Monday, December 15, 2014

GFS vs. Euro. Snow or No?

Monday 12:30 PM Update... I have seen the new morning runs of the GFS and the Euro.  Not much has changed.  You may be shocked to hear I'm siding more with the GFS than the Euro.  I still think this will be a cold rain with a possible change to some wintry weather, but mainly north.  There just isn't a significant amount of cold air around, but that will change the last week of this month!   It's still several days away and can change.  I'll keep you updated.


Everyone who is in the winter weather contest, you can click in the navigation bar above to keep track of the snow and low temperatures.  You can also check out all the entries.  If you see an error, please let me know.  It was a ton of data to put into the computer.  I felt like Peter in "Office Space" entering my TPS reports. LOL.

This time of the year can be a huge headache forecasting, but I love the challenge.  As I mentioned in the previous blog post, we're going to have a parade of storms.  The first one is moving through this Monday morning, but another one will arrive later Wednesday.  This is weak and should only be a cold rain.  A much more significant wave of moisture moves in Friday and Friday night and this is where the models are fighting it out.   In one corner, the American GFS is not as strong and tracks the low further north compared to other models.  The GFS also does not have much cold air with it and thus keeps it all rain, expect a small chance it could change to a wintry mix Friday night over far northern Arkansas.  In the other corner is the European.  It's further south with the track of the surface low and it looks like a classic track for wintry weather.  It's also much colder compared to the GFS.  With all that said, look at what happened today!  The European model advertised a much further storm track to the south several days ago bringing the chance for wintry weather while the GFS went north.  The GFS won that battle.  That's why I'm a little hesitant about buying the Euro later this week.  If I did, it would be wishcasting.  I want the snow more than everyone else.   Could the Euro be right?  sure!  But the best course of action should be a compromise between the two.  A good forecast at this point should call for a cold rain with a possible changeover before ending.  The Euro is more robust with that change over while the GFS is not.  There's plenty of time for this forecast to be fine tuned.  The storm we're watching is over the Pacific and hasn't been sampled by our upper air network.  Once it does in a couple days, the forecast will come into focus.

This is the Euro valid at 6PM Friday.  This shows the amount of precip over the previous 6 hours.  The blue line is a good indicator of the rain/snow line.  Look at the black closed circle over central Louisiana!  That's the surface low with heavy rain north of the track.  If this verified, northern Arkansas would see a significant round of snow/sleet with a cold rain central and south.

This is valid at midnight Saturday.  The surface low is pulling away and colder air is working south at all levels.  Look at the collapse of the blue (540 thickness) line.  This means rain would change over to wintry weather from northwest to southeast as the storm moves to the east.

By 6 AM Saturday, there has been a change over to wintry weather for much of northern and central Arkansas.  Don't get too excited just yet.  Look at the GFS below.
Late Friday, the GFS shows a weaker surface low and a bit further north with the position compared to the European model.  It's also lacking in air cold enough to support wintry weather.  This is a cold rain!
By midnight Saturday, the low is over northern Mississippi with little moisture wrapping around.  The blue line also never makes a significant move south.  That's because the system is much weaker compared to the Euro.  Even though it's weaker, this would still bring good rains to the state.  
In summary, it's too early to make a call on which model to believe.  As mentioned above, the GFS did better with the system moving through today.  That doesn't mean it will do better later this week, but it does give it some credibility.  Many times, neither is correct and it's somewhere in between.  STAY TUNED!

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