From Spring To Winter In 24 Hours !November 23rd, 2012 at 11:35 am by Greg Shoup under Weather
Strong Cold Front Drops Temperatures
A very strong cold front has dropped temperatures from what was one of the mildest Thanksgiving’s in the last 40 years to winter with nearly a 30 degree drop. Thursday we had temperatures around 60 by mid day and today we are struggling to get into the middle 30s. The other part of this story
Something we usually see turn on with regularity late November and early December is the what we like to term ‘The Lake Effect Snow Machine”. Let’s examine what causes this phenomenon.
Lake effect snow forms over warm waters when arctic air moves across it. This mix of temperatures causes a small temperature inversion which essentially creates a cap with cold air being trapped at the surface and flowing over the warm lake waters. After the cold air travels along the smooth surface of the water it begins to pile up as friction is created by the ground that is not as smooth. As the air piles up we see what is called convergence. Basically, the air converges and creates lift over the area, which in turn creates clouds and moisture is already created by the lake waters.
The other factor needed are winds. We call them a ‘fetch’. The winds ‘fetch’ the moisture and carry it across the land. Of course the areas closest to the lakes receive the biggest concentration of moisture. If the ‘fetch’ is strong enough winds will carry the moisture several miles off shore so even places like Fort Wayne and Indianapolis can see some lake effect snowfall. As these winds carry the moisture it does shrink a bit so the snow squalls are not as heavy and usually don’t accumulate like they would close to the shores of the lakes.