WEATHER LESSON 2: CLOUDS Part 2

[MulletMan]

“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.”

Some good news that we aren’t going to get too involved in naming the majority of clouds that have little to do with us on the water. More important to appreciate something about the weather system causing them and how that will be effecting our boating activities.

We can appreciate by now that if our coastal “block” of air, that could be of any size and area up to hundreds or thousands of square kilometres, has sufficient moisture content and is forced upwards through THERMAL CONVECTION (heat) or OROGRAPHIC UPLIFT (terrain) it will expand, cool, condense and form clouds, possibly rain and “weather”. So the example of this mass of air coming in over the ocean may already have a very high HUMIDITY (moisture content) and can turn into weather without a great deal of vertical movement. In fact just a few thousand feet might be enough to produce something as it has all the ingredients and conditions for low level action.

But let’s say this same sized block of air is situated over an inland area or even the outback of NSW/QLD. It follows that it will NOT have the same moisture content as it has been over a hot and most likely drier patch of turf.
So is it possible to get something going in it terms of weather in a similar fashion to the coastal stuff?
We certainly can’t increase the water content but what if we could get it to rise much, much higher in the atmosphere at an extremely fast rate and also toss in some horizontal movement at the same time. In fact what if the example in LESSON 1 was used, being the massive “wedge or shovel” of cold air moving up rapidly from the southern states? And these cold air masses can get along at fair rate of knots, 20 nautical miles per hour or more in a HORIZONTAL movement over the countryside.

The front (important word) of this wedge may be a thousand or more k’s wide and also extend many thousands of feet into the atmosphere. So when this (COLD FRONT) undercuts our mass of warmer outback air, the latter is going to be subjected to enormous vertical movement and whereas the moist air coming from the ocean only needed a few thousand feet to cause weather, this hot and drier air (with its lower moisture content) is going to get “pushed” upwards to around the 20-30000+ feet at tremendous vertical rates (thousands of feet per minute) and of course it will pass through much COLDER areas of the upper atmosphere in the process. So whilst its moisture content is less than our coastal example, by virtue of the fact we are shoving it higher and faster it’s lesser moisture content will still fall subject to the laws of weather.

It will therefore condense, form clouds and rain will form at all levels from the ground to around the 40,000 feet. What do we have? A dirty great storm or in this example a solid line of them called a ………….. COLD FRONT!!
Assuming you are still with me, as our COLD FRONT continues pushing towards us in Brissy, no prizes for knowing that the warmer air in front of it (being closer to the coast) will have higher moisture content and as our storms love water, their buildup and intensity is going to be dramatically increased.

But as the lesson is on clouds, we won’t just yet get into storms and fronts at the moment. Our intrepid Boatie "Lurch" is out at the Sandhills on Moreton, covered in whiting scales and stuffing down a worm flavoured sanger when he casts his eyes down towards the south west corner (where ALL fronts come from). He espies a long line of pretty insignificant clouds low on the horizon that are obviously much too far away to be a problem (BIG MISTAKE) and gets back to the sanger ………………… but he fails to grasp that the sure-fire, guaranteed North Easterly wind that will be blowing is directly linked to the distant clouds!

His “insignificant” little clouds are but the forerunner of a massive cold front advancing rapidly in a north easterly direction (AGAINST THE WIND!!) As Lurch innocently continues to plunder whiting from the 7.0 metre drop off, he now notices that the clouds seem much darker, more widespread, certainly higher and a damn sight closer! #

Unbeknown to him, the BOM radar station at Marburg is starting to show some cloud “returns” from that direction, Nothing too savage just yet (we gotta get more moisture and CONVECTION going first) but there is undoubtedly “something coming”. #Lurch is now aware (but too late!) that it might be a good time to pack up and head for home - while there is plenty of time! Having been protected from the North Easterly by Moreton, he leaves its shelter and is somewhat aghast as his 5.35 metre tinny suddenly finds itself being pushed about by a 20-25 knot Nor-easter. Those clouds are now really dark, very high and Lurch’s bowels start to rumble as he realizes that Manly is a long, long away still …………………..

Our COLD FRONT is now really starting to cook. More responsible and weather wise Boaties on the mainland clearly identify heavy, dark, rain bearing CUMULUS clouds in front of the weather, some STRATUS (low level clouds full of #rain) and “big black clouds” further back in the mess. In fact they are so dark that the closer CB’s can start to take on a deceptive white appearance. And a strange long hard line of cloud now stretches across some sections of the mess (we have a SQUALL LINE on the make). A lucky observer even spots some very high white cloud sticking out through a break in the weather and being an Ausfish reader says, “Ahah, I sees me some high level CIRRUS cloud, probably well over 30,000 feet and being so cold (-45 degrees C) it is composed of ice crystals and is the top of the storm!”

Most probably the real storm “cells” that we refer to as CUMULONIMBUS or TOWERING CB’S are well camouflaged by the mess of clouds, rain and weather that makes up our COLD FRONT. Lurch is getting a long distance, grandstand view of his impending doom and now, having to contend with a 25 knot (gusting 35 knot) NE wind producing a viscous little starboard quartering sea on his stern, is not a happy little black duck any longer. There is now a distinct purplish look to some of the cloud. In fact the water content is not only 100% HUMIDITY it is so dense that it goes beyond black and takes on this purplish/blue tinge.

And the clouds also look green! HAIL is present because we all know ice looks a greeny colour; but why isn’t it hailing yet? ‘Cos the UPDRAFTS of air currents are so powerful the hail keeps getting tossed higher and higher, gathers more moisture on each hailstone, refreezes, gets bigger, falls, gets thrown up again, more moisture and the process keeps going until the hail is simply to heavy to stay up there and then down it comes in a hail storm. #

Just prior to capsizing, Lurch has learnt he didn’t have to be a cloud-identification expert, nor did he need to know that temperature decreases at two degrees per thousand feet, all he needed to know was that the CLOUDS were trying to tell him something. Granted the BOM guys would have had out VERY ACCURATE forecasts beforehand as these FRONTS are easy to track (though their intensity is not) but even with this warning, a sensible and cautious Boatie could have had quite a great day on the water with the knowledge of an impending FRONT on the way.

In other words Lurch didn’t “read the cloud signs” correctly nor tumbled to the fact that the NE wind pattern #was an integral part of the overall system! What will be quickly appreciated as we go along is that rarely if ever does one single weather phenomena give us an end result. The ingredients to every synoptic situation are many, varied and extremely dynamic i.e. ever on the change.

The above example is our typical “moving” storm cloud formation and again qualifying that we are not trying to learn how to handle that weather, just recognize the symptoms.

So, how come in summer we get a single solitary storm that commonly builds up along our SE coastline and is certainly not part of the COLD FRONT process? What we have here is a HEAT STORM or ELECTRICAL STORM.. This type of storm does not cover a great deal of territory but makes a serious racket with thunder and often sheet and forked lightning. Their bark is usually worse than their bite, they tend to form very rapidly, make some impressive sound and light displays, do not always produce severe and damaging winds and oddly enough do not always have a great deal of rain associated with them. They dissipate (or collapse) incredibly fast and can be gone in a very short time once the convection process ceases.

Nonetheless, although this type of storm has been caused by our identical CONVECTION process why therefore is it so different in its characteristics? Firstly it invariably originates from THERMAL CONVECTION where a warm, moist air mass has been “vertically motivated”, is probably located in a somewhat unstable part of the upper atmosphere, has NOT traveled great distances and therefore does not have massive amounts of moisture in its mass. Additionally, the origin of this heat has probably been present for a few days thus providing a reliable and constant source of convection. About all it has going for it is some pretty serious uplift whilst the ingredients simply lack the oooomfff to make it into what it would like to be!

As a storm though it is more than capable of giving us a bit of stick so treat it with respect nonetheless!

Storms, fronts, frost, mist, fog, dew next guys!

[RAGINGBULL]

Keep them comming Pink Panther.
Im learning something

I hope lurch made it to Manly.

Mark