8.5: Alternative Text Descriptions for Investigation 8

Figure 8.1.1: 500 Millibar upper-air map for 1200 UTC on February 28, 2025

This is a weather map of the United States showing conditions in the middle of the atmosphere, at the 500 millibar pressure level. The valid time of the map is 12Z on February 28, 2025.

• 12Z means 12:00 Coordinated Universal Time, which is 7:00 a.m. Eastern Standard Time, 6:00 a.m. Central, 5:00 a.m. Mountain, and 4:00 a.m. Pacific.
• Heights are labeled in decameters, where one decameter equals 10 meters. For example, a contour labeled 570 means the height is 5,700 meters above sea level.

The map shows three main kinds of information:

1. Height contours (solid lines every 60 meters), which show the altitude where the 500 millibar pressure surface is located. Closer spacing means stronger winds and stronger weather systems.

2. Isotherms (dashed lines every 5 degrees Celsius), which show air temperature at this level of the atmosphere.

3. Wind barbs, drawn at many station points, which show wind direction and speed. Each long barb represents 10 knots, and each short barb represents 5 knots.

Regional Breakdown:

• Western United States: Heights are relatively high, around 570 to 576 decameters, which means the atmosphere is thicker here, often associated with fairer weather. Winds are generally lighter compared to the central U.S. Temperatures aloft are around minus 15 to minus 20 degrees Celsius.

• Central United States: A closed contour appears, centered over the Midwest. This indicates a trough, or low-pressure system aloft. Heights dip to around 552 to 564 decameters. The close spacing of the contours shows stronger winds. Temperatures are cold aloft, with values around minus 25 degrees Celsius. This setup supports unsettled weather, including clouds and possibly storms.

• Eastern United States: Heights range from 540 to 560 decameters, with several isotherms running through the region. Winds are stronger in the Northeast, with wind barbs indicating speeds over 50 knots. Temperatures are between minus 20 and minus 15 degrees Celsius.

• Southern United States: Heights are higher, near 576 to 582 decameters, which means a thicker atmosphere. Temperatures are warmer compared to the north, around minus 10 to minus 15 degrees Celsius. Winds are weaker in this region.

Overall Pattern:

• A trough, or dip in the flow, is centered over the Midwest, bringing stronger winds and colder air.

• Ridges, or bulges of higher heights, are located over the western and southeastern U.S., associated with calmer and warmer weather aloft.

• Wind speeds are strongest in the Midwest and Northeast, where contours are packed tightly together.

 

Figure 8.1.2: Upper-Air Station Model

This diagram explains the elements of a station model, which is a compact way meteorologists record and display weather data at one location in the atmosphere.

Key parts shown in this example:

1. Air Temperature: Reported as minus 15 degrees Celsius. This is the current temperature of the air.

2. Dew Point Temperature: Reported as minus 24 degrees Celsius. The dew point is the temperature at which the air becomes saturated with water vapor. A lower dew point indicates drier air.

3. Height: Reported as 572, which equals 5,720 meters above sea level. Heights are written in tens of meters to save space.

4. Wind Data:

   • Wind Direction: Shown using a standard meteorological symbol called a wind barb. The orientation of the barb encodes the direction the wind is coming from.

   • Wind Speed: The same symbol also shows speed. Each long line on the barb equals 10 knots, each short line equals 5 knots, and a filled triangle equals 50 knots. In this example, the wind speed is 10 knots.

Figure 8.2.1: 500 millibar upper-air map for 0000 UTC on December 4, 2017

This image is a weather map at the 500 millibar pressure level, valid at 00Z on December 4, 2017. The map uses solid contour lines to show geopotential height in decameters, dashed lines to show temperature in 5-degree Celsius intervals, and symbols called wind barbs to show wind speed and direction.

Two major features are labeled: a trough and a ridge.

Explanation of terms and map features:

1. Geopotential Height: Values are written in decameters, where one decameter equals 10 meters. For example, a label of 570 corresponds to 5,700 meters above sea level. These heights show where the 500 millibar pressure surface is located in the atmosphere.

2. Trough: A trough is an elongated area of lower heights, which usually represents cooler air and unsettled weather conditions aloft. On this map, the trough is indicated over the western United States.

3. Ridge: A ridge is an elongated area of higher heights, which usually represents warmer air and calmer, more stable weather conditions aloft. On this map, the ridge is indicated over the eastern United States.

4. Isotherms: Dashed lines mark temperatures in 5-degree Celsius intervals. They show how cold or warm the air is at the 500 millibar level.

5. Wind Barbs: Symbols plotted at many stations encode wind direction and speed. Each long line represents 10 knots, each short line represents 5 knots, and a filled triangle represents 50 knots.

Overall Pattern on this map:

• A trough is positioned over the western part of the country, indicating cooler and stormier weather there.

• A ridge is positioned over the eastern part of the country, indicating warmer and calmer conditions there.

• The contrast between the trough and ridge shows how the jet stream is bending across the continent, producing active weather in some regions and calmer weather in others.

Figure 8.2.2: 500 millibar upper-air map for 1200 UTC on February 28, 2025

This is a weather map of the United States showing conditions in the middle of the atmosphere, at the 500 millibar pressure level. The valid time of the map is 12Z on February 28, 2025.

• 12Z means 12:00 Coordinated Universal Time, which is 7:00 a.m. Eastern Standard Time, 6:00 a.m. Central, 5:00 a.m. Mountain, and 4:00 a.m. Pacific.
• Heights are labeled in decameters, where one decameter equals 10 meters. For example, a contour labeled 570 means the height is 5,700 meters above sea level.

The map shows three main kinds of information:

1. Height contours (solid lines every 60 meters), which show the altitude where the 500 millibar pressure surface is located. Closer spacing means stronger winds and stronger weather systems.

2. Isotherms (dashed lines every 5 degrees Celsius), which show air temperature at this level of the atmosphere.

3. Wind barbs, drawn at many station points, which show wind direction and speed. Each long barb represents 10 knots, and each short barb represents 5 knots.

Regional Breakdown:

• Western United States: Heights are relatively high, around 570 to 576 decameters, which means the atmosphere is thicker here, often associated with fairer weather. Winds are generally lighter compared to the central U.S. Temperatures aloft are around minus 15 to minus 20 degrees Celsius.

• Central United States: A closed contour appears, centered over the Midwest. This indicates a trough, or low-pressure system aloft. Heights dip to around 552 to 564 decameters. The close spacing of the contours shows stronger winds. Temperatures are cold aloft, with values around minus 25 degrees Celsius. This setup supports unsettled weather, including clouds and possibly storms.

• Eastern United States: Heights range from 540 to 560 decameters, with several isotherms running through the region. Winds are stronger in the Northeast, with wind barbs indicating speeds over 50 knots. Temperatures are between minus 20 and minus 15 degrees Celsius.

• Southern United States: Heights are higher, near 576 to 582 decameters, which means a thicker atmosphere. Temperatures are warmer compared to the north, around minus 10 to minus 15 degrees Celsius. Winds are weaker in this region.

Overall Pattern:

• A trough, or dip in the flow, is centered over the Midwest, bringing stronger winds and colder air.

• Ridges, or bulges of higher heights, are located over the western and southeastern U.S., associated with calmer and warmer weather aloft.

• Wind speeds are strongest in the Midwest and Northeast, where contours are packed tightly together.

Figure 8.3.1: 300 millibar upper air map for 1200 UTC on February 28, 2025

This is a weather map of the United States at the 300 millibar pressure level, valid 12Z on February 28, 2025. The 300 millibar level is located about 9 to 10 kilometers above sea level, where the jet stream is usually found.

The map shows three main types of information:

1. Height Contours:

   • These lines connect locations where the 300 millibar pressure surface is at the same altitude.

   • Heights are expressed in decameters, which are tens of meters. For example, a label of 936 corresponds to 9,360 meters above sea level.

   • When the contours are close together, winds are stronger.

2. Isotachs:

   • These are lines of equal wind speed, drawn in intervals of 20 knots.

   • They outline areas where winds are especially fast.

   • Tight clustering of isotachs marks the position of the jet stream.

3. Wind Barbs:

   • Plotted at many locations to show wind data.

   • The barb indicates wind direction and speed. Each long line equals 10 knots, each short line equals 5 knots, and each filled triangle equals 50 knots.

Overall Pattern on this map:

• A strong jet stream is shown across the central United States, where isotachs are close together and wind speeds exceed 100 knots.

• Heights are lower in the northern part of the map and higher in the southern part, which is typical at this level of the atmosphere.

• This pattern indicates that weather systems below are being influenced by the fast-moving jet stream overhead.

Figure 8.3.2: Zonal vs. Meridional

This diagram compares two different patterns of atmospheric winds in the upper atmosphere. Both panels show airflow represented by arrows, with one side displaying a straighter pattern and the other side displaying a wavier pattern.

First Panel – Zonal Flow:

• The airflow is relatively straight, following a smooth path across the map.

• This is called zonal flow, meaning the jet stream has little waviness.

• Zonal flow is generally linked to more stable and consistent weather patterns.

Second Panel – Meridional Flow:

• The airflow curves into large waves, with alternating peaks and dips.

• This is called meridional flow, meaning the jet stream has significant waviness.

• Meridional flow is generally linked to more variable weather, with stronger contrasts between calm and stormy conditions.

Figure 8.4.1: Jet Streaks

This diagram illustrates the concepts of convergence and divergence in atmospheric winds. Arrows are used to represent airflow, and a dashed line labeled “axis” separates the two regions.

Convergence:

• Airflow is shown moving closer together, with streamlines narrowing toward the axis.

• This represents convergence, which means air is crowding together in one location.

• When this happens in the upper atmosphere, the air often has no choice but to sink, which can lead to calm, clear weather.

Divergence:

• Airflow is shown spreading apart, with streamlines moving away from the axis.

• This represents divergence, which means air is thinning out in one location.

• When this happens in the atmosphere, air from lower levels tends to rise, which is often linked with cloud formation and precipitation.

Axis:

• The dashed line marks the dividing boundary between the converging air and the diverging air.

Figure 8.4.2: 300 millibar upper air map for 1200 UTC on February 28, 2025

This diagram illustrates a jet streak, which is a localized region of especially fast winds within the jet stream.

Features shown in the diagram:

1. Wind Speed Contours:

   • Dashed lines mark isotachs, or lines of equal wind speed, labeled 30, 50, 70, and 90 knots.

   • These values increase toward the center, showing where the fastest winds are located.

2. Wind Barbs:

   • Symbols are plotted within and around the isotachs to indicate actual measured winds.

   • Each long line represents 10 knots, each short line represents 5 knots, and each filled triangle represents 50 knots.

   • Several of these wind barbs confirm that the highest speeds are concentrated near the center.

3. Jet Streak Label:

   • An arrow highlights the area inside the 90-knot isotach, identifying it as the jet streak.

Figure 8.4.3: 300 millibar upper air map for 1200 UTC on March 13, 2018

This map shows conditions in the upper atmosphere at the 300 millibar pressure level, valid at 12Z on March 13, 2018. The 300 millibar level is typically located around 9 to 10 kilometers above sea level and is where the jet stream is usually found.

Information displayed on the map:

1. Height Contours:

   • Solid lines connect points where the 300 millibar pressure surface is at the same altitude.

   • Heights are written in decameters, which are tens of meters. For example, a value of 930 means 9,300 meters above sea level.

   • Closer spacing of these contours indicates stronger winds and more dynamic weather patterns.

2. Isotachs (Wind Speed Lines):

   • Dashed lines show areas of equal wind speed, drawn at 20-knot intervals.

   • Stronger wind speeds are clustered where these isotachs are tightly grouped.

   • Maximum wind speeds on this map exceed 90 knots in parts of the flow, marking the location of a jet streak within the jet stream.

3. Wind Barbs:

   • Symbols plotted across the map show both wind direction and wind speed.

   • Each long line equals 10 knots, each short line equals 5 knots, and each filled triangle equals 50 knots.

   • Many plotted barbs confirm wind speeds over 100 knots in certain regions.

Overall pattern on this map:

• A strong jet stream arcs across the northern United States, with concentrated regions of faster winds above 90 knots.

• Lower heights appear in the northern portion of the map, while higher heights appear farther south, consistent with the usual slope of the 300 millibar surface.

• The presence of a jet streak suggests areas of enhanced upper-level convergence and divergence, which can influence rising or sinking motion and surface weather systems below.