Producing your own synoptic chart
Without a prepared forecast synoptic chart, any attempt at
DIY forecasting for more than a few hours ahead needs to
begin with the preparation of your own forecast synopsis.
Obviously this is unlikely to be as accurate as one prepared
by a professional meteorologist with high-tech resources at
his disposal, but it can still be a valuable guide.
Ideally, you need to be able to visualise the swirling
mass of the atmosphere - it may help if you can imagine the
ripples and eddies created if you stir a basin of water -
but there are a few general rules of thumb which can help.
Depressions, around us and Europe, usually...
- Move in an easterly or north-easterly direction,
parallel to the line of the isobars in the warm sector.
- If a depression has been moving in a particular
direction for 12 hours, it is likely to go doing so for
another 12 hours unless it meets land or a large
anticyclone.
- Lows slow down and fill up when they meet land, or
when their fronts occlude.
- If the barometer is rising more quickly behind a
depression then it fell when the depression approached,
the depression is probably filling and slowing down (and
vice versa.)
- When a large depression occludes, a smaller 'secondary'
depression often develops somewhere along the trailing
cold front.
- If two similar lows are close to each other they may
merge to form a complex low, with two centres that
rotate anticlockwise around each other.
Fronts
- Each section of a front moves at right angles to the
line reprenting the front itself.
- Each section of the cold front moves at about the
speed of the geostrophic wind behind it. Warm fronts
typically move about 30% slower.
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