Verifying the noon wind at KORD

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 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 PEEPOOSUX 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. 

Preview for May 18, 2020 – KORD

By Matt Gallagher

Good morning everyone! Our first forecast is due tonight, May 17, at 00 UTC (technically May 18), or 7 pm Sunday Chicago time.  Here’s a preview of the setup for tomorrow.

Day 2 image not available

The WPC shows Sunday’s storms largely having cleared to the east Monday morning though the threat of precipitation is still very real in the Chicago area on Monday.  You’ll learn that forecasting precipitation is one of the hardest things to do in the Weather Challenge, as precip can be very localized – areas just a mile or two apart can see very different amounts of precipitation (Forecasters will often use the term QPF, or ‘quantitative precipitation forecast’ as a shorthand for precipitation).  More on this for a future post.  Precipitation is an area where models, more than MOS, can give you the best information on which to base your forecast, but resist the temptation to look at just a single model. You need to gather as much information as you can from all the models, as well as MOS, to best hedge your QPF forecast.

The low that’s currently centered over Illinois will be moving off to the east slowly Sunday and Monday, with precipitation likely Monday and Tuesday. Also watch those winds – as the low moves east, the flow will clock from the SE all the way around to the NE, across the relatively cool waters of Lake Michigan. 

A great place to start – after examining the big picture forecast from sites such as the WPC and considering the threat of severe weather via the SPC  –  is the Area Forecast Discussion. These are issued several times a day by every NWS local office in the country (sometimes hard to find on the individual websites – look for ‘text products’.). These are a narrative of not only the forecast, but also what the forecaster was thinking when they came up with the forecast that they did.  While the quality of these varies widely, one thing does not – the forecaster signs their forecast with their name. Unlike most government bureaucrats, there is accountability not cloaked in anonymity. If you read these daily you start to get a sense of the forecasters’ personalities, but better yet you get the advice of an experienced forecaster with local knowledge. 

So the forecast challenges for tomorrow, I think, really focus around that QPF. Good luck! Feel free to post questions here, or on the Facebook group.

MOS is Boss

By Matt Gallagher 

Most of you are probably familiar with weather models. For those of you who are not, weather models such as the GFS, NAM, Euro, CMC and others attempt to ‘solve’ for the state of the atmosphere by taking an assumed initial state of the atmosphere and then using computer power to simulate atmospheric processes, with the model outputting projected atmospheric conditions (weather) at a given time and location.   Weather models have made tremendous advances in recent years, as both the power of the computers involved and the understanding of the physics of the atmosphere have greatly improved, and indeed, any forecaster worth his or her salt will make reference to weather models in forecasting. However, models are just one thing you should consult as part of your forecast. Future articles will talk more about models and model biases, but today I wanted to start with another tool you should have in your forecasting backpack as we start this challenge – MOS.

MOS is an acronym for “Model Output Statistics”. So what is MOS? How is it different than a computer prog (meteorologist shorthand for ‘prognosis’ or forecast -i.e. a model forecast)? 

The GFS, NAM and the other models you are familiar with are computer-generated numerical models of the atmosphere. They’re also referred to as ‘dynamic models’ and use math and physics to solve for the state of the atmosphere. As a result, they’re pretty idealized and can often swerve far away from the actual state of the atmosphere at a single location. They’re vulnerable to two potential flaws: 1) imperfect data and thus an imperfect ‘initialization’ and 2) models that don’t perfectly simulate the processes in the atmosphere.

When we are forecasting for a specific point (such as the weather station at KORD or your house or a specific harbor), a model often varies from the ground truth (observation), even though it may very well be a good representation of the atmosphere over a larger area. There are a lot of reasons for this; some include issues of model grid resolution (the nearest grid point for the model could be miles away) and inability to model microscale features, like a nearby building causing a wind shadow or a black parking lot nearby affecting local wind currents and temperatures.

To attempt to address these inherent weaknesses in models when forecasting for important locations such as airports, meteorologists turn to MOS. At each specific location for which a MOS forecast is available, meteorologists keep detailed observational records over decades and compare how those observations vary from what the model suggests should be true. They then apply statistical relationships between the models’ forecast output and observational truth. The end result is that MOS can often provide a more accurate forecast of key variables such as temperature, humidity and wind speed than can a pure model output. However, MOS requires a lot of work both in terms of keeping accurate observational data and in developing the underlying statistical relationships. This is manual work and thus can only be done at certain locations, generally airports. MOS doesn’t tell us anything for forecasts between those points.

For this contest, MOS can be a great tool for you, as we are forecasting at airports, for which MOS is readily available (in the US).  MOS is available based on both the GFS and NAM models, and the data is free. 

Here are ways of accessing MOS forecasts:

  • Graphically, on the Penn State e-wall  
  • In text form (more useful for this contest) – The MDL has MOS output based on several models. The most useful for the contest is their short-range MOS. The tables need some interpreting. Spend some time poking around on that site. A key for the tabular forecast data is available and you’ll need to spend a little time in understanding exactly what is what on those tables, but it’s worth it!
  • The University of Wyoming also has a good MOS site –  This includes both tabular and metogram formats (we’ll explain meteograms in a future post). 

A few caveats:

  • Dates and times are all in UTC (Zulu) so you will have to convert to local time. Be careful with dates. Our local midnight-midnight actually cover two “UTC days” – the end of one into the beginning of another. 
  • MOS Is only valid for the location of the forecast. So, for example, the KORD MOS may or may not tell you anything about conditions at Monroe Harbor. 
  • MOS is quite useful for temperature and wind forecasts, but using it for precipitation forecasting can be more challenging.
  • MOS Wind speeds are for the exact time of the forecast. We, of course, are looking for something different – the maximum sustained wind at ANY time during the day. So in most circumstances, you want to take the highest forecast MOS wind and add a couple of knots to get a decent forecast for max sustained wind (but note that this is not ALWAYS true – keep the big picture and climatology in mind). 
  • The local noon wind speed and direction may or may not be available, as MOS is only displayed for certain times UTC which might not line up with local noon at the station. However, surrounding times might give you a hint of direction and speed at the time you care about.
  • Even though MOS is based on models + statistics, it’s not the ‘holy grail.’ You still need to apply your judgment, information from all sources, and keep the big picture setup in mind. MOS is known to ‘bust’ a forecast just like computer progs do. You, as a forecaster, need to apply your judgment and experience to try to minimize the risk of that happening on any given day.

MOS is a very important tool in forecasting for point locations like our airports. However, it is not the beginning and the end, but rather it’s an important arrow in your forecasting quiver.

Chicago (KORD) – Climatology


By:  Winn Soldani

Sweet home Chicago.  The Windy City.

Welcome to the first forecast city for the CYC Weather Challenge, and a challenging one it is.  Though we have many Chicagoans as part of this contest and this might seem easy to you all, forecasting for O’Hare is going to be an interesting way to start off.

While Matt and I will be pointing you to specific day-to-day forecasting resources,  we were trained in our weather classes to start with climatology and bigger-picture thinking about a city we’re forecasting.  So, let’s start here:  what’s the weather normally like this coming week for KORD (the catchy code we use for O’Hare International Airport, based on its IATA airport code)?


Let’s look at the norms (norms are for a 30 year period.  These are for 1980-2010) for Chicago in the week we’re forecasting (all the data below are courtesy of the excellent climate records page at the NWS Chicago): 

Day of Month

Normal High

Normal Low

Normal Precip





















So, looks pretty benign. But one thing we’re going to learn about May in Chicago, even late May, is that it’s still very much spring with alternating shots of cold and hot (how many Memorial Days have you worn a winter coat when you went to the Barbecue, Chicagoans?…don’t lie…). The mild norms here are arrived at by volatile weather.  Sometimes, in May, it’s the cold of April, sometimes it’s the warmth of June, sometimes it’s May…but it can be any of those!  Check out just how wild it can be:


Pause for a moment on this table.   The highest temperature observed in the span we’re forecasting is 95 degrees.  The lowest is 31.  Wow.

Better yet, the high temperature has failed to touch 45 degrees on 4 out of the 5 days we’re forecasting for…and the low temperatures have been in the mid 70s…higher than the normal temps in the first table!

Precipitation…though we won’t be forecasting precipitation type, it’s SNOWED on three of the days in our forecast period!  (Note that “T” stands for “trace” – less than 0.01″ but snow nonetheless!) More importantly, notice the difference between the normal precipitation (typically just over .1 inches) and the record.  1.5 to 2 inch precipitation totals happen!

What about the wind?  Below  is a wind rose for O’Hare.  This may be new to some readers so I’ll explain.  The different colors show the wind speed.  The size of the colors and the direction in which they point show the frequency with which the wind came from that direction and at what speed (in knots).   This wind rose for the week we’ll be forecasting for shows that over the period here (1946-2020), the wind falls largely into two buckets that reflect the battle between spring and summer we’ve described. There are a LOT of observed winds out of the NE/NNE and then a lot—though more spread out—out of the W/SW/S.  SE winds and, especially, NW winds are unusual.  Note that the vast majority of windspeeds are under 15 knots.


What does all this climatology tell us?  Question number 1 we would ask when forecasting for O’Hare is this:  is the pattern more like April or More like June?  And what model(s) seem to have a handle on that pattern?  Because the variability is really, really something (it is much more, than, for instance, what we’ll see in Miami in a few weeks).  Get it wrong and your forecast is a sure-fire bust.


Beyond the big picture (synoptic) question of the spring/summer pattern, there are several smaller-scale (mesoscale) things that we have to think about in Chicago.  Here are a few.

1) The Lake

Current nearshore Lake Michigan water temperatures are in the 50s, but with a very large area of water temperatures in the 40s in the center of the lake.  This cools the overlying air and if that air advects inshore, forecasts can be heroically validated or epically bust.


With this in mind, we have to pay attention to the lake breeze. We all know this but as the land heats, it creates relatively low pressure ashore.  The colder, higher-pressure lake air advects along a lake breeze front.  However, at some point that front no longer has the energy to progress farther inland.  Where that front stops is CRITICAL to O’Hare forecasts

  • If the lake breeze makes it to O’Hare, temperatures will drop. This makes the high temperature occur at an odd time, not the typical late afternoon, but instead in the hours before the lake breeze arrives.  Or, the highs may occur at a normal afternoon time but be lower than model forecasts.
  • Winds will be impacted. Often there will be a brief windier period at the arrival of the front, along with a shift to a more easterly direction.  When this happens, exactly, is important.  If your forecast assumes the lake breeze arrives before 12 PM, your noon forecast is probably for a breeze with some kind of easterly component to it.  Your max windspeed forecast may be low if the front arrives with a bit more “push” than models see.
  • Storms.  Though discussed more below, the lake breeze can act as a triggering mechanism for storms in certain situations.  Again, if it makes it inland far enough, those storms can be over O’Hare.

2) Thunderstorms


As the pattern turns more summery, the main mode of rainfall changes.  It becomes less stratiform rainfall (i.e. widespread showers that tend to cover an area relatively evenly) and more of a convective (thunderstorm) mode.

A key challenge for forecasters is placing the right bets on rainfall in a convective situation.  The trick is that it can rain very heavily in the vicinity of O’Hare when thunderstorms are around, but where, exactly it does can make or break a forecast.  Models can have skill in forecasting that an area (e.g northern Illinois) will have thunderstorms, but until the event is actually occurring, generally cannot say whether storms will impact a specific place (i.e. the weather station at O’Hare).

This can make the difference between no rain and a deluge.  And it can happen either way—forecast a deluge and the storm slides by and you bust.  Forecast dryness and the storm hits home and you’re also done.  Often the best forecast hedges between the two rather than trying to nail the precipitation total!


I hope this overview of Chicago climatology gives you some things to think about in terms of the big picture and small picture of forecasting for O’Hare.  It should be a fun and interesting week!  Please stay tuned for more from us to help you prepare for the week to come!

Registration is now open!

Registration is now open – simply click here or on “Enter” at the top of the page. To enter, you’ll need to provide your name, an unique email address and a user name you choose. Please also let us know if you are a member of one of the clubs listed. Registration is free.

Once you’ve entered, please be sure to check out the rules and follow the blog (hint – you can subscribe by clicking ‘follow’ on any blog post in the lower right). We’ll be sharing information, news, and tips daily once the contest gets rolling. The resources page will be populated with links to models and other forecasting data you might need to help make an accurate forecast. These will be frequently updated, so be sure to keep checking back.

Good luck!

Welcome to the CYC Weather Challenge 2020

Welcome to the Chicago Yacht Club Weather Challenge (CYCWXC—all the cool meteorologist types call weather “wx”).

Key links:

We’re your hosts and guides, Matt Gallagher and Winn Soldani.  As you may know, we are graduates of the Penn State University Online Certificate in Weather Forecasting (which at the time was novel in being online; nowadays it’s the only way to get a degree from a university, it seems).  As part of that program we went through something called the “Wx Challenge”—this is a program where students and faculty from Universities around the world compete to forecast the weather in a series of cities around the US.

And it is an alternately humbling and exhilarating thing to do.  You have good days, bad.  Things you are good at (say temperature) and not so good at (rain).  And every day you have to lay your forecast out there on the line for all to see when you nail it and when you bust.

After we gave our weather seminar last week at CYC, we thought we could take the Wx Challenge model and try it here at CYC and with our friends in the broader sailing community at CASRA and the Storm Trysail Club.  Anyone can enter though! 

We have a lot of people who are super in tune with the weather and who rely on models an awful lot to guide their day-to-day and sailing lives.  We thought it would be fun and perhaps educational to have a little challenge of our own.  So we’ve set this up for all of our fun.

There will be more to come, but here’s how the challenge works at a high level:

  • There will be the opportunity to submit 15 forecasts, across three weeks and three cities:  Chicago O’Hare (KORD), Providence (KPVD), and Miami (KMIA).  You can choose to try to win a week, two weeks, or be grand champion across all weeks.
  • At or before 7 PM CDT the night before the forecast day (so, for example, before 7 PM CDT on Sunday May 21 for the Monday May 22 forecast) you will go to this site and enter your forecast.  The forecast will be for midnight to midnight local the next day for the city being forecast!
  • The forecast will have several elements to it:
    • The high temperature for the period from midnight to midnight for the day being forecasts
    • The low temperature for the same period
    • The liquid precipitation (let’s hope we’re done with snow, but it has been a strange May) down to the hundredths of an inch.
    • The maximum windspeed for the day
    • And the coup de grace—because we’re sailors and our apps can tell us this–the wind speed and direction at noon 

The rules are detailed, but the general idea is that there will be error points assigned for forecast misses.  The error schemes for each variable are a little different (particularly for wind direction, which has a sliding scale) but the idea is the bigger the miss, the bigger the penalty. If you hit all six numbers exactly (which is extraordinarily unlikely), you’d have zero points.  If you miss a forecast, we’ll substitute climatology in from you so you won’t get a complete bust, but the format encourages regular participation!

At the end of each week we’ll total up the error points.  Lowest point total wins.  There will be prizes for each week’s winner and for the forecaster with the fewest error points across the three weeks.  We’ll also crown an overall winner with the lowest error point total, after a few throwouts.  Again, we want to encourage you to play!

Finally, you won’t do this alone!  We’re collecting resources for you and will publish them before the contest begins so you have easy access to tools like the pros use.  In addition, while this is still in process, we’re working on “celebrity” forecasters to come in and discuss the forecast challenges and review what actually happened.  These may include famous sailing weather forecasters, well-known sailors, and some other professionals in the field.

We’re excited to get started.  If you have any questions, post a comment below and we’ll do our best to respond.

This blog will be our main way of communication to you, so please be sure to follow it. We expect to be posting Monday – Friday while we’re running the contest, with education, commentary, results. Click on “follow” in the lower right for options on how to get notified when we post new content here.

Thanks to our generous sponsor for this contest, Doyle Sails Midwest!

Click here to register; learn more about the rules.