MulletMan
06-02-2006, 06:42 PM
“The following information is purely for online self education and in no way replaces the responsibility of the Master of any vessel insofar as his/her responsibilities are at all times to access authorized Queensland Bureau of Meteorology sources of weather, forecasts, validity periods, warnings and the like. In no way whatsoever is any reader to use any extracts, portions or advices herein as a means of assessing weather conditions pursuant to acting as a vessel’s Master.”
Thanks for the replies and expression of support for the weather lessons guys! Good to see how many members want to learn about the weather! With 10,000 characters allowed per posting I have to keep it brief and simple. Kids stuff to start with and push on to more advanced stuff as we go along.
OK, in really generalized terms, if there isn’t any significant movement of air then there won’t be any significant weather!
If the earth was totally devoid of hills, mountains, seas, rivers and even civilized structures, then there would virtually be nothing going on with the weather from day to day. We tend to think of weather as clouds, rains, winds and all the “visible” stuff. It is also much easier to relate to material things such as land, sea, buildings etc. but in fact AIR has as many characteristics as most of the above. But of course we can’t see it so therefore we assume it isn’t there – wrong! And you must remember that AIR is just as easy to WEIGH as we are! I get on the scales and see 100 kgs representing pure muscle, bone and sinew. Another switched on guy takes out a specialized set of scales called a BAROMETER and he can just as easily WEIGH the mass of AIR pressing down ON the scale (1 G Gravity). And instead of KILOS he calls it MILLIBARS or INCHES OF MERCURY or most commonly BAROMETRIC PRESSURE. So the local Postmaster at Longreach records that his little patch of air above the chook yard “weighs” 1013 Millibars (29.92” Mercury) at a particular time and date. He picks up the phone and rings his mate Fred at BOM and tells him the figure. At the same time thereabouts BOM also gets another stack of reports from maybe Police Stations, other Post Offices, Shire Clerks etc. and of course a vast array of automated weather reporting stations right across Australia. Imagine all of these stations also report 1013 MB’s so therefore Fred at BOM can easily put a pin on a large scale map for all the “1013’s” and will in fact have plotted all the points across Australia whereby this 1013 MB “WEIGHT” exists. So what then? He draws a line to link them all up and voilà, he has created a line of equal BAROMETRIC PRESSURE or the dreaded and much feared term - an ISOBAR - being points of equal BAROMETRIC PRESSURE!! Not hard from here to understand that if every single point of equal Barometric Pressure across Australia and its adjacent oceans were joined to together we would have a …….. weather map!! All the little 1013’s, 1000’s, 988’s and everything in between would be joined together individually to make up those little squiggly lines that in turn form a SYNOPTIC CHART. Lets be professional here guys and scrap the weather map bit eh!! The above is all that is required to construct a fully functioning chart so a forecaster can then weave his magic spells and come up with a FORECAST. Moving on now ……………….
It is very important to remember that AIR = WEATHER and AIR has WEIGHT! What is “in” the air is of course what we construe as weather such as rain, snow, ice, hail and all the good stuff that spoils our boating.
I could make the brave statement that if every intending Boat operator fully appreciated the direction, strength and duration of winds then this weather lesson could just about finish right here! A simple example would be that a North Westerly (NW) coming in from the Qld inland for about a week just has to be a hot, dry and dusty wind! There is normally no possible way that you are going to get any rain or bad weather from that direction and conversely if you have a direct Easterly (E) airflow of 20-25 knots that has been flogging the Queensland for a week, then the odds are very high that showers and sometime set in rain will be the result. I’m not saying ALWAYS – just generalizing. But if these latter winds had only been present for say a couple of days at 10 – 15 knots, then worst case might be isolated and showers – if at all! I’ll explain why later on, but alas there is always the exception to the rule whereby a Cyclone or Upper Air Low (Trough) can bring in some dreadful weather in our examples of E and NW winds)
OK, so we have to somehow get this mass of air moving and then there will be some action. The key word of weather is CONVECTION i.e. the upwards movement of a mass of air. If it don’t go up there ain’t gunna be any weather! So easy stuff, you fill a balloon with hot air and up it goes, stick a big fan facing upwards and the “mass” or “envelope” of air above it will start to rise. Or how about if you could somehow heat up a huge area of say bitumen, concrete etc? This would undoubtedly heat up the air over the hot spot and away it will go skywards also. Not much chance of you cranking up your own clouds or rain this way but what if we could have some seriously large heated areas such as hundreds or maybe thousands of kilometers? That should start something surely! And it will, in fact the entire air mass above our hot area will commence to rise and of course we all know that as we increase height (altitude) the TEMPERATURE DECREASES. And from our school day physics we also know that if that happens then the DENSITY of the air mass will DECREASE (forget about Density at this stage) because almost invariably all air has a water content known as HUMIDITY. #You need 100% Humidity to bring down any wet stuff.
Right, we can easily see that an extensive lump of hot air will rise and eventually 100% Humidity may form and that will be recognized by, yep – clouds!! Just water in an airborne shape and probably far too light and fluffy to cause rain - suspended moisture sort of! It’s not a big ask of the imagination to appreciate that the faster this air rises and the higher the initial moisture content is then the bigger, darker and heavier the clouds will be – in fact the actual water content will start showing progressively darker and darker shades of grey until the blue/black stuff begins at which stage you really wish you had started for home a little earlier!
It gets trickier now because as our mass of air has risen what has taken its place? There has to be something or we won’t be able to breathe…. (joke)? COLDER AIR comes a-rushing from wherever and fills the hole! And how would we Boaties know that is happening. Yep, a WIND will start up – movement of air from an area of COLD to one of HOT. So virtually we have created a “column” of air continually being replaced at sea level and rising to do its magic stuff as weather. That is technically a little incorrect as we are getting into the formation of HIGHS and LOWS and it is really the replacement of the rising air with an area of descending air. We won’t go down that path just yet……!
So that somewhat explains how CONVECTIVE clouds are formed from HOT rising air with a moisture content. But what if we had a huge “wedge” of really cold air from down in the southern states that was on the move towards us? To make it easier, imagine it is shaped like a shovel e.g. the blade is scooping along the ground at about 45 degrees and the “HOT AIR” in front of it is being shoveled upwards at thousands of feet per minute! (We are actually talking about a COLD FRONT but more later). Back to our 1000 km long and 35,000 foot high wedge of COLD AIR that is pushing UNDER the hotter air as it approaches Qld. The difference to our above example of hot air rising? Nothing! Exactly the same principle, we have HOT AIR rising, cooling, condensing and forming clouds and then rain! One big difference is that as well as upwards CONVECTION we also have HORIZONTAL movement along the ground, mountains, ranges etc. We gotta big cold front with storms, hail and rain on the way! And the higher it goes the bigger and nastier the storms are!
That’s it! Dun! Finished with how weather is formed! Wrong! The above is a really simplistic explanation and there are many variables that dramatically affect this explanation, but it’s a start nonetheless!
And a strong HINT on ISOBARS – the closer they are together the stronger will be the winds! Do NOT be fooled by the synoptic charts in the papers and on Telly wherein the ISOBARS look a long way apart (indicating light winds) They are ALL 4 MBs apart and very misleading. i.e. One line may be 1000 and the next 1004 – the 1001/2 & 3 are missing) Grab a pencil and mark in the three remain ISOBARS in parallel and see the dramatic difference in the GRADIENT of the winds. What looked nice and well-spaced out ISOBARS now tightens up like a watch spring with stronger winds. # The media is just too lousy with the ink or too ignorant of the repercussions of this poor data display. Many Boaties get fooled by this badly presented information. Check on tonight’s weather TV or get your local rag out and start drawing practice lines. So all you have to do for a bit of homework is look at a Synoptic Chart and work out:
1) # What direction are the winds coming from (Hot/cold/wet/dry origin?)
2) # How long have they been blowing from that direction (Long periods permit more time to uplift sea water/cold or hot air etc)
3) # How strong are they (will pick up more sea water if seas are agitated etc)
4) # Will they travel a long distance (1000 k's+) over water/land in the process (pick up lots of H2O maybe)
5) # Are the winds lighter and getting a bit of coverage along both the coastal land and the ocean (less water to collect)
6) # Don't forget the 4 MB apart thingo - very important!
Thanks for the replies and expression of support for the weather lessons guys! Good to see how many members want to learn about the weather! With 10,000 characters allowed per posting I have to keep it brief and simple. Kids stuff to start with and push on to more advanced stuff as we go along.
OK, in really generalized terms, if there isn’t any significant movement of air then there won’t be any significant weather!
If the earth was totally devoid of hills, mountains, seas, rivers and even civilized structures, then there would virtually be nothing going on with the weather from day to day. We tend to think of weather as clouds, rains, winds and all the “visible” stuff. It is also much easier to relate to material things such as land, sea, buildings etc. but in fact AIR has as many characteristics as most of the above. But of course we can’t see it so therefore we assume it isn’t there – wrong! And you must remember that AIR is just as easy to WEIGH as we are! I get on the scales and see 100 kgs representing pure muscle, bone and sinew. Another switched on guy takes out a specialized set of scales called a BAROMETER and he can just as easily WEIGH the mass of AIR pressing down ON the scale (1 G Gravity). And instead of KILOS he calls it MILLIBARS or INCHES OF MERCURY or most commonly BAROMETRIC PRESSURE. So the local Postmaster at Longreach records that his little patch of air above the chook yard “weighs” 1013 Millibars (29.92” Mercury) at a particular time and date. He picks up the phone and rings his mate Fred at BOM and tells him the figure. At the same time thereabouts BOM also gets another stack of reports from maybe Police Stations, other Post Offices, Shire Clerks etc. and of course a vast array of automated weather reporting stations right across Australia. Imagine all of these stations also report 1013 MB’s so therefore Fred at BOM can easily put a pin on a large scale map for all the “1013’s” and will in fact have plotted all the points across Australia whereby this 1013 MB “WEIGHT” exists. So what then? He draws a line to link them all up and voilà, he has created a line of equal BAROMETRIC PRESSURE or the dreaded and much feared term - an ISOBAR - being points of equal BAROMETRIC PRESSURE!! Not hard from here to understand that if every single point of equal Barometric Pressure across Australia and its adjacent oceans were joined to together we would have a …….. weather map!! All the little 1013’s, 1000’s, 988’s and everything in between would be joined together individually to make up those little squiggly lines that in turn form a SYNOPTIC CHART. Lets be professional here guys and scrap the weather map bit eh!! The above is all that is required to construct a fully functioning chart so a forecaster can then weave his magic spells and come up with a FORECAST. Moving on now ……………….
It is very important to remember that AIR = WEATHER and AIR has WEIGHT! What is “in” the air is of course what we construe as weather such as rain, snow, ice, hail and all the good stuff that spoils our boating.
I could make the brave statement that if every intending Boat operator fully appreciated the direction, strength and duration of winds then this weather lesson could just about finish right here! A simple example would be that a North Westerly (NW) coming in from the Qld inland for about a week just has to be a hot, dry and dusty wind! There is normally no possible way that you are going to get any rain or bad weather from that direction and conversely if you have a direct Easterly (E) airflow of 20-25 knots that has been flogging the Queensland for a week, then the odds are very high that showers and sometime set in rain will be the result. I’m not saying ALWAYS – just generalizing. But if these latter winds had only been present for say a couple of days at 10 – 15 knots, then worst case might be isolated and showers – if at all! I’ll explain why later on, but alas there is always the exception to the rule whereby a Cyclone or Upper Air Low (Trough) can bring in some dreadful weather in our examples of E and NW winds)
OK, so we have to somehow get this mass of air moving and then there will be some action. The key word of weather is CONVECTION i.e. the upwards movement of a mass of air. If it don’t go up there ain’t gunna be any weather! So easy stuff, you fill a balloon with hot air and up it goes, stick a big fan facing upwards and the “mass” or “envelope” of air above it will start to rise. Or how about if you could somehow heat up a huge area of say bitumen, concrete etc? This would undoubtedly heat up the air over the hot spot and away it will go skywards also. Not much chance of you cranking up your own clouds or rain this way but what if we could have some seriously large heated areas such as hundreds or maybe thousands of kilometers? That should start something surely! And it will, in fact the entire air mass above our hot area will commence to rise and of course we all know that as we increase height (altitude) the TEMPERATURE DECREASES. And from our school day physics we also know that if that happens then the DENSITY of the air mass will DECREASE (forget about Density at this stage) because almost invariably all air has a water content known as HUMIDITY. #You need 100% Humidity to bring down any wet stuff.
Right, we can easily see that an extensive lump of hot air will rise and eventually 100% Humidity may form and that will be recognized by, yep – clouds!! Just water in an airborne shape and probably far too light and fluffy to cause rain - suspended moisture sort of! It’s not a big ask of the imagination to appreciate that the faster this air rises and the higher the initial moisture content is then the bigger, darker and heavier the clouds will be – in fact the actual water content will start showing progressively darker and darker shades of grey until the blue/black stuff begins at which stage you really wish you had started for home a little earlier!
It gets trickier now because as our mass of air has risen what has taken its place? There has to be something or we won’t be able to breathe…. (joke)? COLDER AIR comes a-rushing from wherever and fills the hole! And how would we Boaties know that is happening. Yep, a WIND will start up – movement of air from an area of COLD to one of HOT. So virtually we have created a “column” of air continually being replaced at sea level and rising to do its magic stuff as weather. That is technically a little incorrect as we are getting into the formation of HIGHS and LOWS and it is really the replacement of the rising air with an area of descending air. We won’t go down that path just yet……!
So that somewhat explains how CONVECTIVE clouds are formed from HOT rising air with a moisture content. But what if we had a huge “wedge” of really cold air from down in the southern states that was on the move towards us? To make it easier, imagine it is shaped like a shovel e.g. the blade is scooping along the ground at about 45 degrees and the “HOT AIR” in front of it is being shoveled upwards at thousands of feet per minute! (We are actually talking about a COLD FRONT but more later). Back to our 1000 km long and 35,000 foot high wedge of COLD AIR that is pushing UNDER the hotter air as it approaches Qld. The difference to our above example of hot air rising? Nothing! Exactly the same principle, we have HOT AIR rising, cooling, condensing and forming clouds and then rain! One big difference is that as well as upwards CONVECTION we also have HORIZONTAL movement along the ground, mountains, ranges etc. We gotta big cold front with storms, hail and rain on the way! And the higher it goes the bigger and nastier the storms are!
That’s it! Dun! Finished with how weather is formed! Wrong! The above is a really simplistic explanation and there are many variables that dramatically affect this explanation, but it’s a start nonetheless!
And a strong HINT on ISOBARS – the closer they are together the stronger will be the winds! Do NOT be fooled by the synoptic charts in the papers and on Telly wherein the ISOBARS look a long way apart (indicating light winds) They are ALL 4 MBs apart and very misleading. i.e. One line may be 1000 and the next 1004 – the 1001/2 & 3 are missing) Grab a pencil and mark in the three remain ISOBARS in parallel and see the dramatic difference in the GRADIENT of the winds. What looked nice and well-spaced out ISOBARS now tightens up like a watch spring with stronger winds. # The media is just too lousy with the ink or too ignorant of the repercussions of this poor data display. Many Boaties get fooled by this badly presented information. Check on tonight’s weather TV or get your local rag out and start drawing practice lines. So all you have to do for a bit of homework is look at a Synoptic Chart and work out:
1) # What direction are the winds coming from (Hot/cold/wet/dry origin?)
2) # How long have they been blowing from that direction (Long periods permit more time to uplift sea water/cold or hot air etc)
3) # How strong are they (will pick up more sea water if seas are agitated etc)
4) # Will they travel a long distance (1000 k's+) over water/land in the process (pick up lots of H2O maybe)
5) # Are the winds lighter and getting a bit of coverage along both the coastal land and the ocean (less water to collect)
6) # Don't forget the 4 MB apart thingo - very important!