SNOW EDUCATIONAL POST FOR NORTHERN NSW / SOUTHERN QLD
You need 3 key ingredients for snowfall… Very low freezing levels, moisture depth in the atmosphere to cause precipitation and high ground elevation. The slightest changes in any of the above 3 can mean the absolute difference of snow / sleet / graupel or nothing occurring at ground levels. Forecasting snow is tricky and technical this far north however vast computer model data is normally accurate. Let’s break it down…
Temperatures: The temperature at 4500ft needs to be 0ºc or less, temperatures above this level need to be much colder… let’s say -25ºc at 20,000ft with ground temps ideally 10ºc or less. Snow flakes need super cooled air to form or it falls as sleet or tiny hail.
Moisture:This is required to produce precipitation resulting in snow. The depth of moisture in the atmosphere determines how much and what type of precipitation occurs. You need to ideally ave at least 75% relative humidity in the low levels from 3000ft to around 10,000ft. The higher the relative humidity, the better, as it can mean all the difference between a short snow flurry and good ground covering.
Ground Elevation: CRITICAL… Every 1 metre of height counts here! Imagine getting a handful of snowflakes and throwing them off a second floor balcony… Depending on the surrounding air temperature they would melt before reaching the ground! The air snowflakes are in needs to be less than 0ºc or they melt quickly. There is a exception to this where you can have temperatures from 0 to 10ºc on the ground and be high up on a mountain top or range and it will still snow because the cold air gets dragged down to the surface with precipitation. Regardless of this, the higher the elevation, the better your chances are of seeing snowfall. Elevations of at least 1100 metres ASL (above sea level) are ideal in Southern QLD and Northern NSW for snowfall to occur.
Personal Note: I have seen snow in Toowoomba in the Early 80’s, graupel or small hail almost snow on the Bunya Mountains in the 90’s, Snow and sleet at Eukey near Stanthorpe, Snow at Mt Mckenzie Tenterfield and up to 10cm of snow at Guyra and Ben Lomond on the Northern Tablelands of NSW. Successfully forecast and snow chased along with sending many people to locations when forecasts are confident, this is normally 24 to 48hrs ahead of the event. There is a fine line but let me tell you the real time experience you and your children can have lasts a lifetime!
Temperatures at 4500ft ASL, those below 0ºc are ideal for snowfall to occur if moisture levels are high enough. Image – valid for June 27th 2016 via BSCH