What to look for
There are four broad areas you might want to consider for detailed weather reports:
- Convective activity.
- Wintry weather.
- Severe winds.
- Other 'interesting' phenomena.
1. Convective activity
Note particularly the development of the cloud/s giving rise to the thunderstorm/tornado/waterspout/etc. What we are looking for is the rapidity of build of the cloud; its vertical extent in a noted time. Is it building directly upwards, or sheared to one side? Is it possible to determine whether you are observing a single or multi-cell complex? Is any rotation observed in the cloud elements etc? What was the wind regime, before, during and after the event? Note particularly the onset of notable gustiness, changes of wind in direction/speed as compared with onset of precipitation etc. Was a sea breeze front involved? This can sometimes be inferred by a change in humidity (it should 'feel' more humid), and there may be a line of precursor cumulus development, with a change in visibility and wind direction perhaps.
The type, duration and intensity of precipitation (abbr: ppn) should be noted; the Beaufort shorthand notation can be usefully employed for this.
If possible, amounts of liquid and/or solid ppn should be recorded, particularly accumulations of hail and snow, the diameter of hail, the appearance of hail (i.e. cloudy, translucent, mixed layers - these will define the various cloud regimes that the hail-stone has spent its life amongst.); the type of snow/pellets etc., and if possible, determine which portion of the cloud the ppn appeared to originate from. for advice on types of solid precipitation, see here.
In very severe rainfall events, its worth noting how water-butts and other containers fill up and to what extent. Whilst not being used to give a definitive rainfall amount, they can sometimes help to verify the order of magnitude of adjacent reports when the final report is written. Note the winds aloft prior to the storm onset. Severe convective storms form in an environment of marked vertical wind shear, both in direction and speed and this can sometimes be inferred from visual observations. Be careful to judge such motion against a static object though. Its easy to be deceived by relative motion of other clouds. You can usually position yourself in such a way as to have a tree, or corner of a building, or pylon or similar in the eyeline to provide the 'fixed' point.
Note the cloud features preceding the event, in particular any Altocumulus castellatus, floccus or towering cumulus development. Note the damage caused, flooding experienced etc. In particular, the period over which flood waters both rise, and subside, and the horizontal extent of the flood waters. Hail and wind gust damage reports are most useful, and the TORRO event reporting form is the best place to refer to for guidance on these aspects. see: http://www.torro.org.uk/
Although winter doesn't necessarily mean snow, that's the element that interests a great many people dipping in to the newsgroup. As an aside, although the UK radarnetwork can detect areas of precipitation very well, there are problems with detecting areas of rain versus snow, due to the narrow temperature/humidity band within which the phase-change occurs. The more reports of snow (or not-snow) are made, the better is the overall picture. Also, the more reports of snow lying are made the better as the 'synoptic/climatological' network doesn't always pick up the variability of nation-wide snow cover. A record of the times of onset/cessation of 'wintry precipitation', intensity, types etc. should be made, together with accumulations. This means not only noting the total depth of snow, but also the accumulation of fresh snow on top of old snow cover.
Is the snow drifting or blowing? Some types of snow will drift more that others - note whether snow is drifting after having earlier fallen, or is blowing around as it falls. In blizzard conditions the distinction will not always be clear. Note how old snow settles..its continuity (complete or patchy cover) and regularity (an even depth or irregular depth, with drifts)..its persistence from day to day.. try to note the depth/extent etc., at 0900 GMT as this is the reference time for snow cover for climatological reports, and your report can be integrated with other observations. Simply coming on line just after 0900GMT and reporting ....'I've got a snow cover of 2 cm', or ' all yesterdays snow has gone', can be a great help in gauging the overall picture.
Remember that snow can evaporate (sublimate) and settle, as well as melt, so get into the habit during a prolonged spell of snow-lying of always measuring the snow depth in the morning - don't assume its still the same depth just because its still there. Take three samples of undrifted snow that represent the 'general' picture, and average out, but also report notable departures from these readings. Garden canes etc., can sometimes be used as semi-permanent depth markers, provided of course the underlying soil isn't so frozen that you can't push the cane in the ground! In particular, dimensions of notable drifts will always be of interest. Note cases where heavy rain aids snow melt etc. Glazed ice - measure thickness - rapidity of accumulation - temperature fluctuations before and during event. The weather immediately preceding the event. Length of the event and consequences on traffic etc. Photographs of these events are always interesting.
In particular, damage reports are most useful. Is the damage observed in a narrow/focused swathe, or widespread and indiscriminate. What is the scale of damage - i.e. a few minor branches, whole trees, chimney stacks down etc. The period during which the most damage was caused. Any special features .. twisting of branches, tree trunks etc. Other weather changes as damaging gusts occurred .. i.e. cold front/trough passage/squall line/cloud changes/ppn changes etc.
Wind observations are very important, especially when noting severe convective events. Even without expensive anemometers etc., just noting the direction and Beaufort Force of the wind can be interesting. (for advice on using the Beaufort wind scale, see: http://www.zetnet.co.uk/sigs/weather/Met_Codes/codes.htm ... and indeed this is the url for a complete introduction to many of the finer points of coding/de-coding etc.
These reports include such as optical phenomena, coloured precipitation, unusual objects falling in rain showers, unusual (or rarely seen) cloud types etc. As much detail as possible should be included, and if you are not sure what it is you are looking at, someone will do for sure! I have deliberately not gone into details here, as the subject is vast.
A general note on standards etc.: (thanks to Paul Bartlett for additional suggestions here) Some people contributing to the newsgroup will have access to some pretty sophisticated observing equipment which provide valuable record of weather events. However, if all you have is a plastic gauge from the garden centre, or a Six's max. and min on a north wall, don't be put off providing the information.
For reports of wind speed and direction: try using the 16 point compass (and remember that the wind comes from a direction, so a SSW wind comes from the SSW), and the Beaufort scale, as already mentioned above. So, a wind observation might be SSE/4 gusts 5; or, upon a cold frontal passage, SSE/3-4 becoming SW ocnl W 3 gusting 4 or 5.
Reports of temperature should be in degrees C. Don't try for 1/10's degree accuracy unless the thermometer allows it. Try for the nearest half of a degree, but say that that is the standard to which you are observing.
Atmospheric pressure (reduced/corrected to msl) in millibars/mb (or hecto Pascals if you prefer/hPa). Similarly with pressure change: the usual period to note a pressure change over in temperate latitudes is 3 hours, but hourly changes are valuable where possible. [ In subtropical/tropical regions, 24 hour changes are usually used, to eliminate the influence of diurnal changes. ]
Reports of rainfall (or melted snowfall) should be in mm. Dimensions of solid precipitation (e.g. hail), should be cm, as should snow depth.
Cloud amounts can be made in oktas (eighths of sky covered) ...see here for some advice on this, or more generally, the aviation cloud amount classification could be used, as under:
SKC: no cloud at all
FEW: 1 or 2 eighths/oktas of cloud
SCT: 3 or 4 eighths/oktas of cloud
BKN: 5 to 7 eighths/oktas of cloud
OVC: 8 eighths/oktas of cloud - i.e. complete overcast.
Cloud base will be difficult, and I won't go into detail on estimation of cloud bases. The Observers Handbook is your best guide. At present, the foot is still the 'standard' for cloud height observations, but many countries use metres so I suppose either is acceptable.
As to standards, as long as you tell people how you are measuring the variable you report, they can make their own judgement of relative accuracy. It would be a pity to lose data because you might feel its not of sufficient quality. Quite frankly, there is never enough data on current weather, and with the situation in many areas now where official 'eyeball' observations are too expensive to maintain, amateur observations, carefully made and reported, will once again come into their own.
And a final thought...don't be shy of saying you don't know what it is you are seeing. Either someone will pop up with the right answer, and we'll all learn by it, or it might genuinely be something 'new', and stimulate a discussion... which after all is what uk.sci.weather is all about.
Here are some specific notes regarding the observing and reporting of "dust-falls" after rainfall. I am grateful to Stephen Burt for this:.....
" Observing a fall of dust rain is not difficult, but it helps to have some ideas of what to look out for. A daily routine also helps (such as, in my case, the morning inspection of the raingauges) but even a few seconds careful examination of the car windscreen before driving to work can be worthwhile. If you own a raingauge, check the funnel daily for a ring of dust, often pale orange in colour and very fine in texture. The larger the funnel, the better: the largest falls even show muddy streaking. Most dustfalls are considerably less obvious than this, often with only the pale ring at the neck of the funnel visible.
Surprisingly perhaps, the actual rainwater sample collected may not be very obviously different from normal (at least visually). In my experience, dust rain is most obvious with small amounts of rain, certainly less than 1-2 mm, for otherwise much of the evidence is either washed away or so dilute as to be unrecognisable. Perhaps this is the fate of many falls of dust. Many of my observations of dust rain have been in overnight rainfall, possibly because my raingauge is normally checked only once per day at the morning observation.
Another excellent instrument for observing falls of dust is a car, preferably a clean one. Even on a car that is fairly dirty a heavy fall of dust will be very obvious as muddy runs on surfaces that are cleaned regularly (generally the windscreen). A clean car will collect a fall of dust extremely well; the aggravation of having just washed it should be balanced by the thrill of having recorded a fairly rare event! Of course, dust from considerably closer than the Sahara can build up on a car or in the raingauge funnel, particularly after a long dry spell. A regular wipe with a clean damp cloth solves that problem in the raingauge funnel.
Locally-deposited wind-borne dust (especially prevalent during hot, dry summers) is often coarse in texture. Beware of pollen in spring and early summer; light showers can bring down considerable amounts and can deposit a surprisingly yellow ring in the raingauge. Harvesting operations during late summer can stir up a lot of fairly fine dust, but common sense (not to mention a check on the synoptic situation) will usually enable an astute observer to ratify a possible sighting." (Extracted from the paper: Falls of dust rain within the British Isles,Weather 1991, 46, pp 347-353, by SHFJ Burt...text of above also published in uk.sci.weather newsgroup)