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Thread: How do they know...

  1. #1
    Member Dan GTX's Avatar
    Join Date
    Apr 2012
    Pittsburgh, PA

    Default How do they know...

    Ok, real world example here, and this is probably the main thing that bugs me and what I want to learn more about.

    As of this post, this is the outlook for zip 15108 (near where I live):
    Late Afternoon: A chance of showers and thunderstorms. Partly sunny, with a high near 81. Windy, with a southwest wind around 30 mph, with gusts as high as 48 mph. Chance of precipitation is 40%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

    Yesterday, it gave me a 60% chance for "Severe Thunderstorms", and now it's been downgraded to basically a "40% Chance of Rain".

    The low pressure system is out in Michigan and there's no merging of fronts anywhere near here.

    It doesn't help I have no idea what RUC or NAM models mean... lol

    What do I need to read or better understand to help with figuring out how they get their forecasts? (aka: Which maps/models do I need to have a better understanding of?)
    Some people are like slinkies: Completely useless until you push them down a flight of stairs, then they bring a smile to your face.

  2. #2
    Member MClarkson's Avatar
    Join Date
    Sep 2004
    Blacksburg, VA


    The RUC (Rapid Update Cycle) and NAM (North American Mesoscale) are both models run by the NWS. They essentially break down the US into a set of grids and then move different atmospheric variables from grid to grid according to the fundamental laws of physics. You can access their output here:

    A good starting point is comparing some of the model forecasts with what actually happens in your region.

  3. #3


    Agree with the above, the raw NAM and RUC models may be difficult to decipher for a newcomer, but the radar reflectivity and four-panel charts with both upper air and surface parameters are a great place to start. I'd use the RUC for same day events, NAM for 1-3 day events, and the GFS out a few days past (beyond 5 or 6 remains highly questionable).

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