Saturday-Tuesday Rain to Snow Event

The somewhat decent warmth that we have been experiencing this week will come to an end Saturday as a cold front sweeps through. Consequently, it's going to snow Sunday and Monday. How much is still up in the air. It probably will be under 6 inches and that's probably too high.

Blizzard winding up over the Northern Plains

A storm is currently winding up over Nebraska, Wyoming, and Minnesota and is expected to track into SE Canada and cut off from the jet stream. Ahead of the storm, strong winds out of the south will drive temperatures into the mid 60s in the Ithaca region. This will be followed by a strong cold front ushering in subfreezing air as the storm moves to our east and cuts off. Then, it will meander around Canada for a few days. Since we are on the backside of the low pressure system, the atmosphere will be cold enough for snow. The meandering storm will throw lobes of energy around the storm. In addition, strong low level winds will promote upslope and lake effect snowbands. Let me explain what that means

4km resolution NAM model predicts temperatures in the 60s ahead of the cold front on Saturday. Temperatures will rapidly drop into the 30s behind the front, with rain showers expected, turning to snow.

Synoptic snows
Widespread snowfalls are easier for global models like the GFS and the Euro to predict from longer lead times because of the large scale nature. Global models have lower resolution than short term mesoscale models. Examples would be well defined low pressure systems like the one that is in the plains right now. Lead times for approximate track can be as long as a week, as is the case with this event. Details are better left to a blend of mesoscale and global models a day or two out.

Mesoscale snows

Mesoscale snow comes largely from two phenomena around here, Lake effect and Upslope. The mechanisms are similar. Moisture is forced upwards by topography and snow falls but the source of the moisture is different. The moisture in lake effect snow is from a lake. Air humidifies and warms as it travels over warm water before being cooled over land, forcing condensation and the formation of clouds. Moisture for upslope snows are generally synoptic. In this case, the cut off low ingests relatively warm, moist air from the Atlantic, which is cooled as the air is forced to rise over high terrain and it snows. In a way, lake effect snow can be considered a form of upslope snow.  The potential for these events can be detected in global models but specific bands are better resolved with high resolution mesoscale models like the HRRR, NAM, and RGEM. Predicting these bands are hard. It's basically nowcasting. The HRRR is run every hour out to 18 hrs. Just extrapolating based off of radar can be pretty useful. Or you could look out the window.

Back to the forecast: Snow
Since we are far away from the lakes, lake effect snows should be limited to a few passing snowshowers. Our elevation is also a bit too low for upslope snows. However, there will be a bit of synoptic scale influence before the storm moves too far away. I would expect a period of light snow Sunday giving way to snow showers. Total accumulation will probably stay under 3 inches although upside is still possible depending on the exact track. We can defininitely also end up with no snow.  Mesoscale features will be determined by where exactly synoptic scale features end up. It is still too far out to nail down exactly where the storm is going let alone where a snowband will set up. By no means will everyone get their fair share of snow. Some areas will jackpot while some areas will get close to nothing. People with experience with lake effect will know how isolated snow can be in that situation.

Lake effect snowbands behind the cold front moving through the Northeast, also predicted by the 4km NAM. The snow bands are being enhanced by an upper level low that has cut off from the jet stream. The potential is there, the question is will it be realized.

As we approach the expect time of the storm, updates will be provided. As always, thanks for reading.