At the request of the Federal
Aviation Administration, the ADDS development team created a tool specifically
designed to show weather conditions for short-distance and low-altitude flights
that are common for the helicopter emergency medical services (HEMS)
community. HEMS operators are
extremely sensitive to changing and/or adverse weather conditions and need
weather information presented for non-weather experts quickly and
effectively. To meet this need,
the ADDS Flight Path Tool was adapted and simplified to display high resolution
grids of critical weather parameters, particularly cloud ceiling and surface
visibility. Using a highly interactive
and intuitive tool that focuses on small, localized regions, HEMS operators
gain critical weather awareness to make all their flights safe for crews and
patients.
This tutorial describes the technical aspects to use the software effectively.
The regulatory issues related to the use of this experimental software are not documented herein and must be
consulted (via the URL at the top of this document). The following topics are covered in subsections found below:
Weather products in the
HEMS tool include grids of
various weather parameters as well as National Weather Service (NWS) textual
weather observations and forecasts.
Some gridded products are three-dimensional including temperature,
relative humidity, winds, and icing.
Other gridded products are two-dimensional and may represent a
“composite” of a three-dimensional weather phenomenon (for instance the
convection product) or a surface weather variable such as horizontal
visibility. A full list and
description of each gridded product is given below.
Also, the tool displays relevant NWS textual weather
observations and forecasts needed for aviation.
These data are either points of observed weather, often at
airports, or regions of hazardous weather represented by two-dimensional
polygons. A full list of these
products is also found below and very specific configuration options for the
display of these data are found in a subsection below.
The next two
weather products depict the latest radar data with each product updating
approximately every 5 minutes.
There are roughly 150 individual WSR-88D (NEXRAD) radars in the United
States collecting data every 5 to 10 minutes.
These are collected centrally and stitched together by
various entities. Two radar
depictions are provided because each source is currently considered
experimental and each is derived from variations in the original source
data. One is labeled base reflectivity and will often show ground
clutter as well as weather features.
This product primarily captures the radar echo nearest the surface.
No attempt has been made to remove any non-weather
features. The alternative product
is the composite reflectivity that attempts to remove non weather
features from the data. Both radar
products show data with the best possible resolution of approximately 1 square
kilometer grid boxes. Due to
limitations of radar technology, blockage by mountains, and the spacing of
radars, there are weather events when radar data does not detect or show a
complete weather picture. The most
commonly seen example is very shallow clouds with light precipitation
like freezing drizzle or snow. An
excellent web site with more information concerning radar technology and limitations is found
at http://www.srh.noaa.gov/jetstream/remote/radarfaq.htm.
Weather overlays
in the HEMS tool include the
primary relevant aviation weather products from the National Weather Service.
At this time, the available overlays
are METARs, TAFs, PIREPs, AIRMETs, and SIGMETs.
These data are generally unscheduled in time so the application tries to refresh with
the latest data every few minutes.
All of the overlays have specific icons to represent the weather
conditions and moving your screen pointer over any icon causes a text box to
appear containing the original NWS text message.
An example is shown in the figure below in the AIRMETs
configuration section.
The wind barb
overlay is partly associated with the
3D grid of wind speed. Choosing
the wind speed product will automatically activate the wind barb overlay
revealing the direction of the wind.
Placing the cursor over a wind barb will produce a pop-up text message
of wind direction (degrees true not magnetic) and speed.
A reference for how to interpret the
wind barb presentation is found on the web
at http://weather.aero/metars/description2.php.
The density of the wind barbs matches
the wind speed data but would be illegible on the screen if all points were
shown simultaneously. Therefore,
the software decides which wind barbs to plot automatically, but users may use
the configure menu option to control the density manually (details for configure
options are found below).
Enabling specific
gridded weather products will also activate corresponding AIRMETs and/or
SIGMETs. For instance, choosing
either icing product will automatically activate the icing AIRMETs and SIGMETs.
Choosing flight category, ceiling, or
visibility automatically activates the IFR and mountain obscuration AIRMETs;
whereas choosing either radar or convection product automatically activates the
display of convective SIGMETs.
Once enabled, these overlays can be turned off manually using the
Overlay menu options, but they are programmed to return to this default
behavior once you switch to one of the listed choices.
The View menu option contains options related to zooming and
saving, deleting, and showing previously-created regions of interests.
Also found here are the optional toolbar
and optional gridded data inspector
(see the figure at the top of this document).
The toolbar is optional because most of
the zoom and pan operations are more simply accessed using the mouse.
To zoom in, simply double-click with
the left mouse button over the spot you wish to zoom into on the primary
display panel. Consecutive zoom
operations continue to zoom until the software can no longer display anything
reasonable. To zoom out, you can
single-click with the right mouse button.
To keep the same zoom level but shift/pan the map in a specific
direction, simply left-click and drag (while continuing to depress the mouse
button) the map in the direction you desire.
Letting go of the mouse button will stop the pan
operation. The toolbar provides
alternatives to these default mouse actions, and, if you have the toolbar
enabled, the mouse zoom/pan operations automatically become disabled
and will not function until the toolbar is hidden again.
The time controller
interface (see figure) allows users to alter the time of the gridded
weather products. Overlayed data
such as METARs, PIREPs, TAFs, AIRMETs, and SIGMETs are not affected by
changes to the chosen time, they are always
the most current data possible.
The current time is indicated by the red vertical line and the
corresponding UTC and local times are shown above the red line.
The selected time of the gridded
weather product is indicated by the orange square.
The data displayed will be the nearest match in time to the
selection and the actual valid time of the data can be found in the lower-left
corner of the primary display panel.
When in doubt of the valid time, be certain to look here for the actual
valid time of the displayed product(s). Users
may click (using the left mouse button) and drag (while depressing the same
mouse button) this orange square backwards or forwards to select a time in the
past or future. Again, it is worth
emphasizing that only the gridded weather product is changed, not the overlays.
METARs are observations
of surface weather including temperature, winds, moisture,
visibility, ceiling, present weather obstructions (like rain/snow/fog),
altimeter setting and more. These
are NWS textual messages in their original form.
The current application conveys some of the most important
aviation information as an icon for sky coverage and flight category (VFR,
MVFR, IFR, LIFR) whereas the other parameters are available for viewing by this
configuration menu option (see figure).
By default, the pop-up text when the screen cursor passes over a
reporting site reveals the siteÕs ceiling and visibility observation along with
the full original text.
Furthermore, to prevent excessive clutter on the screen, only a minimal
set of data are displayed for all sites.
As soon as the user requests other data (temperature for instance), the
tool will reduce the number of stations shown to keep from completely obscuring
other stationsÕ data. Zoom in and
out operations will result in a de-clutter technique that may remove some sites
and/or reveal others. If the
reporting site you seek is not shown, either zoom closer to that site or use
this configuration dialog box to enable more (or fewer) reporting sites.
PIREPs are pilot
reports of weather, clouds,
icing, turbulence, and other phenomenon that are received by various FAA
services like radio communications between the cockpit and ground
controllers. A small fraction of
these reports arrive via automated reporting systems.
Similar to METARs, these data are represented in this
application by icons (see figure) for icing, turbulence, and cloud coverage.
Placing the screen cursor over one of
the icons produces the full text message as relayed by the NWS.
Abbreviations found in these messages
are standard practice and users are referred to the ADDS web site to learn more
(http://weather.aero/pireps/).
The altitudes displayed for PIREPs are
above mean sea-level, not above ground level (unless specifically stated in the
text, which is uncommon). Users
can control the vertical altitude range of PIREPs that are displayed by using
their mouse to drag either top and/or bottom orange rectangles in the
configuration dialog boxÕs altitude slider bar.
PIREPs either above the top or below the bottom of these
orange rectangles are excluded from the display.
AIRMETs are NWS
advisories for possible adverse
weather conditions including icing, turbulence, IFR, and mountain
obscuration. SIGMETs are significant
weather advisories for known or forecast hazardous
icing, turbulence, or convection.
Each type of advisory may be shown or hidden.
As mentioned in the section about weather products,
activating certain gridded weather products automatically enables their
corresponding advisory product(s) by default.
If these items are not desired, they must be manually hidden
from the display after each switch of the gridded weather product.
AIR/SIGMETs are generally issued every
6 hours unless amendments are needed and displayed in the tool within a few
minutes of receipt by ADDS servers.
As with other overlays, a small icon is placed at the center of this
overlay product and when the screen cursor passes over this icon, the region
covered by the AIR/SIGMET is highlighted graphically and the full NWS text
message is shown on the screen.
Depending on the zoom level of the application, it can be difficult to
see the full extent of this overlay product so users are advised to zoom out if
the highlighted polygon isn’t fully apparent.
As discussed
in the weather overlays section above, the wind barbs are directly
tied to the gridded three-dimensional wind product.
A number of options shown in the configuration dialog box
are not applicable at this time.
The only effective option found here is the wind barb density.
Depending on the domain size displayed
in the primary display panel, the density of wind barb icons may need to be
adjusted for personal preference.
The wind barb overlay option is disabled for certain variables since
wind barbs are a three-dimensional product and it isnÕt logical to assume a specific
vertical level associated with products that are entirely two-dimensional.
For this reason, wind barbs are only
available as an overlay option when the gridded weather product is either
temperature, humidity, icing, or wind speed.
Furthermore, the level of wind barbs displayed matches the
underlying gridded variable.