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.

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:

01/19/2019 to 01/20/2019 CT Winter Storm

We have been tracking the potential for a rather significant winter storm for several-plus days and as we get closer to the weekend this potential not only still exists but the potential is becoming more of a reality. Before I get into the posts I wanted to post a disclaimer. All images that will be posted (unless otherwise noted) will be from the GFS forecast model. I can't post images from the European model as I don't have permissions. Just because I'm posting GFS graphics does not mean I am leaning toward's that model...what I am posting is to just illustrate. 

There are three key features that will be involved; a thermal boundary, southern stream vorticity, and northern stream vorticity. An area of low pressure (perhaps multiple low pressure circulations) will develop along the thermal boundary and strengthen with aid from vigorous vorticity:

There are substantial differences between the GFS and European forecast models with regards to the evolution of the southern stream energy which will play a substantial role in the eventual outcome of this system. The GFS is much stronger or "amped" than the European forecast model. This yields the surface low pressure to actually track either over CT or perhaps slightly west. This solution would yield a snow, to ice, to rain scenario. The Euro not being as amped is slightly farther southeast with the track of the surface low and would result in a snow to potentially significant icing situation across CT. 

Forecast models indicate some very high precipitable water values (PWATS) pushing into the area and feeding into the storm. PWAT values just south of the area are forecasted to be well over 1''...that is suggestive of very juicy air. A very strong temperature gradient will also exist over southern New England which will help to enhance frontogenesis over the region and support vigorous lift. This is shown with the vigorous 700mb vertical velocity values. Very strong warm-air advection (WAA) will further assist in the lift process:

This grab from the 18z GFS is the bufkit overview for Windsor Locks, CT. This is showing exceptional lift overnight Saturday...despite the most intense lift well below the dendritic snowgrowth zone this still shows -20 to -30 units of omega within the zone. Snowfall rates will approach 2-4'' per hour at times during the height of the snowfall:

We will have to carefully watch the exact track of the surface low as the likelihood exists for snow to changeover to freezing rain, sleet, and potentially rain. While the GFS forecast model is not very aggressive with freezing rain here, the European model is. There will be a tremendous amount of cold air just north of us and if the surface wind direction is more northerly as opposed to southerly or easterly this cold air will drain down the CT River Valley. This would keep surface temperatures well below freezing while temperatures a few thousand feet off the ground warm above-freezing...this would result in freezing rain and the potential for significant freezing rain.

Below is what I am currently anticipating in terms of impacts for CT. 

Suppression Depression or Major Storm Threat?

If you're a snow lover living in southern New England you're probably not all that happy with how winter has started. We have had plentiful cold at times, however, we've also had our share of warmth with very little of the white stuff. As we head into the second weekend of January some opportunity exists to bring some excitement to snow lovers. Some work needs to be done to make this happen, however, speaking from a synoptic stand-point (which will be the premise of this post) this weekend will be extremely favorable for cyclogenesis (development and rapid strengthening of a low pressure system)...it's just a question of where the system tracks. This will be answered over the coming days. I will be using the 18z run of the GFS forecast model from January 8th (as this is the most current run available during the composition of this post) to illustrate the key features we will be focusing on. I will also discuss the latest GFS ensembles which will be used to yield what interest level we should have in this event.

Over the next few days the Pacific-North American (PNA) is expected to become more positive in nature as a ridge builds into the western United States. Let's also note the piece of energy to the east of the ridge axis:

The Arctic Oscillation is also expected to DRASTICALLY drop over the next few days. In the animation below notice the very high pressures which develop over the Arctic. This is in response to the major sudden stratospheric warming event which occurred and led to the split of the polar vortex:

This negative AO coupled with the positive PNA will try and dig a trough down into New England. As this occurs the piece of energy (highlighted in the first image) will be progressing across the country. The northern and southern branch jet streams will be phasing (interacting) over the northeast. This will provide sufficient energy and ingredients for a rather potent low pressure to develop:

The jet stream will also be rather strong and this will lead to a very complex (so to speak) atmosphere this weekend with alot of moving pieces. Forecast models have been consistent in some energy moving through the northern stream which 1) may interact with the southern stream energy and further enhance the strength of the storm and 2) may also suppress it south of New England. There is also a rather strong high pressure to the north which could suppress the system:

The latest ensemble run of the GFS, however, still shows decent potential for a snow event here in southern New England. There is certainly a quite a bit of details to iron out through the week, but for snow lovers there is some hope!