Weather Prediction Methods
Published 16:41 on 14 Feb 2025
Our second talk of the year on Weather Prediction Methods was given by Haslar Yacht Club members. Jonathan Clare (Commodore) and Brian Masters (Web Master) at the Hornet Sailing Club Fabrosa Room.
This being a two-part presentation the first section was given by Jonathan he described as the science behind the weather as best could be covered in a 35/45 minute session, he explained this is generally covered by a five-hour RYA Course,
Part 1
1st section of Jonathans presentation was described as the Science: -
Using a presentation screen, he described the basic interaction between the sun heating the land and sea on the earths surface at the equator globally releasing heat polewards by air and sea thus moving from low and high pressure as it travels to the poles. This is affected by other factors such as uneven land distribution, the earth rotating. The spinning earth causes the wind around depressions in the northern hemisphere to circulate anticlockwise and to circulate clockwise around high pressure. Another point discussed was the effect of the jet stream on the air/weather.
2nd section was described as Practical Theory: -
Jonathan went on to describe Synoptic charts, symbol notation. Method of measurement i.e. millibars. Isobar function I.e. like land contours joining places of same pressures also the closer together the higher the wind. Fronts warm and cold and their interaction.
There followed a section on Depressions, low and high fronts and what to expect ahead and behind, air circulation/temperatures and various cloud formations.
Next a description on Fog, the various types and how long they would last.
Jonathan talked about the weather forecast and what the various term meant and how they would affect your decision to sail i.e. Imminent in 6hrs, Soon within 6-12hr, Later within 12-24hrs. Also Wind, Sea state, Weather and Visibility the decision making process.
A more detailed description all of the above can be found in the RYA Weather Handbook.
Part 2
Brian Masters presentation was the practical part of weather information gathering and its place in the skippers decision to sail or not.
Brian started with what should be considered in making a decision,
Wind Direction, Boat Characteristics, Forecast, Sea State, Tide, Crew Experience, Leave and arrive criteria and lastly A Deadline can be a major decider.
Brian went on to show a couple of charts used in deciding weather a rally should go ahead or not; these take consideration of both sail and motorboat requirements.
He showed a chart similar to the Beaufort Scale with additional columns such as wind over tide, tide direction, forecast which he uses himself.
A discussion follows on where to check the latest weather forecast i.e:-
Localised info from weather buoys such as Chimet and Bramblemet, Met office, BBC weather forecasts, Maritime and Inshore forecasts among a few and Haslar Yacht web site has various links to online weather sites. Brian suggested checking the forecasts over a number of days to get a wider picture of weather patterns.
Next followed a description of some websites that Brian uses Meteo France, Windy, Windfinder, Windy.app being his first choice as it can be customised to compare various weather models to get an overall picture of weather trends. Some of these were free sites and others require a subscription an observation from an audience member was that some free sites info can be up to as much as 10/15 hours behind paid for data is better, so be careful.
The ECMWF was expressed as the preferred model for this location, different models are better for different areas.
There followed a Q&A session where someone suggested a Barometer is useful and another a Barograph can be useful to have on board. It was shown that the Bramblemet website displays pressure and temperature charts.
Brian suggested the BBC Week Ahead forecast at night is a good weather forecast.
The presentation ended there and was, in my opinion an interesting and enjoyable talk.
Graham Armitage
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Last updated 18:33 on 18 March 2025