During July the typical weather conditions affecting Darwin area is dry season, mainly SE winds, visibility reduced by dust and haze.
The outflow of air from the Siberian high over northern China and Japan is initially north westerly.
Considering Melbourne in July, the weather is predominantly influenced by the zone of:
A) subtropical high pressure, with the occasional passage of fronts originating in the adjacent zone of westerly waves
B) disturbed temperate low pressure, bringing an almost continuous succession of fronts resulting in strong winds, low cloud and rain
C) equatorial low pressure due to the proximity of the intertropical convergence zone over central Australia
D) Antarctic high pressure due to the absence of any protective land mass between south Australia and Antarctica
July is the southern hemisphere winter. The ITCZ is well north, the southern hemisphere sub-tropical high pressure is over the centre of Australia and the polar front is just south of Melbourne. Source: (http://www.atpforum.eu/showthread.php?t=12073)
8/8 stratus base 200 ft/AGL is observed at sunrise at an aerodrome in the north of France; the QNH is 1028 hPa and there is a variable wind of 3 kt. What change in these clouds is likely at 12:00 UTC in summer and winter?
Winter: OVC base 500 ft/AGL; summer SCT base 3000 ft/AGL
Concerning the variation in wind speed between summer and winter on the North Atlantic between FL 300 and FL 400, the average westerly component is greater in the winter than in the summer. The latitude of the axis of greatest seasonal wind speed is further south in winter than in summer.
Surface visibility is most likely to be moderate in a warm sector of maritime tropical air during a summer afternoon in western Europe.
Satellites images provided by the Weather Service are used to locate fronts in areas with few observation stations.
An anemometer (instrument for measuring wind) is placed on a mast 6-10m above the runway.
Hail causes echoes on meteorological radar screens.
Normally, temperature readings are taken at a height of 4 feet (1.25 m) in a Stevenson Screen.
A cup “anemometer” and remote transmitting vane form the transmitting head of the electrical “anemograph” enables a continuous record of wind direction and speed to be made on a moving chart.
Barometric tendency is measured on a “barometer” and recorded on an aneroid “barograph”.
Best approximation for the wind speed at flight level 250 is by interpolation of the wind information available from 500 and 300 hPa charts, while also considering the maximum wind information found on the Significant Weather Chart.
The radiosonde can directly measure below 5 kts.
A radiosonde (Sonde is French for probe) is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. A rawinsonde is a radiosonde that is designed to only measure wind speed and direction. Colloquially, rawinsondes are usually referred to as radiosondes. Modern radiosondes measure or calculate the following variables:
– Geographical position (Latitude/Longitude)
– Relative humidity
– Wind (both wind speed and wind direction)
– Cosmic ray readings at high altitude
– Radiosondes measuring ozone concentration are known as ozonesondes
All pennants and barbs lie to the left of the wind shaft in the northern hemisphere and to the right of the wind shaft in the southern hemisphere. Source: (http://www.atpforum.eu/showthread.php?t=8361)
A SPECI is an aviation selected special weather report.