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Q for meteorologists here: why SHRA not DZ?

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Q for meteorologists here: why SHRA not DZ?

Old 28th Feb 2014, 20:53
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Q for meteorologists here: why SHRA not DZ?

Today I sit at home in the Sydney area watching the DZ (occasionally perhaps -RA) out the window. It's my boy's 4th birthday party so I consult the YSSY TTF & TAF.

There seems to be a warm moist air mass moving over NSW, so tropical maritime air moving into a cooler region. That sounds like stratiform cloud, drizzle and/or rain to me. Looks like it too.

It really doesn't appear at all like showers of rain: small areas of precipitation from cumuliform cloud, with good visibility between outbreaks.

To the question then: why has BoM said SHRA on all the aviation forecasts instead of DZ or RA?
Oktas8 is offline  
Old 28th Feb 2014, 21:58
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Get a micrometer and measure the drop size - we're getting DZ at my place right now which in my book is that very fine stuff that almost floats rather than falls.

Anyway, it's an important issue and I think we should be told! Get A Current Affair on to it, I say!
Arm out the window is offline  
Old 28th Feb 2014, 22:14
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DZ at my place too Arm! We must be close by...
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Old 28th Feb 2014, 23:02
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Q for meteorologists here: why SHRA not DZ?

Whatever it is, it was really welcome at Albury overnight. First significant DZ since Christmas.
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Old 1st Mar 2014, 00:08
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Oktas8, are you within 5nm? If not then that forecast doesn't necessarily apply you to and you might be getting DZ where you are but around there it might be SHRA
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Old 1st Mar 2014, 06:07
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As Ixixly said, the range of an aerodrome forecast is only 5nm. which means you'll need to consult an area forecast or other forecast from BOM. (unless of course you live within around 10km of sydney airport
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Old 1st Mar 2014, 07:56
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Folks,
Today, where I have been, the WX has been RASHIT ( seriously, I still have a copy of a TTF for Manila in the above terms) and it describes today very accurately.
Tootle pip!!
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Old 1st Mar 2014, 08:48
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Did anyone keep a copy of the BN TAF (or must have been the area) from a couple of years ago - described the forecast entirely in sporting terms (boxing or rugby)? Only wish I'd kept a copy.
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Old 1st Mar 2014, 08:52
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The 5nm is a good point, except...

It's not usually possible to have SH in one place and DZ only a few tens of miles away. One requires an unstable or conditionally stable airmass, while the other requires a stable airmass. Airmasses are larger than the TAF effective radius, obviously.

Also, all the airfields around the Sydney basin were forecasting the same thing.
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Old 1st Mar 2014, 08:55
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Perhaps in an effort to make weather prediction more accurate they've been playing with a weather device/dooms day weapon?! That way they know exactly what the weather is going to be...because they MADE it that way, muahahaha!!!
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Old 1st Mar 2014, 12:50
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described the forecast entirely in sporting terms (boxing or rugby)?
T'weren't there a Christmas Day ATIS in Alice Springs or Darwin yonks ago in a somewhat similar theme?

Paging Tinpis et al!
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Old 1st Mar 2014, 13:18
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Seems a lot of the time they just tell us SH and don't tell us showers of what. Guess then they're not wrong whether it's RA, DZ, or even hail for that matter.
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Old 2nd Mar 2014, 01:10
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It's all about size, Oktas (many women will tell you that too).

Drizzle is the lightest form of precipitation, consisting of water droplets which are only just large enough to fall (average droplet diameter of 0.4mm). Unlike fog droplets, drizzle falls to the ground.
When small water droplets are falling, this is called Drizzle and are very much more numerous than light rain and so accordingly, it reduces visibility more.

Water droplets of larger diameter and velocity are "rain"

SHRS relates to the time period and intensity. "Showers are characterized by the suddenness with which they start and stop, by the rapid changes of intensity, and usually by rapid changes in the appearance of the sky."

Hope this helps
(twas good revision for me)
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Old 2nd Mar 2014, 09:42
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Might be worth remembering that the BoM staff aren't aviators too? They don't really think about the significance of the type of precipitation (or clouds) to pilots. Perhaps mentioning showers is their way of covering their backsides? Showers indicate convection;etc. Perhaps the best bet is to do your own observation and forecast based on their best guess, maybe?
Cirronimbus is offline  

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