Weather Observations

Promised to write about my work here a while back, sorry I am just getting to it now! As I write this it is currently 12:50am here +1 day (NZ time), 11:50am Zulu/GMT, 6:00am Eastern Time and 3:00am Pacific Time. Here’s what it looks like outside:

Weather Dec 22 1am

Actually the clouds rolled in a bit more before I took the observation, and you can only see about 1/4 of the sky here, but hopefully it helps paint a picture! 

Great! Now let’s take an observation!

There are four different types of observations (obs): METAR, Synoptic, Local and SPECI. To take a Local observation we only record the wind velocity (direction + speed), temperature, altimeter (altitude measurement), and barometric pressure. These are recorded by our instrumentation and the information is not time-sensitive, allowing us to log the information hours later if needed. Which is great because that means I can actually enjoy Thanksgiving/Christmas dinners and events on station without having to run to the office every hour!

We switch to taking METAR obs once every hour when flights coming to or leaving from the station have been activated. Our first METAR is taken 6 hours prior to takeoff, and in addition to the above a METAR includes the visibility in meters, present weather, and sky condition. Yikes, what are these things?! Let’s break it down a bit more…

  • Visibility: Essentially, how far can you see, to the horizon? We have big plywood boards that are spray-painted black and strategically placed at recognizable distances to help us determine the visibility. 1600m, 3200m, 4800m, etc.
  • Present Wx: Any precipitation or obscuration at the time of the ob. Common here are snow grains and ice crystals, and sometimes we get blowing or drifting snow that is blown around from high wind speeds.
  • Sky condition: A description of the amount of cloud cover, heights of different cloud layers and the types of clouds. If the sky is clear, then 0/8ths is reported, and if it’s overcast then the cover is 8 oktas. Determining cloud layers/heights is still not my strongest skill, but I have some tools (pictures and lidar) to use that help me out.

Taking a look back up at the picture of current conditions, we can see that the visibility is 9999 meters, or unrestricted because we can plainly see the horizon, and the sky condition is about 6-7/8ths covered (the really thin clouds count!). As for present wx, you can’t tell by the photo but we were getting some light snow grains. When I held up my hands they bounced off of my mittens and they kind of sting as they hit your face.

So here’s our METAR for the hour:
METAR NZSP 211150Z 03006KT 9999 -SG FEW010 BKN030 M28/ A2866 RMK CLN AIR 02005KT ALL WNDS GRID SDG/HDG

And here’s what the code means:
METAR (type of report) NZSP (ICAO station code) 211150Z (time) 03006KT (wind direction 3 digits, speed in 2 digits, KT = knots) 9999 (visibility in meters) -SG (light snow grains) FEW010 BKN030 (sky condition, few clouds at 1000ft and broken clouds at 3000ft) M28/ A2866 (-28˚C and Altimeter 2866) RMK (remarks/additional info) CLN AIR 02005KT (wind velocity in the clean air sector) ALL WNDS GRID (because technically everywhere is North, we use the Prime Meridian as N) SDG/HDG (Unique to Antarctica, I think. “Surface Definition Good/Horizon Definition Good”)

A SPECI (“Special”) report is just a METAR that is transmitted when a sudden a certain criteria is met: shifting winds, reduced/increased visibility, clouds forming at less than 1000 feet, etc.

Lastly, Synoptic observations are transmitted every six hours (12am/pm and 6am/pm Zulu time) at the same time as the METAR observations. Synoptic code is very confusing. There are numbers for every kind of weather phenomena, that are arranged into series of 5 numbers, basically reporting the same info as a METAR but with a tad bit more detail.

Here’s the Synoptic from this hour:   21124 89009 41461 70306 11276 36840 51001 77772 81610 333 11259 21278 81710 87430

Decoded:
21124 – Day (21st) Hour (12) and 4 meaning staffed station
89009 – Station ID
41461 – Precip not measured (4), Weather (1=yes), Cloud height (4 for 1000ft), Visibility (61 for unrestricted)
70306 – Total sky cover (7), Wind direction and speed (03 meaning 030, meaning NE, and 06 meaning 6 knots)
11276 – Code 1, 1 for negative temperature, 276 for -27.6˚C
36840 – Code 3, 6840 for 684.0 mb pressure
51001 – Code 5, 1001 is the three hour pressure tendency and amount of change (you don’t need to know this much detail…)
77772 – Code 7, present weather 77 for snow grains, 7 and 2 mean ice crystals and sky cover >4/8ths, respectively
81610 – Code 8, amount of low/mid clouds (1, because there were few); 6, 1 and 0 refer to the types of low, middle and high clouds
333 – Don’t really know exactly, but this breaks up the report
11259 – 11 for temperature and negative, as above, and the 12-hour high temp (-25.9˚C)
21278 – 21 for 12-hour low temp (-27.8˚C)
81710 – Code 8 for reporting sky cover, 1 is the # of 8ths, 7 is the cloud type (Stratus), 10 is the code for cloud height of 1000ft
87430 – Code 8, 7/8ths, 4 is the cloud type (Altostratus), 30 for cloud height of 3000ft

Of course I have cheat sheet for the Synoptic code—are you kidding?! I couldn’t remember all this!

~~~~

And there you have it! You can all be weather observers in Antarctica now 🙂 Soon I’ll post about launching weather balloons!

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