Sunday, December 23, 2012

The Track is EVERYTHING

11:40 AM Sunday Update...  I just wanted to throw out the latest model data and a few thoughts roaming in my head.  First of all, I want to publicly let everyone know what an incredible wife I have.  Television weather is no longer an 8 hour a day job like it use to be.  Social media along with blogging make it a much longer day to stay on top of the situation and give you what you want, information.  I love doing it since this is not only my job, but my passion since I was 6 years old.  My wife is doing a lot of work around the house and taking care of the kids while I analyze and study what's happening with our forecast.  Just want to let you know that while I will have updates Monday and Tuesday, I will be off from work and spending time with my family.  This will be Preston's first Christmas and I want to celebrate it with him, Blake, and Andria.

Now onto the "weather" thoughts roaming in my head and there's plenty of room for that. LOL.  We really have not had true arctic air in here along with moisture in a very long time due to the mild winter last year.  We must remember a few principles that models will not handle well.  This is not a classic snow set up for Arkansas.  Usually, the cold air is in place when the moisture gets here and winds stay out of the east or northeast.  This is a case where the cold air comes in while the moisture is moving through.  You can still get ice and snow, but it's not classic and it's much more difficult to forecast.

You MUST remember the nature of arctic air.  It's cold, shallow, and very dry.  The true nature of it is usually not handled well by ANY computer model.  This dry, cold air is underestimated by the models.  Once we get into Christmas day, it will be important to look at the surface temperature and dewpoint and compare it to model data.  My gut tells me the models will be a few degrees too warm.  Rain falling into the layer of dry, cold air will undergo a process called "evaportational cooling".  Simply meaning, the rain will cool the air as it falls due to the dryness.  This has a tendency to lead to sleet or sleet and rain mixed.  That's something we MUST keep an eye on Christmas Day. 

Then later, as the colder air works in aloft, the transistion to snow COULD occur depending on what model you look at.  Once again, I will not go out on a limb right now due to the differences in the track stated in today's original blog post.  Please read that.  Some will be happy and others sad.  I continue to think northern Arkansas has the best chance for accumulating snow.  How much and where the axis of heavy snow is not fully understood until a track is determined.  I would rather wait and be right than jump the gun and be wrong.

Check out the maps below from the morning model runs.


This is Christmas morning at 6AM from the GFS.  Those small black lines are surface wind barbs.  They point to the direction from which the wind is coming from.  It's all east and northeast across the state.  See the "1036" at top.  That's a pressure reading around the high coming in from Canada.  That's the source of the cold, dry arctic air.  The air is flowing out of that southwestward into AR.  The colored contours are surface dewpoints.  This indicates they are in the 20s across the north half (white and gray).  This will lead to evaporational cooling at the onset of precipitation and temperatures will fall a few degrees when that happens.  The surface low is in west Texas with that black closed line.  We need that to dig south and east a little for a good snow.  We'll see if that happens.


HUGE model differences.  Here's the early morning run of the GFS snowfall amounts.  The heaviest is up north.
And here's the NAM.  Now do you see why the track is sooooooooooooooooooooooooooooooooooooooooooooooooooooo important????  It's wayyyyyy north with nothing here in central AR.  I would rather wait and be right, but it looks like northern AR will take the brunt of whatever happens.  Stay tuned.
  
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I have held off on my own forecast for snow amounts for a reason and we are seeing why.  Even though we're just 2 days away from this snow/rain event, the models have different tracks.  This is a situation where a shift just a few miles means EVERYTHING.  Some will be happy and others will be very upset.  That's the bottom line.  No snow forecast will be absolutely perfect!  I continue to maintain as I always have that NORTHERN Arkansas has the best chance for accumulating snow.  Areas further south will still likely see SOME snow.  I'm very hesitant to put out amounts due to the differences  in the NAM vs the GFS.  The NAM is trending north with the track ever so slightly and it's enough to cause BIG forecast headaches.  This is why forecasting snow is so difficult.   We're trying to pinpoint the track of the center of low pressure to the exact position and any deviation from that track can mean the difference between 4 inches and NOTHING.

Here's what we're looking at this morning.

This is the Sunday morning run of the NAM valid Christmas at 6PM.  The surface low is moving through eastern AR and into MS.  This is north of all the other models.  The blue dashed line is the indicator for rain/snow, but not exactly. According to this, the heaviest snow is in northern OK into northern AR.  We could actually get "dry slotted in SW into central AR from this track.
This is the overnight run of the GFS valid at the same time.  The low is further east and a bit further south in eastern MS.  This SMALL difference makes a huge difference in what kind of weather we can expect.  This track brings the heaviest snow to central Arkansas.  

In summary, now you see why I'm hesitant to make a snow forecast.  Small differences in the track means everything.  All this will change some more so stay tuned.

5 comments:

Anonymous said...

so what you're saying is, the entire state will have snow, and if not, you will personally apologize????? LOL just kidding Todd. Keep up the good work and here is hoping for a white Christmas in somewhere other than just the standard Ozark mountaintops!

Anonymous said...

Thanks Mr. Yakoubian for all you do! Much appreciated from my house!

Anonymous said...

Everyone think SNOW!! SNOW!! SNOW!!.....
I wish than central Arkansas would get the big snow for once !

LeafHopper said...

Even I can get the snowfall totals right if I wait till Wednesday afternoon to do it.

Anonymous said...

Leafhopper, quit being such a snowbirdbob fanboy and at least try to understand the position Todd is in and how hard snow forecasts are to make.