Light Snow Wednesday Night (02/27/2019)

A weak weather system moving overhead Wednesday night will bring some light snow to the state. While some flurries are possible by late afternoon or during the evening, much of the falling snow will be during the overnight. This may lead to a slick early Thursday morning commute; however, no major impacts are anticipated.

A very fast mid-level jet will be overhead with a 500mb (~18,000 feet off the ground) jet stream exceeding 90 knots. Embedded within this jet will be some shortwave energy. As this shortwave energy moves over the Great Lakes it will acquire some moisture and this will set the stage for some light snow:

The degree of lift or ice crystal production appear to be rather weak with this system. When assessing the NAM and GFS 700mb forecast vertical velocities for Wednesday night, you’ll notice that the GFS is a bit more impressive with the NAM…the GFS has a much more widespread coverage of these green and yellow shadings (indicating about 5 to 10 units of omega and upward vertical motion), however, the NAM is only a bit more sporadic:

There are a couple things to consider here. While the surface flow may be a bit more southeast, the low-level flow will be more northwesterly. This will establish a downsloping component (sinking air) down the east flakes of the Berkshires. This will result in subsidence and drying air. The NAM being a much higher resolution forecast model than the GFS will be able to pick up something like this much better.

Bufkit soundings for Windsor Locks, CT also show a quite a bit of dry air within the snow growth zone; relative humidity values generally less than 95% with relative humidity only sporadic areas where relative humidity with respect to ice exceeds 100%. To save time I am just showing the NAM, however, the GFS in fact is even less with respect to relative humidity:

The result…poor lift and lack of sufficient moisture within the snow growth zone combined with some subsidence will make it difficult for great snow production. There may be some pockets of some heavier lift which could make for brief spurts of near moderate snow. All in all, this should be rather unimpressive.

Wintry Mess Wednesday Evening and Overnight

Another wintry mess is set to impact CT, however, this does not look like it will be a high impact system with the majority of the impacts occurring during the evening and overnight. Road conditions will deteriorate Wednesday evening the Thursday morning commute may have some delays, however, temperatures will warm well-above freezing through Thursday morning.

The big focus for precipitation tomorrow will be largely due to warm-air advection associated with an approaching warm front and shortwave energy riding along the crest of an upper-level ridge:

While snow will break out across PA, parts of southern NY, and NJ as early as Wednesday morning it will take its sweet time not only moving into CT, but falling to reach the ground. This is due to a rather large area of high pressure overhead which will try and act like a wall for the advancing precipitation and dry air that will be in place during the day. As high pressure departs to the northeast the atmosphere will become saturated and snow will begin to fall by late afternoon/early evening:

Bufkit forecast soundings at Windsor Locks, CT tomorrow evening indicate a period of rather strong lift moving through the state. This is associated with the push of warmer air aloft and will yield two things;

1) A band of moderate-to-heavy snow on the leading edge of warmer air
2) Be the boundary between snowfall and snow transitioning over to sleet and freezing rain.

• Snow breaks out 5:00 - 8:00 PM from southwest to northeast across the state.
• Heaviest snow from 8:00 PM to midnight 
• Highest totals north where colder air lingers and coincides with strongest lift.
• Sleet may also be heavy at times overnight and will accumulating up to a coating to 1/2'' in spots. 
• Freezing rain isn't expected to be a major issue, but could accumulate up to 0.10'' across the northern part of the state. 
• Precipitation exits by 5:00 AM Thursday. Early Thursday morning commute may be slick with some delays.
• Most locations away from the shoreline see around 1-2'' of snow, but some localized higher amounts where heaviest banding traverses and heaviest echos occur.

CT Snowfall Update

Some minor changes to the forecast, however, the general idea remains the same. Latest forecast guidance sort of diverges with how things evolve tonight. Some of the latest forecast models develop a rather modest band of moderate-to-heavy snowfall and track it right over CT while some of the higher-resolution short-term models are less aggressive.

As discussed in yesterday's post, there is a pretty strongly confluent flow over the region:

This confluence which increases convergence may result in keeping the heavier precipitation farther south. There is also concern for some dry air. While the atmosphere will saturation, there will be a northern-fringe point to where this may not happen and this very well could be over much of CT.

The NAM and GFS forecast soundings are a bit more impressive with lift into the snow growth zone, indicating there could be a period of moderate...perhaps even heavy snow. However, there is going to be a big battle between a saturated snow growth zone and an unsaturated one and this will be huge in when talking about the formation of bid dendrites (which accumulate more easily) or smaller more fine snow flakes (which don't accumulate as rapidly). Below are bufkit soundings for Windsor Locks, CT from the GFS, NAM, and HRRR. On the left both the NAM and GFS indicate as much as 15 units of omega within the snow growth zone...indicative of moderate-to-heavy snow. However, on the right we are looking at relative humidity in terms of ice and not much above 100% within the zone. The HRRR is even less impressive:

All in all we may see a very narrow band of moderate-to-heavy snow move through the state. This may yield a strip of 4'' of snow, however, most everyone should see anywhere from 2 to 3'' tonight. Expect a slippery Monday morning commute.

Quick Hitting Storm to Bring Accumulating Snow to CT Overnight Sunday into Monday

A quick hitting weather system is set to bring some accumulating snow to CT Sunday night into Monday morning. In addition to snow, there will also be some sleet mixed in as well with the higher likelihood of this along the shoreline. This isn't going to be a major event, however, this could yield a low Monday morning commute with clean-up efforts underway.

The synoptic pattern is characterized by a very potent upper-level jet stream ejecting northeastward out of the Pacific with a trough in the western United States and a ridge in the southeastern United States. This will lead to Pacific moisture being advected into our area. Energy associated with a closed upper-level low across the northern Plains will eject through the Ohio Valley and pass near our area. This will result in the development of a weak surface low pressure:

Thanks in part to a confluent flow aloft we'll have to watch as to exactly how far northward not only precipitation makes it, but the potential for some heavier echos of precipitation. This is huge because it will mean the difference in a general 1-2'' for most and as much as 3-4'':

Much of the lift associated with this system will be more associated with thermal advection (although this will be weakening) as opposed to intense lifting which would occur if low pressures at 850mb and 700mb were passing to the south and east. This will likely result in some embedded echos of moderate to perhaps heavy snow while for the most part snow will fall on the light side:

Bufkit soundings aren't particularly impressive, but they do suggest a several-hour period of light snowfall and again, some echos of moderate-to-heavy snow. The GFS is a bit more robust with lift into the dendritic snowgrowth zone:

Breakdown:

• Snow arrives 9:00 PM - midnight
• Mostly light, but some echos of moderate-to-heavy snow (will be brief)
• Exiting between 5:00 AM and 9:00 AM
• Could see some sleet/freezing rain mix along immediate shoreline
• A couple localized totals of 3'' possible (where the echos of heaviest snow fall)
• Minor impacts for Monday morning commute with some delays likely

Messy Winter Storm to Impact CT 02/12/2019 into 02/13/2019

Tracking the potential for yet another extremely messy winter storm in the late Monday night into Wednesday time frame. Like some of the past few storms, we will have to deal with snow transitioning over to sleet, freezing rain, and even some plain old rain for some. There is the potential for some significant impacts with this system; particularly with regards to the icing potential, however, this will be highly dependent on some features which will be addressed below.

A vigorous piece of shortwave energy associated with a shortwave trough will be progressing the country over the next few days. Associated with this will be an area of low pressure which is actually slated to move to our northwest. Typically when we see such a track we're talking about a warmer solution and either a little bit of winter weather or just flat out rain. However, there are some features which will be in place (along with a developing secondary area of low pressure) which will warrant wintry precipitation.

One of the key features will be an area of high pressure sliding west-to-east(ish) across southeastern Canada. This high pressure is forecasted to be fairly strong (about 1040mb!) as it's passing to our north. Keep in mind that air moves clockwise around high pressure in the northern hemisphere:

This area of high pressure is going to do two things;

1) This is going to create a "wall". Precipitation is really going to struggle to move northward into our area until the high pressure loses its control over our area and this happens as it continues to depart to the east.

2) Going back to what was said just above the graphic, air flows clockwise around high pressure in the northern hemisphere. Given the position of the high pressure, this will funnel down cold and dry air from southeastern Canada and the Canadian Maritime down into our area. The drier air will also make it difficult at first for precipitation to reach the ground, but the cold air (being more dense) is going to sink towards the surface. This is HUGE because with the main storm track to our west this will yield warming of the atmosphere from a few thousand feet above the ground up until about 10,000 feet off the ground. Temperatures will warm above freezing within this layer, however, they may remain below freezing below this layer. This is our recipe for sleet and freezing rain. Which one of these precipitation types is more dominant will ultimately depend on the depth of the colder layer at the surface and exactly where temperatures aloft warm above freezing.

Breaking it down:

• Light snow works into SW CT between midnight and 3:00 AM Tuesday morning and then overspreading the state over the next several hours. 
• Snow will quickly pick-up in intensity with moderate-to-heavy snow. 
• Snow will quickly begin to transition over to some sleet and then rain along the immediate shoreline. Snowfall totals should be minimal. 
• 1-3'' of snow is likely across much of interior CT away from the immediate shoreline with the highest totals across the extreme northern part of the state where they may hold onto snow a bit longer. 
• Snow will begin to transition to sleet and then freezing rain across central CT. The potential exists for some significant icing somewhere. 
• Sleet is more likely across the extreme northern part of the state. 
• Significant travel impacts are likely Tuesday through the Wednesday morning commute. 
• Winds could gusts 25-35 mph, especially along the shoreline. 
• Coastal flooding is likely in some spots as well with flash flooding in some spots along the coast.