Significant Winter Storm Update

 I have been very impressed with the potential for heavy banding to materialize across Connecticut all along and we we get closer to the event I've become way more impressed. There are signals for a hellacious band of extremely heavy snow to impact southwestern Connecticut and northeastern Connecticut. It is a bit more challenging in the Connecticut River Valley (Windsor Locks, Hartford, this corridor) as subsidence could lead to totals on the lower end of the range. 

Forecast models are indicating extreme frontogenesis traversing the state by Monday afternoon into the early evening. Now, usually when forecasting higher end totals (getting above 15-18'') you would like to see the signal for banding stall and pivot. While this isn't necessarily happening here, very high snowfall ratios (perhaps 15:1 - 18:1) combined with hefty QPF totals tell me that it will dump 2-3'' per hour for several hours:

Below is looking at White Plains, NY. While not Connecticut, this is just over the border and not far from Greenwich. The two isotherms (-12C and -18C) highlight the dendritic snow growth layer (DGZ). This is the layer in which snow growth is maximized. At this location, this is showing the most extreme lift just below the DGZ, however, in southwest Connecticut, we may maximize this lift into the layer. This is a very strong signal for extremely heavy snow:

Let's break all this down:

• Snow begins likely during the pre-dawn hours Monday morning (especially across southern Connecticut) with snow spreading north through the early morning. 
• Snow rates quickly increase by late morning and early afternoon. 
• The absolute heaviest of the snow falls between 12:00 PM - 8:00 PM EST. This is when snowfall rates could approach 2-3 inches per hour (potentially even 4).
• Some thunder is possible
• Winds increase out of the northeast to 15-25 mph (25-35 along the shoreline) with gusts 40-50 mph (upwards of 55 along the shoreline). This will bring about blizzard conditions with extremely poor visibility, drifting snow, and isolated power outages.
• Afternoon and evening commute may be near impossible and extremely dangerous due to rapidly accumulating snow, very poor visibility, and high winds. 
• Light snow continues well into Tuesday morning.
• There will likely be some sleet and freezing rain involved along the shoreline and even extending well inland, especially during the overnight as precipitation intensities wind down and the storm takes a wonky track. 

Below, is my update:

Significant Snowstorm to Impact Connecticut to Start February

 There continue to be signals for a significant and long-duration winter storm to impact Connecticut as we begin the month of February. While all the pieces are there, a lot has to play out correctly for this to happen. I am on the aggressive side with this forecast, however, I feel quite confident these pieces will evolve in such a way that a band of very heavy snow traverses the state. Should this system materialize just a bit quicker, more of the state could get into even heavier snows. Why am I so aggressive? I'll explain below. Note: Just because I'm using graphics from a particular forecast model does not mean I am basing my forecast off that model. I am just using the graphics for illustrative purposes. 

Baroclinic Zone:

I am very impressed with the temperature gradient in the lower-levels of the atmosphere which will be in place across New England. Choosing the 850mb level (~5,000 feet above the ground) too illustrate, temperatures in the warm sector may as as warm as +7C. Meanwhile, temperatures at the same level across interior New England may be as cold as -6C to -7C. Also note the very strong easterly winds in the warm sector (the flags indicate 50+ knots of wind feeding into the storm). This will provide sufficient moisture into the storm. This is all even more impressive if we were to look down around 2,500 feet (925mb). This favors very strong lift (upward vertical motion) across the region.

Forecast models indicate the 700mb low closing off south of Connecticut with the low tracking to our south and east. There are uncertainties regarding the exact evolution of this feature which poses some challenges to the overall forecast. As modeled, this might be a bit farther south than I would like for heavy snow into Connecticut, however, given this low does not become very tightly compacted (the more "rings" or circles" the more compacted and tightly closed it is) and is more elongated indicates to me that the band of heaviest snow would actually be displaced farther northwest than usual. That would place this band over Connecticut:

In terms of how much liquid will fall (this can be a huge assistance when forecasting snow totals), forecast models generally are not very impressive here in Connecticut as they keep the heaviest south and east of the state. I feel very strongly that this is underdone based on analysis of the setup. I feel based on the degree of warm inflow into the very cold air mass that will be in place combined with the strong baroclinic zone and favorable region-wide large-scale lift, we will certainly see a band of heavy snow traverse the state.

Here is a breakdown of my thoughts:

• Snow begins during the overnight Sunday into Monday morning. 
• Snow intensities begin to increase rapidly thorough Monday morning (especially the southern part of the state) with conditions deteriorating rapidly. 
• Winds begin to increase out of the northeast or north-northeast and may gusts between 40-50 mph during the height of the storm. This may lead to blizzard-like conditions at times along with potential for drifting snow and isolated power outages. 
• The heaviest of the snow falls from late Monday afternoon through early overnight Monday. Light snow may even stick around through the first half of Tuesday. 
• Snowfall rates during the peak range between 1 to 2 inches per hour. 
• Monday late afternoon and evening commute will be extremely difficult due to heavy snow and snow covered roads. Given how cold it is the snow will stick rapidly and easily. 
• There are some wildcards to consider, including the potential for dry air to filter in the lower-levels from the north. This could put a major wrench in totals.
• Below is my initial forecast:

Significant Storm Potential Around February 1, 2021

 There are signals for a rather significant winter storm to begin the month of February. In a winter which has been well...non-existent in terms of the snow department and chances few and far between, it makes monitoring this that much more fun. For us here in Connecticut, there are a wide range of possibilities from a small hit, very large hit, or no hit at all as the storm could miss out out to sea or well off to the south. How the overall pattern progresses through the weekend will determine what type of solution we have.

Since our massive snowstorm back around mid-December two things have been constant;

1) A negative North Atlantic Oscillation (NAO)

2) A positive Pacific-North American (PNA) (however, the PNA has become more negative recently)

Now...typically when you see this sort of combination there are two things you can expect;

1) Colder temperatures

2) Snow...and lots of it

Well neither of these have happened...but we won't get into that here. 

Moving towards the first of February we start to see some changes occur. The NAO trends more positive while the PNA, which has become more negative recently, is expected to become more positive:

When both the NAO and PNA are in this transitory process, this can be a signal for a major East Coast storm. 

The 12z GFS ensemble mean for 500 hPa height anomalies come Monday morning features a very exciting look for snow fans;

1) A ridge across the Inter-mountain West and Great Plains region

2) Trough amplifying across the East with a trough axis into the Southeast

3) A large area of anomalous above-average height anomalies over much of Canada. This will create a "block" and when combined with the look of #1 and #2 sharply increases the likelihood for a storm to develop and either sort of ride up the coast or if it comes from the Ohio Valley, the block should keep the storm farther south and also supply us with cold air. 

One thing we've been lacking all winter is a baroclonic zone off the East Coast. Baroclinicity is a huge driver in cyclogenesis and that has been lacking. 12z GFS forecast temperatures at 850mb indicate there could be a pretty decent barloclinic zone across our area with temperatures about 5,000 feet above the ground to our south as high as +6C with across northern New England they could be as cold as -10 to -12C. This type of steep temperature gradient favors strong upward motion and favorable conditions for low pressure development and strengthening (cyclogenesis):

Forecast models are indicating the potential for energy riding around the crest of the ridge out west digging and amplifying as it moves into the eastern trough. This will be a focal point for the development of low pressure which could rapidly intensify. 

Being nearly a week out, it's way too early to get into details or specifics, however, the signals are there for a pretty significant winter storm which could impact Connecticut around February 1. Details should become clearer moving through the week.

Tuesday, January 19 - Wednesday, January 20, 2021 Clipper Potential

 After the mid-December snow event, winter has been a zzzzzzzzzz fest in the snowfall department and in the cold department for that matter. While it may not seem like it, the overall pattern hasn't been all that terrible, however, a few nuisances; particularly with the state of the Pacific have prevent us from cashing in on the pattern. We have also seen a more southern stream dominant pattern which well...sometimes works and sometimes doesn't. However, moving into the third week of January, we will be dealing with northern stream energy and these can offer up clipper systems and sometimes these clipper systems produce...so will this one? Let's take a look!

A textbook rex block pattern will evolve across the west coast at the beginning of the week with a cutoff low pressure across the Southwest (or just off the Southwest coast) with high pressure building into the Pacific-Northwest region. This results in the jet stream splitting into two across the western United States with the two pieces finding love again across the eastern United States:

Within this pattern, there are two key features to focus on for the clipper potential. Shortwave energy digging in from southeast Canada within the fast-moving northern stream and shortwave energy across the southwestern United States:

If that shortwave energy across the Southwest remains more off the west coast (or even weakens more rapidly than forecast) this will provide further room for the northern stream energy to amplify as it digs into New England. Should this amplify enough with the main piece of energy passing south of Long Island, this would promote a high likelihood for a rapidly strengthening system with a rapidly blossoming precipitation field. Given there will be sufficient cold air available, this precipitation would be in the form of snow!

Should this northern stream energy amplify enough to strengthen, we could see a light-to-moderate snowfall event unfold Tuesday night into Wednesday morning. Accumulations would certainly be possible. What kinds of accumulations would be looking at? Too early to tell, however, something certainly just getting into plowable territory would be in the cards. 

This is still several days out, however, that potential looms and for those starving for snow, we hold onto any hope we can get in these dire times.

Happy Snow Watching!