Monday, February 05, 2018

Winter Ain't Going Away

11AM Update... the NAM continues to be the coldest of the models and the new GFS is coming in colder, but not as cold as the NAM.  I continue to think this reaches winter weather advisory criteria for the northern 1/3 of the state.

As I stated below, this is a classic set up, BUT there are two limiting factors.  1st, the highest amounts of moisture should fall south of the subfreezing air.  2nd, the temperatures across northern Arkansas will be marginal.  

I have learned through experience, an east-northeast wind transporting arctic air will be colder than models project.  At this time, I think our high in Little Rock will be in the mid and upper 30s which of course is above freezing, but not by much.

The 12Z run of the GFS is further south with the freezing rain.  I like the idea of the northern 1/4 to northern 1/3 of the state with the highest chance for LIGHT icing.
The NAM is the most bullish and has it further into central Arkansas.  This is possible, but I think it could be a touch too far south.  I will continue to monitor for you.

The criteria for an ice storm warning requires amounts .25'' or higher.  At this time, I do NOT think it reaches that level.

You thought winter was over? LOL!  This is a classic set-up for ice Tuesday into early Wednesday.  However, there are 2 issues which should prevent it from becoming widespread and a major storm.

First, moisture will override the low level cold arctic air at the surface with a layer of warmer air aloft.  This layer of warm air will prevent snow production and whatever falls will be liquid.  Again, classic for ice.  

However, there are 2 limiting factors.  The air cold enough (32° or lower) will be confined to far northern Arkansas.  While it will be a cold rain for everyone along with a few thunderstorms, freezing temperatures will only be found across northern Arkansas.  The NAM is the most aggressive with the furthest extent south.  I tend to believe it since it is a hires, short range model which usually is able to see the low level cold air better than any of the global models.  How far south you might be asking?  I think the northern 1/3 will have the highest chance.

The next limiting factor is moisture.  While there will be some moisture in the subfreezing air, the highest amounts of precip will fall across southern and southeast Arkansas.  

Nevertheless, it does not take much ice to cause issues on the roads and I would expect a winter weather advisory northern Arkansas Tuesday.  I'll keep you updated.  Thanks.

The RPM is usually a bad model to rely on until you're within 12-24 hours.  However, it does show LIGHT icing in a small section of northern and northeast Arkansas.  I expect future runs to expand this area.

The GFS (a global model) is seeing the icing potential and has taken further south compared to past model runs.  This is indicating very light icing far north, but once again, it does not take much to cause a few slick spots.

The NAM is by far the most aggressive and continues to be with the newest run.  It takes light icing amounts down to Mena over to Searcy on up towards Jonesboro.   I tend to believe when all is said and done, this will be closer to reality.  It might not be this far south, but I think this is a good indicator as to where this is going.

As indicated above, it's a classic set up, but the highest amounts of precip will fall in air which should be above freezing, southern Arkansas.  So that's a limiting factor in all this.

In summary, light icing will be possible late Tuesday mainly across northern Arkansas.  When I see low level arctic air and a wind out of the east-northeast, LOOK OUT!  Those are ingredients for problems.  However, the highest amounts of rain will be south of the subfreezing air.  There should be enough LIGHT amounts of moisture for a winter weather advisory northern Arkansas and a few slick spots too.

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