METAR ADVANCED INTERPOLATION - ZERO WIND

[neilfwright 0]

........and at many other regional airfieds in New Zealand. Unfortunately, SP1 did not fix the problem.Neil

[JSkorna 137]

Hi All,I would need to know the interpolation details for each situation. Remember that if an actual station is a long ways away, the effect of that data will be small on the interpolated station.

[vadriver 248]

JimI suspect NZ is one of those rare examples of having only 3 NOAA stations (NZAA, NZWN & NZCH) basically north south of each other and an average of about 180nm apart. There are no stations east or west within any worthwhile range.Any interpolations are thus somewhat limited - but one assumes in the case of NZQN its interpolation is mostly NZCH based as it is south therof again (ie of the most southern one reported.)This fact / interpolation is accepted as a limit for ASE - but to me it does not "explain" why the wind is always 225 @ 0, no matter what it is at NZCH and that at the same time an interpolation for the airport's navaid nearby has plausible wind & temperature.I did at one time suspect that the fact that NZQN and my other regular airport (with the same problem) NZRO are about 1000` elevation may be an explanation / clue.For now, I will continue taking notes !CheersJohn

[vadriver 248]

Hi All,I would need to know the interpolation details for each situation. Remember that if an actual station is a long ways away, the effect of that data will be small on the interpolated station.

JimAttached 2 screenshots - one for NZRO & one for NZQN - of NZ airports where this zero wind problem continues to occur.Hope you can use these to sort out an answer !CheersJohn

[JSkorna 137]

Hi John,In the first example one station is 2700 miles away, one is 4150, and the other 925. There is no way any of those stations can have an affect. Then the other is almost 200 away. So all their influence is going to be near zero.The second example has 1100 and 3100 mile distant stations, a 200 and then the only one with a chance is 100 miles away.I did just try at NZRO and got a 5kt wind. I do have DWC On in ASE.

[vadriver 248]

JimAs you replied, and about an hour apart, there was firstly a "plausible" metar (a first for me) & then a zero wind / low temperature one - at NZQN and with continuous use of ASE.You will note in the first instance the blank interpolation details !!I am not a user / fan of DWC, so maybe the subtle difference ??Cheers againJohn

[JRBarrett 3,078]

In the first example one station is 2700 miles away, one is 4150, and the other 925. There is no way any of those stations can have an affect. Then the other is almost 200 away. So all their influence is going to be near zero.

One of the stations (NZSP) is at the Amundsen-Scott base in Antarctica, with a temperature of -66C (which is -86 F!). Even if that station is only contributing say 3% to the interpolation mix (due to distance) would not that extremely low temperature be enough to cause the interpolated temp at NZQN to be 10 degrees too low?Or, to put it another way, something is causing the NZQN metar to be too cold - if it's not coming from the Antarctic station at 2700 nm, then where?Any chance that the "NZ" prefix of the South Pole station is causing it to have more weight in the interpolation than it should otherwise? Based only on the prefix, it would appear to be a New Zealand airport, even though it really isn't.Jim Barrett

[JSkorna 137]

Hi,NOAA is reporting M59 right now so M66 was accurate then.So look at the temps of the other 3 airports 24, 8, and 12. Then factor in the M66 and M06 is possible. Also ASE doesn't base anything on the IACO codes, only what is the closest station with data.All of this is just a limitation of the data when actual stations are so few and far between.

[JRBarrett 3,078]

Hi,NOAA is reporting M59 right now so M66 was accurate then.So look at the temps of the other 3 airports 24, 8, and 12. Then factor in the M66 and M06 is possible. Also ASE doesn't base anything on the IACO codes, only what is the closest station with data.All of this is just a limitation of the data when actual stations are so few and far between.

Yes, it staggers the mind to think that it can be that cold on the earth's surface - but not at all unusual for Antarctica (or in Siberia during the N. Hemisphere winter).I suppose the only solution insofar as ASE is concerned would be a sanity checking routine in the interpolation logic, to reject a temperature entirely from the mix if it differs from the other 3 stations by more than a given amount. Jim Barrett

[vadriver 248]

GentsMay I refer to the topic's initial inquiry, namely wind & to a lesser concern other weather elements.In all examples - except the one that had wind (without DWC) plus plausible temp / cloud / visibility elements - the stations for the interpolation had wind, yet irrespective of their "distance away", the interpolated weather had zero wind.I remain more curious about this than temperature & why on an odd occassion one gets (plausible) interpolated weather without any apparent "reason" !!CheersJohn

[JSkorna 137]

Hi,Because their distances are too far away to have an effect.

[tanj 0]

Hi,Philippines, which has really few METAR stations (maybe just three ? RPLL, RPVM and RPMD) really suffers from this problem.All wind directions are 225 with 0 knots on ground.Example for RPUN, which is 75NM away from the nearest station RPVM: RPUN 222351Z 22500KT 10SM FEW038 BKN113 27/25 A2968