Links to local weather information - Merriwa is situated about half-way between Mudgee and Scone, so it is useful to consider forecasts for both Upper Hunter Valley and Central Tablelands weather districts.

Merriwa AWS - Last 72 hours - BOM Officially online 03/09/2007
Hunter District Forecast from BOM
Central Tablelands District Forecast from BOM
7 Day BOM forecasts for towns in NSW - just click on the map (includes Scone and Mudgee)
Newcastle Radar (where it is raining now) (256km LOOP)
Namoi (Gunnedah) weather radar now online  (256km LOOP) New online Sept 13, 2010. BOM media release 
MERRIWA 7 day forecast from OzForecast.com.au.
Rainfall data from BOM FLOODWARNING division. Australia-wide coverage, but this particular link covers NSW Mid North region - Wyong to Coffs Harbour, West to Ulan, Coolah and Boggabri. (New format October 2011)
Current weather data - Hourly Automatic Weather Station reports for the Hunter District - BOM data, Australian Weather News text format 
Current weather data - Hourly Automatic Weather Station reports for the Central Tablelands District - BOM data, Australian Weather News text format
HunterWeather.com - more information than you could poke a stick at

NSW Water Information *Link added Sept 2010* Up to date info on NSW rivers and dams

Australian Bureau of Meteorology

Various forecast models - possibly the ULTIMATE feast of links if you are mad about forecasts. From Laurier Williams AustralianWeatherNews; includes brief overviews of each linked site.
Essential Energy Storm Tracker
Historical radar images - choose to look at any sequence of images from the previous two weeks of data. Also cloud and lightning. This link has changed (Sept '11) and now requires a free registration for personal access. It is very useful, e.g. you may need to have an idea of where heavy rain fell during the night, etc.
Wunderground (commercial options - free current data for most parts of the world)