Update On This Weekend’s Storm
Update included below in red. Most recent update 1/7/17 at 12:58AM
Things are already shaping up for this weekend’s winter storm for the east coast. We continue to get a clear picture of the overall evolution of this system from when the mid-level energy rounds the base of the trough, the surface low forming off the east coast, and its northeast track just off the coast.
While we are starting to see some consensus among the models with regard to this system, there are a few minor details that could have a large impact over some locations along the east coast. Of all the models I’ve seen so far, the NAM has been somewhat of an outlier against the other models. This is primarily due to the model showing greater phasing with the downstream trough which has drawn it closer closer to land than its counterparts. The long term effect of this would be an overall warmer solution with more rain than frozen precipitation.
The GFS and Euro have come together quite well (not perfect but we’ll take it) with regard to track and timing. The major question that comes into play when looking at both of these models is how much is the warm air (if any) will impact precipitation type at the surface and ultimately precipitation totals. Taking a look at the 12Z runs from the two shows the GFS with a much colder thermal profile inland than the Euro. The Euro is a little more aggressive with the warm air aloft than the GFS, thus the forecast total differences between the two. So the question now becomes, how much warm air infiltrates the cold air inland? The answer will have a large impact on forecast totals for this weekend.
As the low passes offshore (assuming it takes the GFS/Euro track which seems most likely at this stage) a heavy band of precipitation will be onshore over ENC. This heavy band will be in place regardless of precipitation type at the time. If the warm air aloft is able to move inland far enough, areas receiving that heavy precipitation would likely see sleet or freezing rain. The forecast is for all the precipitation to change over to all snow before departing late Saturday. So the longer the sleet is the dominant precipitation type during this period of heavy precipitation, the dramatically less snow you will see as the end result. It is because of this that there will be a large total snow gradient setup somewhere along the coastal plains. A change in the track of the low would push that gradient further inland or further to the coast.
It is because of this uncertainty that current forecasts like mine below could be a bust just because the low went 25 miles east or west of where it was forecast to be. So when you look at these forecasts, bear in mind that even the seemingly insignificant changes in forecast track could have long-term consequences in the forecast.
My best attempt at a forecast map below though I warn it could change between now and the start of the event.
This was put together really quickly so the details aren’t really well defined but should work as a general idea of what things could look like Saturday. I didn’t color below the NC/SC border which doesn’t mean SC won’t see snow but I am only focused on ENC right now.
Update (Friday morning): After examining the models this morning, I do not feel there is any need to change my forecast at this time. The only potential change that I can see happening at this time is for those totals in the graphic above to shift westward some in response to a track closer to the coast. A shift westward would take the Outer Banks from the 1-2″ category and drop them into the T-1″ category. I will post later this afternoon with updated information.
Update (Friday afternoon): We are beginning to see light showers moving into ENC. This should continue and become more numerous as the afternoon and evening progress. The progression of this storm is a little faster than previous forecasts which will have a slight impact on the overall snow totals we will see across the area. My main concern has turned to significant icing that will be taking place over several counties prior to the transition to snow. Models indicate that sleet/freezing rain accumulations could reach 0.25″ or more which will make driving dangerous as well as cause some power outages. I will be following the storm late tonight for real time updates regarding this storm. I will be using this website to communicate rather than Twitter but will still be monitoring Twitter some throughout the night.
Update (Friday evening): Over the last 48 hours, models have been shifting the track of the low closer to the coast. This scenario changes the overall threat for a large portion of ENC. With this shift in track, we can expect warm air aloft to nose further inland complicating the precipitation type forecast. With this setup, there will be an extended period of sleet and freezing rain overnight which will cut significantly the overall snowfall total for these areas. The accumulation will create travel problems overnight and into Saturday morning. This will also increase the potential for power outages in the affected areas. The precipitation will transition to snow briefly before ending Saturday afternoon from southwest to northeast. How much snow will accumulate will depend on how quickly the warm nose exits the area and how much moisture is left on the back side of the low. I have adjusted forecast totals further west and reduced accumulations over ENC. There will be a sharp gradient in snow accumulation around where the rain/sleet line reside during the peak of the storm. Where this will exactly setup is tough to predict at this time which is why the forecast map I made tonight could end up being off a couple of inches in some areas. I will keep updating as the night progresses. At this point we switch from forecast mode to nowcast mode.
Update (Friday midnight): Warm air aloft will spread further inland than previously forecast. At this time I expect most of the precipitation over most of ENC will remain either as rain/freezing rain/sleet with little to now snow accumulations. At midnight, there had been very few reports of frozen precipitation across ENC with the most credible reports near the VA border. Ice will become the dominant precipitation type around 3:00AM or so. Significant ice accumulations are possible over many parts of the region. The areas with the best chance of snow accumulations will be the far northern counties. Given the sharp accumulation gradient, forecast totals will increase significantly over a smaller distance. Unless there are any major changes to the weather situation tonight, this will most likely be my last update before the end of the storm.
Important note: Make sure to follow the NWS online or through your NOAA Weather Radio for more information regarding this weather event.
Looking beyond this weekend’s storm (as difficult as it may be – me included), cold temperatures will be the big story as temperatures plummet to the coldest of the season. Several areas across the east could see temperatures drop into the teens at night as for the next several days. High temperatures will also be well below average as an Arctic airmass hangs in the area. Temperatures don’t make a comeback until the middle of next week where we could see a chance of rain back in the forecast. Make sure that after the storm Saturday that you are well prepared to handle the extremely cold conditions that will quickly follow.
I hope everyone stays safe this weekend.