By Matt Gallagher
Well, today sure is turning out to be challenging for a first day for the contest! The weather at KORD has been a bit unsettled, to say the least. We won’t know until tomorrow how our forecasts turned out when the Daily Climatology Report is issued, but if you want to follow along in real time, the KORD METAR reports are the place to start. They’re available here. Plus, with the noon forecast already complete, you can check on your noon wind speed and direction forecast now.
The aviationweather.gov website does a nice job of translating the raw METAR format for you, but knowing how to read a raw METAR is a useful skill, so I am going to walk you through today’s noon METAR as an example. METARS are a very condensed way of transmitting and receiving observational data, and you’ll run across them all over, so it’s worth having a sense of how to read them. A great article explaining how to read them is available. COD has a good pageexplaining how to read METARs, and here is a cheat sheet you should download, but I’ll walk you through today’s as an example. Most of what you need as a forecaster is pretty easy to understand. (The Federal Meteorological Handbook has a complete breakdown of METARS in Chapter 12, but it’s dense! However, it covers pretty much every conceivable weather observation.)
This is the 12 noon Central Time report from today, which we’ll use to verify your 12 noon wind forecast:
KORD 181651Z 02009KT 6SM HZ FEW006 BKN014 OVC065 16/13 A2976 RMK AO2 SLP074 T01560128 $
First, because you all care, the winds were at 020 at 9 knots. That’s the answer. Here’s how you get there.
KORD – The IATA code for the observation station, in this case, KORD – Chicago O’Hare. (Here’s the interesting historyof why it’s called ORD instead of OHA or something similar, as well as the history of a few other fun airport codes such as PEE, POO, SUX and FAT)
181651Z – The date and time, in UTC (or Z). 18 is for May 18, the calendar day. 1651Z is for 1651 UTC. But wait – why am I calling this the 17Z METAR? Because the official hourly METAR observation is taken somewhere between 10 and 5 minutes before the hour, to allow time for processing, error correction if needed, and dissemination. So 1651 is the official observation for 17Z.
02009KT – This what we came for – wind speed and direction. The first 3 digits are the wind direction to the nearest 10 degrees – so in this case the wind is blowing from 020 true. The next two digits are the wind speed in knots (represented by KT), so in this case 09 knots. So any of you who forecast 9 knots coming from 020 congrats! If there were wind gusts, it would be reported as well, so for example 35014G23KT means wind from 350 at 14 knots gusting to 23 knots.
6SM HZ – The visibility fields, critical for pilots (METARS come from the world of aviation). In this case, 6SM means 6 statute miles of visibility, and the HZ means that Haze was present.
FEW006 BKN014 OVC065 – Again critical important for pilots, these are all the cloud layers noted, stating their cloud cover amount and altitude in hundreds of feet above ground level. So in this case, there were FEW clouds at 600 feet, another BroKeN layer at 1400 feet, and OVerCast at 6500 feet.
16/13 represents the dewpoint and temperature, in degrees celcius. If either were negative, they’d insert a M in front of the two-digit number.
A2976 represents the Altimeter setting in inches of mercury used by pilots (why not in millibars like most other weather charts? Who knows. Tradition I guess). Altimeter setting is something used by pilots to standardize how their altimeters read. This is NOT the same thing as sea level pressure.
RMK AO2 – RMK stands for remarks, something non-standard. In this case, A02 means that the site is automated and HAS a precipitation sensor. If it were AO1, there would be no precipitation sensor.
SLP074 tells us the sea level pressure, in mb. (Why mb and not inches like the Altimeter setting? Who knows). This takes some interpretation. Only 3 digits are shown and you need to make sense of them. Knowing that normal sea level pressure is in the range if 980 – 1050, and knowing the last digit is 10ths of a MB, we interpret this 074 as 1007.4.
T01560128 is a temperature field. There are many, many optional pieces of information which can be included – see the COD page for some examples. This temperature field tells us a more precise measurement of temperature than does the 16/13 above. Here we have temperature of 15.6C and dew point of 12.8C. Other things that can appear here include precipitation amounts, snow information (shudder), lightining and many other pieces of information relevant.
So as you can see, unpacking a METAR can help you understand a lot about the observations taken around the world (this is an international standard). For the purposes of our contest, to verify wind speed at local noon, you can find the METAR taken within 10 minutes before the relevant time in UTC, look for the wind field, and read the wind speed and direction.