Disc: Although temperatures will average above normal for the foreseeable future, it will also continue to be stormier than normal.  As we get deeper into winter, even temperatures a bit above normal can support wintry weather, especially for interior locations.

Currently: A complex storm system was affecting the region.  The old "parent" low pressure system was located over the Great Lakes.  A trough with weak waves of low pressure attached to it was located over the Appalachian Mtns of VA and TN.  Meanwhile, a secondary low was developing over the Jersey shore.  With most of the low pressure systems west of our area and not much of a cold air source, precipitation has been almost exclusively rain across the state.

Tonight: Steady precipitation will generally wind down, but with all these low pressure systems, it will take some time.  Expect precipitation to wind down in the west around or just after midnight, but not until dawn in the far eastern sections.  As for temperatures, the GFS has initialized 5 to 8 degrees too warm, so most of that guidance is discounted.  Even having said that, the NAM looks a degree or two too cold.  So I'll go with lows closer to, but not all the way down, to the NAM guidance.  Therefore, expect lows in the upper 20s to mid 30s.  Fortunately, the "colder" areas will likely see precipitation shut off before temperatures fall below freezing, while the "warmer" areas will see rain continue to fall.  The only exception could be NE CT.  Temperatures aloft are much too warm for anything other than rain.   So this area may need to be watched for a period of freezing rain tonight.

Tomorrow: I will do the same with temperatures tomorrow as I did today.  The GFS just doesn't seem to realize we have cold air advection occurring.  In addition, convective temperatures are low, so even if we did surge upwards in temperatures, clouds would quickly develop and put a lid on the temperature rise.  So even though NAM temperature guidance generally exhibits a cold bias, I'll go much closer to it than the GFS.  Expect highs tomorrow in the 40 to 45 degree range.  Some spots in the NW Hills could stay in the upper 30s.  As for precipitation, I'll keep it out of the forecast, because I don't think anyone measures.  But with a ULL spinning overhead, I can't rule out a flurry late in the day.  The best chances for that would be west of I 91.

Tomorrow Night/Wed: With thicknesses as low as they are progged, my feeling is that temperature guidance is way too warm.  In fact, even the NAM may be a bit too warm, so I'll go under everything.  Gridded data also supports my reasoning.  (Even if the air mass origin is not that cold, it is still January).  So expect high temperatures generally in the upper 30s, maybe a few low 40s in the I 91 corridor.  Otherwise, a sunny, normal winter's day.

Long Term (Thursday through the weekend):  For Thursday, with the wind flow turning SW, temps will moderate.  Temperature guidance is not as bad by then, but I still may need to shave off a degree or two with lingering LL cold air.  So expect highs in the 40 to 45 degree range.  

The next storm system affects the area on Friday.  There are a lot of questions still lingering with this system, mainly regarding speed and total precipitation.  I will go with the GFS on speed, which is faster than most of the guidance.  But since the model has been consistent with this and we are not in a blocky pattern, I see no reason to believe that the system will not scoot right along.  I will go wetter than the GFS, however, since it has trended wetter and generally runs too dry at that range.  Overrunning precipitation overspreads the state very late Thursday night and precipitation could linger until very late Friday night.  However, some of the new guidance is indicating that there could very well be a break later Friday afternoon into early evening hours, so it may not rain the whole time.  Despite what the calendar says, there is no question with precipitation type with this system.  Thermal profiles, even at the surface, support all rain for the duration for the entire state.  I will go several degrees colder than the GFS temperature guidance, since it tends to like to blast warm fronts through the area when they really do not make it this time of year.  Additionally, even if we do get a break, we likely will not see any sun, as most of the state will not see the break in precipitation until after sunset.  Therefore, there shouldn't be any solar insolation to boost temperatures.  So expect highs generally in the low 40s, although I could be a degree or two too cool in a few locations.  It's best not to get too cute this far out.

For Saturday, I'll go a few degrees under temperature guidance because I think we're more cloudy than the GFS indicates.  It wants to clear us out too fast.  However, the air mass is quite warm. So even after lowering guidance temperatures, we're still looking at highs around 50 degrees throughout the state.

With a strong cold frontal passage Saturday night, albeit a dry frontal passage, Sunday's temperatures should be much cooler.  As is typical this far out, GFS temperature guidance does not seem to recognize there is cold air advection occurring.  So I'll lower those temperatures by about 5 degrees.  Expect high temperatures generally in the mid 30s.  A few upper 30s are possible along the I 91 corridor.

Finally for Monday, a chilly winter's day is in store.  With plenty of sun and high pressure overhead, I see no reason to stray too far from temperature guidance.  Expect highs generally in the 30 to 35 degree range, except perhaps a touch warmer along the I 91 corridor.

Looking into the long range, although there could be a cold shot from time to time, temperatures generally look to average above normal as far as the eye can see.  However, we are entering the heart of winter, and even above nornal temperatures with a well-timed storm can yield wintry precipitation, especially in the northern parts of the state.  The pattern does look to continue active and stormy, so stay tuned!

Now, let's take a graphical look at systems slated to affect the area in the next week.  Since there is only one significant system affecting the area this week and no record breaking temperatures, I'm only going to post one map.  This map, valid Friday morning around dawn, captures the evolution of that system very well.  You can see precipitation ongoing across the state at that time, with more moving in.  You can also see the break headed to the region with more rain on the other side of the break.

​

Anyway, that's all for now! See you next week and have a happy new year!

​-GP!

Good afternoon from SCW!

In our first call yesterday, Don laid out the setup that’s coming to the state tonight into tomorrow; a strong low is cutting to our west and warming the mid levels while at the same time, high pressure to the north is causing colder air to filter down into the state. This is a classic setup for an ice storm, and if temperatures were a couple of degrees colder, we would be looking at a significant to potentially historic ice storm in the state. 

The good news is that we have a warm antecedent air mass in place and the high that’s coming in isn’t positioned in quite the right spot to see really effective cold air drainage, so the impacts will be substantially reduced from what they could otherwise have been. However, we are still expecting icing across portions of the state, with the potential for a high impact icing event (0.5”+ of ice) in the northwest hills. Winter Weather Advisories are up for all of the northern counties, with the exception of northern Litchfield county where an Ice Storm Warning is in effect. 

Here’s a look at our final accretion map for this event.

Since yesterday, the guidance has remained relatively steady, advertising significant icing in the northwest hills, but little to nothing elsewhere. Don wrote yesterday how models tend to under-estimate surface cold, and for whatever reason often fail to “see” the high pressure to the north that will keep temps lower. The more classic depiction of scenario is when a cold airmass is already in place and models are too quick to move it out, but the same theory applies here to cold seeping in as well. In those sorts of situations you tend to see a last-minute tick colder as the models recognize the influence of the high and that surface temps will remain cooler, and interestingly here we haven’t really seen that, if anything, the guidance has wobbled slightly warmer today, and if you believe the models, this is mainly just a cold rain outside of the northwest hills. However, we are meteorologists and forecasters, not modelologists, and I’ve seen this setup enough times to not take it at face value. It is certainly possible that everyone outside of the hills wakes up to a cold rain tomorrow morning, and in fact I think it’s just as likely that we see little to no icing as it is that we see significant accretions. That said, given the impacts that even a trace of ice can have, it’s important to be aware of and highlight the possibility of an overperformer in this situation.

A notable exception to the guidance consensus is the HREF ensemble, which has accretions across most of the northern portion of the state. As an extremely high-resolution model, it may be more adept at noticing the cold air drainage than some of the other global models, and so the fact that it’s showing this scenario is worth considering.

Here’s total ice accretions from the last three runs of the NAM (showing the slight warming trend) and also from the most recent run of the HREF.

Given the slight warming trend and the absence of the models “recognizing” the cold, we’ve tightened up the zones a bit to focus on the inland areas above ~800 feet where we believe cold air will be more likely to hold. That said, surface temps are very terrain dependent, and we expect significant variation in icing within very small distances based on the topography of a specific town or even neighborhood. It’s entirely possible that a sheltered hollow in our glaze zone will end up with a quarter of an inch of ice, while a wide open area in our 0.3”+ zone will get just a glaze or a tenth of an inch of ice. It’s impossible to illustrate the thousands of micro-climates within the state on a map, so we’re forced to broad-brush and hope for the best, but take the ranges as guidance, not as absolutes. Unlike a snow map, this isn’t the sort of map that we’re expecting to be correct for everyone.
For the southern portion of the state, we are reasonably confident that this is a cold rain event. I wouldn’t rule out a light glaze in the elevations of Fairfield and New Haven counties, but beyond that, I think this is an annoyance more than it is a winter event. 

For northern areas outside of the hills, I still think this is primarily a cold rain, but a glaze of ice is certainly possible and I do expect some totals up to about a tenth of an inch of ice or so to occur in the favored areas. In the hills, where elevation will make things just a touch colder, this will be a much higher-impact event. Guidance is in good agreement that the highest elevations of NWCT may never turn over to plain rain, and a half of an inch of ice or more is a distinct possibility there. On the fringe of the NW hills and in the NE hills, I would look for generally a tenth or two of an inch of ice accretion, but I think it is there that the biggest surprise could be in store; if guidance is under-estimating the depth of the cold even slightly, there is the potential for significant icing there as well.

All in all, we’re expecting rain/freezing rain to move into the state late this afternoon/this evening, with temperatures gradually warming throughout the day tomorrow and changing everyone outside of the hills over to plain rain. One thing to watch is whether the development of a coastal low will allow for cold air to reestablish itself in northern Connecticut, bringing more wintry precipitation. We will see rain persist through Tuesday morning, but things should clear out in time for NYE festivities; right now it’s looking like temps in the low to mid 30s for Tuesday night as shown on the hi-res NAM below.

Impacts

Icing--No Impact Southern Connecticut/Low-Moderate-High Inland  
There is no impact expected in southern Connecticut when it comes to icing. For most of northern CT, this should be a relatively low impact event, but in the hilly sections of NW and NE CT we are expecting more of a moderate icing impact. In the highest elevations of the NW hills (>1000’), this has the potential to be a high-impact icing event. As I explained earlier, I’d hedge towards the lower end of the ranges for most or even below that, but the possibility exists for a more impactful event and it’s important to highlight that.

Wind--None
I do not expect any significant wind with this storm. 

Power Outages--Low/Moderate in NWCT
I would expect some scattered power outages in the NW hills and possibly in the NE hills should the system overperform, but do not expect widespread issues.

Timing--Low
The storm starts on a Sunday night and although Monday's morning and afternoon commute could be impacted, with kids at home for vacation and many workers doing the same, the roads should be less congested and our crews should be in a good place to keep major roadways in good shape. 
​
Road Conditions--Low/Moderate
In areas where it's just raining, the normal level of caution should be exercised. In areas of central CT that do not receive a lot of icing, you should be careful but I expect main roads to be passable. However, it only takes a small amount of ice to cause serious issues if roads are not continuously treated, and so I expect that there will be difficult travel on secondary and tertiary roads in the hills tomorrow. 

All in all, while this is likely just annoying cold rain for most of us, the potential exists for an icy day tomorrow, especially in our elevated areas, and it’s important to be aware of the potential and plan accordingly if needed. It’s worth mentioning that to our north this is expected to be a severe ice storm, with half an inch or more of accretion in the Berkshires and Hudson Valley up into Vermont and southwest NH, so I would not plan on travel that passes through those areas. 

We’ll have updates through the day tomorrow as necessary, and please feel free to ask any questions you have on our social channels. Thank you for reading SCW!
-SA

Good evening from Southern Connecticut Weather. 

After a fast start to winter in early December and a thaw during the middle of the month, we are looking at a potential winter storm bringing some impacts to parts of Connecticut to end this month. This is a complex system, and will pose quite a forecasting challenge, so as you read the discussion below I encourage you, especially if you live in northern Connecticut, to remember that this is a forecast that will evolve. Let's dive in. 

Here is our ice accretion map for the coming system. We are not expecting accumulating snowfall. Note, as currently forecast we are expecting most to receive icing on the lower end of the forecast, especially for central and southern portions of the icing zones. For southern Connecticut, only rain is expected. 

As mentioned in the title, the northern four counties are under a Winter Storm Watch. Even in these areas, not all locations will receive warning level icing of .50". In fact, as currently projected, I think the majority of folks fall below that threshold. 

Overview
A strong area of low pressure that is developing in the Midwest will cut to our west over the next 24 to 48 hours. Tomorrow will be fine most of the day, and by the late afternoon and evening we will see warm air overrun colder air at the surface as high pressure builds in. This system is a bit different in the sense that just about everyone may start off with a cold rain, and then as colder air advects into New England we see a switch to mixed precipitation of sleet and freezing rain in our highlighted areas. Late Monday we will see this low "redevelop" off the coast, but with a poor airmass it is not looking like we see a flip to snow but rather a potential period of more widespread mixed precipitation. The storm should be over by the Tuesday morning, and while there might be some lingering showers and snow showers, New Year's Eve activities look fine statewide. 

There is significant uncertainty that remains over how far southwest that cold air will filter down into Connecticut. That will not be resolved tonight, and will need to be monitored closely over the next 24 hours. 

Above is the latest high resolution NAM depiction of the storm from about 7pm tomorrow through approximately 1am on Tuesday. Despite the lack of mixed precipitation verbatim on the surface depiction, we are expecting more wintry precipitation because of how guidance tends to underestimate surface cold in these situations. I think freezing rain is most likely because of a relatively thick layer of above freezing temperatures in the column. 

Impacts
Icing--No Impact Southern Connecticut/Low-Moderate Inland  
There is no impact expected in southern Connecticut when it comes to icing. For our glaze and .10" inch zones, we are expecting a low impact, and in the hilly sections of NW and NE CT we are expecting more of a moderate icing impact. Again, we expect most to fall on the lower end of our zones as of this discussion. We have the higher zones in case we trend at the last minute toward a more impactful event. 

Wind--None
I do not expect any significant wind with this storm. 

Power Outages--Low
If we see higher icing occur in northern CT, there may be some isolated to scattered power outages, but currently I am not expecting a high end event. 

Timing--Low 
The storm starts on a Sunday night and although Monday's morning and afternoon commute could be impacted, with kids at home for vacation and many workers doing the same, the roads should be less congested and our crews should be able to keep up with any mixed precipitation that falls outside of the elevated areas of CT. 

Road Conditions--Low 
In areas where it's just rainy, the normal level of cautions should be exercised. In areas of central CT that do not receive a lot of icing, you should be careful but I expect main roads to be passable. It is the areas that receive prolonged icing that will have a higher (moderate) impact. 

Overall, this system will have no winter weather impact in southern Connecticut and a low to moderate (in hilly areas in particular) inland impact. Stay tuned for our forecast tomorrow as we expect details to be sharpened as we get closer to the event. 

A​s always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.

Thank you for reading SCW. 

-DB​ 

Disc: With a winter blast in place across the region and bitter temperatures outside after snow squalls yesterday and a significant ice storm this week, many will be happy to hear that the pattern will relax for a while.  But it does not look like winter is over.  Of course, being that it's only the 3rd week of December, it usually is not over at this point.

Currently: Arctic high pressure over the Appalachians is in control of our weather today.  This will keep very cold temperatures over the region the next few days, with a small moderation trend.  This will also shield the region from a coastal low, that will remain hundreds of miles out to sea, thanks to the high pressure.

Tonight: With warm air advection commencing, I will go with the warmer NAM MOS guidance for tonight.  Under clear skies, temperatures should only fall slightly, with lows generally in the teens.  Although a few single digits are possible in the NW hills.

Tomorrow: I'll go with the cooler GFS guidance for tomorrow's highs.  With most areas still with at least a little snow and ice on the ground, temperatures should struggle to rise.  Expect highs somewhere around the freezing mark for most places.

Tomorrow Night/Saturday: The combination of one final small push of cold air advection and some high clouds spreading in from the coastal low well to our southeast (although high clouds is all we will see), I'll go a degree or two below all guidance.  High temperatures should be strikingly uniform, given that the clouds will be thicker to the south.  I'll go with highs of 30-35.  Although it is possible that I could be a bit too cool if the coastal low goes further south than expected.  But for now, this looks like the best way to go!

Long Term (Sunday and beyond): Look for normal to above normal temperatures and fairly tranquil weather (at least no large, deep storms) during this period. I am not going to write a very long discussion, when there really isn't all that much to talk about.  So let's take a quick look at the dailies.

Sunday: Despite warm air advection and sunshine, surface albedo and a lingering bitter air mass do not usually promote warming as fast as the GFS statistical guidance thinks it's going to happen.  Therefore, I'll go a few degrees under MOS guidance and call for low 40s for highs.

Monday: On the other hand, Monday looks to feature plenty of sun again, along with some downslope flow.  This presents itself as a good opportunity for temperatures to rise.  In addition, being the 2nd day with a warmer air mass in place lends itself to being able to warm much more easily at the surface.  Therefore, I'll go a couple degrees above guidance on Monday.  I'll call for highs in the mid 40s.  A few places in the I 91 corridor may get into the upper 40s!

Tuesday: Clouds may increase a little, but no precipitation is expected. I see no reason at all to quibble with temperature guidance and will just ride it.  Expect highs in the mid to upper 40s.

Wednesday (Christmas Day): Now for Christmas Day, I don't see any reason to go as warm as guidance is advertising.   There will be more clouds and a slightly cooler air mass aloft.  So I'll undercut guidance by a few degrees.  This results in temperatures almost exactly the same as those on Tuesday.

Finally for Thursday, I'll undercut guidance fairly significantly here.  With pcldy/mcldy sikes and a developing NE wind, I can't see how we get nearly as warm as MOS indicates.  I'll go with highs in the low to mid 40s.  The only caveat is that we get a bit more sun than I am expecting.  Then we could be a few degrees warmer than what I am forecasting.  

One more addition to the long term forecast, an Alberta Clipper system looks to pass over the region later Thursday into Friday.  Right now, it looks like the most this system will produce for the state is light rain showers, gradually transitioning to sleet or snow showers later Thursday into early Friday.  However, there has been a trend in some of the modeling to develop a coastal low near Cape Cod on Friday.  This location is probably too far NE to affect most of the area, some models do give NE CT a period of decent accumulating snow on Friday, so this could be something to watch.

Looking into the long range, the long range is a bit muddled today, but most LR models are at least hinting at something of a pattern change in the long range, back to something more wintry, perhaps centered around or just after the New Year.  We are also getting into the time of year where you don't need a perfect setup to get a moderate winter weather event.

Now, let's take a graphical look at some of the features affecting our weather in the near term.  Since we don't have a whole lot going on, I'll post the low temperatures for tonight and then a quick look at the day 7 Miller B potential (although it is day 7 and models are bad at resolving a situation like that on day 2), but there really isn't that much to post about.

This map shows the entire state in the teens. I think these temperatures may be a degree or two too warm, since they're an hourly snapshot, rather than min temps,  But you can get an idea.

​

Finally, on this map, you can see NORLUN trough development bringing accumulating snow to NE CT.  Please keep in mind, that this type of a feature has poor accuracy scores inside 60 hours, so we're not talking about something that's easy to forecast.  But then again, there isn't much else to talk about.

​

Anyway, that's all for now! See you next week and have a great holiday season!

-GP!

Good evening from SCW. 

As expected, Winter Weather Advisories now cover the entire state, as our third winter storm of the last two and a half weeks approaches Connecticut. This is expected to be another moderate to high impact event, with high impacts for areas away from the immediate shoreline. In fact, some schools and school districts are beginning to close, and I expect widespread cancellations tomorrow across the state. 

This is not a snow dominant event, but rather a mixed bag storm where we have an elevated risk for significant icing away from the shoreline.

Above is our snowfall map.

• The 1-3 and 2-5 inch ranges cover total snow and sleet accumulation. 
  
  
• There is special text that shows our expectation of a glaze of ice along the shoreline and between .25-.50 inches of icing for interior Connecticut.
  
  
• Greater icing will be toward southern portions of the purple zone, while higher snowfall/sleet accumulations will lie toward the northern end of the purple zone. 

The Setup
Overall, there is no change in the synoptic look of this event. High pressure has established itself over our region, which will lock in low level cold as a surface low develops and passes to our south. As the precipitation advances this evening, snow will begin overnight. This is a Cold Air Damming situation (CAD) where surface temperatures will be hard pressed to rise above freezing (especially in the valleys) even as the upper levels of the column warm above freezing. 

Timing
For most, the snow will begin in earnest after midnight. The exception is SW CT where things may begin an hour or two before midnight. As warmer air filters into the column above the surface, we will see a gradual transition across the state from snow to sleet and then freezing rain. Along the shoreline, this transition will be relatively quick. Eventually, the immediate shoreline may change over to plain rain during the late morning hours. This is not a reason to let your guard down though, as just a degree to two will make the difference between a cold rain and additional freezing rain that could bring a little more than a glaze.  

For inland areas, we are looking at the greatest impacts taking place during the morning hours, with moderate to briefly heavy snow early in the morning transitioning to sleet and then freezing rain. Inland areas are unlikely to go above freezing. How quickly the transition from sleet to freezing rain is critical, as icing becomes more significant with more prolonged freezing rain. Interior areas of southern Connecticut are at the greatest risk of prolonged freezing rain, while northern areas of CT are more likely to see more snow and sleet. 

Mixed precipitation is likely to continue in Connecticut throughout the day, though there will be periods of lighter precipitation. This may actually work against interior CT, as freezing rain generally accumulates more efficiently on surfaces during lighter periods. This is why widespread cancellations, rather than delays, are now expected. 

Above is the latest high resolution NAM depiction of precipitation from approximately 1am to 7pm Tuesday. Note how the state starts off as moderate to heavy snow, followed by a period of mixed precipitation. The rain is confined to the shoreline, and it will likely be the case that just a few miles inland we see icing. The afternoon brings lighter precipitation, but impacts are still likely. 

Impacts
Let's break down the impacts in more detail. 

Snowfall Accumulation--Moderate
If you could have a scale within a scale, this would be on the lower end of moderate. With an upper end of 5" expected and the vast majority of the state below that number, snow is not the story. Sure, some isolated locations may produce a 6 spot, but my belief is that the transition happens quickly enough where we don't get too far over 5 inch maximums in the state. 

Snowfall Rate--High
Although snowfall accumulations will be relatively low, I do expect a period of moderate to heavy snow, with a period of moderate to heavy sleet. That will make road conditions, especially in the morning, an issue statewide. 

Icing--Moderate
There is an elevated risk of a significant icing event, especially when it comes to freezing rain. We really see major issues when there is more than .50 inches of freezing rain accretion, but that is the higher end of our forecast. Issues are expected well below that threshold. Some guidance has shown much more freezing rain, but due to questions over how efficiently ice builds in this case in a few hours, we are not projecting over .50 inches of icing. This is something to watch closely. 

Wind--Low
I do not expect much wind with this storm. 

Power Outages--Low
I am tempted to go moderate here, but I think any power outages are more isolated to scattered rather than widespread. If there were more wind, I would be more concerned. In fact, there may be issues after the Arctic front if the ice hangs on through late Wednesday. 

Timing--High 
The timing is terrible. The heaviest is likely to fall during the AM commute, and mixed precipitation is likely to continue for most through the day, even as it becomes more spotty/lighter. 

Road Conditions--High
The combination of moderate to heavy snow to start and then prolonged temperatures below freezing as mixed precipitation continues through the day has me inclined to call this high impact, though with so many cancellations expected I think road conditions may be better than if so many were out and about. It's certainly a bad day to be on the roads. 

Overall, this is another moderate to high impact event, this time due to timing and the potential for icing. We will be providing updates throughout the storm. 

A​s always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.

Thank you for reading SCW. 

-DB​ ​