Saturday, December 20, 2014

Wiggle Room


Read the post below and you know about "wiggle room".  The forecast is never 100% until after it happens in the world of weather.  I'm going to have to tweak my forecast a little to include a little snow, but I think mainly north late Tuesday into early Wednesday.  Right now, I still think there will not be a white Christmas, but I reserve the right to have "wiggle room". LOL

I mentioned how horrible the models have been in the medium to long range and I'm going to give you a classic example below with this situation coming up Tuesday into Wednesday morning.  It should be mentioned, the models usually struggle this time of year anyway.

How do I think this will all play out?  Temperatures will go well above average Monday ahead of the cold front.  Rain will increase during the day and continue into Tuesday.  The high Tuesday will be set early with falling temperatures into the 30s and 40s late.  As the system starts to exit, moisture may wrap in from the north and the rain COULD change to some wet snow, but mainly north.  This would be brief and finished by Wednesday morning.  The American Global Forecasting System (GFS) is the most aggressive with this and the European is not.  The GFS brings flakes as far south as central Arkansas, but the Euro keeps most of it into Missouri.  I'll take a compromise between the two and say any brief transition will be mainly northern Arkansas, but given the variability in the data, let's watch this carefully.

Regardless, Christmas will be dry and cool/mild with highs in the 50s to near 60.  A new front arrives Friday into Saturday with another shot of cool air.

This is the GFS run from last Tuesday valid for Christmas Eve morning at 500 mb (@20,000 feet up).  This shows you the troughs and the ridges and all the pieces of energy (disturbances) working through the river of air in the atmosphere (jet stream).  You can clearly see the model showing a trough oriented from northwest to southeast from the Great Lakes to the eastern seaboard.  That places Arkansas in a dry northwesterly wind flow aloft.
Here's the GFS run from this Saturday morning valid at the same time.  WOW!  That's different and has major implications in the forecast.  The trough is carved right over the central United States and would bring us more unsettled weather.  
This is the GFS run from Saturday morning at the surface courtesy of weatherbell.com.  See the surface low over the KY/ Indiana border at 994 mb?  That's fairly strong.  The flow of air on the back side of that could change the rain to snow according to this model as it ends Tuesday night/Wednesday morning.  REMEMBER, THE EURO  IS NOTHING LIKE THIS!!!!  It keeps any snow north of the state.   At this time, the best forecast is for mainly rain with any transition northern Arkansas.  Stay tuned!
Check out the new experimental GFS.  This may have the best idea.  It's faster with the storm and only has the change over for northern Arkansas late Tuesday.

Friday, December 19, 2014

Dreaming Of A White Christmas?


If you're dreaming of a white Christmas, keep dreaming.  Now that we are within the 7 day window, confidence is growing we will NOT have snow flying or on the ground Christmas Day here or anywhere around Arkansas.  I will say this... the models have been a little erratic lately and I will always leave that wiggle room to say things could change, but you can't deny what that data has said and is saying today (Friday).  In the world of weather, there is NEVER a situation with 100% confidence until after it happens.  You'll get burned at some point. 

We're going to get a strong cold front in here late Monday with a quick shot of cold air.  This air mass does not have arctic characteristics so I'm not expecting a drastic cool down.  It moves in and out rapidly.  The operational GFS and European indicates we'll be between system Christmas Day with temperatures above average.  As a matter of fact, if you believe the data this morning, we could have highs in the 60s.  Again, I'll leave a little "wiggle room" since this is a forecast out to 7 days.  There will be a cold front moving in by Friday.  What if it gets here faster?  The last week of the month still looks chilly with a good chance for below average temperatures. 


This is the operational Euro valid Christmas Day.  The Canadian area of high pressure moving in Tuesday is gone and located over Florida and a wave of low pressure is located over eastern Colorado.  That's the closed black circle over the eastern portion of that state.  The flow of air is counterclockwise into that low.  That's evident with the black lines (isobars) so the flow of air has a southerly component and we all know what that means.... NOT COLD!

And here is the operational GFS showing a very similar set-up, but not as strong with that wave of low pressure over Colorado.

In summary, I guess things can always change, but you see the agreement here so confidence is building we will not have any snow.  Like your favorite football team (unless it's Florida State, Alabama, Oregon, or Ohio State), the saying goes, "there's always next year".

Thursday, December 18, 2014

Christmas And Beyond. The Cold To Get Colder.


Yes, this is a long and almost 14 minute video, but I think it's loaded with good information.  While it's impossible to get specific with a forecast that is 7-10 days out, this does show clear trends.  It will be chilly to cool around Christmas, but arctic air is looming.  It's arrival is uncertain and any precipitation is uncertain as well.  This goes over everything you can possibly imagine as we end 2014.

The maps used in this video are courtesy of weatherbell.com