Thank you my honourable friend.
In short. Low pressure causes air to rise, as that air rises it is creates a gap into which surrounding air rushes. That's a very basic principle of wind.
Imagine a circular Low pressure system moving steadily East across the Atlantic towards Blighty. The top half of the system is filling up with Arctic air from the north, the south is full of milder air from all of our favourite holiday destinations. When it arrives, anyone south of the middle of the system will get mostly rain, maybe some "back end" snow as the cold front of the low system swings round in its wake. To the north, heavy snow.
Now, with 2 days before that system arrives, you have to forecast the exact path of the system as the difference means rain, sleet, wet snow* or dry snow at any one location. Bob from Chester gets rain, Ted in Warrington gets heavy snow. You make your forecast and add an element of caution but the papers just see "10 cm of snow" and that's it. The world is expecting a foot of snow and, oh I hear there's 2 foot of snow coming. My mate said it was blizzards actually, for a month.
*A vague term but generally means snow that's melting as it falls. Hits the ground and disappears.