Monday, December 24, 2012

A Christmas Miracle... Snow?

TWITTER: KATV_WEATHER

5:30 PM Monday update.  Below you will find the Channel 7 forecast for snow.  Even at this late stage in the game, this can still shift.  The trend with the modeling today is a shift to the south so it will have to be watched carefully with tonight's data.  I expect some rain and sleet in the morning as well, then the changeover to snow late in the day is still on schedule.   There will be a very, very sharp snowfall gradient.  This means there will be a short distance where the snow amounts will change drastically from nothing to several inches.  Where this sets up is difficult to pinpoint at this time.

Also, the other BIG story will be the wind!  If  you live in northern Arkansas, especially, the heavy snow and wind combined will cause power outages.  Be prepared for that Tuesday night and into Wednesday morning.  

Check out the maps below.

Again, this is still subject to change, but this is our forecast at Channel 7.  The immediate metro area could see 1-3 with 3-5'' possible just to the north in northern and western Pulaski county up towards Conway.  Look how the amounts drop off the further south you live.  5-8'' or up to 10'' could fall across northern Arkansas.


This is the morning run of "Futurecast" indicating slightly higher amounts so this will have to be watched.  This is just a model though and we'll see if the southward shift continues.
 ____________________________________________________________________
   10:40 AM Monday update... This is just a quick update with a quick glance at the new data.  The NAM has shifted south a little and so has the GFS in respect to snowfall amounts.  I'm not going to get indepth with this update, but I will show you the two models forecast for snow depth.  If the GFS is correct, we will have to add higher amounts of snowfall further south.  So yes, as I have said, this situation can change and indeed there's a high chance for that.  At the same time, I urge caution because I am concerned about surface temperatures being to warm in the metro.  However, if you get heavy wet snowflakes to fall, it will cool the air to near freezing.  Stay tuned for more updates.

The 12Z GFS snow depth off twisterdata.com shows very high amounts in excess of 8'' across the higher elevations of west central AR with another bullseye across the northeast section.  IF this is correct, central AR would have a VERY tight snowfall gradient, but this does show significant snow further south.
 
The NAM continues to hit northern AR with the highest amounts and a strong gradient just north of Little Rock.  So you see the differences and the possibilities here.

___________________________________________________________________

We know how rare it is to actually get snow to fall and accumulate Christmas day in Arkansas!   If it happens, it will be the first time in more than 80  in Little Rock.  Also,  if we get more than 2.5'', it will be the most ever on Christmas day in Little Rock weather history, HOWEVER, I will explain why this will be difficult to achieve.  Here are the past snow amounts in the metro.

1939) .1'' of snow
1926) 2.5'' of snow
1913) 1.5'' of snow
1897) 1'' of snow

Remember, we have had snow on the ground from a previous snow.  That happened in 2004.

As I have said, the focus for the heaviest snow will be northern Arkansas and the southern extent is in question in my mind.  

Let's talk about Little Rock which is obviously a major population center.  Once the changeover to snow occurs late Christmas day, temperatures will be above freezing.  It's possible to get accumulations, but the snow must come down at a high rate.  I have seen this time and time again.   The city COULD retain enough heat to limit accumulations within the heart of the metro, HOWEVER, just a few miles away from the city center into the higher elevations of west Little Rock or just north of the metro could see a nice coating and I think it's these areas could receive 1-2'' and IF we're lucky 3''.  

Please don't misunderstand me, I do think flakes will fly late Christmas, but accumulations will be more likely west and north of the city.  Southern Arkansas, I think you will see flakes fly at night, but amounts will be nothing to maybe a dusting.

The other big story will be the wind.  Look for sustained winds late Tuesday around 20-25 mph with gusts exceeding 30 mph.

Due to the track of the low, south of it will have the potential for a significant severe weather outbreak across portions of southern Mississippi into Alabama.  While we're watching snow, remember lives are threatened there.  This storm has the potential to be violent and we need to keep those people in our thoughts and prayers Tuesday.

Below are maps from the NAM which isn't perfect by any stretch of the imagination, but does convey what I think may happen. Also, my preliminary snowfall map.  I'll explain.

This can change between now and Tuesday, but this is my preliminary first map for snowfall.  Look how I have the immediate metro area out of accumulations, but just north and west of it could see 1-2'' and maybe 3''.  The best chance for heavy snow will be from near Mena to near Conway northward.  There will be the possibility to see isolated higher amounts which could exceed 6'', especially in the higher elevations.  AGAIN, THIS IS PRELIMINARY AND CAN CHANGE SO STAY TUNED.
This is the NAM valid at noon Christmas.  The green is the rain, orange is mix, and blue is snow.  Most of AR is covered up with rain with a mixture across the north.  It's snowing hard in Oklahoma.  Watch that red dashed line from north TX to Tulsa into southern Missouri.  That's a good indicator of the rain/snow line.  North is snow, south is ice or rain.
The cold core low is punching into AR here and the red dashed line is making a move into western AR by 6PM and the transition to all snow is occurring and probably happening further east and north than this model depicts.
By midnight, it's snowing across much of the northern half of the state an the cold air aloft is in place.  Surface temperatures are falling and winds are howling out of the north.  See those brown lines?  Those are isobars around the surface low which you can clearly see near Jackson, TN.  A strong north wind is blowing!  South Arkansas will have some light snow and flurries at this point, but the heaviest stuff is across the north.  By sunrise Wednesday, it's all out of here.
Here are the watches and warnings from the NWS.  Blue is the watch and pink is the warning.

1 comment:

Anonymous said...

Is that a dry slot on the 18z gfs? Wouldn't surprise me. I knew this was too good to be true!