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This section contains a number of self-test questions on the material in Chapter 5 Weather. For ease of use / reference, the questions are listed under the section heading where you (should have) learned to answer them! Click on the heading to go to that section.
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1 What do "veering" and "backing" mean?
2 What do "imminent", "soon" and "later" mean?
3 What do "moderate" and "poor" visibility mean?
4 Roughly how many knots is a Force 5 wind?
5 You listen to a forecast, deciding whether to take a small boat out that morning. The forecast is Force 2 to 3, increasing Force 6 to 7 "later". What other information do you need to know when to expect the stronger wind?
6 You look at the notice board at a marina, and see a five-day forecast. You also see that you are now on day 4 of the forecast. Do you use this information? What do you do?
1 On a bright sunny day with a brisk wind from the north, you find a sheltered cove with a good beach on the south-facing coast of Lyme Bay. Paddling in flat calm conditions, with the odd little gust of wind, what would you expect conditions to be like further off-shore? What advice would you give to an inexperienced windsurfer setting out from the beach?
2 You are sailing from Falmouth to Fowey in 16 to 18 knots of wind and it seems to be picking up slightly if anything - anything stronger and you would want to reef the sails. You are about 2 miles away from Dodman Point, a prominent headland. What do you do?
3 What's the best indication of the wind at sea, when you are in the flat calm of a sheltered harbour early in the morning?
4 You are beating up-wind parallel to the coast, in a light breeze, at 9 a.m. on a fine summer day. What change in wind direction might you expect in the next hour or two? Would it help to tack well away from the shore, or might it be better to stay reasonably close to the coast?
5 It is a sunny cold clear day in early spring, and you see a large black cloud and heavy rain shower up ahead. What do you do? After the rain shower has gone through, the wind drops to about 5 knots. Someone suggests putting up a larger headsail. What do you do?
6 After a clear night in September, you wake up in a harbour to fog, with visibility of about 200m. Is it likely to:
a) get worse during the day
b) be clearer or thicker out to sea?
7 Sailing across the English channel in the afternoon in early summer, with a light warm south westerly wind, you notice fog up ahead. What is the likely cause of this fog? What conditions do you expect for the rest of the trip?
1 In which direction does the wind circulate round an area of low pressure in the northern hemisphere?
2 What term is used to describe the thin area of high pressure you get between two lows?
3 What are the lines of equal pressure on a synoptic chart called?
4 True or false? You generally get fair weather with an anticyclone.
5 What is the name of the "force" that explains why things move in a curved path on a rotating surface (rotating frame of reference)?
6 True or false? When the isobars are close together you get strong winds associated with the steep pressure gradient.
7 The barometer has been falling for several hours, the sky clouded over - high cloud at first, getting lower, and it's now drizzling. What is going on? What will happen to the wind?
8 A few hours later the wind is Force 6 from the south west when suddenly the sky clears and the sun comes out. What is happening, and what do you expect the wind to do?
9 A few hours later the wind backs and strengthens. It is raining again. What's happening?
10 When the rain stops again, is the air likely to be warmer or colder? The barometer rises. Will there be more rain?
ANSWERS
Weather Forecasts: 1 Both mean the wind is changing direction: veering in a clockwise direction (south - west - north) and backing in an anticlockwise direction; 2 They refer to the time when a forecasted event will happen: imminent is within 6 hours of the time of the forecast; soon is between 6 and 12 hours of the time of the forecast; later is 12 to 24 hours from the time of forecast; 3 Moderate is between 2 and 5 miles: poor is between 1000m and 2 miles; 4 Force 5 is defined as 17 - 21 knots. The apparent wind will be stronger if you are sailing into it, lighter if you are going downwind; 5 You need to know the time of the forecast (NOT the time when it was broadcast); 6 Look at it for interest, but the forcast is very unlikely to be accurate. Tell the marina office that it is misleading to display an old forecast, and ask them for an up-to-date one. Then, for interest, compare the new forecast with the old one.
Local Weather: 1 Away from the shelter of the coast the wind will be brisk and the waves reasonably large for a small craft. Tell them that they might have considerable difficulty getting back to shore if they go out any distance; 2 Expect the wind to pick up as you approach the headland - so put the reef in now; 3 Look at the speed and direction of movement of the clouds; or flags/trees etc on the top of a hill, or see if trees/flags lower down are being affected by gusts. Listen to the forecast, or ask someone who is coming in! 4 You expect the wind to be angled more on-shore as the sea breeze develops. If this new direction is helpful to your progress (e.g. allowing longer tacks nearly parallel to the coast) stay reasonably close in, because further out to sea, the sea breeze effect will be weaker or absent; 5 Expect a sharp (and possibly very sudden) increase in wind in the vicinity of the shower: get some sail down. Wait before putting more sail up. The wind is light because the shower, which has just passed, is counteracting the general wind. Expect the wind to get back to where is was before the shower arrived; 6 This is radiation fog. It will either clear up as the sun warms the air, or it will hang around if the sun isn't strong enough. It probably hasn't formed out at sea, so you expect it to be clearer there; 7 This is advection fog, caused when warm damp air blows over cold sea. It may have formed over quite a wide area, so be prepared for it to be around for the rest of the passage (it will probably clear only when the wind changes).
Wide Area Weather: 1 Anticlockwise (westerlies to the south of its centre, easterlies to the north); 2 A ridge; 3 Isobars; 4 True. An anticyclone is an area of high pressure; 5 Coriolis; 6 True; 7 This is the typical approach of a warm front with a low pressure system. The wind will pick up, probably from the south west; 8 The front has passed, and the wind will veer quite quickly to the west or north west - and possibly moderate as the warm front recedes; 9 This is the typical pattern for an Atlantic low: a cold front is approaching; 10 Colder. There may be heavy sharp showers in the wake of the cold front.