11.4: Alternative Text Descriptions for Investigation 11

Figure 11.1.1: Surface Weather Conditions

Overview of Map Features:

The map includes:

• Surface observations using standard station models (showing temperature, dew point, wind, pressure trend, and sky cover).
• Radar reflectivity data overlaid using color-coded shading for areas of precipitation.
• Isobars drawn every 4 millibars
• Fronts include cold fronts, warm fronts, stationary fronts, and occluded fronts.
• High (H) and low (L) pressure centers are marked.

Weather Highlights:

1. Precipitation and Radar Reflectivity:

• A band of moderate to heavy precipitation stretches from the central Plains through the Midwest and into the Northeast.
• The highest radar reflectivity values, indicating the most intense rainfall or storms, are located over parts of Illinois, Indiana, and the Northeast U.S.
• Additional scattered showers and thunderstorms are seen across the Southwest, southern Plains, and Gulf Coast.

2. Frontal Systems:

• A cold front extends from the Great Lakes southwestward into Oklahoma and Texas.
• A warm front is draped across the Mid-Atlantic region.
• Several stationary and occluded fronts are positioned in the Midwest and South.

3. Pressure Systems:

• Multiple low-pressure centers are located across the Midwest, Northeast, and southern U.S., with central pressures ranging from 1004 to 1008 millibars.
• High-pressure systems are centered over the western U.S. (1022 mb), Gulf of Mexico (1014 mb), and Atlantic Ocean.

4. Surface Observations:

• Station models report temperatures ranging from the 40s in the northern Rockies to the 90s in the southern Plains and Southeast.
• Wind barbs show wind directions and speeds at each station; stronger winds are observed near frontal boundaries.
• Many stations show overcast or cloudy skies, particularly in areas with precipitation.

Figure 11.2.1: A Stüve Diagram over Topeka, Kansas. 

This image shows a Skew-T log-P thermodynamic diagram generated by the University of Wyoming for Topeka, Kansas (station 72456), valid at 12Z (7:00 AM Central Daylight Time) on May 28, 2019. The diagram provides a vertical profile of atmospheric temperature, humidity, and stability indicators used for evaluating the potential for cloud formation, convection, and severe weather.

Plotted Sounding Data:

• A jagged line on the right represents the environmental temperature profile (observed air temperature from the surface to the upper atmosphere).
• A second jagged line to the left of the temperature profile shows dew point temperature, indicating atmospheric moisture.
• A smooth line indicates the parcel path, representing how a parcel of air would change temperature if lifted from the surface.

Thermodynamic Indices:

• CAPE (Convective Available Potential Energy): 427.7 joules per kilogram, suggesting modest instability.
• CIN (Convective Inhibition): -440.0 J/kg, indicating a strong cap that resists initial parcel lifting.
• LCL (Lifting Condensation Level): 290.2 millibars, showing the height at which a lifted parcel becomes saturated.
• LFC (Level of Free Convection): 634.5 millibars, where the parcel becomes warmer than the surrounding air.
• EL (Equilibrium Level): 249.6 millibars, where the rising parcel stops accelerating upward.
• PWAT (Precipitable Water): 33.80 millimeters, a measure of total atmospheric moisture.
• Other indices include lifted index, SWEAT index, and bulk shear values.

Figure 11.2.2: Severe Thunderstorm Categorical Outlook

The map shows forecasted areas of thunderstorm activity and severe weather risk across the contiguous United States. Risk categories range from general (non-severe) thunderstorms to high-end severe thunderstorm outbreaks.

Geographic Scope:

The map includes all 48 contiguous U.S. states. Individual states are outlined, and risk areas are superimposed as enclosed shapes. A star symbol marks a specific location within a region of elevated severe risk, centered in the eastern part of Nebraska and western Iowa.

Severe Weather Risk Categories from lowest to highest risk, the outlook areas include:

1. TSTM (Thunderstorms):

• Broad, lightly shaded area covering much of the western U.S., parts of the Southeast, and southern Texas.
• Represents areas where general thunderstorms are expected, but no severe weather is forecast.

2. MRGL (Marginal Risk):

• A larger area inside the thunderstorm region covers parts of the Southwest, Southern Plains, and Midwest.
• Indicates isolated severe thunderstorms are possible but limited in duration and/or intensity.

3. SLGT (Slight Risk):

• Covers an arc from eastern Oklahoma and Texas northeast through the Ohio Valley and into the Mid-Atlantic.
• Indicates scattered severe storms possible, with isolated intense storms.

4. ENH (Enhanced Risk):

• Located in the central parts of Kansas, Missouri, and Illinois.
• Indicates numerous severe storms possible, some of which may be intense.

5. MDT (Moderate Risk):

• A smaller, more focused region inside the Enhanced Risk area, located in southeastern Nebraska and southwestern Iowa.
• Suggests widespread severe storms are likely, including long-lived and intense storms.

Figure 11.2.3: Severe Weather Reports

• The map outlines the United States with state boundaries shown.
• Severe weather reports are plotted as symbols across multiple states.
• A few symbols are marked with centers indicating particularly intense events:
• A center on a wind report symbol means wind gusts of 65 knots or higher
• A center on a hail symbol indicates hail 2 inches in diameter or greater

Report Summary:

• Total reports: 276
• Tornado reports: 26
• Wind reports: 100 (including 1 significant wind event)
• Hail reports: 150 (including 28 significant hail events)

Geographic Distribution:

• Tornado and large hail reports are heavily clustered in parts of the central U.S., especially across eastern Kansas, Missouri, and western Illinois.
• Wind damage reports are more widespread, extending from the southern Plains through the Midwest and into the Northeast.
• Additional scattered reports appear in the Mid-Atlantic, Southeast, and southern Great Plains, with isolated events reaching into Oklahoma, Texas, and Virginia.

Figure 11.3.1: Tornado Occurrence 

This image is a dual-axis line and bar graph from the National Weather Service Storm Prediction Center, showing the daily and cumulative number of U.S. tornadoes reported in 2019, compared to the historical average trend for the years 2005 through 2015.

Axes and Labels:

• The horizontal axis at the bottom represents the calendar year from January through December.
• The left vertical axis shows the daily tornado count, ranging from 0 to 80.
• The right vertical axis shows the running total of tornadoes (annual count), ranging from 0 to 1800.

Lines and Bars:

• A line shows the average annual trend in tornado counts from 2005 to 2015. This line gradually increases throughout the year, ending at 1402 tornadoes on December 31.
• Another line shows the 2019 cumulative tornado count, which rises more steeply than the average and ends at 1676 tornadoes, surpassing the historical trend by over 270 tornadoes.
• Vertical bars represent the average number of tornadoes per day (from 2005 to 2015).
• Other vertical bars show the actual number of tornadoes reported per day in 2019. These vary widely, with significant spikes in April, May, and early June, some reaching 50 to 70 tornadoes in a single day.

Figure 11.3.2: Severe Weather Reports

This map shows filtered storm reports received on October 31, 2018, across the southeastern United States. It includes preliminary data for tornadoes, damaging wind events, and large hail.

Geographic Coverage:

• The map shows the contiguous United States with state borders outlined.
• The majority of storm reports are concentrated in the Gulf Coast region, especially across Louisiana, Mississippi, and Alabama, with scattered reports extending into Georgia and parts of Florida.

Storm Report Totals:

• Tornado reports: 63
• Wind reports: 198 total, including 1 high wind report (65 knots or greater)
• Hail reports: 0
• Total storm reports: 261
• A small asterisk on any dot indicates a significant event:
• For wind, that means gusts of 65 knots (75 mph) or greater.
• For hail, that would mean 2 inches in diameter or larger.

Clustering and Patterns:

• A notable concentration of dots is visible across southern Mississippi and Alabama, where multiple tornadoes and reports of wind damage have been filed.
• A dense cluster of wind reports is present along the central Gulf Coast, likely due to a line of severe thunderstorms.
• No hail reports are shown for this day.