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Question About Pressure


johnhk

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I really wanna ask... It is a MUST that low pressure will bring worse weather but HIGH pressure always bring fine weather to that place??

Today, 2/6/2006...there is a though of LOW PRESSURE affecting Hong Kong....according to the Weather Chart,

pressure in Hong Kong is about 1008mb which giving Hong Kong worse weather.....rain and thunderstorms for about

4-6hours which are quite heavy.

Weather Chart from Hong Kong Observatory

wxcht05.gif

Isohyet Chart from HKO

rfmap1230e.png

Thanks for answering

John :D

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Posted
  • Location: Coventry,Warwickshire
  • Location: Coventry,Warwickshire

    Generally low pressure gives more unsettled weather and high pressure more settled weather. This is due to the fact that air tends to sink in high pressure conditions and rise in low pressure conditions. As air rises it cools and releases moisture to form clouds. Other mechanisms can force air to rise and form clouds for example where an area of cold air moves in at low levels rising up the warm air ahead of it (a cold front) or by convection which often gives thunderstorms. Convection is where air does not cool down fast enough as it rises compared to the surrounding air and keeps rising until it hits a warmer layer high up.

    Although high pressure generally mean settled and warmer conditions it does depend on the direction the high pressure is moving and where the air has been as to the specifics of the weather. High pressure moving north can often give grey blankets of cloud especially if the air has become moist over the ocean.

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    Posted
  • Location: Lincoln, Lincolnshire
  • Weather Preferences: Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.
  • Location: Lincoln, Lincolnshire

    I tend not to favour words like "better", "good", "bad" and "worse" as they are highly subjective- while the majority of the population prefer warm dry sunny weather, there is variation from individual to individual.

    What Brick says above is accurate. In general, low pressure is more likely to be associated with fronts (which bring bands of persistent rain) and strong winds. When there is no major frontal activity associated with the low, as is illustrated on those charts, conditions will tend to be "convective", with sunny spells but also showers and thunderstorms, so you will get quite a mixture.

    High pressure weather is "settled" in that the weather tends not to change much during the day. High pressure is often, but not always, conducive to warm, dry and sunny weather. Sometimes fronts trapped within the high, or a moist airmass trapped within it, will bring blankets of cloud. The high prevents air parcels from rising high into the atmosphere and producing convective rainclouds, but it can also cause cloud embedded within the high to spread outwards rather than upwards, resulting in dry cloudy conditions and maybe a little drizzle.

    However, the above considerations of cloudy drizzly weather and persistent rain are probably more of a British climate thing than something that applies much to Hong Kong- I reckon that in most cases, high pressure in HK would equal warm dry sunny weather, and low pressure would equal sunshine, showers and thunderstorms.

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    lol, I forgotten the basic concept of pressure for me asking this stupid question. Anyway, I learn more than I learnt from school textbook.

    Thanks for answering anyway, I would not using those subjective words to describe the weather next time, thanks for reminding.

    Hong Kong will still affect by those though of low pressure....

    Thanks anyway.

    John...(noob)

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