Dec 24: Potential Snowstorm Update

Note: The 5-Day Forecast was updated through Monday only. A full 5-Day Forecast will be posted tomorrow.

As mentioned below, due to new uncertainty with the storm, a special update will be issued late tomorrow morning, and it is possible that snow and heavy snow watches may be issued depending on tonight’s model runs.


Today was a mainly sunny day across the area with slightly cooler temperatures as the storm that was stuck over the Northeast for the last several days began moving out, bringing more sunshine and less windy conditions. Temperatures tomorrow will be again chilly, similar to today’s temperatures, however cloud cover will be increasing ahead of this storm. Up until now there was a lot of uncertainty with this storm, and there is still uncertainty, however some models are trending towards a solution that might perhaps bring the potential of widespread heavy snow as far west as New Jersey.

Sunday – Monday Storm: New Trend May Change Forecast

Yesterday’s models were consistent with the more east solutions that we observed with Wednesday and Thursday’s model runs, and the discussion removed snow chances a little as there was increasing consistency in an out to sea solution. As briefly mentioned above, however, some of these models have started a trend which may put the NYC area in the potential for heavy snow. While it is too early to determine whether this is a real trend or just an error, this potential needs to be watched as more models continue to catch onto this possibility.

Model Analysis: The main model that started forecasting this storm as a blizzard, the ECMWF, remains out to sea with today’s runs, as well as the GGEM and the UKMET. The GGEM model trended west in its 12z run today, but remains out to sea. The main highlight of today’s models, however, were the GFS and NAM models, which trended west today to bring several inches of snow to the area.

The 12z GFS suddenly trended well west of its 06z run, producing over a foot of snow near and east of New York City. The 18z run went even more west, with over a foot of snow in NYC, northeastern New Jersey, Long Island and Connecticut. The NAM model also trended west with today’s runs, with its 18z run bringing several inches of snow to the eastern parts of the area. While it was first determined that there were some errors with the way how the GFS and NAM initialized leading to these solutions, the 00z NAM, which uses new data, came in even more west of its 12z run, with snowfall amounts potentially between 7 and 9 inches in NYC and over 10 inches for Long Island and Connecticut.

While this may be an error, it is still too early to determine anything out of this potential trend. The 00z model runs, especially the ECMWF and GGEM will be important to see if they trend west, as well as the 00z/06z GFS to see if it remains consistent with its solution and if the NAM continues to trend west. If at least most of the above happens, this will confirm that this is most likely a trend. If not, we will have to continue following the models and making observations with the storm compared to the forecasts to determine which solution may happen. A special update will be issued late tomorrow morning about tonight’s runs.

Forecast Set Up: Up until at least Sunday, the storm track is generally consistent with the models, however as soon as Saturday there are already differences with the models. The main difference comes with the phasing of the storm and how quickly it intensifies and starts to become neutrally/negatively tilted. Once the storm becomes neutrally tilted, it will start to move more NNE then north instead of going out to sea, but the question is where this happens. The latest GFS and NAM runs trended earlier with this, showing the storm already with a neutral tilt when near the Carolinas, while the further east models still have a positive tilt, meaning that the storm will continue to move NE and out to sea from that point. That is an important thing to follow with the model runs tonight and tomorrow, as the earlier the storm phases and shows a neutral/negative tilt, the further west it will be.

Thoughts For NYC Area: This was a very difficult forecast to make, and it may not be until the day of the storm itself that we know exactly what happens. Taking into account the western model solutions as well as the eastern models, I made very little changes to the forecast from 2 days ago, with a 40% chance of snow inland, 50% chance of snow for the immediate NYC area, and a 70% chance of snow for Long Island/S CT, which may be raised tomorrow depending on the model trends. It should be noted, however, that even if the storm misses the area well to the east, an upper level low will still bring scattered snow showers, so whether the main storm hits the area or not, at least some snow is likely to fall in at least parts of the area in the easternmost scenario.

As previously mentioned, tonight’s model runs will be very important when trying to determine whether the western model runs tonight were off runs or if this is in fact a new trend. I will make a special update for this late tomorrow morning, and changes to the forecast may be made. If the main models remain east, there will not be many changes to the forecast. If, however, the GFS model remains west and the other models trend west, snow probabilities will be increased for the area, and snow and heavy snow watches may be issued for the appropriate parts of the area. There will also be the potential for up to or even over a foot of snow to fall in the eastern parts of the area if this solution is to verify. Stay tuned for more information on this storm and how it may affect the area.

Longer Range Update: Mild And Wet Start To New Year

As mentioned yesterday, the cold pattern will temporarily fall apart once the storm ends. Temperatures next week will be steadily warming up, meanwhile by the last day of the year, a significant storm will be taking shape near the Rockies, which will lead to a much warmer air mass spreading across the eastern and central United States. There is uncertainty with the exact track as this is in the longer range, but this storm will lead to mild temperatures for New Year’s Eve and New Year’s Day, with the storm’s cold front then making temperatures briefly even warmer followed by rain. After the storm ends, the latest models show the potential of a cold pattern returning again, and this potential will be watched.

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