State the significance of forecast or observed low level moisture to flight

It is fitting that this should be the last objective in this manual, as it is, in my opinion, one of the most important
objectives in the Civil Aviation Authority Advisory Circular AC61-3 meteorology syllabus. 

Most weather-related accidents and incidents in the GA community are related to one of two things. The first, and
most important is: 

Low-level visible moisture. 

And the second is: 

Wind and wind related occurrences. 

Any observed or forecast low-level moisture should raise a warning flag for a pilot; that is not to say that you should
immediately abandon your current or proposed flight, but rather you should give serious weight to its significance. 

 Increasing low-level moisture will inevitably lead to the development of low cloud and poor visibility in our
mountainous terrain. The combinations and rising dew points and rising ground, with an onshore flow must result in
cloud formation if sufficient lifting occurs. And if that increasing moisture is due to an approaching frontal system,
the cloud bases may start out quite high, however they will lower, and sometimes very quickly, as the dew point
temperature increases. 

And don’t be fooled into thinking you need a mountain or a large hill for this to occur either. The height that the cloud
forms is not related to how high the hills are, but rather how close the temperature and dew point temperatures are.
On several occasions, I have observed broken stratus cloud at around 50 -100ft above Ohakea in moist westerly
flows. Out to sea, the air is clear of all cloud, but as this very humid air comes ashore, two things happen. Firstly, the
air is forced to rise over the sand dunes which are no more than 50 -100 ft high, so this results in lifting and therefore,
cooling. Secondly, as the air encounters the dunes, it slows down slightly because of increased friction. The air coming in from the sea is not being slowed, so it runs into this slower
moving air resulting in convergence, which adds to the lifting – sufficient for low-level cloud to form.

Another smart thing to do is monitor the dew point temperature over time. If the dew point temperature is rising,
more low-level moisture is entering the area. This will not necessarily result in cloud immediately, but if the trend
continues, at some point, low cloud becomes inevitable. 

Often, a front will sweep through an area and dump quite a lot of rain. All through the rain period and often after the
rain has stopped, this added water will evaporate into the air causing the dew point to rise. If this time of rising dew
point temperatures corresponds to a rapidly falling temperature in the clear air of evening, radiation fog becomes a
distinct possibility. 

Too many pilots have lost their lives by continuing to fly into deteriorating weather, which, whether forecast or not,
was either clearly visible before departure, or became visible ahead of them during the flight. In either case, such
weather is always avoidable if good decision-making processes are followed. 

Flying can be heaps of fun, however when things go wrong – and they will from time-to-time – it can rapidly become
a very stressful pursuit. Some things, like a sudden engine failure for example, are drilled into you through practice,
practice and more practice. You hope the engine will never fail, but you instinctively know how to deal with it when it
does happen. 

Being caught out by bad weather though, is simply something that should never happen. ALL flights at PPL level into
poor weather must have resulted from a poor decision by the pilot. Either you took off in already existing poor
conditions or you decided to continue the flight into poor weather ahead – forecast or not. 

A Decision-making Flow chart:
Figure 102 presents a GOOD decision-making flow chart for any flight with regard to poor weather. The aim of every
flight should ultimately be to reach the yellow highlighted box. You don’t have to have a beer and tell war stories, but
the fact that you could if you chose to, means you have reached the ultimate goal – you’re still alive and, hopefully,
the aircraft is still in one piece. 

Everything that has gone before in this book, has been written to educate you, and prepare you, for some of the
weather experiences you will come up against during your flying career as a recreational pilot. 

A bad forecast, a good forecast, or even the lack of a forecast, never killed anyone. Forecasts are simply planning
data written on a piece of paper or on a computer display. They are certainly designed to help you make good
decisions, but they don’t make the decision for you – you make those decisions yourselves

As pilots, you alone hold the key to a long and enjoyable participation in aviation. Train yourself to set your own
weather limits and don’t ever push those limits. The weather can be very unforgiving to aviators. Don’t let that one
bad decision become the last decision you ever make.

Insert Flowchart of good decision making during a Cross Country Flight

With reference to information contained in GRAFOR, AAW, GNZSIGWX, TAF, TREND METAR, SPECI, METAR AUTIO. GSM, ATIS, AWIB, BWR and Pilot Reports, decide the following;

• a) Decide which forecasts and reports should be considered for an individual flight between given locations 
• b) Utilising the forecasts and reports, and the application of local knowledge, demonstrate sound planning and decision-making

(a)  Decide which forecasts and reports should be considered for an indicated flight between given locations;  

Within MetFlight, there is a wide range of information available to recreational pilots and at times, the scope of this
data can seem quite daunting. But knowing what information to consider and how to interpret that information is
crucial to planning and executing safe flights. 

If your intended flight is just to do circuits then, obviously, you don’t even need to look at the forecasts – right? You
can see what the weather is doing and while you are in the circuit, you can keep an eye on the weather. Anecdotal
evidence suggests however, that pilots doing circuit consolidation are often so focused on the task at hand that they
fail to recognise when the weather begins to deteriorate. 

This early stage in your flying training is a great time to put good aviation practices in place which will hold you in
good stead for the rest of your flying life. As you become more proficient with your down-wind checks in the circuit,
consider adding a weather check to the list. 

Generally, though, when in the circuit, the runway is always in view, and if the weather does start to change, it’s an
easy call to knock it of and land. 

And of course, checking the weather prior to every flight is an example of good airmanship, and is a good habit to get
into. 

Cross-country flights are another matter. Let’s consider the met requirements for a flight from Hamilton to
Paraparaumu via the tiger country between Mt Ruapehu, Mt Taranaki and Whanganui. Your planned route is to fly to
the west to Raglan, then follow the coast south to about Awakino, and then proceed due south across the tiger
country to Waverley, and on to Whanganui. After refuelling at Whanganui, the plan is to follow the coast south to
Paraparaumu. 

 (Note: The term ‘Tiger Country’ is a well-known and often used metaphor for this part of the Taranaki/Whanganui
districts. Pilots have used the term for many years to describe this area where navigation is dificult and a number of
aircraft have crashed in poor weather). 

 As a minimum, the following products should be considered for this flight: 

• The appropriate AAW (Aviation Area Winds) for the proposed flights. 

• The GRAFOR (Graphical Aviation Forecasts) charts. Be sure to consider all charts that are appropriate
for the length of flight being conducted.

• The GNZSIGWX (Graphical New Zealand Significant Weather) charts. In particular, pay attention to any
forecast of moderate turbulence and icing, and again, be sure to consider all charts that are appropriate
for the length of flight being conducted.

• TAFs for departure and destinations: 

 NZHN, NZWU and NZPP 

• TAFs for alternative airfields: 

NZNP, NZAP, and NZPM 

• METAR AUTOs for all the above TAF locations: 

NZHN, NZWU, NZPP, NZNP, NZAP and NZPM 

• And most importantly, the GSM (Graphical SIGMET Monitor) if applicable, for any severe weather
occurrences. 

Additional information:
The products listed above are the absolute minimum you should take into consideration for this cross-country flight.
In addition, other products which are freely available in the MetFlight web-site may be of help when planning this
flight. These are; 

1. The latest MSL analysis and prognosis maps will give you a good clue as to the current situation and how it
is changing. 

2. The latest satellite and radar imagery may help you identify areas of moisture which may be of significance
to your proposed flight. 

3. Webcams – there are many high-resolution webcam images available within MetFlight. Most are located at
aerodromes, but a few are located at places in the mountains where flights frequently take place, and more
are planned. These images may help you make informed decisions. 

In addition, ATIS (Automated Terminal Information Services), AWIB (Aerodrome and Weather Information Broadcast),
BWR (Basic Weather Report – as reported by friends or fellow pilots you may know along the route), and Pilot
Reports issued through the ACNZ reporting system may be available to help with your decision-making process. 

(b) Utilising the forecasts and reports, and the application of local knowledge, demonstrate sound planning and
decision-making. 

So, let us consider using the forecasts and observations listed in (a) above for a departure time of 11.30 am on 16th
October 2017. The minimum products as listed above are displayed below (figure 93 – pages 148 to 153). The
highlighted parts will be discussed further.

Image

So, let’s consider the products shown in figure 93 above and determine whether your flight should proceed or not.
Note that a PPL pilot with many years of experience may well cope with this scenario more than adequately. This
case study however, assumes a PPL student, or qualified pilot with limited experience. 

First up, I have highlighted any mention of precipitation in yellow in the GRAFORs, TAFs and METARs. While at a
glance it doesn’t look too bad with regards to showers, there are four things worth noting – things that I would keep
in the back of my mind if I was to conduct this flight. 

1. The TAF for Paraparaumu has visibility reductions to 7000 m from 3 pm (0200 UTC). This is after our
planned arrival time, so it shouldn’t present too much of a problem, and in any case, if the showers arrive
early, there are several airfields available if we need to backtrack, including Otaki airstrip and Foxpine. 

2. The forecast for New Plymouth is also mentioning visibility reductions to 7000 m in showers, but not until
after 5 pm. OK, this shouldn’t be a problem, but it should still get my attention, because along with the
Paraparaumu TAF, it suggests that there is a gradual tendency towards increased moisture content in the
low-level air as the afternoon wears on. 

3. While the GRAFORs don’t mention that the showers are likely to be isolated in nature, a quick look at the
latest radar imagery will indicate this fact. There is also a direct link in MetFlight to the MetService home
page (by clicking on the button), where the district forecasts for the Waikato,
Taranaki, the Manawatu and Horowhenua confirmed that the showers would be isolated. Again, if this is
what happens, then I would see no reason not to continue the flight based on forecast visibility reductions
in showers. Any light showers encountered should be easy to fly around, or even through. 

4. HOWEVER, to repeat – the forecasts do indicate an increasing moisture trend into the later part of the
afternoon, so I will note this fact, and be prepared to change my plans if necessary. 

Next, I would quickly look at the forecast and actual visibilities (outside of showers). These are highlighted in blue.
And here, I note a slight problem. All the forecasts state the prevailing visibility is going to be between 20 and 30 km,
however the reported visibilities in the METAR AUTO reports vary from 31 km at best, down to 13 km at worst at
Whanganui. And although I haven’t included the METAR or METAR AUTO for Ohakea, I know that the visibility at
Ohakea at 11 am was 12 km (and this information would have been freely available in MetFlight if you chose to look for
it). 

The question which immediately springs to my mind is WHY? Why is the actual visibility worse than the forecast?
The answer comes down to wind and sea – the wind is quite strong – 23 knots gusting to 33 knots at Whanganui, so
the action of the wind on the sea waves is creating salt spray which is creating an abundance of sea salt aerosols in
the air, and these in turn are reducing the visibility more than the forecaster originally thought they would. So, there
are now two more points worth noting: 

1. The visibility is not the best, and because we know what is generating the poor visibility, we can assume
that the worst visibilities (outside of showers) will be near the coast where the efects of the wind on the
sea are greatest. Of itself, visibility of say 12 to 15 km is not that bad, however I know from experience that
when these visibilities are accompanied by cloudy to overcast skies (as is the case here), the definition
between cloud and the visible horizon is degraded appreciably. Now, if you are cruising at 120 knots and the
visibility is say, 12km, the total picture you observe in front of you will change completely in less than 3½
minutes. This isn’t necessarily a problem, but it is sure worth noting, because it means that if the weather
starts to deteriorate in front of you, you only have 3½ minutes to react to those changes.

2. There is moderate turbulence forecast everywhere along the route below 10000 ft, because of the wind
strength (see the GNZSIGWX chart). Yes, you could probably handle this, but it’s not going to be pleasant or
comfortable. 

 On this planned route, there are no problems with terrain until you get to the leg from Awakino to Waverley where the
Minimum Safe Altitude (MSA) is marked on the map as 2700 ft amsl. 

Now we come up against a real problem, because the cloud bases (highlighted in green) as forecast in the GRAFOR
are expected to be at 2000 ft amsl from about Stratford southwards, and the MSA through this area is 2700ft amsl.
This should immediately be seen as a deal breaker for the planned route. 

And finally, the SIGMET is suggesting some severe turbulence below 10,000 ft to the west of Paraparaumu, however
it is expected to weaken, so it shouldn’t pose a threat to this flight. 

Based on the discussion above, clearly this flight, as planned, cannot be completed due to the forecast low cloud
across the tiger country. However, there are seven possible alternatives you might like to consider. 

1. Let’s ponder the inland route via Taupo and the Desert Road corridor. Taupo is reporting no cloud – that’s
good. However, the cloud bases through the Desert Road summit area are forecast to be 2000 ft amsl, which
is well below summit height, so this is not a viable option. 

2. You could consider flying the route as planned and having a ‘look’ at conditions through the tiger country to
see if it is passable, but this would probably only be a viable option if the visibility was as originally forecast
i.e. 20 – 30 km. With visibilities of 12 or 13 km, this may be a risky proposition. 

3. A third option exists – that being to fly on down the coast to about Waitara, then head due south overhead
Stratford to Hawera, and then on down the coast to Whanganui. This may work out as the MSA along this
route is 1700 ft amsl, however, it doesn’t leave much room for error. If the cloud base is just 300 ft lower than
forecast, it’s a ‘no go’ option. 

4. Another option – try to get on top of the cloud if possible for the leg across the tiger country. HOWEVER,
there is an element of risk involved in this course of action. If the cloud cover increases to the point where
there are no suitable holes to get back beneath the cloud, you may find yourself in a nasty situation. Being
trapped on top of cloud (whilst not as bad as being trapped in a cloud layer), can still be very disconcerting,
especially if fuel is becoming an issue. And don’t forget, the tendency is for low-level moisture to increase
during the afternoon. 

5. You could consider flying east from Hamilton into the Bay of Plenty, then down the east coast of the North
Island – after all, the weather in much of the area is forecast to be fantastic. The problems? It adds a lot of
extra miles and therefore cost to the trip, and its likely you will run into the front somewhere near the
Manawatu Gorge, with a risk of isolated TCu and showers with visibility down to 7000 m. 

6. The best option however, if you absolutely must make this trip on this day, would be to stick to the coast
south of Awakino, and go via Cape Egmont. This way, alternate airfields at New Plymouth, and Hawera
become options and all high ground is avoided. 

                              Note however – a ‘must fly’ cross country flight should never be an imperative.

                                Too many pilots
have lost their lives by flying in poor weather conditions.  

                                   Get-there-itis is a very real and
dangerous threat, especially at PPL level.

7. A seventh, and final option also exists – if it is not important that you make it to Paraparaumu on this day,
consider rescheduling the flight to a day with better forecast weather.

Let’s now consider the additional products listed at the end of 8.52.2 (a) above, to see if any extra useful information
can be gleaned.

(Metservice, satellite images, radar image)

So, to summarise the procedures for accessing and interpreting weather conditions for a proposed flight… 

1. Before you start, set your own weather limits based on your level of training and experience. If needs
be, ask your instructor to help you complete this process. Note: as time progresses and you gain more
experience, you can push these limits out little by little. 

2. Access ALL the required forecast and observational data for the planned flight from MetFlight
(including the additional products as described in 8.52.2 (a) above, and in detail in 8.52.4 below). 

3. Take note of forecast and observed: 

4. Precipitation 

5. Visibility reductions 

6. Turbulence en-route 

7. Cloud bases and amounts 

8. Compare these weather variables with your own personal weather limits, and against the MSA values
noted on your navigation chart. 

9. Use local knowledge to help you make a go/no-go decision. ASK your instructor or some other
knowledgeable person for advice (but don’t rely solely on that advice). 

10. It is a good idea at this stage to make a few notes regarding any possible problems you could possibly
encounter weather-wise during the flight. 

11. Use the forecast winds to plan fuel consumption, and plan alternates for any unexpected poor weather
encountered and for refuelling purposes if needed. 

12. Make a mental or written note to continually monitor the weather, both ahead of, and behind you, and
be prepared to terminate the flight at any stage. 

Describe the limitations of non-aviation – specific weather information

There is a myriad of different sources of weather information available to anyone who cares to look for them: 

  

• • Internet 
•   Newspapers 
• • Television news bulletins 
• • Radio 
• • Your Aunt Daisy’s bunions 
• • A mate who lives 17km from the airfield you plan to fly into in the Southern Alps 
• • MetFlight 

Every one of these sources can get the forecast right on any given day (even if only by chance). And of course, any
one of these sources could give you a crook steer on the day. So, let’s look at each of these sources and assess their
usefulness or otherwise. 

Internet 

To test the weather information available on the internet, I searched for ‘Geraldine weather forecast’. 

There were many sites offering various forecasts for Geraldine, most of them from multi-national weather forecasting
companies and most obviously producing forecasts directly from global weather models. None of the companies
mentioned what model they were using. The shortest term of forecast was eight days into the future and the longest
gave daily forecasts out to 35 days in advance. 

Three things concern me as a forecaster. 

One – accurate daily forecasts beyond about 5 days are more a function of
luck, rather than good modelling, and 35 days and beyond is just ridiculous. 

Two – these multi-national companies
have no interest in the real flying weather anywhere in New Zealand. In fact, it’s highly unlikely that a human ever
looks at any of the New Zealand forecasts they issue, apart from perhaps Auckland, Wellington and Christchurch.
Three – the third thing that concerns me is the complete lack of detail. If a pilot were to consider flying somewhere in New
Zealand in say 12 days’ time based on one of these forecasts, they would be foolhardy in the extreme. 

Newspapers    

Newspaper weather pages are, for the most part, compiled by MetService and sent in camera-ready format to the
newspapers about 12 hours before publication. They typically contain a lot of local climate data, plus general NZ and
world forecasts. While these forecasts are OK, they are not written with aviation in mind. They are 12 hours old before
you see them, and possibly up to 24 hours old before you use them. 

Television news bulletins 

These forecasts are very good for general use, but they lack the detail appropriate to aviation use. And of course, if
you are viewing an evening weather bulletin, the forecast is for tomorrow, and you should really be accessing more
up-to-date aviation forecasts on the day that the flight takes place.

Radio
Forecasts 

Forecasts over the radio are an interesting proposition. There are a few suppliers in the market, but once again these
forecasts are not tailored to aviation. In addition, although some radio stations get regular updates, others, because
of the type of station they are and the audience they are targeting, pay lip service to accuracy and have been known
to read out yesterday’s forecast today. 

Your Aunt Daisy’s bunions 

There’s no doubt that a bunion or a dickey knee can play up just before rain, but as a forecasting tool for aviation,
they completely lack credibility. 

A mate who lives 17km from the airfield you plan to fly into in the Southern Alps 

Calling a mate down the line is fine if he has been trained to pass on Basic Weather Reports (BWR), and he is very
familiar with the local conditions etc. However, this method of gathering data for a pending flight can be fraught with  danger. Firstly, he may not be trained in properly assessing the weather. The weather where he is may be startlingly
diferent from a nearby mountainous airstrip, and while it may be fine at your departure point and at his location,
there could well be foul weather en-route. 

MetFlight 

It will not surprise anyone that I would recommend MetFlight to all recreational pilots in New Zealand. And now that
the government has made MetFlight available free-of-charge to private and recreational pilots, there is no reason for
pilots not to make good use of it. 

The forecasts in MetFlight are written by dedicated aviation forecasters who are writing these forecasts to exacting
standards, and who are truly dedicated to producing the best aviation forecast products that they can. From my time
as an operational aviation forecaster, I know that following a day where the forecast did not go according to plan,
most if not all the forecasters will come to work early the next day to pore over the previous day’s data and try to
spot clues as to why the weather didn’t do what they expected, and they will try to learn from the experience. 

BUT – and this is a big BUT. In mid-latitudes where we live, there is no such thing as a forecaster who gets his or her
forecasts perfectly right every time. Every forecaster, no matter who they are, who they work for, or where they work
will, from time-to-time, get the forecast wrong. Weather is an inexact science – especially in mid-latitudes. 

                        FORECASTERS DO GET THE FORECASTS WRONG FROM TIME-TO-TIME. 

And because the forecast is not a guarantee of the weather you are likely to encounter, it becomes crucial that you
understand what the forecast is telling you; that you learn about local effects and that you have a plan B or even C, if
your original plan begins diverging from that which you expected. 

The last chapter in this book, chapter 8.52 looks at how to select and interpret met information, and how to apply
local knowledge to your decision-making process. More importantly, it will help you recognise situations where the
weather is deteriorating (or is likely to deteriorate) and make appropriate in-flight decisions to survive when it does

With respect to NZ VFR operations interpret radar imagery available in MetFlight in terms of the following;

• a) Likely Cloud Types
• b) Precipitation types and intensity
• c) Speed of movement and timing and the expected impact at given locations

a) Likely cloud types;   Cloud types can be inferred from the precipitation signatures displayed in radar imagery.
In figure 90, all the precipitation signatures are of rain or drizzle, either in continuous or intermittent form. Rain and
drizzle only fall from stratiform cloud.
In this image, a rain-band is pushing down onto New Zealand from a sub-tropical low, which means this airmass
originated in the sub-tropics. This supports the idea that this precipitation is falling from layered stable cloud. So, in
this image we can infer that the cloud types are low-level stratus, along with stratocumulus, nimbostratus, altostratus
and cirrostratus.

(b) Precipitation types and intensity;    

In figure 90, although the precipitation is either rain or drizzle, it is falling in several different forms and intensities. 

•  The blue returns inside the red polygons: 
•  These are areas of continuous moderate to heavy rain. 
•  The yellow echoes within the light blue polygon: 
•  This is an area of continuous light rain and/or drizzle. 

 The blue echoes within the green ellipse: 

 These are areas of intermittent moderate to heavy rain. 

 The yellow echoes within the green ellipse: 

 These are areas of intermittent light rain and/or drizzle. 

 The yellowy/grey echoes within the purple polygon: 

 This type of precipitation signature frequently indicates the presence of virga (precipitation evaporating before it
hits the ground). Sometimes, light snow can also look like this. 

In figure 91, the showers of rain, hail, snow or sleet are of light to moderate (yellow), or moderate to heavy (blue)
intensity. 

(c) Speed of movement and timing and the expected impact at given locations.    

Predicting the onset of rain (from stratiform cloud) using radar imagery can be problematical, especially if a travelling
band of rain comes up against higher land. This is because rain ‘develops’ as a function of the depth of the cloud. For
example, rain spreading down from the NW onto the north Taranaki coast frequently appears to stall for a number of hours before suddenly and rapidly spreading into the Whanganui and Manawatu regions. The
phenomenon happens regularly in other parts of New Zealand as well. 

While not always accurate, the forecasts give you the best indication of when the rain will start to fall, as forecasters
have access to model data which considers this type of ‘sheltering’ effect. 

Bands of showers, however, will often move at a steady rate, and plotting the movement of the leading edge of a line
of showers using the radar imagery will often give quite accurate results. 

Figure 92 demonstrates how to calculate the arrival of a band of showers, or the leading edge of a swarm of showers
at Hamilton Airport. 

 Use the New Zealand Radar montage for this exercise. 

1. When the line of showers first appears on the edge of the radar image, use a water-soluble pen to draw a
line along the leading edge (for example, line A drawn at 2258Z). 

2. An hour or two later, check the radar again, and draw a second line along the leading edge (B at 0058Z). For
the purposes of this exercise, I have used a two-hour interval. 

3. Now draw parallel lines ahead of this second line with a similar spacing and continue these lines until you
have drawn a line past the location you are interested in. These lines, labelled C and D, represent the
approximate position of the leading edge, in this case at 0258Z and 0458Z.
4. Now you can interpolate between lines C and D to get an estimation of the arrival time of these showers –
in this case, the estimate for time of arrival at Hamilton will be approximately 0445Z (4.45pm NZST, or
5.45pm NZDT).

8.50.2 With respect to NZ VFR operations, using satellite imagery available in Metflight, identify the following;

• a) Areas of stable and unstable air
• b) Frontal cloud bands
• c) Position of lows and anticyclones

Figure 88 shows one of the standard satellite images available in MetFlight – the Tasman/NZ (IR) image. The same
image is shown in figure 89 with the addition of overlay information which highlights points (a), (b), and (c) for this
objective.
Fig. 88 An Infra-Red Sat

(a) Areas of stable and unstable air; 

Area 1: In figure 89, the areas marked with the number 1 indicate low-level stability. These areas are characterised
by vast slabs of stratocumulus cloud (coloured grey), or no indicated cloud at all, and are a classic signature
of stable anticyclonic conditions. 

Note: at times, low-level cloud like this will not show up on an infra-red image. This is because the
temperatures of the cloud tops and the underlying ocean or land are the same – therefore the sensor on the
satellite thinks it is looking at the sea or land surface and fails to register any cloud at all. At other times,
especially during winter, and mostly overnight or in the early morning, large portions of Australia, and inland
New Zealand will indicate a solid grey cloud layer, when none exists. This is because inland frosts have
cooled the surface to such an extent that the sensor on the satellite thinks it is detecting cold cloud tops
associated with a thick layer of stratiform cloud. These are both common traits of IR imagery. 

Area 1a:   As above, but with remnants of old high cloud above. 

 Area 2:  This area (within the green boundaries) shows mid-level and high-level cloud (bright white) associated with
both warm and cold fronts. Much of this cloud will be stable in nature, however, there will be large areas of
embedded Cb clouds, especially near the cold fronts. Part of this cloud is also due to the presence of a
high-level jet stream however, it is difficult to distinguish the frontal cloud from the jet stream cirrus. 

Area 3:   This is an area of cloud associated with a weak cold front. It is mostly stratiform with some embedded TCu. 

Area 4:   This area is very unstable and contains active cumulonimbus clouds (light grey clumps) which are slightly
spaced out as individual cells. Meteorologists refer to this type of cloud mass as ‘open cellular’ clouds, and
they deliver showery conditions with occasional thunderstorms. 

Area 5: This area is also open cellular, however this airmass, whilst still displaying evidence of instability, is nowhere
near as unstable as area 4. Area 5 is full of cumulus and small towering cumulus clouds (speckled grey) and
delivers mostly light showers.

(b) Frontal cloud bands;   The fronts on figure 89 are indicated as follows: 

• Light blue lines            Cold fronts (note the dashed blue line is a weak cold front). 
• Red lines                     Warm fronts or sectors. 
• Purple line                   Stationary front. 
• Dashed orange lines   Trough lines. 

(c) Positions of lows and anticyclones.   These are all indicated by L’s and H’s on figure 89.