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Strange METAR or TAF / METAR or TAF interpretation

EGKK 260502Z 2606/2712 VRB03KT 3000 BR FEW035 PROB30 2606/2607 0600 FG BKN001 BECMG 2607/2610 9999 NSW PROB30 2700/2707 5000 BR BECMG 2707/2710 10010KT TEMPO 2709/2712 7000 RA

Take a flight tomorrow (27th) after 0800Z.

This is interesting in two ways.

Firstly they have

BECMG 2607/2610 9999 NSW

and that extends all the way to the end of the TAF. Yet they have

TEMPO 2709/2712 7000 RA

but how can NSW be the case with RA, practically? Could there be RA with a cloudbase which was previously high enough to warrant NSW?

From here

If no significant weather is expected to occur during a specific time period in the forecast, the weather group is omitted for that time period. If, after a time period in which significant weather has been forecast, a change to a forecast of no significant weather occurs, the contraction NSW (No Significant Weather) will apear as the weatehr group in the new time period. However, NSW is only included in the BECMG or TEMPO groups.

I can't find a definition for NSW itself. It certainly isn't CAVOK but what are the requirements?

The other subtlety worth a mention is that the RA is forecast till 1200 but since the TAF itself is valid till 1200 also, the rain is in effect forecast to potentially exist past the end of the TAF.

Administrator
Shoreham EGKA, United Kingdom

Without looking up the defination, I would read it as, No significant weather being the prevaling conditions but temporary conditions, lasting less than 50% of the forecast time, there will be some rain.

Ie. Generally good, but occasional showers.

EIKH Kilrush

I can't find a definition for NSW itself.

In NSW "Weather" refers weather phenomena a list of which can be seen here: http://www.crh.noaa.gov/lot/aviation/tafcode.php#Weather

EDDS - Stuttgart

That's the URL I posted in my 1st post.

If instead of

BECMG 2607/2610 9999 NSW PROB30 2700/2707 5000 BR BECMG 2707/2710 10010KT TEMPO 2709/2712 7000 RA

they had written

BECMG 2607/2610 9999 NSW PROB30 2700/2707 5000 BR BECMG 2707/2710 10010KT TEMPO 2709/2712 BKN 015 7000 RA

that would make sense to me.

Administrator
Shoreham EGKA, United Kingdom

That's the URL I posted in my 1st post.

:-) (That happens when you write "here" in your posting instead of the full text)

that would make sense to me.

You are right. But probably they can't even make an educated guess at this time regarding the cloud base, therefore they only predict weather phenomena.

EDDS - Stuttgart

OK, I think I get it.

RA is a "phenomenon" but e.g. BKN002 is not a "phenomenon".

So you could have BKN040 followed by NSW followed by BKN002 RA but the BKN002 will be left out.

Administrator
Shoreham EGKA, United Kingdom

RA is a "phenomenon" but e.g. BKN002 is not a "phenomenon".

Yes, only what comes out of the cloud but not the cloud itself (or the effect but not the cause). It's logical in a sense, because they also don't predict the location of the high and low pressure areas (the cause) but the resulting wind (the effect).

EDDS - Stuttgart

RA is a "phenomenon" but e.g. BKN002 is not a "phenomenon".

Exactly. The only thing that doesn't make sense to me is NSW in corelation to BR. Or visual limitation is not considered as phenomenon as well?

LDZA LDVA, Croatia

Not quite sure what you feel the problem is. What you've effectively got is

VRB03KT 9999 FEW035 NSW TEMPO 2709/2712 7000 RA

So prevailing condition is no sig wx, but temporarily rain. (NSW in the first part would be omitted, it's only there because it was part if the BECMG)

Could there be RA with a cloudbase which was previously high enough to warrant NSW?

You don't mean that, I think. You mean "Could there be RA with a cloudbase which is high enough to warrant NSC (or if the vis is 9999, CAVOK)?" And the answer is yes.

You don't mean that, I think. You mean "Could there be RA with a cloudbase which is high enough to warrant NSC (or if the vis is 9999, CAVOK)?" And the answer is yes.

I did mean what I wrote, but it seems to be based on my non-understanding of NSW.

I thought NSW trumps the FEW035. Clearly not.

It's also very unlikely to have RA coming out of FEW035, but clearly it's possible.

Administrator
Shoreham EGKA, United Kingdom
102 Posts
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