Winter Storm Update

We are hours away from the onset of a winter weather event here in CT. This has been a bit of a forecast challenge this past week, however, for the most part the ideas of what may transpire have been rather consistent...it's just been a question of how they transpire.

Over the past day we've seen our weather forecast models actually trend towards the warmer side...not necessarily because of a farther north storm track, but with how the system strengthens. The more rapid strengthening and farther southwest helps to draw in warmer air from off the Atlantic. Some of our forecast models are even going to the degree of bringing in 40's and 50's into CT...but that's just not going to happen. 

There is currently a lot of dry air in place (dewpoints down into the teens in CT and single digits and even below zero across northern New England). 

As long as the surface winds are more northerly/northeasterly...cold air will continue to drain down the valley into CT. While the drier air may initially hurt when it comes to snow reaching the ground initially, the atmosphere is expected to saturate.

While we won't stay snow for long, it should rip heavy snow for a good 3-4 hours. Snowfall rates during this time will range from 1-3'' per hour. The window for the heaviest snow will be from 10:00 PM Saturday through 2:00 AM Sunday. Forecast models indicate some very intense upward vertical motion moving through:

After about 2:00 AM or so we will begin to see precipitation change. Along the immediate shoreline the changeover will happen earlier...closer to 11:00 PM. The shoreline will go from snow to a mixture of sleet/freezing rain and then over to rain. I don't think there will be significant icing issues along the shore, however, flooding is going to become a concern due to extremely heavy rainfall. A few thunderstorms may be possible too.

My biggest concern area for icing is right along the I-84 corridor. While forecast models do warm temperatures into the mid 30's (again some models much warmer) I am hesitant about this much warming. Establishing a snowpack of several inches could also favor keeping colder temperatures in place. Here is the difference between significant icing issues and not...about 2F. If surface temperatures are closer to 28...29...even 30 we will have MAJOR problems. If surface temperatures are 31...32...33...well we avoid major problems, but we will still have icing to deal with. 

Regardles, as the storm departs very strong cold air advection is going to occur and temperatures are going to drop very quickly. This will result in the likelihood for flash freezing (this is something that tends to get overplayed alot, but this is a situation where this might actually happen). 

Breakdown:

• Light snow/flurries begin between 4:00 PM and 7:00 PM this evening.
• Heaviest snow between 10:00 PM and 2:00 AM. Snowfall rates 1-3'' per hour
• Rain changes to sleet/freezing rain then to rain across the shoreline during the early overnight. 
• Heavy rain across the shoreline through late tomorrow morning leading to flooding concerns.
• Snow transitions over to sleet/freezing rain inland. A narrow zone of significant icing sets up. As much as 0.50'' to 0.75'' of ice possible. Can't rule out total close to 1'' in spots.
• Scattered to widespread power outages for the areas hit hardest by icing.
• Precipitation winds down late Sunday morning.
• Winds may gust 25-35 mph. 
• Temperatures drop VERY quickly through tomorrow afternoon allowing any liquid water to freeze. 

Snow/Ice map: