Wednesday, January 21, 2015

A Few Flakes May Fly

7:50PM Wednesday update... here's a quick video update.  I share my thoughts about this Thursday and Friday using the afternoon run of the GFS from Weatherbell.

When the 00Z NAM came out Tuesday evening, it got a lot of attention.  It would have been a winter wonderland for sure across many areas of Arkansas with several inches of snow.  Throughout my twitter and facebook posts, I had two concerns about such a scenario: the surface temperatures and storms along the Gulf Coast.

All of the models, including the NAM, point to readings well above freezing in the lowest thousand feet of the atmosphere with much colder conditions aloft.  Can this be overcome? Yes.  If the precipitation rate is high enough, it could prevent those snowflakes from fully melting.  This is a situation where large, slushy snowflakes make it to the surface.  The icy mixture can help drop temperatures down to 32-34 degrees and it begins to accumulate on grassy surfaces, etc.   The other concern I have will be the effects of large thunderstorms along the Gulf Coast.  There are times when they "rob" significant moisture advancing to the north.  This decreases amounts, coverage, and intensity.  I guess you can add a third concern too.  Ground temperatures are quite warm after almost hitting 70 degrees three days straight.

So what has happened since that 00Z NAM model run?  The next run of the NAM (06Z) backed off on the initial wave of snow and is now hitting on snow chances with the upper level low on Friday with lesser amounts across western Arkansas and higher amounts central and east.  The GFS wants none of this.  It does show the possibility for snow to mix with the rain, especially the higher elevations where those peaks can tap into the colder air aloft. It also shows a little snow with the upper level low, but not much.   The Euro is not snowy like the NAM either.  

So where do I stand? The NAM is erratic with its depiction.  Will it be right?  Only one person knows for sure.  As of Wednesday morning, I will lean towards the GFS/Euro solution.  There's more time to fine tune this forecast.  The surface temperatures are a huge concern for me (being too warm) and storms along the Gulf Coast will have to be overcome.  

As of today, I think the best chance for any snow will be across the Ozarks and Ouachita Mountains Thursday, then a chance for some portions of the state Friday with the upper level low and that very much depends on the track.  Right now, amounts would not be much in those higher elevations...  little to none.  Temperatures Friday will be above freezing too so not expecting much there.


The first 4 maps are courtesy of Weatherbell

Here's the GFS valid Thursday from noon to 6PM.  It's a cold rain for southern Arkansas with only light rain or sprinkles further into central Arkansas.  The blue line (35 degree line) is north.  Most of the surface temperatures are in the 40s.
With the affects of the upper level low and further cooling at the surface at night, the rain COULD change to snow on the north side of the precipitation shield Friday morning.  Notice the darker greens along the coast have shifted east.  If it turns into a case where storms rob the northward advancement of moisture, it would be over by this time.  Temperatures here are marginal so I would not expect much if any accumulation due to that, the warm ground, and the fast movement of the moisture.  The track of this upper level low is still in question as well.
By noon on Friday, it warms several degrees with a rain/snow mix over northeast Arkansas.
The snowfall amounts are very light and there's questions if this verifies.  If there are any accumulations, it would be Thursday night into Friday morning according to this model.  Once again, if this verifies, it would be on grassy surfaces and elevated objects.
Here are the past 2 runs of the NAM and it's erratic.  Notice the heavy snow over western Arkansas on the 00Z run, then it shifts it northeast on the 06Z run.  The 00Z NAM showed snow with moisture on Thursday and again Friday.  The new NAM is only hitting on the upper level low on Friday now.  Very erratic and I'm not buying into it at this time.
Once again, here's the GFS.  MUCH DIFFERENT!  It's hitting on snow chances Friday as the upper low pulls out.  Amounts here are well under an inch.

In summary, do I think the NAM will be right? I have serious doubts.  I don't think we'll have a real feel on how this unfolds until tonight, but at this time I'm leaning towards the GFS scenario.  For us snow lovers out there, let's hope the GFS starts going the NAM's direction.  I'll keep you updated.

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