2/12 11:30 update

Up to a third of an inch of ice accrual is possible tonight as light to moderate freezing rain will continue through through daybreak.  Temps will likely not exceed 31 degrees.  Along with the wind this should cause power outages and significant tree limb breakage just before and through daybreak.

1-2 inches of snow is looking more likely as the deformation band makes its way through the triangle tomorrow afternoon.  Brief heavy snow is possible, especially the western half of the triangle.

8:15 update Wed morning

Snow will begin falling before noon.  Sleet will mix in later this afternoon and during the early evening it will change to mostly sleet, before changing to freezing rain closer to midnight.  It will end as snow or drizzle.

2-6 inches of snow and sleet and 1/3 of an inch of ice accrual is possible.

Timing moved up just a bit 2/11 7:50 PM

I now believe that we will see a little snow move into the area by lunch time based on the latest High Resolution Models, which can now be used since the storm is so close (They only go out 18 hours into the future).  In fact there could be a quick burst of heavy snow in the afternoon.  I also think we could see some enhancement of early onset precip in the triangle due to the convection along the frontal boundary in the Gulf.  It also looks like the changeover to freezing rain may be delayed by several hours.

So I'm going to up the snow/sleet totals before the changeover to freezing rain to 1-4 inches.  Still think some light to moderate snow is possible before it ends on Thursday in which we could pick up another 1-2 inches.  Freezing rain accumulations still look to be significant, but we may be spared catastrophic icing.  I'll update again late tonight.

2/11 1:00 PM Winter storm update

The first ingredient for a significant winter storm has arrived.  Cold dry arctic air has invaded the triangle.  The next ingredient should arrive tomorrow afternoon as a low pressure moves along or just south of the Gulf coast.  Eventually the low will translate into the Atlantic before moving up through the Outer Banks.  This will allow lead to lifting which will cause widespread precipitation to fall in the southeast.  As the precip begins to fall in the triangle a classic cold air damming high will be situated east of the Great Lakes.  This will cause cold air to remain entrenched near the surface east of the Appalachian mountains and west of I95.  Warm/moist air from the Atlantic will override the cold air creating lift in the upper levels.  Precip will fall from the clouds as snow, melt and refreeze either just above the surface or at the surface.  As of now it appears the majority of the precip will fall as sleet and freezing rain.

Timing:  Snow and sleet will begin to fall Wednesday afternoon.  Accumulations of around an inch are possible.  Wednesday evening expect the snow/sleet mix to change to sleet and eventually mix with and change to freezing rain.  A chance of snow is possible Thursday morning and could drop 1-3 inches on top of any ice.  The temp will get above freezing on Thursday which should melt any ice accrual.

Precip type:  Snow/sleet quickly changing to sleet/freezing rain.  It's still not clear if sleet or freezing rain will be the predominant precip type.  WPC is going with the Euro model which show mostly freezing rain and even a bit of rain for about an hour before temps fall back below freezing.  But with that in mind they are also predicting the low to travel 40 miles east of the Euro, which would keep the temps below freezing.

Precip amounts:  Snow/sleet up to an inch possible Wed afternoon.  Sleet/ice accumulations of .50 to 1.00 liquid equivalent possible.  If it's mostly sleet then we could see 2-3 inches of sleet on the ground.  If it's mostly freezing rain than half an inch to 3/4 of an inch of ice accrual is possible.  With winds of 10-15 mph this would cause widespread power outages.

2:00 2/10/14 Update

All of the major models are in agreement that a significant winter storm will impact the triangle on Wednesday through Wednesday night.  The timing and precip type is still yet to be determined.  

As of now I believe precip will begin to fall sometime after noon on Wednesday.  It will likely fall as snow and quickly mix with sleet.  I believe that during the evening it will change to a sleet and freezing rain mix.  Snow/sleet accumulations of about 1-3 inches are possible with half and inch to one inch of ice accrual.  It is also still possible that the freezing rain could change over to rain early Thursday morning, although this scenario appears unlikely at this time.  Expect the precip to end as snow or drizzle.

It is also possible that some snow could fall Tuesday afternoon and evening however, as of now it appears the majority of the precip on Tuesday and Tuesday night will be south of the triangle. 

Here are the three scenarios and the likelihood they each could occur.  This is for the Wednesday afternoon/Wednesday night time frame.

Most likely:  Snow/Sleet changing to Freezing Rain.  1-3 inches sleet/snow and significant ice accumulation possible.

Less likely:  Snow/sleet changing to sleet/freezing rain late Wednesday night.  3-5 inches of snow/sleet but less ice accrual.

Least likely:  Sleet changing to freezing rain and then changing to rain late Wednesday night.  Signficant ice accumulation possible before the change over to rain.

Likelihood of a potential major winter storm for Wednesday increasing. 2/9 3:23

Most of the models are slowly converging on a major winter storm Wednesday.  At this time it appears that snow will begin to fall early Wednesday morning and then mix and change over to sleet and potentially freezing rain after noon.  Before the precip ends it will likely change back over to snow Thursday if precip is still around.

NOAA's Weather Prediction Center prefers a blend of models outside of the GFS.  The GFS shows the least amount of precip but is easily the greatest outlier.

This system is still a few days away and things can change quickly.  Minor changes can make a big difference in terms of precip rates, timing and precip type.

Welp.. 2/9/14

And just like that the models have shifted south and weak with the Tuesday night system only giving RDU a slight chance of light snow and rain Tuesday night.

On the other hand the models are converging on a major ice/sleet storm starting Wednesday morning and lasting through Wednesday night.  This has the potential to be a devastating ice storm for the triangle with temperatures in the upper 20's throughout the event.  The good news is that the temperature will warm above freezing on Thursday for after the precip exits.

The models are having a very difficult time with this system and forecast confidence remains extremely low.  It could completely change again.

Winter Storm ALERT! 2/8/14

Potential significant winter storm late Tuesday through Wednesday.


A rain/snow mix could begin late Tuesday before quickly changing to all snow and continuing through the night into Wednesday.  The snow may mix with and potentially change to light sleet and freezing rain, ]near the end of the potential precip.  The amount of precip associated with this type of classic southern winter storm could be significant.  One model is weaker with the system and produces less snow than some of the other models, but it is an outlier and as of now is being disregarded by the National Weather Service Model diagnostic team.  This same team is essentially going with a blend between the medium and high impacts shown by the models (But not the highest impact North American Model which gives almost all of North Carolina 13 inches of snow!).  Models show anywhere from 4 to 13 inches at this time.  It's still too early to officially predict potential snowfall amounts.

Potential impacts:

- Snow potentially mixing with and transitioning to sleet then freezing drizzle.

- Significant accumulations of snow possible, well above warning criteria...Ice accumulation appears minimal at this time for RDU, but could change if the surface low trends stronger and warmer.  In this scenario we could get a major ice storm, but it's not predicted by the models at this time.

- High uncertainty exists on amounts and timing of start time and any potential changeover.

Final prediction

I think for my final call I'm going with 4-7 inches.  Snow may start a bit later as RAP continues to push timing back, but it should last a bit longer as well.  Thinking the heaviest snow will fall between 10 and 11 and it could be heavy.

3 PM update.

RAP has verified well with this storm, and it now shows about eight inches.  12z 4km NAM also increased totals.  Storm has over performed in north Bama and Georgia.  850 low in a good spot.  Now leaning toward 5-9 inches for the triangle.

10:45 AM update

Some enhanced warming aloft could lead to a bit of sleet mixing in with the snow as well as lower liquid to snow ratios a bit.  Because of this I'm going to lower the minimum amount of snow to 2 inches.  I'm actually going to increase the max as well though.  High resolution models are showing a bit more precip then anticipated.  So while we might get more precip, some of it may fall as sleet or graupel.  

So now we're looking at 2-6 inches.  6 inches if it stays a nice fluffy powder and 2 inches if sleet mixes in.

1/27/2014 9:30 PM update

No change in accumulation prediction.  3-5 inches for the triangle.  In fact confidence continues to increase that we will see that 3-5 inches.  I now expect precip to begin between 2 PM and 3 PM and fall as snow until about 1 AM and potentially in end as freezing drizzle by 4 AM.

Weather update 1/27/2014

My first prediction in regards to the upcoming winter weather event is 3-5 inches of snow starting late Tuesday and ending Wednesday morning for the triangle.  Expect less on the NW side of the triangle (Chapel Hill) and more accumulation on the SE side of the triangle (Garner).  The cut off for winter warning criteria snow will be pretty sharp and looks to be near the I85 cooridor and west of 501.  So that would put all of Wake County in the 3-5 inches of snow category.  Another 50 mile jog to the west and we're looking at 6-9 inches.  Another 50 mile jog to the east and we're looking at 1 or 2 inches.

I'll have an update later when the GFS model run becomes available.