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Aviation weather thread

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    #152
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Carnacalla wrote: »
    Dublin's Temperature has been fairly jumpy!

    20:00 0c
    20:30 -3c
    21:00 -1c
    21:30 -3c
    22:00 -2c

    A bit strange. The synops gave a steady cooling trend as the sky cleared. I don't think those half-hourly METARs are correct. Very unlikely to get such fluctuations in these conditions.

    18:00 2.1 (2/8 cloud)
    19:00 0.9 (1/8 cloud)
    20:00 0.1 (1/8 cloud)
    21:00 -1.0 (0/8 cloud)
    22:00 -1.9 (0/8 cloud)


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    #153
    JCX BXC
    Registered Users Posts: 18,114 ✭✭✭✭JCX BXC


    Reporting -4 now!


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    #154
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Carnacalla wrote: »
    Reporting -4 now!

    And yet only -2.8 on the 23Z synop. The metars are wonky.


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    #155
    smurfjed
    Registered Users Posts: 10,044 ✭✭✭✭smurfjed


    synops
    Where are the synops measured?


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    #156
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    smurfjed wrote: »
    Where are the synops measured?

    The same as the metars. Both are manually reported. Just not sure why the metar temps seemed off on the half hours, though the 23.30 one looks more in line now.


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    #157
    JCX BXC
    Registered Users Posts: 18,114 ✭✭✭✭JCX BXC


    FZFG in the forecast for NOC,ORK and DUB for the morning.


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    #158
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Carnacalla wrote: »
    FZFG in the forecast for NOC,ORK and DUB for the morning.

    And Casement now too.

    TAF EIME 242000Z 2421/2506 28005KT 9999 SCT025 SCT045
    TEMPO 2423/2506 4000 BR
    PROB30 TEMPO 2503/2506 0800 FZFG FEW004=


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    #159
    bronn
    Registered Users Posts: 482 ✭✭bronn


    Carnacalla wrote: »
    FZFG in the forecast for NOC,ORK and DUB for the morning.
    Sounded like you sneezed there. :pac:


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    #160
    BMJD
    Registered Users Posts: 2,694 ✭✭✭BMJD


    Gaoth Laidir wrote: »
    And yet only -2.8 on the 23Z synop. The metars are wonky.

    They aren't wonky. There can be a few minutes' difference between the metar and synop reading hence the apparent fluctuation. The M04 could well have been a reading of -3.6 (rounded to -4) so the difference could have been 0.8 degrees, which isn't huge.


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    #161
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    BMJD wrote: »
    They aren't wonky. There can be a few minutes' difference between the metar and synop reading hence the apparent fluctuation. The M04 could well have been a reading of -3.6 (rounded to -4) so the difference could have been 0.8 degrees, which isn't huge.

    The wild fluctuations to -3 only on the half hour and back up again on the hour on an otherwise steadily decreasing trend in clear and calm conditions are highly unlikely. On the hour they agreed with the synops, but the half-hourlies were anomalously low at -3 (even if that was -2.6) e.g. jumping from 0.1 to -2.6 to -1.0 to -2.6 to -1.9 every 30 minutes. I just don't buy it at all. This could be possible in different conditions of higher wind or variable cloud cover, but not last night.

    18:00 2.1 (2/8 cloud)
    19:00 0.9 (1/8 cloud)
    20:00 0.1 (1/8 cloud)
    20:30 -3 METAR
    21:00 -1.0 (0/8 cloud)
    21:30 -3 METAR
    22:00 -1.9 (0/8 cloud)
    22:30 -4 METAR
    23:00 -2.8 (0/8 cloud)
    23:30 -4 METAR
    00:00 -3.5 (0/8 cloud)

    378649.png


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    #162
    BMJD
    Registered Users Posts: 2,694 ✭✭✭BMJD


    So you're saying it's impossible?


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    #163
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    BMJD wrote: »
    So you're saying it's impossible?

    I underlined it above. It is highly unlikely in the conditions we had that night. Nigh on impossible. I think human error is vastly more probable. I'm running out of quantifiers here...


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    #164
    JCX BXC
    Registered Users Posts: 18,114 ✭✭✭✭JCX BXC


    Currently Foggy with a his of 400m at SNN. Ironically it's currently the only foggy airport, and last night it was the only major airport without fog in the forecast.


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    #165
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Carnacalla wrote: »
    Currently Foggy with a his of 400m at SNN. Ironically it's currently the only foggy airport, and last night it was the only major airport without fog in the forecast.

    Slightly up on its 300 m earlier this morning. It had been reporting 12 km with shallow fog for a few hours.


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    #166
    BMJD
    Registered Users Posts: 2,694 ✭✭✭BMJD


    Gaoth Laidir wrote: »
    I underlined it above. It is highly unlikely in the conditions we had that night. Nigh on impossible. I think human error is vastly more probable. I'm running out of quantifiers here...

    For human error to have occurred, that would mean that somebody overrided an automatic weather system 3 or 4 times for no reason. If it was a computer error, which it couldn't because they have alarms for large variations, as well as back-up systems in case of instrument failure. ATC would probably have requested a temperature check too.

    It's unusual but obviously not impossible.


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    #167
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    BMJD wrote: »
    For human error to have occurred, that would mean that somebody overrided an automatic weather system 3 or 4 times for no reason. If it was a computer error, which it couldn't because they have alarms for large variations, as well as back-up systems in case of instrument failure. ATC would probably have requested a temperature check too.

    It's unusual but obviously not impossible.

    The reports are coded manually so human error is indeed the most likely reason.


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    #168
    BMJD
    Registered Users Posts: 2,694 ✭✭✭BMJD


    Gaoth Laidir wrote: »
    The reports are coded manually so human error is indeed the most likely reason.

    They aren't.


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    #169
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    BMJD wrote: »
    They aren't.

    The metars and synops are 100% manual observations at DUB, 24/7/365.


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    #170
    BMJD
    Registered Users Posts: 2,694 ✭✭✭BMJD


    Gaoth Laidir wrote: »
    The metars and synops are 100% manual observations at DUB, 24/7/365.

    Temperature, wind and pressure values are all automated; the only human input is to review and send the data. The only way human error can occur is if those values are manually changed.


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    #171
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    BMJD wrote: »
    Temperature, wind and pressure values are all automated; the only human input is to review and send the data. The only way human error can occur is if those values are manually changed.

    My point exactly.

    Human input also involves visibility, cloudbase, type, coverage, present/past weather, etc. All collated together with the other data and sent off in coded format.


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    #172
    BMJD
    Registered Users Posts: 2,694 ✭✭✭BMJD


    Gaoth Laidir wrote: »
    My point exactly.

    Human input also involves visibility, cloudbase, type, coverage, present/past weather, etc. All collated together with the other data and sent off in coded format.

    I'm not sure how that validates your point about this:
    Gaoth Laidir wrote: »
    I think human error is vastly more probable.

    I will say it again: those temperature values were not inputted manually. At no stage of the production of a metar or synop are they manually entered or coded - it is automated. Before they are transmitted they are reviewed. That is the only human input regarding the temperature/dew point.


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    #173
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    BMJD wrote: »
    I'm not sure how that validates your point about this:



    I will say it again: those temperature values were not inputted manually. At no stage of the production of a metar or synop are they manually entered or coded - it is automated. Before they are transmitted they are reviewed. That is the only human input regarding the temperature/dew point.

    And I'm saying that this review was erroneous. It gets back to simple physics. In years of studying meteorology I have never seen consistent fluctuations such as those highlighted above happening in the conditions in which they did. There is no atmospheric process whereby this can happen in such conditions. Therefore it is down to instrument or human error. If it's instrument error then the human review did not pick it up. Either way, those half-hourly metar temperatures were "wonky".


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    #174
    BMJD
    Registered Users Posts: 2,694 ✭✭✭BMJD


    And yet Belfast Aldergrove showed a similar, though less pronounced, series of variations that evening:

    METAR EGAA 231720Z 34005KT 310V010 9999 FEW045 04/M01 Q1022=
    SA 23/02/2016 17:50->
    METAR EGAA 231750Z 33004KT 290V360 CAVOK 03/M02 Q1022=
    SA 23/02/2016 18:20->
    METAR EGAA 231820Z 35003KT CAVOK 02/M02 Q1022=
    SA 23/02/2016 18:50->
    METAR EGAA 231850Z 00000KT CAVOK 01/M03 Q1022=
    SA 23/02/2016 19:20->
    METAR EGAA 231920Z VRB02KT CAVOK 01/M02 Q1022=
    SA 23/02/2016 19:50->
    METAR EGAA 231950Z 00000KT CAVOK M01/M03 Q1022=
    SA 23/02/2016 20:20->
    METAR EGAA 232020Z 00000KT CAVOK M01/M03 Q1022=
    SA 23/02/2016 20:50->
    METAR EGAA 232050Z 00000KT CAVOK M02/M04 Q1022=
    SA 23/02/2016 21:20->
    METAR EGAA 232120Z 15003KT CAVOK M03/M04 Q1022=
    SA 23/02/2016 21:50->
    METAR EGAA 232150Z 19003KT CAVOK M01/M03 Q1022=
    SA 23/02/2016 22:20->
    METAR EGAA 232220Z 19002KT CAVOK M02/M03 Q1022=
    SA 23/02/2016 22:50->
    METAR EGAA 232250Z NIL=
    SA 23/02/2016 23:20->
    METAR EGAA 232320Z 16004KT CAVOK M01/M03 Q1022=
    SA 23/02/2016 23:50->
    METAR EGAA 232350Z 19003KT CAVOK M02/M03 Q1022=
    SA 24/02/2016 00:20->
    METAR EGAA 240020Z 18003KT 9999 FEW042 M00/M01 Q1021=
    SA 24/02/2016 00:50->
    METAR EGAA 240050Z 19004KT 9999 BKN042 M00/M02 Q1021=
    SA 24/02/2016 01:20->
    METAR EGAA 240120Z 20004KT 9999 BKN046 00/M01 Q1021=


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    #175
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Well in this case the difference is even worse! Absolutely no correlation with the synop values, so I'm not sure if they actually have different sensors for different types of reports or what.

    The metars are 10 minutes before the hour and half hour, so every hour there are 3 readings plotted in the space of 30 minutes, e.g. 19:50, 20:00, 20:20. The chances of natural fluctuations up and down between such close metar and synop reports is zero. This is even more proof that there is some other reason, be it instrumental or human, here too.

    Cloud cover from the hourly synops is also shown below.

    378704.png

    Here's Dublin again in clearer form.

    378707.png


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    #176
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Recent sleet has now turned to light snow at Cork at 6 pm.

    METAR EICK 261800Z 36016KT 4000 -SN BKN003 BKN006 02/01 Q1000 NOSIG=


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    #177
    JCX BXC
    Registered Users Posts: 18,114 ✭✭✭✭JCX BXC


    From what I've learned, should snow not drastically decrease the visibility?


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    #178
    Negative_G
    Registered Users Posts: 1,339 ✭✭✭Negative_G


    -SN (Light snow) would not drastically decrease visibility.

    SN OR +SN would see a larger reduction.


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    #179
    Growler!!!
    Registered Users Posts: 1,980 ✭✭✭Growler!!!


    Carnacalla wrote: »
    From what I've learned, should snow not drastically decrease the visibility?

    9999 in the metar means in excess of 10km met vis. A decrease to 4km is a good drop but not an issue for approaches. Biggest issue with snow is contaminated runways, taxiways and it will affect hold over times when de-icing.


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    #180
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Up to 3 cm of snow forecast at Cork tonight.

    EICK AD WRNG 01 VALID 261756/270300 SNOW FBL 1 TO 3CM FCST =

    At 7 pm it was reported at <1 mm.


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    #181
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Back to light rain at 8 pm.


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