Weekend Outlook: Where human forecasters add value

The heavy snow that caught many by surprise on Thursday and the weather over the next couple days reminds me again of the difference between a human forecasters and automated weather services. There are still some subtle things that experienced forecasters can tease from the raw weather model data that the public can find everywhere online.

Take Thursday's snow; the automated weather forecasts suggested somewhere between 5-10 cm of snow, but a human forecaster looking at the three-dimensional picture aloft could tell that the physics of the snow would create what's called high ratio snow and contribute to higher than normal snowfall for a typical Alberta Clipper.

 Looking forward to Friday and Saturday this weekend, we see the automated forecasts talking about scattered flurries.  Meanwhile, a human forecaster will see that the temperature that snow forms aloft is too warm for the formation of ice nuclei and so instead the more likely precipitation will be super-cooled water droplets that result in freezing drizzle when temperatures are at or below freezing.

 Temperatures climb back to near +1°C on Friday with overcast skies and the chance of that freezing drizzle and maybe the odd flurry on and off through the day. Overnight lows linger near 0°C and end up near -1°C Saturday morning.

 Overcast skies hang on into Saturday with another risk of freezing drizzle early in the day. Temperatures start near the freezing mark and then gusty northwest winds arrive in the afternoon to quickly cool things off in the late afternoon and overnight. Overnight lows into Sunday will certainly drop to near -15°C, possibly -20°C in outlying areas.

 Sunday will be cold with daytime highs near -10°C under a mix of sun and cloud. The colder than normal temperatures remain in place well into next week.