Meteorological Acronyms

 National Centers

NOAA National Oceanographic and Atmospheric Administration
NWS National Weather Service
NCEP National Centers for Environmental Prediction
SPC Storm Prediction Center
NHC National Hurricane Center
NCDC National Climatic Data Center
NSSL National Severe Storms Laboratory

A more complete list can be found here

 Models

NGM Nested Grid Model
MOS Model Output Statistics
AVN Aviation
GFS Global Forecasting System
MRF Medium-Range Forecast
RUC Rapid Update Cycle
NAM North American Model, formerly ETA
MM5 Mesoscale Met. Model, Version 5