iPhone AppSurface Data Details
Surface data is reported hourly from places like airports and automated observing platforms. The types of plots using surface data include a composite surface map, weather depiction for aviation, regional plots for the US, Canada, Mexico and Alaska. Contoured analyses of various parameters including temperature and pressure. Finaly, there are meteograms which are time cross-sections for individual cities. These data are updated hourly at around 30 minutes past the hour.
Composite Surface Map
Sample_surface_map
The composite surface map portrays as much information
about surface weather conditions as possible. This composite map contain
the following analyses:
Radar summary (color filled/stippled areas),
Surface data plot (composite station model),
Frontal locations (in various bold lines) and
Pressure contours (in thin blue lines).
Radar Summary Plot
The radar summary displays areas where precipitation is
falling based on returns from a weather radar. The intensity is based on color
where:
| Color | Intensity | Description |
| Blue | Light | light rain or snow |
| Cyan | Moderate | |
| Green | Heavy | light thunderstorms/moderate rain showers |
| Yellow | Very Heavy | moderate thunderstorms |
| Red | Intense | potential flooding rains/severe thunderstorms |
| Magenta | Extreme | flooding rains |
Surface Data Plot
The surface data plot gives the following information:
| Data | Description |
| temperature (F) | plotted upper left |
| present weather | symbol plotted center left (see below) |
| dewpoint (F) | plotted lower left |
| pressure (.1 mb-coded) | plotted upper right as last 3 digits (987=998.7mb, 024=1002.4mb) |
| cloud cover | center circle. white fill indicates % cloud coverage (see below) |
| winds | wind barb (see below) |
Weather Symbols
Frontal Location Plot
Frontal locations are denoted by bold lines in the following colors:
High and Low pressure systems are plotted with H and L and the associated pressure in millibars is displayed below the letter.
NOTE: Frontal data are only available every 3 hours so fronts may not exactly match the weather conditions. A label at the bottom left denotes what time the fronts are valid.
Pressure/Isobar Contours
The pressure contours (or isobars) are plotted as blue lines every 4 millibars and indicate positioning and extent of various pressure systems.
Surface Weather Depiction
Sample depiction
The weather depiction chart is a composite chart aimed at aviation. The data plotted are:
Flight rule depiction (color filled/hatched
areas),
Depiction data plot (composite model),
Frontal locations (in various bold lines)
Flight Rule Depiction
Shaded and hatched areas represent current flight rules:
| Plotted | Rules | Comments |
| gray solid | IFR | Ceiling < 1000 ft or Visibility < 3 miles |
| gray hatched | MVFR | Ceiling < 3000 ft or Visibility < 5 miles |
| clear/black | VFR | Not IFR or MVFR |
Depiction Data Plot
| Data | Description |
| cloud cover | center circle. white fill indicates % cloud coverage (see symbols above) |
| present weather | symbol left center (see symbols above) |
| cloud ceiling | below (in 100s feet) |
Frontal Location
The frontal analysis is also added to aid in determining general
weather conditions.
Fronts
Frontal Location
Plot of frontal locations for most of North America. Frontal locations are denoted by bold lines in the following colors:
High and Low pressure systems are plotted with H and L and the associated pressure in millibars is displayed below the letter.
Regional Data Plots
Sample regional plot
These are simple data plots for various regions of the
US, Canada and Mexico. The information plotted is using the surface station
plot.
Surface Data Plot
Contour Plots
US Temperature Contour
Contour plot of temperatures (F) for the contiguous US.
North America Temperature Contour
Contour plot of temperatures (F) for North America.
24 hour Temperature Change
Contour plot of the temperature change from current hour to the same hour
the previous day for the contiguous US. Areas below 0 represent where the
temperatures are currently colder and reflect the passage of a cold front.
Areas above 0 represent where the temperatures are warmer and often reflect
the passage of a warm front.
US Wind Chill Contour
Contour plot of wind chill temperatures (F) for the contiguous US. The wind
chill is the effective temperature of the skin from heat loss due to winds at
cold temperatures. Wind chill temperatures less than -20F are considered low,
temperatures less than -40F are extreme and temperatures less than -60F are
considered dangerous.
US Heat Index Contour
Contour plot of heat index temperatures (F) for the contiguous US. The heat
index is the effective temperature of the skin due to the inhibiting effect
of humidity to allow the body to cool through sweating and evaporation.
Heat index values of greater than 90F are considered high, index values
greater than 100F are extreme and index values greater than 110F are
considered dangerous.
US Pressure Contour
Contour plot of sea level pressure (mb) for the contiguous US. The maximum
and minimum values reflect the location of high and low pressure systems.
3 hour Pressure Change
Contour plot of the change in pressure from the current hour to 3 hours
previous for the contiguous US. This is a good indicator of the movement
and intensification of pressure systems. If the pressure change is negative
in the region of a low pressure system (see above chart), the low is
deepening. If the negative pressure change is out in front of the low
pressure system, it indicates movement. The location of the maximum pressure
drops indicate the possible direction of the low pressure system.
US Dewpoint Contour
Contour plot of the dewpoint temperature (F) for the contiguous US. The
dewpoint temperature indicates the amount of moisture (or humidity) in the
atmosphere. The amount of moisture in the atmosphere can affect how you feel
and is used in the heat index computation (see above). Dewpoints above 65
reflect humid conditions. Summer dewpoints can reach the low 80s. Dewpoints
above 50 mean that there is enough moisture in the atmosphere to generate
thunderstorms. The higher the dewpoint, the easier storms form and the
more potent they can become. An additional factor of low level wind
convergence is also needed to help storms form (see below). Intense storms
can form at dewpoints of 55 if the right conditions are in place including
high convergence values.
US Moisture Convergence
Contour plot of the convergence of surface winds weighted by the moisture
in the atmosphere represented by the surface specific humidity. Positive
areas represent where winds are converging and thus forcing upward motion.
Negative areas often reflect the presence of sinking motion. Since this is
weighted by the moisture, high values of convergence can often represent
areas where forced convection (possible thunderstorms) may occur.