# How does a constant pressure chart affect your preflight planning?

Would you choose a route or altitude based on the information in a constant pressure chart? How does a constant pressure chart help a pilot plan his or her flight?

As others wrote, I don't think in and of itself the constant pressure chart will help with a go or no-go decision by itself. However, I do believe it would help to get the big picture of what's happening with the weather; fronts, etc. Knowing the big weather picture is more important depending on what kind of flying you do. The constant pressure chart can help with that. Regarding choosing a flight level or altitude to fly in I would use winds aloft, airspace charts like a sectional, anticipation of ATC given altitudes in the area you plan to fly in, etc. Like many others have said: with regards to weather the more you know the better off your preflight planning will be and the constant pressure chart adds to your knowledge of the weather.

A constant pressure chart by itself doesn't provide any useful data for flight planning.

As it shows a height of a given pressure level, you can make some assumptions about air mass temperature and pressure systems. You could also determine wind velocity and direction to some accuracy.

However most of the information available is usually shown in a pre-computed and pilot-friendly way in other charts, such as sw-charts and wind/pressure charts.

• A constant pressure chart by itself doesn't provide any useful data for flight planning If that is the case, then why are they produced? Crews piloting aircraft in the flight levels may find them useful for flight planning since they are flying on a constant pressure surface such as those depicted in these constant pressure charts. – J Walters Feb 20 '16 at 18:50
• Maybe the main target group is some other than aviation or flight planning? – Sami Feb 20 '16 at 18:58
• I do think the main target group would be the meteorologists that produce the charts, but that does not mean that they are not useful to pilots for flight planning. I have used them frequently myself, even for flights under the flight levels; for example, the 500 mb chart shows winds that primarily effect storm movement. – J Walters Feb 20 '16 at 19:09
• Never the less, as an airline pilot, I've never seen or used one in flight planning. – Sami Feb 20 '16 at 19:56
• @Sami the wind at the levels those charts are produced for are generally geostrophic, so the wind barbs are parallel to the height contours. e.g. if all you have are the height contours then you can infer almost everything about the wind direction and make judgments about where it is fast and where it is slow. As an additional utility you are going to burn slightly more fuel flying from low heights to high heights and save a bit of fuel going the other way. You might not directly use this, but whatever software your dispatchers use might take it into account. – casey Feb 20 '16 at 21:46