Climatology versus Forecast models


A lot has been said over the last few years about Global warming and that is an entirely different discussion. I want to address the difference between Climatology and real world forecasts (forecast models).

First off all we need to recognize the difference between Climatology and weather forecasting and the difference is pretty basic. Weather and weather forecasting happen today, tomorrow and onward. Climatology is all the weather that happened yesterday. So todays weather will be Climatology tomorrow. 

Climatology is data, the highs, the lows, how much rain fell, all weather parameters, all the weather that has happened. It would be nice to have hard weather data from a million years ago, but we don’t. We can go back and take slices of earth/rock/Ice even trees and see what has happened in the past, but when we try to figure our what the temperature was, or was it a sunny day, we can go back over 200 years in some areas to find specific data. 

The following paragraph comes from the NOAA web site;The early American colonial years are peppered with events and stories referencing weather observations. The first systematic weather observations in North America were made in 1644 in Wilmington, Delaware, by Reverend John Campanius Holms. Observations of storm movement and weather patterns were first noticed by Benjamin Franklin when he documented the movement of a hurricane from Philadelphia to Boston in 1743. During the signing of the Declaration of Independence, Thomas Jefferson noted that the high temperature for Philadelphia on July 4, 1776, was 76 degrees Fahrenheit (24 degrees Celsius). Presidents such as George Washington and Jefferson were some of the first weather observers in the county. And, during their trip to explore the western U.S. in 1804-1806, the Lewis and Clark expedition made regular weather observations. 

So, at best, it appears actual recording of data goes back over 250 years and that is for only a few locations. From the data we have we can calculate daily, weekly, monthly, seasonal even yearly averages based on the actual data.

Climatology is a good resource if you are planning to visit a destination say next year and you want to find the warmest, driest, or hottest month, or maybe the most snow fall. The data gives you what the weather should normally be for that time of the year. 

Climatology is also available for weather over the worlds oceans, based on years and years of observations from ships at sea. Observations have been found from as late as the 18th century and that data has grown and grown over the years with the vast numbers of ships traveling from point A to B. There are are thousands of ships on the water at any give time, recording regular observations of wind direction, sea heights, water temperature on a regular basis all around the world. 

It is from all these observations climatology of the words oceans can be made. Climatological Atlas’ have been made that shows what is considered the average wind direction, speed, sea height, swell, tropical cyclone formation area, visibility, even ocean currents and more. They are known as Pilot charts. Using a Pilot chart you can see what is considered the normal conditions on a voyage from SE Florida to Puerto Rico and what would be the expected wind direction/speed and how strong the average ocean current is. 


Weather forecast models take the current observations from around the world and use complex mathematical calculations to predict where parcels are air will be in the future. From that, data is generated that gives forecasted temperatures, precipitation, wind, etc… 

The history of weather forecast models goes back to the 1920’s but it wasn’t until the 1950’s when forecast modeling started to gain traction as a viable way to forecast weather for the next days or two with the development of computer technology. By using computers and eventually super computers the observations that were taken from the land, sea and air, could be entered into the complex calculations that would, eventually, generate output. The output would result in a forecast of the different levels of the atmosphere. A forecast of conditions of upper level conditions including temperature and humidity help put out a surface forecast. A forecast of major weather system like High, Lows, cold fronts.  It is this output that a Meteorologist looks at and uses to predict the weather for a given area for the day, next day and onward. 

One of the first computer generated models used in the United States was the LFM  model (Limited Fine Mesh) in 1971. This model was used, exclusively until 1986 when it was discontinued with the development of the NGM (Nested Grid Model). Both these models would produce output over the next 48hrs of generation, twice a day, at 0000UTC and 1200UTC. 

These models were considered cutting edge for their day and I remember using both models while in college.At times there were notable differences in output between the two models. This became a big challenge trying to make the most basic forecast. Trying to forecast if severe thunderstorms or Tornados would develop on this day, at this time would be a challenge. 

 Predicting a developing Noreaster was met with its own challenges, as these storms are difficult to predict to begin with but add in the additional complexities of rain mixing with and/or changing to snow (or remaining all snow) increased the chances kids looking for a snow day would be disappointed. 

Since then there have been plenty of improvements in short term and long term model data that include the NAM (North American Model,  GFS (Global Forecast System), ECMWF (European Centre for Medium-Range Weather Forecasts)and many others. 

Forecast modeling is not the same as climatology. Even though climatology can give you what the weather is supposed to be at any given time, forecast model data and how it is interpreted is what tells you whether or not you have a weather window to sail this weekend or not or which route to take across the Atlantic Ocean for the Med Sea. 

The data you are looking at, whether it is from a weather app or a website, that data/output you are viewing is made entirely from a computer. No human interaction. Relying soley on this data on a regular basis can come back to bite you especially if you are trying to thread the needle and beat an approaching cold front, or worse yet, a tropical cyclone.  It is not uncommon (especially over the last few years) to see notable changes in forecast output in short term and long term data.

As a whole, forecast models do a good job at predicting all parameters of weather like wind direction/speed, precipitation/temperatures, sea heights and more in the short term, less than 5 days and in some other areas, you can go a week or more (like the tropics) and get a reliable forecast over a 7-14 days period. 

During the early days of forecast model output,  models predicted conditions every 12hrs for a 48hr period. Once a day (after the 1200UTC data run)  a 5 day forecast/outlook chart was generated by NOAA for the continental/US, North Pacific and North Atlantic. Today some forecast models predict conditions every hour of the day for the first 5 days, then 3-6hrs intervals out 10-15days. To this day even with the advances in super computer technology, forecasting the location/intensify of high pressure/low pressure areas and weather fronts. beyond 5-7 days can still be very challenging. Changes in the larger weather systems can make huge differences in local conditions from the expectation of a clear day to a day full of clouds/rain or a windy day versus a light wind day.  

Forecast model data should be always looked at as a guide. Too many people, (including Meteorologists) base a forecast strictly on what the data output shows. The main model data updates twice a day at 0000UTC and 1200UTC but now there are intermediate model updates in between the main model runs.  This means there are updates every 6hrs, but the intermediate updates do not include data from weather balloons as they are still launched at 0000UTC and 1200UTC daily (currently 8am and 8pm eastern daylight time) .

Forecast model prediction also includes the tropical areas with numerous forecast models that predict the location, intensity, tracks, over the next 5 days and more.  Advances in model technology has helped improve the short term forecasting of Tropical Storm and Hurricane prediction. However, even with the advances in the forecast models relying on a forecast track beyond 5 days can still result in 250nm+ track errors. Model data is also just starting to get a handle on forecast intensity. Over the last several years there have been a few Hurricanes that were forecasted to slowly intensify, but ultimately, rapidly organized become a major Hurricane in less than 24hrs, day sooner than the model data was showing.

Keep in mind that the more time before your planned trip (60 days and more) the more likely you would be looking at climatological data. Considering there are still notable errors in model output still occurring 7-10days+, depending on the location or the voyage/route you are planning, you would be better off flipping a coin. 

There will always be errors in forecast modeling. No forecast model is 100% accurate and no Meteorologist makes an accurate forecast 100% of the time. Future advances in super computer technology and forecast model output will lead to to better forecasting in the short time and even the long term…. It is just a matter of time. 










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Ocean Marine Nav. Inc.

Bob Jones

Marine Meteorologist
Ops Manager
Toll-free: 1-866-505-OMNI (6664)
Fax: 1-908-548-0880


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