Preliminary Snow Forecast : Sunday 2/7/21

Seemingly hot on the heels of our storm 5 days ago… we’re tracking another storm for Sunday.  This storm is a particularly difficult system to forecast, as it is developing as it approaches the east coast.  The atmosphere dynamics trying to steer it up the coast are not very strong, so there is considerable uncertainty with the details of the forecast.

Timing :
– 5am to 9am : Snow begins from south to north
– 9am to 2pm : Steady snow, possibly heavy at times
– 2pm to 6pm : Snow tapers from west to east

Impacts :
– Quick system, fast mover, 6 to 8 hours in any location
– Snow rates around mid day could be up to 1″ per hour
– Cold, snow accumulates on all surfaces
– Considerable uncertainty regarding intensity and strength of system

Snowfall Forecast:
– Entire Hudson Valley : 2 to 6 inches

*Notes : likely to get a better handle on track and strength of system on Saturday, we may have to adjust snow totals up or down just a bit for final forecast Saturday PM

Discussion

This storm system at first look 5 or 6 days ago, was projected to be a major snowstorm for the region.  Then early/mid week… the models lost it entirely, sending it harmlessly out to sea.  Then 48 hours ago, the models detected a bit more energy in the southern jet, and this system has come back into play for the weekend.  The big question however, is just how strong is that southern branch energy?
– Is it going to help the system deepen quickly, and track right along the coast? … or…
– Is the energy flatter, keeping the system weaker and further off shore?

If the answer is the first… we could have a potent little storm system in the Hudson Valley.  One capable of dropping snowfall rates of 1″ per hour for several hours in the middle of the day.  The stronger storm would track closer to the coast and then out to sea by sunset.  By the time it tapers off… the snowfall in the northeast could look like this:

Stronger Solution : Closer to the coast = higher snowfall amounts

However, the computer guidance has been fluctuating from a stronger solution, to a weaker solution, as the models try to get a handle on the energy in the southern branch of the jet stream.  The difference in the atmospheric energy is small, but the end results are noticeable.  The slightly weaker solution means the low pressure doesn’t deepen as much.  If the storm doesn’t deepen as much, it won’t be pulled as far up the coast.  If it doesn’t come as close to the coast, the precipitation amounts in the Hudson Valley will be less… and as a result, snowfall totals will be less.

Weaker Solution : Further from the coast = lower snow totals

Unfortunately, we’ve seen next to no consistency in the guidance.  It’s been like a roller coaster, going up, then down… then back up… then down again.  The very latest guidance, is the image you see above.  The system is weaker, and pulls out to sea faster.  As a result, the northern edge of the snow is stunted, and begins to push east as it gets over the Hudson Valley.  Areas south of I-84 would see 3 to 5 inches, and the rest of us would likely see 2 to 4 inches roughly.

Does this mean we’ll only see 2 or 3 inches?  Possibly.  But we always look for the trend when forecasting, and right now we’re not seeing one.  That should change on Saturday, as the energy comes out of the Rockies, and dives into the Tennessee Valley.  So for that reason, we should be able to post our Final Snowfall Forecast by early evening on Saturday (roughly 12 hours before the start).  If the trend for a weaker storm continues, expect a downward adjustment in the snow totals.

We’ll see what the data holds on Saturday.

6 thoughts on “Preliminary Snow Forecast : Sunday 2/7/21”

  1. Just a suggestion–one of my main concerns is always the potential for power outages, so wind velocity and/or freezing/icing cycles causing tree branches to fall would be a helpful addition to any winter forecast.

    Reply

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