Surface Analysis Chart – An article from NAV
CANADA
Recently, based on requests from our users, NAV CANADA began posting an earlier
version of the Meteorological Service of Canada’s (MSC) Surface Analysis Chart
on the NAV CANADA Aviation Weather web site (AWWS).
The chart is depicted using a polar stereographic projection, true at N60o and
provides coverage of Canada, the United States, Arctic regions and coastal
waters.
The main difference between this and the chart previously found on the AWWS, is
that the previous chart covered a much larger geographic area thereby giving a
much smaller view of Canada and the US.
The surface analysis chart is based on North American synoptic data,
supplemented by hourly reports as required and is essentially a preliminary
analysis that is produced as quickly as possible after observation times (0000,
0600, 1200 and 1800 UTC) - and is available approximately 2 hours earlier than
the previous chart.
The chart is primarily plotted and analyzed by the MSC supercomputer, although
some fields do benefit from human input by a MSC meteorologist.
Mean sea level pressure is depicted with isobars, lines of equal or constant
atmospheric pressure, analyzed at 4 hectopascal (hPa) intervals (1 hectopascal =
1 millibar). The isobars are one of the fields that are redrawn by a MSC
meteorologist, where improvements can be made.
The positions of synoptic high and low-pressure centres are marked with an ‘H’
and ‘L’ respectively, with central pressure values labeled in hPa. Unlike the
previous chart, the history of synoptic pressure centres is not given.
Frontal positions are analyzed and drawn by the MSC meteorologists. Satellite
pictures are of great use when determining frontal positions over oceans and
land areas where data is sparse.
It should be noted that although we (NAV CANADA) feel that the surface analysis
chart currently found on the AWWS is better than the previous one, we
acknowledge that it is still not an ideal chart for aviation purposes.
We receive this chart free of charge from the Meteorological Service of Canada
and hence, make it available to our customers. We do intend, when the financial
climate allows, to invest in an aviation specific surface analysis chart. In the
mean time, we will continue to make the current chart available.
The surface analysis chart can be found on the NAV CANADA Aviation Weather Web
Site at:
http://www.flightplanning.navcanada.ca.