10 PM Update: Forecast On Track

At this 10 PM update there are not going to be any changes to the going forecast.  Most model data that has come out to this point continues to support the going forecast for the region.  If trends continue, I may lower inland snowfall amounts down to the same as coastal areas just because their additional hours of snow will be canceled out by less precipitation, but I am not yet ready to do that as only a few weather models have a tight enough gradient for it to make a difference.  Other than that, the guidance coming out thus far has been bouncing around so much that there are no reasons to see any consistent trends.

The 21z Short Range Ensemble Forecasts came out and they remain northwest and far too wet to be realistic.  What happens in a mean is a storm with intense dynamics can often be played up as too warm because some very amplified, unrealistically warm weather models get averaged into the mean, which appears to be the case here.  The SREF mean is consulted for track, and if the track of the SREF mean were taken then the results would be much colder as the storm would rapidly intensify.  The 0z NAM came out as well, and it is very interested as it keeps the storm almost entire snow for all of Southwestern Connecticut.  Once again, the NAM is highlighting my concerns about crashing temperatures at 850mb in the atmosphere remaining just marginal enough for a very heavy, wet snow, maybe followed by drizzle between heavy rounds of snow.  The rain/snow line would actually set up across Fairfield County per the model, with Route 25 being a dividing line by the coast and areas to the west staying all snow and areas to the east mixing with rain/drizzle briefly.  Don’t take this verbatim as the model will keep jumping around, but it has remained fairly consistent with this scenario, which is why I am not willing to completely throw it out.

What a lot of this storm comes down is two scenarios, both happening thousands of feet above in the atmosphere at 500mb.  Up there, there is a trough of low pressure that may or may not close off into a true defined low pressure center.  The earlier that happens, the more it will slow down, pull west, and strengthen the low pressure at the surface.  This will have the impact of allowing warmer air to rush into Southwestern Connecticut but will also result in a more dynamic atmosphere that could cool itself more in the heaviest precipitation.  This would also create more precipitation overall and a longer lasting storm later into Thursday night.  The NAM does not have the storm become defined at 500mb, so instead the storm is slightly faster moving, a little further east, and there are less dynamics with less precipitation even though it is a little colder.  Either way, there is no easy scenario to more/less snow for Southwestern Connecticut, instead every small change in the forecast has multiple impacts that makes it even harder to forecast.

This is why I am staying with the forecast for 6-12 inches at the coast and 8-14 inches removed inland.  If trends continue I will change inland to 6-12 inches too, but I remain very confident that all of Southwestern Connecticut will see at least 6 inches and very likely at least 8 inches from a very heavy thump of snow at the beginning of the storm.  Models continue to agree that Thursday morning will be all heavy snow throughout the entire morning rush, and this is what will close schools and snarl up traffic.  It remains after that 12/1 PM time frame that things get interesting, and some models, including the NAM, then have another burst of snow between 6-10 PM Thursday night that could lay down up to a few more inches of snow as there is strong banding on the backside of the rapidly deepening surface low pressure center.  I will continue to track all aspects of the storm and there are numerous important weather models coming out over the next few hours that I will be sure to tweet about.  If necessary, a blog post may be made between 11 and 11:30 PM should there be major model changes tonight, but if not expect one around noon tomorrow with all of the latest information and overnight trends.  Stay tuned for the latest on this impending large-scale storm.

One response to “10 PM Update: Forecast On Track

  1. Just came across your weather blog and absolutely love it. Sure sounds like this Storm “Pax” a punch.

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