I designed a very large weather site about 7 years ago. We used weather.com (TWC) as our weather feed and they had the best interpolation algorithms.
(Before I go into this, DO NOT take this as excusing weather forecast accuracy, it's crap, especially so here in Seattle).
Weather sites have point data that they get, for free, from NOAA/National Weather Service (it tends to be at airports and other semi-official locations). If you live close to one of these, then it will have pretty accurate reporting, if not forecasting. If you live far from one, or close to one but up/down a mountain, or next to a large body of water, then weather companies, such as Weather.com have interpolation algorithms that try to "tweak" the actuals (and the forecast) to be closer to accurate. This means it will never be right, but if they do their job correctly it will be pretty close. We didn't think much of it when using Weather.com, but then we changed to another weather forecaster from Europe, we quickly realized how much better Weather.com's algorithms where. The new company was scrambling to improver their models, as our customers complained very loudly. It was very hard to do and not something that can be just whipped up over a 6-week sprint.
From what we saw, TWC/Weather.com had the most sophisticated algorithms so they were reporting closer-to-accurate temperatures.
I won't say anything about forecasts. Around here we are lucky to have an accurate forecast for today, and anything more than is about as accurate as any local's guess.
(Before I go into this, DO NOT take this as excusing weather forecast accuracy, it's crap, especially so here in Seattle).
Weather sites have point data that they get, for free, from NOAA/National Weather Service (it tends to be at airports and other semi-official locations). If you live close to one of these, then it will have pretty accurate reporting, if not forecasting. If you live far from one, or close to one but up/down a mountain, or next to a large body of water, then weather companies, such as Weather.com have interpolation algorithms that try to "tweak" the actuals (and the forecast) to be closer to accurate. This means it will never be right, but if they do their job correctly it will be pretty close. We didn't think much of it when using Weather.com, but then we changed to another weather forecaster from Europe, we quickly realized how much better Weather.com's algorithms where. The new company was scrambling to improver their models, as our customers complained very loudly. It was very hard to do and not something that can be just whipped up over a 6-week sprint.
From what we saw, TWC/Weather.com had the most sophisticated algorithms so they were reporting closer-to-accurate temperatures.
I won't say anything about forecasts. Around here we are lucky to have an accurate forecast for today, and anything more than is about as accurate as any local's guess.