud can be as long as the wind. Langmuir streaks occur in a mildly unstable depth of the atmosphere bounded by a stable layer or boundary. Langmuir conducted his research for the ocean but the atmosphere is just an ocean of air with us at the bottom. The spacing between Langmuir streaks are more apt to be irregular.

A Generalized Langmuir Streak Conceptual Model

Unstable layers of the atmosphere are those where the potential temperature of the atmosphere decreases with height. Parcels of air in an unstable atmosphere keep rising after being disturbed from their original level. Convective clouds like all types of cumulus reveal that the atmosphere is unstable. Langmuir streaks in the lower atmosphere are typically called turbulent stratocumulus cloud streets.

Turbulent Stratocumulus Streets in the Boundary Layer

The planetary boundary layer which is that layer of the atmosphere that exchanges heat, moisture and momentum with the ground is typically unstable during the day. Heating of the ground by the sun creates the instability and encourage and give rise to turbulent stratocumulus cloud streets.

Langmuir streaks in the upper atmosphere tend to be identified as jet stream cirrus and form below the stable layer at the top of the troposhere - where most of the weather we experience occurs. These high level Langmuir streaks parallel the central channels of the warm and dry conveyor belts.

Gravity Waves Perpendicular to the Wind
Like Waves on a Lake

Are the clouds Perpendicular to the Wind? Gravity wave clouds are only as long as the width of the wind flow. Gravity waves occur within a stable layer of the atmosphere. The spacing between gravity wave bands are very regular. The wavelength or spacing between the gravity waves increase with the wind speed.

Stable layers of the atmosphere are those where the potential temperature of the atmosphere increases with height. Parcels of air are returned to their original level after being disturbed by a fluctuation in the wind or a barrier.

For example the planetary boundary layer is typically stable during the night. Cooling of the ground through the outward radiation of surface heat energy creates this nocturnal stability - cool temperatures at the surface and unchanged warmer temperatures aloft at the top of the planetary boundary layer. Gravity waves are commonly observed at the top of the planetary boundary layer after a night of cooling.

Frontal boundaries between air masses is the other location where one will typically find deviations in stability from that typically found in the atmosphere. Warm fronts direct warm air aloft which creates a stable situation. Cold fronts advance cooler air near the surface and these boundaries can be unstable.

Both Langmuir streaks and gravity waves reveal the wind within the atmospheric frame of reference which are the winds studied in the Conveyor Belt Conceptual Model. The Langmuir streaks align parallel to both the warm and dry conveyor belts. The Langmuir streaks are typically more obvious within the moisture of the warm conveyor belt. The gravity waves are everywhere perpendicular to the atmospheric frame wind. The regular waves caused by gravity in a stable layer can be most useful in finding the swirls as illustrated in #2378 "Singleton Classic Cirrus Summer Sunset".

Here is the clincher though - the Deformation Zone is your new best friend! I described how deformation zones are formed in Cloud Shapes and Lines in the Atmosphere. A Closer Look at Lines in the Sky describes the deformation zone process in even more detail.

Any sharp boundary between relatively moist and dry air must be a deformation zone. This is my favourite conceptual model as it reveals everything you could hope to discover about the atmosphere. These deformation zone lines are also very common and are a big part of the Conveyor Belt Conceptual Model. Deformation zones come in all sizes and shapes and occur throughout the depth of the atmosphere. In fact a three dimensional deformation zone skin encases the air masses and their circulations. The quasi-horizontal intersections between layers of cloud and the three dimensional deformation zone skin only reveal the linear cross-sections. The entire three-dimensional deformation zone skin requires your imagination.

The Deformation Zone Conceptual Model

Deformation zones (the double headed green arrow) are perpendicular to the strongest winds in the atmosphere. Watch the cloud move along the sharp boundary to reveal the generally weaker swirls that comprise the deformation zone conceptual model. Using your right hand, curl your fingers in the direction of this cloud motion. Your right thumb will point in the direction of the secondary motions in the atmosphere resulting from the deformation zone process. An upward pointing thumb means that the air is rising in the cyclonic companion of the flow - you can expect more cloud and instability. A downward pointing thumb means that the air is descending in the anticyclonic companion of the flow - you can expect less cloud and more stability - and more gravity waves too.

If one could see the dry air parcels on the opposite side of the confluent asymptote of the deformation zone, you would flip your right hand keeping your fingers pointing in the same direction - but the thumb must turn to point in the opposite direction for that paired swirl. In this way an "X" must be paired with an "N" across the confluent asymptote of the deformation zone - and vice versa too.

The Warm Conveyor Belt and Gravity Wave Orientations

An astute weather observer can now locate the portion of the Conveyor Belt Conceptual Model that is currently crossing their location. An understanding of the Conveyor Belt Conceptual Model and the mid-latitude storm will allow the weather observer to further anticipate what is likely to happen in the future.