10.4: Alternative Text Descriptions for Investigation 10

Figure 10.1.1: Cross-section of a warm front

A diagram showing a warm front where warm air gradually rises above cold air. The slope of warm air over cold air extends for hundreds of kilometers. Different cloud types form along the slope, including stratocumulus near the surface, stratus, nimbostratus producing rain, altostratus, cirrostratus, and cirrus at higher altitudes. Fog occurs near the ground ahead of the front, rain falls closer to the boundary, and snow occurs farther into the cold air mass. Altitudes from the ground up to twelve kilometers are labeled, with cloud positions marked.

Figure 10.1.2: Cross-section of a cold front

A diagram showing a cold front where dense cold air pushes beneath warm air, forcing it upward rapidly. The rising warm air forms large cumulonimbus clouds producing thunderstorms and heavy rain. Other clouds shown include altocumulus, cirrostratus, and cirrus at higher altitudes. The diagram marks air masses, the cold front boundary, wind flow, lightning, and the vertical extent of clouds up to twelve kilometers.

Figure 10.1.3: Meteogram for Kerrville, Texas

A meteogram from the Plymouth State Weather Center for KERV covering 0000Z to 2300Z on December 27, 2015.

• Temperature: Values begin near 70 degrees Fahrenheit and remain steady during the early hours. Around mid-morning, the temperature decreases quickly to the mid-40s and then continues a gradual decline into the upper 30s by late in the period.
• Reported weather: Periods of light precipitation occur in the morning and around midday.
• Precipitation amount: Accumulated precipitation reaches three-tenths of an inch by midday.
• Visibility: Mostly 10 miles, with reductions to 7 miles in the morning and briefly to 5 miles near the time of peak precipitation.
• Wind: Sustained winds generally between 10 and 20 knots. Gusts occur frequently, reaching as high as 27 knots.
• Cloud cover: Conditions vary between broken and overcast. Cloud bases are reported mainly between one thousand and five thousand feet, with some higher layers.

Overall, the meteogram indicates a frontal passage with a sharp temperature decrease, measurable precipitation, reduced visibility, gusty winds, and persistent cloud cover.

Figure 10.2.1: Weather Map at 1200 UTC on July 28, 2019

A surface weather analysis valid at 12Z on July 28, 2019, displaying isobars, pressure systems, frontal boundaries, precipitation radar, and surface station data across the contiguous United States.

• Pressure systems:

  • Multiple low-pressure centers are charted: one in the central Plains around 1009 millibars, another in the northern Plains near 1008 millibars, and several in the western U.S. ranging from 1006 to 1012 millibars.

  • High-pressure centers are located in the Southeast (around 1024–1025 millibars), the central Rockies (1020–1022 millibars), and the Northwest (1026–1028 millibars).

• Isobars: Contours drawn every 4 millibars outline pressure fields, with tighter spacing near the northern Plains indicating stronger gradients.

• Frontal boundaries:

  • Cold fronts extend through parts of the Midwest, the Plains, and the Southeast.

  • Warm fronts are present in the Northeast and northern Plains.

  • Stationary fronts are indicated in the central Rockies and along portions of the eastern U.S.

  • Several trough lines extend across the West and Southwest.

• Precipitation (radar reflectivity):

  • Moderate to heavy precipitation is concentrated in the northern Plains and Upper Midwest.

  • Lighter precipitation areas appear in the Southeast, Ohio Valley, and Gulf Coast.

  • Small scattered areas of precipitation are also shown in the Rockies and Southwest deserts.

• Station observations:

  • Each station model provides temperature, dew point, wind, sea-level pressure, pressure trend, and present weather.

  • Temperatures range mostly from the 60s to 80s Fahrenheit, with higher humidity in the central and eastern regions, as indicated by higher dew points.

  • Wind barbs show variable flow: southerly winds in the central U.S. around 15–25 knots near the low-pressure system, lighter winds elsewhere.

Overall interpretation:
The map depicts a broad low-pressure system dominating the central U.S., associated with fronts and widespread precipitation in the northern Plains. High-pressure systems in the Southeast and Northwest provide more stable conditions there. Tight pressure gradients in the Midwest suggest stronger winds and unsettled weather.

Figure 10.2.2: Weather Map at 0000 UTC on July 29, 2019

A surface weather analysis valid at 00Z on July 29, 2019, showing isobars, pressure systems, frontal boundaries, radar-based precipitation, and surface station reports across the contiguous United States.

• Pressure systems:

  • Multiple low-pressure centers are charted across the central U.S. and the West, with values near 1006 to 1009 millibars in the Plains and Midwest, and around 1008 to 1010 millibars in the Southwest.

  • High-pressure centers are located in the Southeast, Mid-Atlantic, and portions of the interior West, with pressures from 1015 to 1021 millibars.

• Isobars: Contours drawn every 4 millibars depict the pressure field, showing gradients around the central Plains low and the high-pressure ridge across the East.

• Frontal boundaries:

  • A cold front extends from the northern Plains southward into the central Plains.

  • Stationary fronts run across the central Rockies, Southwest, and southern Plains.

  • Warm fronts are indicated in parts of the Midwest and Northeast.

  • Trough lines extend through the West and the Gulf Coast.

• Precipitation (radar reflectivity):

  • Moderate to heavy precipitation is concentrated over the central and northern Plains and the Midwest, linked to low-pressure systems and frontal zones.

  • Scattered areas of lighter precipitation are noted in the Southeast, Gulf Coast, and parts of the Rockies and Southwest.

• Station data:

  • Observations include temperature, dew point, wind, pressure trends, and weather conditions.

  • Temperatures are generally in the 70s and 80s Fahrenheit across much of the country, with dew points showing high humidity in the central and eastern states.

  • Wind reports show stronger flow near the central low-pressure system, with gusts and sustained winds in the 15–25 knot range, lighter elsewhere.

Overall interpretation:
The map depicts a central U.S. low-pressure system driving unsettled weather, including widespread precipitation and stronger winds in the Midwest and Plains. High pressure over the East provides relatively more stable conditions, while scattered showers continue across the Gulf Coast and Southwest.

Figure 10.2.3: Meteogram for Bismarck, North Dakota.

A meteogram from the Plymouth State Weather Center for KBIS (Bismarck, North Dakota), valid from 0700Z on July 28, 2019, to 0700Z on July 29, 2019.

• Temperature: Air temperature begins near the upper 60s Fahrenheit in the early period, increases steadily through the afternoon to around the upper 80s, then decreases overnight to the mid-60s. Dew point temperatures begin near the mid-60s, decrease through the day into the mid-40s, then rise slightly late in the period.

• Weather reports: Symbols indicate light precipitation or weather activity between 0800Z and 1000Z.

• Precipitation amount: A small total accumulation of 0.02 inches occurs during the morning.

• Visibility: Generally 10 miles, reduced briefly to 6 miles in the morning, returning to 9–10 miles for the remainder of the period.

• Wind: Sustained winds shift during the day, with speeds varying around 10 to 20 knots. Gusts are stronger in the afternoon and evening, peaking between 25 and 30 knots.

• Cloud cover: Reported as variable. Cloud base heights range between 1,000 and 5,000 feet, with occasional mid-level layers up to around 10,000 feet.

• Pressure: Surface pressure starts near 1013 millibars early in the day, falls steadily to around 1010 millibars by evening, and then rises overnight back toward 1015 millibars.

Overall interpretation:
The meteogram shows a warm daytime period with decreasing humidity, gusty winds, and a brief episode of light precipitation in the morning. Conditions stabilize overnight with rising pressure and cooler temperatures.

Figure 10.3.3: Satellite image of the Eastern United States. 

A satellite image from July 29, 2019, at 16:51 UTC, showing the continental United States, Mexico, Central America, the Caribbean, and part of the Atlantic Ocean.

• Cloud cover:

  • Widespread cloud systems extend across the central U.S., with organized bands stretching over the Midwest and Plains.

  • Additional cloud clusters are present along the Gulf Coast, across Florida, and offshore in the Atlantic.

  • Dense cloud areas are visible over Mexico and parts of Central America, associated with convection and storms.

  • Scattered tropical systems are developing in the western Atlantic near the Bahamas and north of the Caribbean islands.

• Geographic coverage:

  • The image outlines state and national borders for the U.S., Mexico, and Caribbean islands.

  • The Gulf of Mexico, Atlantic Ocean, and eastern Pacific are included within the frame.

Overall interpretation:
The image depicts multiple weather systems, including frontal cloud bands across the U.S., convection over Mexico, and tropical disturbances in the Atlantic basin.

Figure 10.3.4: Weather Map at 1200 UTC on July 29, 2019

This map shows surface weather conditions for the United States, valid at 12Z on July 29, 2019.

Information displayed on the map:

1. Isobars (lines of pressure):

   • Solid lines connect points of equal atmospheric pressure, drawn every 4 millibars.

   • Lower pressures are marked with “L,” and higher pressures are marked with “H.”

   • Tighter spacing of isobars indicates stronger surface winds.

2. Fronts:

   • Symbols show the positions of surface weather fronts.

   • A cold front marks the leading edge of advancing cooler air.

   • A warm front marks the leading edge of advancing warmer air.

   • A stationary front marks where warm and cold air masses meet but neither is advancing.

   • An occluded front marks where a cold front has overtaken a warm front.

   • Boundaries can also include outflow boundaries from thunderstorms.

3. Radar data (precipitation):

   • Shaded areas represent radar reflectivity, showing where rain and storms are occurring.

   • Stronger shading indicates heavier precipitation.

   • On this map, a line of thunderstorms extends across parts of the central United States.

4. Station models:

   • Plotted at many locations, providing surface observations.

   • Each includes temperature, dew point, pressure, wind speed, wind direction, and current weather.

   • These observations help confirm the position of fronts and precipitation areas.

Overall pattern on this map:

• Multiple high and low pressure systems are spread across the country.

• A line of thunderstorms is associated with a frontal boundary in the central United States.

• High pressure areas are generally linked with calmer and clearer weather, while low pressure areas and fronts are linked with unsettled weather.

Figure 10.3.5: Upper-Air map at 1200 UTC on July 29, 2019

This map shows conditions at the 500 millibar pressure level, valid at 12Z on July 29, 2019. The 500 millibar level is located about 5 to 6 kilometers above sea level, often referred to as the “mid-levels” of the atmosphere.

Information displayed on the map:

1. Height Contours:

   • Solid lines connect points where the 500 millibar pressure surface is at the same altitude.

   • Values are written in decameters, or tens of meters. For example, a value of 588 means 5,880 meters above sea level.

   • When contours are close together, winds are stronger at this level.

2. Isotherms (Temperature Lines):

   • Dashed lines mark equal temperatures, drawn every 5 degrees Celsius.

   • Temperatures are written near plotted stations, mostly ranging from about minus 5 to minus 15 degrees Celsius across the U.S.

3. Station Plots:

   • Symbols show observed data at 500 millibars for specific locations.

   • Each includes temperature, dew point, wind speed, and wind direction.

Overall pattern on this map:

• A broad ridge of higher heights is present across much of the southern United States, suggesting warmer and more stable mid-level conditions.

• Lower heights are located across the northern U.S., consistent with cooler mid-level air.

• The temperature field shows relatively warmer air in the south and cooler air in the north, typical for summer.

• Winds are stronger where the contours are closer together, such as near the northern portion of the map.

Figure 10.3.6: Weather Map at 0000 UTC on July 30, 2019. 

This is a surface weather analysis map valid at 00Z on July 30, 2019. The map displays isobars, pressure systems, fronts, radar data, and station observations for the United States.

• Isobars: Solid lines connect locations of equal surface pressure, drawn every 4 millibars. Closer spacing indicates stronger winds.

• Pressure Systems: High pressure centers are marked with an “H,” indicating more stable surface conditions. Low pressure centers are marked with an “L,” indicating more unsettled surface conditions. Several high and low centers are spread across the country.

• Fronts: Symbols show surface boundaries between different air masses. Cold fronts, warm fronts, stationary fronts, and occluded fronts are indicated. Boundaries separate regions of contrasting temperature and humidity, where precipitation is more likely.

• Radar Data: Shaded areas represent radar reflectivity, identifying where precipitation is occurring. Higher reflectivity suggests heavier precipitation or thunderstorms. A broad band of precipitation stretches across the central and eastern United States, with localized clusters of storms in the Plains, Rockies, and Southeast.

• Station Models: Weather stations across the map display temperature, dew point, wind speed, wind direction, and current weather. These observations help confirm the location of fronts and precipitation.

Overall Pattern:

• High pressure systems are located over parts of the western and southeastern United States.

• Multiple low pressure systems and associated frontal boundaries are located across the central and northern United States.

• Radar shows precipitation bands and clusters of thunderstorms aligned with these frontal zones.