Met.Net.NZ Met Notes
Rosie Weather


Time
GMT, UTC and Z (Zulu time) are practically the same.
However, there is a difference of nearly a second between GMT and UTC. UTC at Greenwich, whose time zone is denoted by Z, is often given the suffix Z.
Also see Time & Space
Radio Bulletins
Radio NZ

This National Radio site has the latest reports for urban and coastal forecasts.
Weather bulletins (following the news at these time)
Short: Hourly, except 7:00am (and not 7:00pm on weekends)
All districts: 5:30am & 6:30am (7:00am on weekends)
Regional centres: 7:30am (also 8:30am on weekdays)
Long-range: 12:30pm
Coastal: 3:00am & 5:00am
Mountain: 4:00pm
There are other briefs for main centres only (go the the link above).

Listen to it
AM/FM Frequencies, Shortwave, Internet, Sky Digital &: FTA Satellite


Radio New Zealand International Shortwave Service

RNZI provides weather bulletins for the Pacific (but few on weekends). Their complex and changeable frequency plan is published twice a year. Note that they will provide cyclone advisories outside their normal programme

MetService Radio Fax

MetService operates a radio-facsimile service (ZKLF) broadcasting marine weather charts over the Pacific Ocean south of the equator.

IR satellite images
Lower level cloud is often warmer. It therefore shows as less white than the frozen upper level clouds in the infrared images.

Weather radar images
Ducting and false echoes can affect radar images. Take this into account when viewing. The radar reflects off water droplets. Often only the leading edge of rain clouds are observed as they leave little signal to return from further back in the cloud. Ice and snow do not reflect radar except that there is usually some melting that makes it reflect brightly like a thin band of enlarged (by the icy cores)raindrops.
NWP tips
Typical Numerical Weather Prediction models provide a set of computer generated charts presenting a useful range of meteorological variables defining the global troposphere at various times. The variables include: relative vorticity, 500hPa altitudes, 850hPa temperatures, 300hPa streamlines and isotachs, ocean wave height, relative humidity, precipitation rate, mean sea level pressure (MSLP) and surface wind speed and direction. What more could you ask for?

I believe that checking the difference between the models can, to a degree, indicate the level of chaos or predictability in the situation.

'The [COLA charts] show both the surface and upper situation on the same map. Surface pressure isobars are shown as solid lines (coloured on the MRF charts), and the pressure is marked on these lines (e.g. 996, 1020). But also look for the dashed lines (solid black on the MRF charts). These are known as thickness lines and measure the distance between the 1000 and 500 hPa levels as you go up in the atmosphere. The average distance is about 5.5km, or 550 decametres or 5500 metres, which are the measures used on the maps. Warm air is thicker than cold air, so lines marked 550 (or 5500) and above indicate that the bottom 5km or so of the atmosphere is fairly warm. A thickness below 540 (or 5400) indicates a pretty cold lower atmosphere, and below 530 is really cold!
The ECMWF charts show the surface and upper forecast situations separately, and the upper chart shows the height of the 500hPa pressure level above the surface. This is not quite the same as thickness, but in practical terms is similar.
If you are comfortable interpreting surface weather maps, try to become familiar with the upper situation too, as upper 'cold pools' and tongues of warm tropical air pushing down from the north are just as important as the surface pattern in deciding our weather.
Be very careful to check the times and dates for which each chart is valid.'
(Text copied from Laurier Williams' site)
Vorticity & synoptic-scale circulation
On the surface in the Southern Hemisphere
- negative relative vorticity is cyclonic
- wind around a cyclone blows clockwise (map view)
- with the wind at your back, the cyclone is to your right (Buys Ballots Rule)
- cyclonic wind is convergent below, upward and stretching through and divergent atop
- convergence also occurs where sea wind slows as it meets land, is lifted by land or frontal slope, or is funnelled (confluence)
- cyclonic areas have lower air pressure than surrounding areas
- 'friction' layer below about 3000ft causes the slowed wind not to follow isobaric lines
- a Nor-West wind comes from the North West
- a NW wind at < 30deg. to normal on the line along the Southern Alps supports a Canterbury foehn Nor-Wester
- tropical cyclone degrade to become tropical storms
- cyclones generated outside tropical latitudes are referred to as depressions

Integrated Publishing's free online information
Aerographer's / Meteorologist's basic training series
Aerographer's / Meteorologist's intermediate training series
Vorticity


Last updated: 8 March 2006
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