Yet if you go searching in the National Weather Service database for the current conditions in the mountains, there's only one place that takes official observations, and that place is in Stampede Pass -- not exactly a popular driving route.
Why Stampede over Snoqualmie? It has to do with aviation. There's a reason most official observation stations are at airports -- pilots need detailed weather information near the runway to know exactly what they're flying into. While most cars and trucks use I-90 to get over the mountains, pilots of small planes prefer Stampede Pass, which is along a section of the Cascade Mountains that has much lower terrain and thus more friendly to pilots. On the other hand, Snoqualmie Pass is very rugged and narrow, making flying through more difficult.
So think of Stampede Pass as the "I-90" of the friendly skies, and that's why there's an observation station there, to help pilots navigate the weather up there.
Incidentally, the Dept. of Transportation has a few unofficial reporting stations along Snoqualmie Pass that can help you plan your travels.
These sites for I-90/Snoqualmie Pass and U.S. 2/Stevens Pass are great snapshots of current conditions, web cameras and forecasts.
You can also use this DOT site of the Snoqualmie Pass Conditions, which has weather data at the exit to the Alpental Ski area.
And finally, there's this link from the Northwest Avalanche Center that will show you the past 24 hours of weather at several locations in the mountains. You can also gauge how much snow has fallen there recently.