Upper Air Data Details

Upper air data is taken from balloons which measure upper air conditions over a particular location. The plots of data include plots on common mandatory and height levels, contours of various upper air parameters and a set of sounding plots for all US sites. These data update once every 12 hours at around 9:45 EST.

Meteorology uses pressure as the vertical coordinate and not height. This works out better for thermodynamic computations that are done on a regular basis. Pressure decreases in the atmosphere exponentially as height increases reaching 0 pressure in space. The standard unit of pressure is millibars (mb or hectopascals-hPa) of which sea level is around 1015 mb. Standard pressure levels and approximate heights:

Mandatory Level Plots

Sample 300 mb plot

850 mb Map
700 mb Map
500 mb Map
This is a composite upper air plot for the 850, 700, and 500 mb level. The plot contains a individual station reports for that level along with contours of height (bold light gray lines) every 30 meters (60 at 500 mb) and temperature (yellow dashed lines) every 5 degrees Celsius.

Sample 500 mb plot

300 mb Map
200 mb Map
This is a composite upper air plot for the 300 and 200 mb level. The plot contains a individual station reports for that level along with contours of height (bold light gray lines) every 120 meters and wind speed (blue dashed lines) every 20 knots at 10,30,50,70,... knots. Wind speed areas between 70 and 110 knots are shaded in stippled dark blue. Wind areas between 110 and 150 knots are shaded in solid blue.  Winds greater than 150 knots are once again shaded in stippled dark blue.

Upper Air Data Plot

The upper air data plot gives the following information:

Current Mandatory Level Plots

Constant Height Plots

Sample 24,000 ft plot

3000 ft Plot
6000 ft Plot
9000 ft Plot
12000 ft Plot
18000 ft Plot
24000 ft Plot
30000 ft Plot
36000 ft Plot
This is a set of upper air charts for various flight levels primarily for aviation concerns. The plots include plotted data, temperatures are contoured in yellow, and wind speeds are contoured in blue. Increasing speeds are highlighted in varying shades of blue. The lowest speeds are not shaded. Above a certain level, the winds are shaded in alternating dark blue stippled and solid blue on 20 knot levels.  The lowest level of shading is 30 knots for 3, 6, 9 and 12 thousand feet. It is 50 knots at 18 and 24 thousand feet and 70 knots at 30 and 36 thousand feet. The data plotted include:

Current Constant Height Plots

Hemispheric Plots

Northern Hemisphere 500 mb Plot
Southern Hemisphere 500 mb Plot
Sample 500 mb plot

These two maps are composite 500 mb height and sea level pressure maps for the entire northern and southern hemisphere. The color contours are the 500 mb height field which shows middle level air flow around the mid-latitudes. Air follows the contours and the tighter the packing, the faster the flow. Where air is moving from north to south, temperatures are generally below normal. Where air is moving south to north, temperatures are generally above normal. The sea level pressure field is plotted in black lines. High and low pressure systems can be determined from the locations of Hs and Ls on the plot. Low pressure systems usually have some kind of precipitation associated with them whether it be rain or snow.

Northern Hemisphere 850 mb Plot
Sample 850 mb plot

This plot is comprised of 850 mb temperatures and 850 mb heights. The color contours are 850 temperatures in C with an interval of 2C. These are the temperatures at roughly the 5000 ft level and can be used to determine maximum temperatures.

The line contours are 850 mb heights at an interval of 60m. This shows the location of high and low pressure systems at the 5000 ft level and the contours can be used to describe the flow at that level.

Northern Hemisphere 300 mb Plot
Sample 300 mb plot

This plot is comprised of 300 mb wind speeds and 300 mb heights.  The color contours are 300 mb wind speeds. The maximum speeds at this level denote the location of jet streams and/or cores.  A jet core is a discontinuous area of strong winds often greater than 100 knots.

The line contours are 300 mb heights contoured at 120m. This shows the direction of winds at this level.

Current Hemispheric Plots

Contour Plots

500 mb Height Contour
This is a contour plot of 500 mb height in meters with a interval of 60 meters. The 500 mb level is often referred to as the steering level as most weather systems and precipitation follow the winds at this level. The winds follow the height contours and generally run from 30 to 100 knots. The speeds can be roughly estimated from the 300 mb winds as roughly 2/3rds their magnitude. This level averages around 18,000 feet above sea level and is roughly half-way up through the weather producing part of the atmosphere called the troposphere.
Current Plot

850 mb Temperature Contour
This is a contour plot of temperature in Celsius at the 850 mb level. The interval is 5 degrees. The temperature field shows where warm and cold air are located. Temperatures at this level do not show the diurnal temperature changes from morning low to afternoon high we see at the earth's surface. The 850 temperature is also a decent indicator of the type of precipitation. Since most precipitation forms at 5000 feet or above, a temperature of freezing (0 Celsius) or below would indicate snow whereas a temperature above freezing would indicate rain.
Current Plot

1000-500 mb Thickness Contour
This is contour plot of thickness in meters with an interval of 60 meters. Thickness is a measure of mean temperature in a layer of the atmosphere and ranges from 4900m in cold wintertime atmospheres to 5900m in warm summertime atmospheres. The 5400 meter line is often used as an indicator of the rain-snow line.
Current Plot

300 mb Wind Speeds
This is a contour plot of 300 mb wind speeds in knots. The contour interval is 10 knots. This level is referred to as the jet stream level. Areas of strong winds at this level (winds > 100 knots or 115 mph), commonly referred to as jets, indicate areas of high atmospheric energy. These are created by strong temperature contrasts in the lower and middle tropopause and reflect areas of potential storm development. A strong jet (winds > 130 knots) can indicate the potential for the development of a strong low pressure system especially when if moves over the Rocky mountains and into the Plains states. A strong jet hitting the west coast can indicate the existence of a strong precipitation producing system.
Current Plot

300 mb Wind Streamlines

This is a streamline plot of 300 mb winds. The lines follow the direction of the wind. Small arrows denote actual direction.  The streamlines are collored based on their speed.

Current Plot

Precipitable Water Contour
This is a contour plot of precipitable water in inches. The contour interval is .2 inches. Precipitatable water reflects the amount of water contained in a vertical column above the surface if it were all precipitated out. This is a good indicator of how much rain or snow might fall as a result of a thunderstorm or low pressure system.
Current Plot

Lifted Index Stability Contour
This is a contour plot of lifted index with a contour interval of 2 degrees Celsius. The LI field shows instability in the atmosphere by lifting a parcel of air from the surface to 500 mb and comparing its temperature to that of the environment. Where LIs are less than 0, thunderstorms are possible. The lower the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms could become. Values of -4 or lower indicate areas where severe thunderstorms are possible. Values > 10 indicate areas of stable weather where skies are generally clear.
Current Plot

Total Totals Index Stability Contour
This is a contour plot of total totals index with a contour interval of 2. The TT field shows instability in the atmosphere based on the lapse rate from 850 to 500 mb plus dewpoint at 850 mb. Where TTs are greater than 45, thunderstorms are possible. The higher the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms could become. Values of 52 or higher indicate areas where severe thunderstorms are possible. Values < 40 indicate areas of stable weather where skies are generally clear.
Current Plot

K Index Stability Contour
This is a contour plot of K index with a contour interval of 4. The KI field shows instability in the atmosphere as it relates to the development of air mass thunderstorms. It is based on the 850 to 500 mb lapse rate plus 850 mb dewpoint minus the 700 mb dewpoint depression. Strong Springtime thunderstorms often require dry air at mid levels to cap the convection. On the other hand, summer air mass thunderstorms need a very moist atmosphere at mid levels to prevent evaporation through entrainment. Where KIs are greater than 35, air mass thunderstorms are likely.  the higher the number, the higher the probability. Values < 10 indicate areas of stable weather where skies are generally clear.
Current Plot

CAPE Contour
This is a contour plot of CAPE or Convective Available Potential Energy. CAPE represents the amount of energy a parcel might have if it were lifted. Often this reflects the strength of updrafts within a thunderstorm. CAPE values of greater than 2000 represent enough energy to produce thunderstorms. A value greater than 3000 represents enough energy to produce strong thunderstorms. Values < 1000 denote a reletively stable atmosphere.
Current Plot

Helicity Contour
This is a contour plot of helicity which is the amount of storm relative rotation/shear in the atmosphere. Helicity is used to indicate where rotation/shear is high enough to allow thunderstorms to organize into severe or supercell storms. In the lack of helicity, storms develop vertically and the precipitation will snuff out the updraft killing the thunderstorm. Severe storms need helicity to maintain an organized structure allowing hte storm to develop to severe limits. A value of 400-500 is often needed to produce severe storms.  Often this is used in conjunction with CAPE to determine severe storm location.
Current Plot