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.

A skillful model forecast improves on the average expected weather at the given location for the time of year. So if Winnipeg has an average of 10 rainy days in June then a forecast for tomorrow of 33% chance of showers for all 30 days may be "correct", in a sense, but has no skill and is useless for anyone who is familiar with June weather in Winnipeg.

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:
Tue03/Day1 Wed04/Day2 Thu05/Day3 Fri06/Day4 Sat07/Day5 Sun08/Day6 Mon09/Day7
Tue10/Day8 Wed11/Day9 Thu12/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: 2024/12/05 18:00 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.

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