This is a “How Too” for the Learning Comparison Routine within WRET which, when run, checks your past forecasts against you own weather data of what actually happened and comes up with an average correction which WXSim then uses when doing a forecast run.
Note: This will only work if you have WXSIM Pro version!
Open WRET and make sure your archived forecasts (f13050103.wxf) are listed in the “Retrieve data” area, top left.
Note: The data & time of the forecast run is in the file name:
f13050103.wxf = Year - 2013
f13050103.wxf = Month - May
f13050103.wxf = Day - 1st
f13050103.wxf = Forecast Run Hour - 03:00
Choose a forecast file from, say, a month ago by clicking on it in the list and then click the “Compare to Actuals” button. This will open that forecast run and compare it to what actually happened. Click on the “Set as Earliest Date” in the WRET window and make sure that the “Starting Day” is set to 1 and “Number for days” is set to 4.
Now, with the forecast window still open, go back to the WRET and click on a recent forecast run.
Note: This forecast run MUST be more than four days old!!
Now click on the button marked “Auto Select” and WRET will scroll through the forecast files until it comes the first one you chose and a new window will open with “Auto Compare” at the top. WRET will now compare all the forecast runs from the first file to last file you selected and the forecast, actual and error temperatures for the 4 days will be displayed.
This will take some time, especially if you selected to compare a few months worth of forecasts, so just let it run.
Note: The page may go blank if something else on the PC runs at the same time or if you click on another window, but the routine will continue to run, even though it doesn’t look like it is, so just leave it to do its thing.
When the run has finished it will display the results, you may get a window warning about “Temperature correction (slope) out of expected range…” I normally just click OK, there will a graphs button to display what it’s done and it asks if you want to accept the values, click either YES or NO.
If you accepted the values then open WXSIM and go to Preferences > Settings > Model bias and learned correction factors (pro mode only) > put a tick in the box next to "Use learned bias corrections > click “Apply All Changes” and you’re done.
Do this every 3 or 4 months and you can go back as far as you want, just remember how long it’ll take to run the comparison though.
Edit: I have produced a short video which shows the process and this can be found on YouTube.
Martin.