**Andrew wrote:**
**I have been trying to draw isobars on unanalyzed upper air charts,**

Defintions:

Surface Charts

Isobars -A line of equal or constant pressure;

Upper Air Charts

I usually call them height contours, but also are called isoheight or isohypse.

Some definitons below, basically all mean the same thing.

Contour -A line of constant elevation above a certain reference

level on a previosuly deined surface,

Isoheight -A line of constant height.

Isohypse -A line of equal geopotential height

Other terms:

Interpolation -Estimating data values,

Isoline -A line of equal value.

Isopleth -A line of equal value.

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Are you using the following contour intervals when making your charts:

200, 250, 300 charts: contour interval of 120 meters (12dam)

500 mb charts: contour interval of 60 meters (6dam)

700, 850, 925 mb charts: contour interval of 30 meters (3dam)

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Upper Air Data Plots and Contour intervals on Constant Pressure Charts:

200 mb chart, the first digit is 0 or 1 and is not usd

and the last digit is 0 and is not used. Uses the 3 middle digits.

Example: 200=12000 meters

188, 200, 212, 224, 236, etc would be the height contours you would draw.

Also you can label them if you want like 12000, 12120, etc

250 mb chart, the first digit is 0 or 1 and is not used

and the last digit is 0 and is not used. Uses the 3 middle digits.

Example: 960=9960 meters 008=10080 meters, 012=10200 meters

960, 008, 020, 032, 044, etc would be the height contours you would draw.

Also, you can label them if you want like 9960, 10200, 10320, etc.

300 mb chart: the last digit is 0 and is not used. Uses first three digits.

Example: 912=9120 meters

888, 900. 912, 924, 936, etc, would be the height contours you would draw.

Also you can label the contours, 9000, 9120, etc,

500 mb chart: the last digit is 0 and is not used. Uses first three digits.

Example: 558=5580 meters

540, 546, 552, 558, 564, etc, would be the height contours you would draw.

Also you can label the contours, 5400, 5460, etc.

700mb chart: the first digit is 2 or a 3, and that is not used. uses last three digits.

Example: 997=2997 meters, 000=3000 meters

294 ,297, 300, 303, 306, etc, would be the height contours you would draw.

Also, you can label them 2970, 3000, etc.

For 850mb the first digit is a 1 and is not used. Uses last three digits.

Example: 550=1550 meters,

147, 150, 153, 156, 159 etc, would be the height contours you would draw.

Also, you can label them 1470. 1500, etc.

For 925 mb, uses only three digits.

Example: 780=780 meters, 810=810 meters

780 ,810, 840, 870, 900, etc, would be the height contours you would draw.

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Some tips:

-Always use a pencil and sketch lightly, when first making your charts

-Height contours (isoheights) should not branch or fork

-Height contours (isoheights should not end abruptly, except for the edge of the map,

-Height contours (isoheights) cannot touch or cross

-Interpolate between values to place the height contour (isoheight)

-Label your height contours (isoheights)

-Locate high and low values of geopotential heights.

-Locate ridges and troughs

-Smooth your height contours (isoheights)

Some hints in locating lows:

-Locate low values of geopotential heights

-Look for troughs, cyclonic (counterclockwise) circulation

for possible upper level lows

-Remember that wind flow (geostrophic) is nearly parallel

to the height contours (isoheights), think of yourself standing

with your back to the wind, lower heights (pressure) will be

on your left, Buys-Ballot's law, exception to this might be

some tall mountains.

Source: Various notes, I have collected. Hope this will help.

Mike