NY NJ PA Weather Forecasts

Thoughts On The Afternoon Model Guidance

9:20 PM

There’s a lot of excitement over the trend of the model guidance towards a colder solution for Tuesday night and Wednesday, specifically the 18Z GFS. 

While I can understand the excitement, I want to state that the 18Z GFS does not exactly have the strongest of support.  While I agree that a coastal low is likely to form on early Tuesday morning in response to the strong negative NAO block, the continued theme in the guidance is for the primary low to remain over the Ohio Valley for the majority of the time period the storm impacts the forecast area. 

What would need to happen for the 18Z GFS or any significantly colder solution to verify?  Well for one, the upper low over the Yukon would need to get crushed.  The 18Z GFS and 12Z NAM certainly do this, which allows the building of the ridge over the West coast.  As a result, the entire pattern can amplify and the disturbances can dig a bit further south. 

Further, the disturbances will have to move much faster than seen on most guidance.  There is truth that the ECMWF tends to be too slow with southern stream disturbances, which is why I am including a start of snow for the forecast area on Tuesday.  However, I think the change needed to turn this storm into an all snow event would go beyond the ECMWF error range and into a change in the pattern configuration. 

Finally, the primary low will have to transition towards the coast much faster and that include upper level features like the 850 MB low and 500 MB PVA.  No guidance at this time supports that idea, even the 18Z GFS which tries and fails to transition the 850 MB low to the coast on Tuesday evening. 

So my forecast idea at this time is to have a quick few inches of snow to fall on Tuesday morning followed by a change over to rain along the coast.  The interior locations like northeastern Pennsylvania, northern elevations of New Jersey, the Hudson Valley, and interior Connecticut appear to be setting up for a snow to ice event with a potential for significant ice accumulation before a possible change over to rain.  Details are a bit too hazy to lay down right now, but I’ll hopefully get a snow/ice map out by Sunday evening as a first call.

So now we know what to look for in the 00Z guidance.  Hey, look.  I hope I’m wrong and this turns out to be a blizzard, but I wouldn’t bet on that.

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