Plotting isobars on a weather map?

Question

I have to plot isobars on a weather map for meteorology class but I have no clue how to do it. A friend of mine told me that you start a new line every .08 millibars...?

Help please

Hmmm... my recorded pressure usually falls in the 30.0- region. We plotted ALT pressure..

Ahhh, I am an idiot. I don't know why I said millibars. -_- Sorry for the confusion and thanks for the great responses! They were all very helpful! :)

Answer 1

If your numbers are like 30.12 and all that, that isn't millibars. That unit of pressure is inHg (inches of mercury). In that case, you could plot it every 0.08. That would be about like plotting every 3 millibars or so.

Here's how you do it. The point of "isoplething" (drawing lines like you're being asked to do) is to draw the lines so that all the values higher than that line are on one side of it, and all the lower values are on the other side.

For example. Your 30.04 line. All the pressures higher than that should be on one side and all the pressures lower than that should be on the other. You'd then draw another line for 29.96. Ideally, everything between those two lines should be between 29.96 and 30.04.

It's just like the colored temperature maps you see where red is hot and blue is cold, only you're just drawing the lines and not filling in the color.

Answer 2

If you are in meteorology class, it surprises me that you are not using hectoPascals. Millibars were the unit in the centimetre/gram metric system. In the world standard system which uses metres and kilograms, the unit is the hectoPascal. The actual figure is the same as millibars so it was unnecessary to change all the altimeters in aeroplanes. The only people who use inches of mercury are the general public in the USA, no meteorologist does.

Look at the chart. The observations will be plotted on it with pressures in the upper right corner. Below that there could be pressure differences such as +07 or -06. Look at the satellite picture and the previous chart. Determine where your fronts are. The previous chart, the satellite image and the isallobars (pressure differences) will show you.(Pressures fall as a front approaches and rise behind it). Plot your fronts, first estimate anyway.

Look at the range of pressures on the chart. Choose one that is near the middle 1000hPa is likely. Draw the isobar so that all pressures lower than that are to one side and all pressures higher are on the other side. If the isobar crosses the front don't forget the sharp change of direction. Draw other isobars at 4hPa intervals and then, if you need them, draw the 2hPa isobars. It takes practice but you can do it.

I'm an operational meteorologist and draw charts every day.

Answer 3

When you look at weather maps for the same day but from different origins, you'll notice that some will have a H or a L where the other one has not. That is the art of the meteorologist who has to read data samplings and draw something that makes sense. I don't think there are special rules other than the feeling and experience of the meteorologist.

Answer 4

Normally they are plotted every 4 mb. Try to start with 1000 mb interpolating between stations plots to the best of your ability. Station plots should have surface pressure plotted in the upper right hand corner. These will look like this:

if it is written as 410, it is 1041.0 mb
if it is written as103, it is 1010.3 mb
if it is written as 987, it is 998.7 mb
if it is written as 872, it is 987.2 mb

After 1000 mb look for 1004 mb then 1008 mb and so on.

I hope this helps

Answer 5

You start a new line at any number in millibars that you'd like. It doesn't matter.