What a difference two weeks make. We have moved from potential pattern change, to pattern change, to the waiting game, to production (for most). Now, our pattern is changing back to an above normal regime, and we all turn our eyes to what February holds. 

Grading the last Outlook

Precipitation departure from normal the last two weeks courtesy of the Northeast Regional Climate Center

Temperature departure from normal for the last two weeks courtesy of the Northeast Regional Climate Center

Week one—Friday January 15 to Thursday January 21
Temperatures—below average (moderate confidence) Wrong
Precipitation—average (low confidence) Check
Wintry Precipitation—normal (low confidence) Check

Week two—Friday January 22 to Thursday January 28
Temperatures—above average (moderate confidence) Check
Precipitation—average (moderate confidence) Wrong
Wintry Precipitation—normal (low confidence)​ Check

I think this outlook faired better, even though I missed a bit on total precipitation. In week one, the two systems that I wrote about ended up occurring. The first system was a warm rainer, and the second system (the scraper blizzard) happened at the very start of the second week. As I thought, the second event was the potential event worth following, and the pattern did relax after the massive east coast event, which has brought us into a warmer regime. As an aside, I have been quite surprised by how warm and dry we have been during meteorological winter. Overall grade: B+

Two Week Outlook Summary

* Note—high confidence (70% or greater belief of event occurring), moderate confidence (36-69%), low confidence (0-35%); nothing significant (less than 1” snowfall and .25” ice)

Week one—Friday January 29 to Thursday February 4
Temperatures—above average (high confidence)
Precipitation—below average (moderate confidence)
Wintry Precipitation—below normal (moderate confidence) 

With the passage of the Blizzard of 2016, which was listed as the fourth most impactful winter storm to hit the east coast in modern times just today, the pattern has relaxed. Overall, the signal looks warmer and perhaps a touch drier, with a chance of light mixed precipitation on Friday, and a signal for a storm that cuts to our west (meaning warm and wet conditions) by the middle of next week. 

Week two—Friday February 5 to Thursday February 11
Temperatures—average (moderate confidence)
Precipitation—average (low confidence)
Wintry Precipitation—normal (low confidence)​

By week two, the transient pattern that brings us warmth begins to fade away, moving back toward what I think will be a pattern that favors colder temperatures and storminess for the rest of the period. There could be a period of interest at the very end of the period, but confidence is (obviously) low at this time as this system, much like the scraper blizzard at long range, looks to be far south at this time. 

​Technical Discussion

Week one ​

After a blizzard that hit a large part of the east coast, but scraped New England, we return to a warmer than normal regime. Like I have said in the past, warmer temperatures do not automatically preclude wintry precipitation from falling, but in this setup, wintry precipitation looks unlikely outside of Friday and maybe the weekend. If you have been following us for a while, you probably already know what to look for.

Above you see one of today’s run of the European ensembles, or EPS. Remember, that this is a snapshot in time, and uses slight tweaks in initialization conditions when a model runs to account for inherent errors in predicting atmospheric conditions that occur the further out you go in time.  

What are we looking at? We see a move toward higher heights over New England (the red shading) and ridging (lines pointing poleward) which would allow for warmer conditions. In addition, you see troughing and colder air located out west, opening the door for storm tracks that are less than ideal if you like snow in the east.

In the second image, you see the American, or GFS Ensembles for accumulated snow moving forward. You see the various outcomes on the individual models, but pay attention to the last image. That is the ensemble mean, and it shows almost no accumulated snow. This reflects a weak signal for snow over the next seven days. 

Going back to the first image, you can see that by the end of the forecast period, the troughing begins to push west. The Pacific pattern begins to look better, and that brings us to week two…

Week two

By the second week, we see a strong signal for ridging in the west, which implies a +PNA and neutral to -EPO. This is a signal for shots of cold air intrusions and opens the door for northern stream systems (think clippers) to provide light events for the region. When I see the long range pattern in the west, I think of a far less extreme version of last winter. In the Atlantic, the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) do not look as robust as what we saw in January, but not outright hostile either. If we are looking for a big storm, generally you want to see a negative phase of the AO and NAO to provide storms with the ability to amplify and ride up the coast. We will see if that happens.

Above you will see the GEFS output for high and low temperatures during the period. Remember, this should only be read to identify a pattern, not sensible weather on a given day. The GEFS supports the idea of a warmer than normal pattern turning colder by the second week of the forecast period. Images courtesy of WeatherBell Analytics.

The image below is the second half of the GEFS run for accumulated snowfall. Here, you see a stronger signal for accumulated snow in week two of the forecast period, but it is not terribly strong with plenty of solutions showing little snow. 

Much like the last outlook, this one had something for everyone. Week one provides warmer than normal temperatures for those that are already tired of this winter, and the second week opens the door for a return to a favorable pattern for cold and storminess. As a result of the blizzard, Connecticut has become the dividing line for normal this season. In southern Connecticut, many have made up their seasonal snowfall deficit or come close to getting to normal. In northern Connecticut, a season without (substantial) snow continues.

I do believe that February becomes an active month and a colder month, but for now, warmer and drier rules the roost. 

As always, don’t forget to like us on Facebook and share our discussions, and follow us on Twitter @southernctwx and retweet our posts!

Thanks for reading SCW.​​

-DB

As Southern parts of the state dig out and we really dig out here in New Jersey where I write this from, the overall pattern will relax, and the most dominant features in the pattern will be weak short waves without much moisture, at least for about the next week or so.  Thereafter, the pattern may turn more active, but more on that at the bottom of the discussion.

For tonight, temperatures will be a bit challenging, especially in the snow-covered southern portions of the state.  We've seen extreme radiational cooling the past two nights because of clear skies and fresh snowpack, and how much the temperatures drop tonight could depend greatly on cloud cover.  Clouds should increase after midnight, but even so, temperatures should manage to get into the 20s.

Temperatures could also be a bit tricky for the same areas tomorrow.  We have warm air advection, but at the same time, we have a generally cloudy day and deep snowpack.  These two factors may cancel each other out a bit, so temperatures will probably be a few degrees cooler than they otherwise would- probably not too far from 40.  Regarding precipitation, we do have a weak warm frontal feature moving through early in the day.  This feature will have very little moisture, so probably will not produce precipitation, which is a good thing, because if precipitation did fall in the morning, soundings support freezing rain.  The better chance for precipitation will be in the afternoon and early evening, ahead of a cold front.  For the most part, this precipitation should fall as all rain.  However, there is a chance that precipitation could mix with, and/or change to snow before ending, depending on the timing.  The most likely chance of that, of course, would be up north.  Accumulations should be very little or none, because temperatures will still be above freezing, and any snow would be fairly light.

Tuesday Night and Wednesday: We'll dry out behind the front.  A weak wave of low pressure will try to develop along the cold front Wednesday.  However, anymeasurable precipitation associated with this feature should remain well south of the state.  However, I wouldn't be surprised to see a few snow flurries at any time across the state, due to the combination of the frontal wave being fairly close and lingering instability with the front being close.  As far as temperatures, low temperatures Tuesday night should be within a few degrees of freezing and high temperatures on Wednesday should be in the low 40s.  Since temperatures won't freefall below freezing Tuesday night, a black icing situation is not expected at this time.

Longer Term: Thursday: Cold air from behind the front will move in more efficiently on Thursday.  Temperatures will return to near normal, with highs in the mid to upper 30s and lows in the teens and 20s.  Skies should be generally clear.

Friday: Models had a threat from a coastal storm.  However, nearly all models now agree that this system will stay too far offshore to affect the state.  However, given that we're still four days away, it will still be monitored.  What really tells me this system should remain offshore is that in order for it to make it up the coast, it would have to take in some energy from an Alberta Clipper diving down from the Great Lakes.  For now, there is a large separation from the two systems, and minimizing any chance of precipitation even further is the fact that the coastal low passes just close enough to steal any moisture that the Clipper has, thus dampening it out before it gets far enough east to affect Connecticut.  So the upshot of it is for now, Friday should be a dry day with temperatures close to seasonal normals- lows in the 20s and highs in the mid to upper 30s.

Over the weekend, a series of weak systems with just enough lift and moisture to produce precipitation will affect the state.  Although it is far too early to nail down the specifics, here is how it looks like it will play out for now.  Saturday should be a fair day, but with increasing clouds later in the day.  Later Saturday night into early Sunday morning, very light precipitation will move into the state.  Across the south, it should be all rain, but in the north, it could be freezing rain- maybe even sleet or snow earlier on.

Yet another wave will spread light precipitation into the state Sunday night for a few hours.  Once again, this precipitation looks to be rain in the south, but some sleet could be possible across the north.

Monday should be fair with mild temperatures as we'll be in between systems.

As far as temperatures in the long term, Saturday should have lows in the 20s with highs around 40, Sunday should have lows around 30 with highs 40-45, and Monday should have low temperatures around the freezing mark, with highs 40-45.

There is the potential for a larger storm system on Tuesday and Wednesday next week.  At this time, it appears a brief period of frozen precipitation, followed by a change to heavy rain.  However, there is strong high pressure to the north, and if the models are underdoing the strength and/or staying power of that high, this could present the chance for a colder system than what is currently modeled.  We will continue to monitor that system for you.

Beyond that, there are increasing hints that the Arctic will be unleashed on New England, almost reminiscent of last February!

Here is a quick map, not really much to post today in the way of maps- but this is a good look at how Friday's system is currently modeled to stay too far south and east to affect the state! You can see the coastal low well off the coasts of New Jersey and Long Island, and the weakening Alberta Clipper feature over the Toronto area- neither affecting the state.

-GP!

​

Overview
Phew. We made it. It’s been a long week here at SCW, with the first major snowstorm of the season being one of the more difficult forecasts I can remember making during the almost three years that we’ve been doing this. We had our ups and downs for sure, with model guidance going from big hit to miss to small hit back to a big hit, but for only some of the state, within the span of a day or two. Rather difficult for a forecast team to process and communicate, and it most certainly made for some late nights and stressful model runs here at SCW. However, in the end, we came to a forecast that I thought verified, on the whole, exceptionally well, and I’m very happy with how we did during this system.  
 
This discussion will be primarily a post-mortem of the system that we just had, where we take a quick walk back through the timeline leading up to it, break down our forecast, and grade ourselves on our performance (and you can grade us also!). We decided to introduce this discussion format because far too often in meteorology, forecasts die when the event takes place, and they are never analyzed and revisited, whether good or bad. We felt that it would be a good learning experience for us to go back and walk through our forecast (as well as hear from you all about how you think we did), and hopefully it will allow us to better serve you all in the future. We’ll have a quick forecast outline for the week ahead at the end of this discussion, with a detailed full forecasters discussion coming tomorrow evening.
 
But first, welcome!
 
We’ll go into more detail about the event and what we noticed from it(as well as grade our own forecast) in a minute, but first, I would like to welcome our new additions to the SCW family! We had quite the surge of traffic over the last few days, with over eighteen thousand people visiting the website for the first time and over a hundred and thirty thousand people viewing our posts on Facebook (In case you’re curious, that’s our third highest total of all time behind the lead up to the system on January 22nd, 2014 and the leadup to the Blizzard of 2015 on January 27th, 2015). To all our new readers, we’re glad that you found us, and we hope that you will continue to read and interact with SCW for many more storms to come. To our loyal regulars, thank you for spreading the word about us to your friends and for continuing to be unquestionably the best readership base of any website out there, meteorological or otherwise. We wouldn’t be where we are today without all of you.
 
A look back
 
Back to the storm. As you may remember, we were tracking this system from quite a ways out, with the system first making an appearance on guidance late last week. Originally, it was modeled as a large storm regionwide, and excellent model continuity on that front continued through all of last weekend and into last Monday. As such, we began to sound the alarms last Monday night, with Greg’s forecast discussion outlining the potential for a significant event to impact the state this weekend. However, within a few hours after hitting the post button on that discussion, model guidance began to shift rapidly, with an area of strong confluence introduced to our north and the development of an additional piece of vorticity that would interact with the low and pull it east appearing on the models. As such, the northern edge of the storm was quickly slashed, and the model consensus for the state very quickly went from a strong winter storm to almost nothing.
 
While we began hedging our wording in our discussions to account for the possibility of a miss, behind the scenes, the team was generally still confident in at least some snow for the state. The modeling continued to be bleak, however, with most guidance continuing to show a miss well south of us. In fact, Thursday morning, after issuing an initial snow map that showed a minor system for most of the state, accounting for what we believed would be a continued minor north trend that had begun the night before, the 12z guidance dropped even further south, with most of the state seeing nothing at all. We were about ready to pull the plug and cancel any idea of a significant impact from the storm when the 18z NAM rolled out, and the northern edge of the storm was hundreds of miles north of the previous consensus.  A head scratcher for sure, especially since the NAM’s track record has been atrocious when it comes to winter storms, with the model being notoriously overamped and precipitation happy, extending precipitation shields far greater than reality on a consistent basis. Matters were only compounded when the 18z GFS, a far more reliable model than the NAM, made a definitive nod towards it and shifted a substantial amount north as well. We were now in a situation where the model consensus brought an inch or two of snow to the shoreline and little elsewhere, while the NAM would result in a blizzard for the entire state.
 
We hedged our bets, dropping totals across most of the state while increasing them along the shoreline to account for the possibility of the edge of the sharp band of heavier snow catching the shoreline. Turns out that we didn’t increase them enough, as the NAM proved to be more correct than not with the idea of a further north track, and while it’s northern edge was overdone as it usually is(Otherwise the whole state would have seen the totals we saw on the shoreline), it’s main idea of a much further north solution than the current consensus proved to be correct, as over the next 24 hours, we saw almost all of the global guidance continue to tick north, and with no signs of the trend stopping, we became confident in a significant snowstorm for the coastline with the meat of the heavier band of snow falling squarely on Southern Connecticut. As such, on the evening of the systems arrival, we upgraded the shoreline to warning level amounts, and advised preparations for a high-impact system, and we increased totals somewhat across the rest of the state as well.
 
As a reminder, here are the three forecast maps that we issued, from oldest to newest left to right, for this system.

 Verification
So how did we do? Overall, I, and the rest of the team, think we verified pretty well. There were definitely some areas that we could have done better on, specifically, the western portions immediate shoreline and the northeast corner of the state, both of which received more snow than we forecast, but overall, I think we did pretty well. Many have asked why we did not upgrade our map to include higher amounts for the shoreline once it became clear early on in the storm that there would be some totals over a foot. The answer is twofold. First, our resources during a storm are limited, and we felt that they were better used answering reader questions, doing rapid-fire radar updates, and communicating with those who rely on us for forecasts rather than taking time away from what was going on right now to issue a new map(Each of our maps takes about an hour to make). In the grand scheme of things, the difference between 12” and 16” of snow is not all that large, as both are significant events that require preparation and planning. Since we had already forecast a significant event for that area, we felt that upgrading was not the best use of our resources since the eventual end impact would not be substantially different. We did mention several times in text and comments that we thought some snow totals would be higher on the shoreline than we had forecast once the storm was underway.
 
As far as the northeast corner of the state goes, that was our only true “bust” of the storm in my opinion. We as a forecast team were skeptical that the heavy band would make it that far north, and once it did and proved us wrong, it was too late to issue an updated map, as most of the snow came in a short period of time and it became a nowcast situation.
 
On the positive side, I’m happy about our performance in the northern portions of the state overall. Several models brought warning level snows all the way to the northwest corner of the state, and several forecast outlets, including the National Weather Service, jumped on those models and issued Winter Storm Warnings for the whole state. We remained relatively constant with our prediction as to where the cutoff of the heavier snow would be, and except for the northeast corner, verified that almost perfectly. Nailing such a sharp cutoff is not an easy thing to do, and I’m very happy with how close we were able to come to it.
 
Grading
Initial recognition: A SCW recognized this systems potential as far as a week out, and had a detailed discussion on it illustrating the potential for a major storm five days out. Those are very impressive lead times in meteorology.
Midrange: B I think we backed off the idea of a major storm a bit too much, but overall I think we did a good job illustrating the shifts in guidance and the fluctuating potential.
Preliminary forecasts: B-: Our initial maps, while getting the gradients reasonably correct, were too low on amounts for a large chunk of the state.
Final forecast: B+: Overall, I think our final call was pretty good, although we missed the higher amounts along the shoreline and the northeast corner of the state. I was very happy with our positioning of the cutoff of the heavier snows.
Rapid fire updates/communication B+: We recognized quickly that the storm would be a bit more intense than forecast for most of the state, and I think we did a good job communicating current conditions and uncertainties.
Overall Grade B+: A solid start to the season for us.
 
We want to hear what you think! Click here to be redirected to a quick survey about how you think we did with this last system. Your feedback is greatly appreciated and will help us to do better for you in the future!
 
Here’s an awesome visual satellite image from this morning. Look at the sharp gradient of snowfall in northwest Connecticut! If you're interested in the unofficial final snowfall reports that were sent to the National Weather Service, you can find them here(for the shoreline counties), here(for Litchfield county), and here(for Hartford, Tolland and Windham counties).

​Looking Ahead
 
Generally calm and warmer weather appears in the cards for most of the week, with our next substantial snow chance coming on Friday from a late-developing Miller B system to our east. At this time, the UKMET, along with Euro and it’s ensembles, favor a solution that would bring some snow to the state on Friday, while the GFS and GGEM are further out to sea and as a result keep the precipitation shield off the coastline to our east. Temperatures are marginal, but most likely snow supporting for most away from the immediate coastline. At this point in time, I will simply add a chance of rain and snow to the forecast for Thursday night through Friday, and we will address this potential system in much more detail later in the week should it remain a possibility on model guidance. I have also included a slight chance of snow on Wednesday night from a frontal wave that develops along a cold front to our southeast, which most modeling keeps offshore. However, the Canadian model brings a light snowfall to our area from this wave, with an inch or two in the southeast corner of the state, and as such I will paint in a slight chance of snow to account for this possibility.

Otherwise, slightly above normal temperatures throughout the forecast period are expected.
 
Here are the dailies
Monday: Mostly sunny, with highs in the mid to upper 30s.
Tuesday: Mostly cloudy, with highs in the lower 40s.
Wednesday: A slight chance of snow, especially in SE sections of the state, otherwise, mostly cloudy, with highs in the mid to upper 30s. Chance of precipitation is 20%, except 35% southeast of a line from New Haven to Willimantic to the RI border.
Thursday: Mostly sunny, with highs in the mid 30s.
Friday: A chance of rain and snow, otherwise, mostly cloudy, with highs in the mid 30s. Chance of precipitation is 40%.
Saturday: Partly cloudy, with highs in the lower 40s.
Sunday: Partly cloudy, with highs in the lower 40s.
 
Much more on the forecast and a look at the long range is coming tomorrow evening, until then, have a great start to the week and thanks for reading SCW!
-SA

​Good evening from Southern Connecticut Weather!
 
Below, you’ll see our final call map for the upcoming system that will impact the state tomorrow and tomorrow night. Greg wrote a full discussion earlier this afternoon, which is included in an edited form in this post, but we wanted to give a quick and simple summary for those of you just looking to get the information you need to know now. 

First, snow amounts.
Model consensus has generally shifted north over the past several runs, and we have finally seen a global model(the 18z GFS) join the mesoscale models in predicting a statewide impact of larger scale. While we don’t expect it to verify, should a straight mesoscale/18z GFS solution prove to be correct, pretty much the entire state would see warning level(6”+) snows. As of now, we think that is about a one in four shot, but that’s not an insignificant number and so we mention the possibility here.
 
As far as our current forecast, model consensus is now quite strong on the coastline being just far enough north to make it into the heavier snow band for an extended period of time, and thus, we have upped our forecast snow range to six to twelve inches. We expect that most parts of this zone will remain in the 6-10” range, but have left the possibility for up to 12” in the forecast to account for localized heavy banding and the possibility of an even further north increase of precipitation.
 
In the next tier, we think that the heavier snow band will make an appearance for at least a short period of time, which will be enough to drop a few inches of snow, with lighter snow falling on either side. As such, we are forecasting a 3-6” snowfall for the central portion of the state.
 
In the northern tier, while the system has come far enough north to introduce light precipitation into the area, we still don’t have enough confidence in the heavier snow band making it that far north to go with a heavier forecast, and as such, are forecasting 1-3” for the northern tier of the state, with a small area of C-2” in the far NW corner where latitude and longitude together create a very unfavorable situation for any periods of heavy snow.

​In addition, winds will be an issue with this system. It will become very windy along the south coast, regardless of how much snow falls. Winds could gust to 50 to 60 MPH right along the coast. This could cause power outages, especially if significant snow falls as well. Winds like that can cause power outages without any additional help, and if heavy snow falls in addition to those winds, it will make any power problems worse. Coastal flooding will certainly be an issue along the south coast, as well, as tides are already astronomically high. 
 
Timing
Midnight-7 AM: Light snow develops over the southern portion of the state and gradually works its way north.
7 AM-1 PM: Heavier snow and stronger winds move into the southern portion of the state, while snow breaks out in the northern tier.
1 PM – 5 PM: Heavier snow continues over the southern portion of the state, while lighter snow continues up north, with brief periods of heavier snow in the northern zones.
5 PM-midnight: Snow tapers off from west to east across the area, with most precipitation being clear of the state by midnight Saturday night.

From here, I'll turn you all over to Greg for a more detailed technical discussion which also has more information on non-snow impacts that are expected. Thanks for reading SCW!
-SA


5:30 PM Update: The NAM has continued to be wet, and the latest GFS has continued to trend wetter, especially along the Northern fringe, namely the South coast! Therefore, after conferencing, we have decided to raise totals, especially in southern and central areas. The new totals are as follows: 6-12" along the south coast, basically the Merritt Parkway South, 3-6" in most of central Connecticut, 1-3" in most of Northern Connecticut, except a coating to two inches in the far Northwest corner of the state. It has become more likely that the south coast will see a significant snowfall. It is still likely that very little snow will fall much North of Hartford and parts of extreme Northern Litchfield County may struggle to see a flake. The most difficult zone will be basically between the Merritt Parkway and I-84 (basically interior central Connecticut). These areas are right on the line between significant snows and very little, and any slight shift in modeling will have drastic impacts on their snow totals.

Here's a look at the 12z and 18z GFS QPF totals, showing the significant jump north.

Original discussion from 2:30 PM(Note that we have increased snowfall totals since this discussion was released, therefore, some of the references may be outdated): Most modeling has trended northward this afternoon, which would increase snow amounts on the south coast. However, no changes will be made to the going snow map, just yet. It is certainly possible that the south coast sees more than what is currently being modeled. Most of the models are in fairly tight agreement, with the exception being the NAM. Since the NAM has a very wet bias, it is OK to weight the forecast 90% away from the NAM at this time, and then if need be, adjust upward later on. Most modeling also agrees that the northern half of the state may see an inch or so more than mapped at this time, but not much more than that. Again, the exception is the NAM. If the NAM were to verify, blizzard conditions would probably be felt throughout the state. Again, the forecast is weighted heavily against that- for now. So what should we look for? How do we determine which guidance is right and wrong? Most of the mesoscale guidance, such as the NAM, that bring very heavy precipitation into the southern half of the state and significant precipitation into the northern half of the state, have the snow starting much quicker than the other guidance. The faster the snow starts, therefore, the more accumulations we'll see. The reasoning here is fairly simple... Obviously if snow falls for a longer time, there will be more accumulation, but it is deeper than that, too.

If the snow makes rapid progress northward, it means two things: One, the low pressure system is moving further north, and Two, the moisture is encountering less resistance as it moves into drier air. So that is definitely going to be something to watch for and we'll know by midnight tonight. So for now, the basic reasoning remains the same. Snow amounts will remain unchanged, but we will need to closely follow radar and observations to see whether the very snowy models are verifying or if the drier models are verifying, or if it's somewhere in between. No changes will be made for now, but for now, I would think small upward adjustments in accumulations would be more likely than downward, especially on the south coast. The NAM will not be used much in this package, but because of its consistency and other models getting wetter, we should at least consider it in the backs of our minds as a possibility and watch to see what real-time trends to. But of course, it's a lot easier to adjust upward as the event unfolds if necessary, rather than make a huge adjustment upward and then scale back again. There is going to be a huge cutoff to the snowfall amounts. It is entirely possible a place on the south coast gets 10", and just on the other side of the Merritt Parkway, only a couple inches fall. The locations are not absolute; I simply am using this as a reference for Connecticut residents to point out how close the line may be between big accumulations and not much at all. Of course, there will be a very small area that receives something in between, but that area is going to be so small it is impossible to fit on the maps we produce. As such, we have chosen to broad brush a bit more than the eventual result will likely wind up being to highlight the range of possible outcomes depicted on guidance.

​In addition, winds will be an issue with this system. It will become very windy along the south coast, regardless of how much snow falls. Winds could gust to 50 to 60 MPH right along the coast. This could cause power outages, especially if significant snow falls as well. Winds like that can cause power outages without any additional help, and if heavy snow falls in addition to those winds, it will make any power problems worse. Coastal flooding will certainly be an issue along the south coast, as well, as tides are already astronomically high. For now, the vast, vast majority of any precipitation that falls will fall as snow. There is a small chance of a few sleet pellets mixing in at times along the immediate south coast, as with almost any nor'easter, but the percentage of sleet anyone can expect at any given location and the chancy nature of it happening would yield me to just go with a straight snow forecast. I may very well update this again later on as newer model data comes in. If we need to update the snow map again, that will also be done later.

There are a range of products out from the National Weather Service for this storm, including Winter Storm Warnings along the coastline, Winter Weather Advisories inland, and Blizzard warnings to our southwest. Here's a map showing the various products that have been issued(Blizzard warnings continue all the way down past PA, but a near term Special Weather Statement has been issued which is overlaying the Blizzard Warnings and making them not visible there). 

​Remember to like us on Facebook and follow us on Twitter if you haven't already done so, as we'll be using those platforms to issue rapid fire radar updates and current conditions throughout the day tomorrow. Thanks for reading SCW!
​-GP

Most modeling has trended northward this afternoon, which would increase snow amounts on the south coast.  However, no changes will be made to the going snow map, just yet.  It is certainly possible that the south coast sees more than what is currently being modeled.
 
Most of the models are in fairly tight agreement, with the exception being the NAM.  Since the NAM has a very wet bias, it is OK to weight the forecast 90% away from the NAM at this time, and then if need be, adjust upward later on.  Most modeling also agrees that the northern half of the state may see an inch or so more than mapped at this time, but not much more than that.  Again, the exception is the NAM.  If the NAM were to verify, blizzard conditions would probably be felt throughout the state.  Again, the forecast is weighted heavily against that- for now.

So what should we look for? How do we determine which guidance is right and wrong? Most of the mesoscale guidance, such as the NAM, that bring very heavy precipitation into the southern half of the state and significant precipitation into the northern half of the state, have the snow starting much quicker than the other guidance.  The faster the snow starts, therefore, the more accumulations we'll see.

The reasoning here is fairly simple... Obviously if snow falls for a longer time, there will be more accumulation, but it is deeper than that, too.  If the snow makes rapid progress northward, it means two things: One, the low pressure system is moving further north, and Two, the moisture is encountering less resistance as it moves into drier air.  So that is definitely going to be something to watch for and we'll know by midnight tonight.

So for now, the basic reasoning remains the same.  Snow amounts will remain unchanged, but we will need to closely follow radar and observations to see whether the very snowy models are verifying or if the drier models are verifying, or if it's somewhere in between.  No changes will be made for now, but for now, I would think small upward adjustments in accumulations would be more likely than downward, especially on the south coast.

The NAM will not be used much in this package, but because of its consistency and other models getting wetter, we should at least consider it in the backs of our minds as a possibility and watch to see what real-time trends to.  But of course, it's a lot easier to adjust upward as the event unfolds if necessary, rather than make a huge adjustment upward and then scale back again.

There is going to be a huge cutoff to the snowfall amounts.  It is entirely possible a place on the south coast gets 10", and just on the other side of the Merritt Parkway, only a couple inches fall.  Neither of these amounts are in the forecast or expected at this time, but I simply am using this as a reference for Connecticut residents to point out how close the line may be between big accumulations and not much at all.  Of course, there will be a very small area that receives something in between, but that area is going to be so small it is impossible to fit on the maps we produce.

It will become very windy along the south coast, regardless of how much snow falls.  Winds could gust to 50 to 60 MPH right along the coast.  This could cause power outages, especially if significant snow falls as well.  Winds like that can cause power outages without any additional help, and if heavy snow falls in addition to those winds, it will make any power problems worse.

Coastal flooding will certainly be an issue along the south coast, as well, as tides are already astronomically high.  

For now, the vast, vast majority of any precipitation that falls will fall as snow.  There is a small chance of a few sleet pellets mixing  in at times along the immediate south coast, as with almost any nor'easter, but the percentage of sleet anyone can expect at any given location and the chancy nature of it happening would yield me to just go with a straight snow forecast.

This product will be updated again in a few hours with longer term information, as well as some maps.  I may very well update this again later on as newer model data comes in.  If we need to update the snow map at all, that will also be done later.

-GP