Wet snow sunday?

There is a chance of some wet snow this weekend, probably Saturday night into Sunday, 11/24/2019.
The 06z ECMWF was onboard. At the time it was south (and therefore colder) than the GFS model solution which was all rain since it had low pressure driving into western NY. The most recent GFS run (12z) has moved towards the ECMWF solution although it is still warmer.

Forecast:  1-3" of wet snow, mainly Sunday; possibly mixed with rain
 
Discussion:
Although there is a good signal for precipitations, this is a relatively low confidence forecast for accumulating snow. The ECMWF solution gives us a chance at some wet snow, with temperatures near freezing throughout the air column. In this case temperatures may even rise above freezing as the storm winds down due to the lack of cold high pressure to the north. The GFS suggests that cold rain is a possibility. This comes down to how quickly the storm strengthens. The ECMWF brings a more mature cyclone past us while the GFS is weaker and messier. A stronger storm would have a more defined western precipitation shield but too strong and the return flow ahead of the storm will drive us above freezing. The hills around Ithaca will probably have a higher chance of seeing accumulating snow this weekend.

12z GFS Run Simulated Radar (tropicaltidbits.com)

06z ECMWF run

Winter begins: The first cold blast of the season for the East Coast

Current synopsis and overview:
Winter is fast approaching and I figured that it’s about time to resurrect the blog ahead of the requests for “When is it going to snow and how much?” Now that I have more time, I can write my thoughts out again.
A cold front passed through this morning, around 7AM as evidenced by a wind shift from the South to a Northwest wind at the Ithaca Airport. Temperatures have dropped from a high of 45 in the morning to 39 currently. Over the next week, temperatures will remain well below normal as arctic air pours out of Canada into the Eastern US. We will likely see our first snows during this period. Currently, I am looking at two chances of accumulating snow over the next week.

12z (7am) analysis of fronts and observations (WPC/NOAA)

Wave 1 Thursday into Friday (11/7-11/8)
A weak low pressure system is currently forming along the front which will direct moisture northwards. Precipitation is expected to start as rain but is expected to change over to snow as temperatures drop from the 40s into the low 30s.

The following forecast for this event is done based on the short term models the HRRR and the 3k NAM:
The changeover will first occur at the higher elevations surrounding Ithaca around 3-4 PM. Changeover for the city will probably be delayed for 1-2 hours due to warmer temperatures.
Steady light to moderate snow will end around 8PM tonight as the front passes and the weak wave moves offshore. Expect that very little snow will accumulate due to warm surface temperatures and weak snowfall rates, perhaps a dusting on elevated surfaces.

HRRR model showing rain and snow associated with the cold front and low pressure wave

As the low draws away, colder air will filter in from the NW, resulting in the development of lake effect snow bands. Current model trends suggest that we could receive 1-2 inches of windswept snow during the day. Temperatures will fall into the lower 20s Friday night as the winds lessen.

NAM 3K model forecast for Friday morning into afternoon showing lake effect snow showers

The following forecast is done based on global models:

Arctic front Sunday into Monday (11/10 -11/11)
Sunday night, a weak disturbance will pass to our north as the arctic front makes its way through. Strong southerly winds the Sunday will ensure that temperatures spike above freezing to the mid to upper 40s before dropping again. A few rain or snow showers can be expected with the frontal passage. This front will set the stage for the next potential event.

Wave 2 Tuesday into Wednesday (11/12 -11/13)
Southern stream energy will combine with northern stream energy to for some kind of low pressure  during this time. Although models have been more consistent on the presence of the energy, but are not in agreement on the evolution. The general progression is that after the front swings through, low pressure will ride the front northwards. Southern stream energy will be drawn in and interact with northern stream energy to energize the system. However, how consolidated the storm(s) are is still up in the air. More northern and southern stream interaction, called phasing, will result in a stronger, more consolidated storm that takes a more westerly track. Less phasing results in two more distinct waves of precipitation, one from the northern stream and one from the southern stream.
In the more phasing scenario, tropical moisture from the southern stream system will act to juice up the system, resulting in more precipitation but a stronger and more northerly storm. Depending on the front position, we would be looking at a all snow or rain to snow scenario. This scenario would bring the highest chance of significant snow accumulations over 6in. In this case, only part of the southern stream energy is expected to phase.

In the less phased scenario, the northern stream energy would likely run out ahead of the southern stream. Snow is still possible, but would probably be a light to moderate event similar to the one today. We would likely be too far north for the southern stream system to impact us.

Of course, another option is that all the disturbances wash out and we are left with just a dry frontal passage with lake effect snow. In conclusion,, given that the storm is still 5 days away, there are a multitude of scenarios that could possibly happen. I am currently leaning towards a s less phased solution with moderate (2-6 in) snowfall. In any case, we can probably expect some more lake effect snow showers as temperatures plunge into the teens following the cold front.