Monday, December 20, 2010

My two cents on forecast models.

So multiple times this winter I have talked about our chances for a significant chance for snow storms.  I want to give you an inside "look" at what is happening.

There are a handful of forecast models, but I want to focus on three: GFS, NAM, and  RUC.  The RUC is a very short-term model that goes out 18 hours, and by the time the data initializes it only goes out about 15 hours....throw that out the window.  We are now down the the NAM and GFS....

NAM model goes out 84 hours and is considered a "short term" model.  The GFS goes out 16 days and is a traditional long term model.  Both computer generated forecast models are generated by thousands of equations based on current observation data at our surface weather sensors and weather balloons to try to get a 3-D image of the atmosphere.

Breakdown for this La Nina year (not like many other years):
Ok so you know they are computer and equation based models, but I am not going to give a little personality to the forecast models.....personification for any English teachers I had....

The GFS is a child waiting for a snow day..... The NAM is a superintendent hoping for better weather in order to not "use up" a snow day.

Since the NAM only goes out about 4.5 days it is hard to get a gauge on the long term storms.  However, the GFS has complete freedom to do whatever it wants...  for the last three days it has been forecasting at least 10" for Christmas morning, on top of what we already have seen..... It just wants to dump as much moisture as possible on us.....  However, when we start getting close to the 4.5 days, the GFS settles down a bit and starts backing off a bit.  Right now it has us seeing about 3-5" on Chirstmas and some areas seeing a little more..... but still a HUGE cut back from the 10".  I think the school kid got in eye site of the superintendent and started taming back a little bit.  Anyway, while the NAM is away, the GFS is out to play.... and it plays really, really, REALLY hard.  It isn't until the NAM shows up, that the GFS settles down and plays properly.

(To anyone who reads regularly, or forecasts regularly, I hope you enjoyed that, cuz I know the NAM or GFS didnt.... what's true is funny)

Your Buck-cast: (Mind you, I am on vacation, but can't stop forecasting)
We will see up to 1" of snow overnight turning to a wintry mix in the morning, turning to rain showers for the  southern Miami Valley for the afternoon, back to a wintry mix, back to snow and accumulations less than 1".  We will see a break until Friday midday.  The snow will start and as long as we stay below freezing we could see about 3-5" if not a little more in some areas.   Winds will increase causing a lot of blowing and drifting snow.  This will be a big problem on Christmas put up wind guards on your roof now for Santa....

I will be back tomorrow, and hopefully a little happier with the forecast models, stay warm, drive safe, and most importantly: have a good one!

Andrew Buck Michael

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