Instructions on how to create your own forecast, Part 2


A couple of articles ago I introduced how you can create your own weather forecasts using the weather model data available on the WunderMap weather page located at www.wun derground.com. Hopefully some of you have taken a bit of time to check it out. In this issue I would like to go into a little more detail on how to use the data available at this site to improve your forecasting skills.


For those of you who didn’t read the previous article or haven’t checked out the website, here is how you locate the correct web page. First, go to www.wunderground.com then click on the Maps and Radar tab near the top of the page. From the drop-down list select WunderMaps. When this page loads it should automatically be focused on the part of the world where you live. For those of you who have used Google Maps or Google Earth, then you will recognize how to navigate around the map.


Some of you might notice that this page has changed a bit as they have updated it over the last couple of weeks. To successfully use this page you’ll need to zoom out so you can see most of Canada and the United States. You then want to go to the right-hand side of the page and using the Map Layers, unclick the Weather Stations and Radar layers and then click on the Model Data layer. You then need to click on the little blue gear symbol to open up the display options for the weather models.


You can play around with different ways to move from day to day, but what I find easiest is to use a couple of shortcut keys. Hitting the letters D and A on your keyboard will jump you forward and backward by 24 hours. The letters L and J will move you forward and backward one model time frame. This is every three hours for the first seven days and then every 12 hours to day 16 (at least for the GFS model).


Models


The weather model I start with is the GFS model and the first piece of information I like to look at is the MSL map which shows you pressure patterns and precipitation amounts. If you mouse over the word “Map Type” it will tell you more details about the map you are looking at.


Once I’ve gone through these maps I then switch to the ECMWF model and do the same thing. What we are looking for is to see how closely the two different weather models are agreeing on what will happen. The closer they are to each other the more confidence we have in the forecast. The other thing that you need to do to create a reliable forecast is to check the weather models over several model runs to see if they are in agreement.


The GFS model recreates its maps every six hours based on the latest data. The ECMWF does this every 12 hours. If the information or forecasts the models have created is changing significantly every model run, then confidence in the forecast is not that high. The more you watch what these models are doing the better you will get at doing this.


Once you have a good idea of what the general weather pattern will be over the time period you’ve chosen to look at you can use some of the other pages to get more detail. The 2mAG map type will show surface temperatures. Just remember that when you are looking at this data the time shown at the top of the page is in GMT. To convert this to MST subtract seven hours. This map is colour coded 
with the temperature scale shown on the bottom of the page.


The other map I find useful is the Wind map type. This map uses colour shading to show wind speed and streamlines to show the wind direction. Wind speeds are in knots and if you want to do a quick conversion to km/h then multiply the values shown on the map by two (it’s actually 1.8 but two is a heck of a lot easier to do). The stream lines can be a little tough to see, but if you look closely you will be able to see the arrows indicating the direction of airflow.


So, if you haven’t tried to create your own forecast I recommend that you do. At least then you will have no one to blame for a bad forecast but yourself!



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