@connorjuvonen
During the assimilation phase of the model computation, millions of observations are used. All reports from official weather stations, including those from airports, are used for this calculation, but most data additionally comes from aircraft, radiosondes and satellites.
As said in this Wikipedia article:
“ The World Meteorological Organization acts to standardize the instrumentation, observing practices and timing of these observations worldwide. Stations either report hourly in METAR reports,or every six hours in SYNOP reports. These observations are irregularly spaced, so they are processed by data assimilation and objective analysis methods, which perform quality control and obtain values at locations usable by the model's mathematical algorithms.The data are then used in the model as the starting point for a forecast”
