Wintry Mess on Wednesday, February 7th, 2018

Our active weather pattern looks to continue and we are tracking quite the mess for Wednesday as an approaching storm system looks to give us accumulating snows with much of the state even transitioning over to sleet, freezing rain, and rain. The northwest hills stand a better likelihood of remaining mainly all snow.  This is a very challenging setup with many uncertainties and those uncertainties will all be looked at in detail below:

Wednesday morning an area of low pressure will approach from the southwest. Initially, temperatures statewide will be cold enough to support all snow, however, with a southerly flow developing and becoming established in the lowest 5000' of the atmosphere this will eventually change snow over to sleet, freezing rain, and even rain for extreme southern CT. One of the biggest questions right now is how long does the cold air remain in place and another big question is do we lock in colder air at the surface which could enhance the potential for a prolonged period of freezing rain and this could be a major concern for some. 

At 500mb (about 18,000' off the ground) a shortwave trough within the northern stream will dig into the upper mid-west on Wednesday morning. This main shortwave energy will lag quite a bit behind the surface low pressure which indicates a "tilted" system. Strong shortwave energy within the southern stream will help with the generation of a surface low pressure across the Gulf coast states/Tennessee Valley:

 With a big disconnect between the main upper energy and surface low pressure, this will work to establish a southwesterly flow in the lower levels of the atmosphere which will promote the advection of warmer air in the lowest 5000' of the atmosphere. Initially the temperatures through the troposphere will be cold enough to support precipitation to begin as snow state wide, however, with warmer air working in aloft, this will promote snow to begin transitioning towards sleet, freezing rain, and even rain for extreme coastal CT:

One of the bigger questions and challenges at this time is what happens with the track of the surface low pressure as this will play a big impact on surface temperatures which will be key in how precipitation transitions. While there is a bit of uncertainty with regards to where the surface low will track, the general idea seems to be for the surface low to either track over CT or track just to the southeast of CT. If the track of the surface low is over CT this will allow for a southerly flow to become established across a good portion of the state which will allow for warmer air off Long Island to to work in at the surface. This would yield a transition from snow to sleet/freezing rain to plain rain for many. If the surface low track is more southeast of CT this would enhance the likelihood for colder air at the surface to remain in place and this would increase the odds for more in the way of sleet and freezing rain for many. One feature we need to watch extremely closely is an area of surface high pressure just to the north of Maine. This feature could work to keep colder locked in place across a good part of the state, especially if the surface low tracks just to the southeast of CT. This would be a strong signal for a prolonged period of freezing rain and this has to be watched very closely:

Another challenging aspect of this system is with regards to how much snow falls before we see snow begin to transition over to sleet, freezing rain, and rain. The potential exists for upwards of several inches of heavy, wet snow to fall across portions of the state (with the highest totals across the northwest hills where they will remain mainly all snow) before the transition process occurs. 12z GFS bufkit data for some locations across the state indicate the potential for a several hour thumping of heavy wet snow before any changeover occurs. The below soundings are from Waterbury, CT and Windham, CT. They show excellent snowgrowth with high values of omega and relative humidity within the snowgrowth zone. This is a strong signal for moderate to heavy snows:

Given the marginal temperatures in the lower portion of the atmosphere, this will make for snow to become very wet and heavy and will also yield snowfall ratios likely on the order of around 8:1 (maybe even slightly less). The snow will not be fluffy by any means and will stick to trees and utility wires. This will pose a major problem for any areas which see a prolonged period of freezing rain. 

What are we looking at right now?

• Snow begins to break out across the state between 7:00 AM and 9:00 AM Wednesday morning. 
• Snowfall rates quickly increase and could approach and exceed 1''/hour at times. Expect snow to be heavy and wet making it difficult to move. 
• A several hour period of moderate to heavy snows can be expected, especially across the northern portion of the state and northwest hills. The northwest hills will likely remain all snow. 
• By early afternoon we begin to see snow transition to sleet/freezing rain across much of the state. The immediate shoreline will see this changeover happen by late morning thus much less snow will be expected here. The shoreline is expected to transition over to all rain, however, a further south and east track of the surface low would mean more in the way of frozen precipitation. 
• There is the potential for a moderate-impact freezing rain event with the possibility for some areas to receive upwards of 0.25'' of freezing rain accretion. If this occurs on top of heavy, wet snow this could yield power outages and some tree damage. This potential needs to be watched EXTREMELY closely. 
• Everything begins to wind down early evening. 
• Travel on Wednesday is not advised and numerous school closings should be expected. Road conditions will deteriorate extremely quickly and travel will become especially dangerous with the onset of freezing rain. 
• Below is what I am expecting right now: