An upper level trough digs into the eastern portion of the country, and intensifies from Gulf moisture. 250 mb jet anaylsis indicates very strong divergence aloft for this weekend over New England, coupled with 500 mb positive vorticity values as well. This is indicative of intense lower level convergence and is supportive of strong vertical motion on the synoptic scale for New England, particularly Saturday night and Sunday. One aspect of this storm which is incredible is the warm and cold advection 850 mb and 700 mb. Incredibly strong warm and cold advection exist at these levels, and this is the result of a large thermal gradient across the system and cross-isobaric flow. A very cold arctic blast of air from Canada is associated with an upper level shortwave. This tries to phase with our trough, and the meeting of the warm Gulf air and freezing artic air is what is going to drive strong winds and intense convection associated with this storm. An important feature to note of this system is that it is not vertically stacked, or the center of pressure of the storm is not lined up vertically through the atmosphere. It is instead tilted, on an axis, and this allows for cold air and warm air to slide over one another. This “tilt” of the storm is an important aspect that I will talk about later on.
The Timing and Precip:
The GFS and NAM models agree that snow will possibly start late Saturday afternoon, possibly the early evening. Snowfall will intensify as it nears midnight, as a switchover to sleet, wintry mix will occur sometime during the early morning Sunday. Strong convection will be evident with high omega values and intense vertical motions on the simulated soundings for early Sunday morning. Depending on when the switchover is, we could see some significant accumulations of snow across the state of more than 6”, higher in the northern portions of the state, and possibly less along the immediate SE coastline of the state. A lot of the times the models struggle with the thermodynamic aspect of a storm, and with this one, it is possible that cold air could hang around longer than expected and therefore prolong the period of snow. As a result, snowfall totals could potentially be significantly higher for the state, but we are treading a mighty fine line with this system’s track and the thermal features of this storm.
By early morning Sunday, around 4 am, there will be a changeover to a wintry mix for the state, and freezing rain for the SE coastline. This is because of the “tilt” I had mentioned before. Warm air from this system will slide over the cold dense air at the surface, making for an inversion layer. This will cause widespread sleet, freezing rain, and ice for a majority of the state heading into Sunday. By midday temperatures along the SE coastline could climb above freezing, leading to a possible rain/freezing rain mix. But a very developed inversion seems to persist throughout most of the day Sunday, which would indicate sleet/freezing rain. By midafternoon Sunday, the cold arctic air with this system will begin to move into the state from the NW. A gradual change back to snow will occur before the tail end of the precip moves out by late Sunday evening.
The models vary slightly with the track of the storm. The GFS is keeping the system to our north slightly more than the NAM and the Euro, and this would indicate warmer temperatures across the CT shoreline, and could indicate a period of more rain than rain/sleet. While the NAM and Euro is more favorable for a prolonged period of snow, and a wintry mix/freezing rain for the majority of the state. The track of this storm determines on the phasing of the upper level trough and the Canadian shortwave. If the two phase better, we could see a northward track of the system, but if they do not, it could favor a southerly track which would support more snow.
In terms of snow/sleet, depending on how long the snow period lasts we could see totals ranging from 4-10 inches across most of the state, and significantly less across the SE shoreline. Right now, I feel it is better to not underestimate this storm. Therefore, we decided to go for 6-10” for the NW corner of the state, 4-8” for the majority, and 2-5” for the SE coast. Ice accumulations could be up to half an inch on the high end. Rainfall is possible along the SE coast, and there could be a slight threat of flooding due to the accumulation of snow, rain, and ice for Sunday.
For anyone who has plans on Sunday, it would be in your best interest to cancel. It will be a mess. Due to the strong thermal gradients winds will be 10-20 mph with gusts in excess of 20+. This coupled with snow, sleet, hail, and freezing rain will make for extremely dangerous driving conditions so be sure to stay off the roads as much as possible. Probably the most incredible part of this storm is the deep freeze that will occur after the cold arctic air has passed through the state Sunday night. Temperatures are expected to drop to or even below zero. Whatever snow, slush, or rain that has accumulated all day Sunday will freeze immediately, and that will make for tough travel Monday morning. This storm has all the makings for a dangerous storm, particularly the icing and sleet.
We will continue to provide you updates on the lead up to this storm so stay tuned in for updates. And don’t forget to share us on social media to let others know about the weather! Once again thank you for reading SCW and have a good evening!