Looking around Souther Ontario the weather would be described as Poo Poo. That is a technical aviation term meaning crappy :) As you can see in the above image which is from Environment Canada and is an Aviation Graphical Area Forecast (GFA) there is a warm front (the red line with humps on it) extending from around the Manitoba border east south east towards Timmins. Now you can also see lines on the map, these are isobars (lines of equal atmospheric pressure) and depending if they are around a Low (which in this case is just off the map around Winnipeg) or a High pressure (the big H over Quebec) the wind moves parallel to these lines of equal pressure (above 3000 feet because near the surface, surface friction and the sorts cause them to angle in towards the low or away from the center in a high). Around a Low winds circulate counter-clockwise. So in this case the winds are coming from the south west in effect pushing the warm front up. Around a high pressure the winds rotate clockwise around the center of pressure which in this case means the High over Quebec is moving air in the same direction as the low pressure. Now basically what is happening is warm moist air is coming up from the south and meeting some cooler air and causing it to condense and cause bad visibility and low ceilings over Southern Ontario. I am really skimming the surface here but today the weather is quite bad over a large area so I wanted to write about.
Now if I was planning a trip today I would first go to Navcanada's weather site and put in my route of flight so that it will pull up METARS (basically weather observed within 5 miles of the aerodrome) and is updated hourly. It also comes up with TAF's (Aerodrome forecasts which cover within 5 miles of the aerodrome and give predicted winds, visibility and ceiling.) Now today I would pull up the following weather.....
What I have learned so far is that when you feel things aren't adding up....they aren't. Here is a picture of when the gut feeling was reaffirmed by a wall of cloud and snow showers flying through the rockies....go with the gut instinct!
Sorry for my incoherent jumping around but there is just so much to discuss when it comes to weather.