Tuesday, February 19, 2013

Parade of Storms Continues. Winter Fights Back!


8:20 PM Tuesday Update... Here is a very in depth video update using the European model. 




The idea of ice and snow Thursday was discussed here on the blog almost a week ago.  It's yet another example of low level arctic air undercutting warm moist air aloft.  These situations usually produce ice and this will be no exception.  I continue to think the majority of the icing will take place across northern Arkansas.  However, there will be some in central and western Arkansas, but at some point Thursday, a change over to plain cold rain should take place.

There could be a little snow early in this event for far western and northern Arkansas so winter weather contestants will have to pay close attention to Harrison.  There are some differences with the modeling.  Euro is warmer while the overnight run of the GFS is much colder and a little scary.  Remember, the Euro has performed very well this winter and was the first model to hint at this situation to unfold.  Let's get straight to the maps.

This is the Euro valid at midnight Thursday.  Notice the dark blue line.  That's the 32 degree line near the surface.  It's draped over northern Arkansas showing the higher elevations really getting some ice and snow accumulation.
By noon Wednesday, the only locations below freezing continues to be northern Arkansas with significant ice accumulation possible there.  All the green and blue blobs are precip amounts over the past 6 hours ending at noon Thursday.  Look at the legend to the right as a guide.
And it keeps coming Thursday PM.  That 32 degree line stays up there all day while the rest of the state has a cold rain.  This is valid at 6PM Thursday.
This is total precip according to the European model.  Much of central and southern Arkansas could see up to 2'' of rain.  A small fraction of that could be freezing rain/sleet at the beginning of the event.  Look at northern Arkansas where that 32 degree line stays all through the storm.  That's indicating amounts could reach .5'' or higher!  IF THAT VERIFIES, IT WOULD PRODUCE VERY SIGNIFICANT ICE AMOUNTS FOR FAR NORTHERN ARKANSAS, ESPECIALLY THE HIGHER ELEVATIONS.
This is the overnight run of the GFS which is much colder.   Look at the large area circled with 32 degrees or colder across western, central and northern AR.  This is valid at noon Wednesday with precip over portions of that area of the state.
By Thursday morning at 6AM, it's 32 degrees or colder over the northern 2/3 of Arkansas.  This is MUCH colder than the more reliable Euro, but it bears watching because low level cold air is at play here and the models usually underestimate it.
By Thursday at 6PM, The freezing line drifts north according to the GFS.  This means there would be a transition to ALL rain for much of Arkansas except the far north.  So here in central AR, I would expect a period of ice later Wed into Thursday AM, then a cold rain after.  Again, it's northern AR which should see the brunt of the icing.
It seems like HPC is going with the colder scenario here.  They are saying there's a high chance for at least .01'' of freezing rain over much of Arkansas between Wed at 6AM and Thurs at 6AM.
HPC continues the very high chance for at least .01'' of freezing rain over much of Arkansas between 6 AM Thursday and 6AM Friday.  Much of this will be over late Thursday.
This storm will be huge and will produce very significant amounts of snow for all of NE, KS, MO, and Iowa.  Far northwest AR is under a winter storm watch.
Our own model, "Futurecast" indicates some snow possible before it transitions to ice.
And to add more interesting weather to the whole equation.  There will be a slight risk for severe thunderstorms over southern Arkansas which we will watch for you.
In summary... there will be marginally cold enough air for  a wintry mix Wednesday into Thursday.  Aloft, temperatures will become quite warm as the event unfolds.  This leads to icing and NOT snow for much of the concerned area.  I would expect reports of icing as early as Wednesday across western and northern Arkansas.  The icing will continue to grow in coverage Wednesday night into Thursday morning for much of the northern half of the state including the metro.  Thursday AM, temperatures at the surface will jump above freezing leading to a cold rain.  It's far northern AR which has the highest risk of staying below freezing much longer.  IF THE INTENSITY OF THE COLD AIR IS STRONGER, THEN THE CHANGE OVER COULD BE DELAYED FURTHER SOUTH.  I'll keep you updated.

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