Snow before frost? A first for Montreal in more than 70 years
Montreal sees an unusual weather twist as October comes to a close
Typically in the fall, we psych ourselves up for temperatures cooling down to the first frost of the year -- well before we start talking about snowfall sticking to the ground.
But this year, a rare event lead to the exact opposite.
A first in over 77 years
Montreal recorded their first measurable snowfall before dipping below the freezing mark, something that's only happened one other time in recorded history.
The set up:
To have a first snowfall, it is necessary to have a system to bring in moisture and cold temperatures, but how cold?
Snowflakes require below freezing temperatures in the atmosphere in order to develop, but they can accumulate on a ground that is above 0°C. This above freezing layer must be very shallow and close to the ground, so that the snowflakes do not have time to melt fully. Instead the result is wet, and heavy snow.
On October 30, Montreal measured 2 cm of snow while staying no colder than 0.3°C.
PHOTOS: First snow of the season blankets southern Quebec
To have a first frost on the other hand, two conditions must be met: cold temperatures and a clear sky to allow the surface to cool overnight.
In this particular situation in Quebec, it is indeed cold above the surface. However, the sky had not been clear. Instead cloud cover had acted like a blanket, keeping surface temperatures above freezing until Tuesday morning.
One day after the snowy scenes on Monday, the city finally fell below 0°C for the first time this season on October 31, which is actually well behind schedule.
The only other time in recorded history Montreal experienced this was on October 1 in 1947 where measurable snow fell, and their first frost did not occur until a whopping 17 days later!
