Feb 3: Forecast For This Weekend

Verification for Tuesday Night: I expected Periods of snow, with low temperatures in the lower to mid 20s north and west of NYC, and in the mid to upper 20s for NYC and closer to the coast. I expected snow accumulations between 1 and 2 inches. The forecast was correct.
Score: 4/4

Verification for Today: I expected light snow ending in the morning, with high temperatures in the lower to mid 30s north and west of NYC, and in the mid to upper 30s for NYC and closer to the coast. My forecast temperatures were slightly colder than the actual result, with places north and west of NYC in the mid 30s, while NYC was in the upper 30s to the lower 40s.
Score: 3/4

Tonight: Partly Cloudy. Low temperatures will be in the upper 10s to lower 20s north and west of NYC, in the lower to mid 20s for the north and west suburbs, and in the mid to upper 20s for NYC and closer to the coast.

Tomorrow: Mostly Sunny. High temperatures will be in the lower to mid 30s north and west of NYC, and in the mid to upper 30s for NYC and closer to the coast.

Tomorrow Night: Mostly Clear. Low temperatures will be in the lower to mid 10s north and west of NYC, in the mid to upper 10s for the north and west suburbs, and in the upper 10s to lower 20s for NYC and closer to the coast.

Friday: Increasing Clouds. High temperatures will be in the lower to mid 30s north and west of NYC, and in the mid to upper 30s for NYC and closer to the coast.

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Short Term Forecast (Wednesday Night to Friday):

Temperatures tonight will be quite chilly, in the upper 10s to lower 20s north and west of NYC, in the lower to mid 20s for the north and west suburbs, and in the mid to upper 20s for NYC and closer to the coast. Tomorrow will be a mainly sunny day, with high temperatures remaining near average, similar to today. Skies tomorrow night remain mostly clear, with lows being slightly colder than tonight. By Friday, we still get temperatures to warm up early in the day with partly sunny skies, though cloud cover then increases through the afternoon hours, with skies becoming cloudy by the late afternoon to early evening hours.

Forecast for the Upcoming Weekend:

The forecast for this weekend was a very difficult one to make. We could end up with anything from a disruptive heavy snowfall to a light snow accumulation that would be nothing unusual to the area. While I mentioned yesterday that the chances for this storm to impact us are becoming greater, today we are seeing an even greater model spread.

The majority of today’s model runs have trended south, decreasing precipitation amounts for the area, with the GGEM only bringing a few flakes at best. The only model that continues to show a big snowstorm for the area is the NAM, which I think is too far north with its solution, considering almost every other model is to its south. Below is the 66 hour frame on the 18z NAM run (under the “850mb Temp, MSLP, 6hr Pcpn” section):

**For those who do not know how to read this map, the green, blue and purple are the areas where precipitation is shown to fall, with the following intensity scale:
Green = light/moderate
Blue = moderate/heavy
Purple = heavy
North of the southernmost blue line, frozen precipitation typically falls, with rain to the south of the blue line. A wintry mix usually happens near that line. In this case, we are well north of the blue line, meaning that any precipitation that does fall will be plain snow.**

As you can see, the NAM would show moderate/heavy snow over the area, with the storm tracking just ESE of Delaware. The total run would bring us between 0.75 and 1.25 inches of precipitation, which would be about 7.5 to 12.5 inches of snow. And this is the northernmost run, so I would put about 10 inches as our maximum potential snowfall at this time.

Now looking at the GFS, this model was further south than the NAM. The GFS is also faster than the NAM, so on its 18z run, on hour 66, the storm is already exiting the area on the GFS while it’s in the middle of affecting the area on the NAM, so for comparison purposes I am going to show hour 60 of the GFS below:

It is very easy to tell that this is further south than the NAM showed. On the NAM, New York City would get 0.5 to 0.75 inches of precipitation in 6 hours during the height of the storm, while on the GFS, we only get 0.25 inches of precipitation in 6 hours during the height of the storm. The blue line is also further south on the GFS, well south of southern New Jersey, while the NAM has that line up to southern NJ. And the NAM tracked the storm east southeast of Delaware, when the GFS takes it just east of the Virginia/North Carolina border near the coast.

The total GFS run brings New York City 0.25 to 0.50 inches of precipitation which would be 2.5 to 5 inches of snow, compared to the NAM’s 7.5 to 12.5 inches of snow. And considering that both of these runs are the two extremes, this puts our potential snow range between 3 and 10 inches of snow.

You can see the NAM, GFS, and some other weather models in their NWS page: http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/.

At this time, I do think that the GFS is slightly underdone with precipitation amounts, and that we could end up seeing a tight precipitation gradient in the northern side of this storm (which happens to be us). That is something we’ve seen in the late December 09 storm, and also why New York City got 10-15 inches of snow while Bergen County, just to the northwest, ended up with 4-8 inches of snow. The NAM has also been a relatively accurate model this winter, and has correctly forecasted the late December storm before the other models caught on to its potential, so I would also not completely dismiss its solution.

Overall, at this time, I would go for something in between these two models. There is still a lot of uncertainty, so we have quite a big range at this time, which I would put at 3 to 10 inches of snow, with the average being 5 to 6 inches of snow. The rest of the Mid Atlantic could end up with a major to a potentially historic snowstorm, with over a foot of snow for Washington DC and Baltimore possible, but further north than that is still a question. So at this time, I think that we could end up with moderate snow accumulations for this storm, with 4 to 7 inches of snow possible, but remember, nothing is final yet, as there is still a big spread with the model solutions. Stay tuned for the next update tomorrow.

Longer Range Update:

Of course, we can’t forget about the longer range. While I am focusing on this weekend for now, our next storm potential will be during the middle of next week, between Tuesday and Thursday. This storm also appears to track to our south with the more likely precipitation type being snow. There is still a lot of uncertainty for that time period, so I will begin focusing on this storm once we get past this weekend, which is when we should have a better idea of what this storm might do.

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