Long range forecasts: 3 to 10 days into the future
The trick to using long range forecasts is to know when there is or isn't skill ▾ in the forecast for your location.
The latest 10 day MSC GDPS model forecast is shown below in 6 hour steps. Cold air is blue/purple, warm air is yellow/orange. The blue sprinkles indicate precipitation. Storms grow where warm and cold air approach each other to form a stronger jet stream (where the coloured bands are tightly packed) and particularly in southwest flow.
Here are six forecasts for the same time today but made 7 to 10 days ago - chaos?
These were made in the last 3 days - order!
These forecasts for today were produced every 12 hours over the last 10 days. If the forecasts were perfect they would all be identical - All 20 forecasts
Here are the latest forecasts valid near midday for Canada on
each of the next 9 or 10 days:
Wed04/Day1 Thu05/Day2 Fri06/Day3 Sat07/Day4 Sun08/Day5 Mon09/Day6 Tue10/Day7
Wed11/Day8 Thu12/Day9 Fri13/Day10
Location is important. If you are located away from the jet stream then you will likely have a better forecast for further into the future.
The above illustrates the problem and for day-to-day use we also have map charts of the chance of precipitation on the EC/MSC website (fancy name: "The Calibrated Probability of Equivalent Precipitation").All frames are valid for the same time: 2024/12/04 00:00 UTC.
"ISSUED": the forecast issue time followed by the valid time (eg. "+120HR" indicates a 120 hour/5 day forecast).
Reset the animation to Current GDPS 10 day forecast.
