A complex and long duration winter storm to potentially impact the region Sunday into Monday……
Timeline– Sunday 2PM-5PM thru Monday 8PM-Midnight
Precipitation Types- Snow, Sleet, Rain (Depending on Locations)
Accumulations By Probability %-
(Probabilities are dependent on North vs South in region and elevation)
Confidence- Medium Confidence
Synopsis- There are a lot of moving parts to this upcoming winter storm, lets try to explain some of the details, a warm southerly flow ahead of an incoming upper level low will help create warm air advection over colder air in place across the region, we are not dealing with a deep arctic air mass but more of a shallow and stale cold air mass. Precipitation will overspread the region Sunday afternoon or evening, which will be heavily dependent on how much dry air is on place ahead of the storm. Precipitation will become more widespread and steady overnight, but warmer air will also be slowly eroding the cold air across the region, this will result in the potential mixing of sleet and rain across parts of the region. This is one of the unknowns at this time frame, if the colder air is deeper we may see more snow than mixed precipitation.
The plot thickens, as warm air advection begins to weaken Sunday overnight, we may see a lull in the precipitation, at this time a surface low will be forming off the coast of the Mid Atlantic, this will help to reignite precipitation by Monday AM, at this time we may still be dealing with some warmer layers of atmosphere and therefore the exact precipitation types are questionable. Now if this didn’t all seem complicated enough, the upper level low mentioned earlier will be sweeping in from the west, this will not only cool down the atmosphere but slow down the surface low from escaping and help to persist the precipitation throughout the day Monday into the evening.
As you can see there are a lot of moving parts to this system we need to iron out but there is now a high probability that we will be dealing with a period of winter weather in this timeframe that will have impacts on travel. Here are the GFS and European model take on this scenario..
Lets start with the European, a few things to point out here the european model has only in its most recent run shifted the axis of snow fairly far south vs all other guidance, while it can’t be discounted we are viewing it as somewhat of an outlier at the moment, as always the snow map isn’t to be taken verbatim. Next is the probability of 6″ or more as per the European, it helps highlight where it thinks the bullseye may be. The next two images are the Ensembles, this is the euro model running 50 additional solutions, these are useful to look for trends and also to see what the majority of models are projecting, as you can see there aren’t many that leave us unscathed from the storm at this point with a lot of members showing the bullseye further North, which is why we take the first image with a grain of salt….
Next up is the GFS model, now the first thing that stands out here is the GFS is taking a more northern approach to the axis of heaviest snow, which is a plausible outcome given the current setup, you can see that the accumulations and probabilities are all much further North than the European model.. With all of this said, at this timeframe we are simply beginning to discuss some of the probable outcomes of this upcoming storm. We will continue to monitor the data as it comes in and we will dial in the details throughout the day tomorrow into the weekend, but it’s best to continue to factor impacts to your Sunday and Monday plans with the upcoming storm.