Light to Moderate Snow Across CT Tuesday Afternoon into Evening

Embedded pieces of shortwave energy in a fast jet stream flow aloft are set to dive south of CT during the afternoon and evening hours Tuesday.  In response to this energy an area of surface low pressure will develop and will produce a several hour period of light to moderate snows:

  While we aren't expecting a great deal of snow, the timing of the snowfall (afternoon through the evening hours) will yield a rather slow afternoon rush hour commute which will lead to numerous delays.  Extra care should be taken if out traveling.  There are some differences, however, in our computer forecast models on some features of the system and with that we see some differences as to the extent of the water liquid equivalent which will fall.  While the NAM, GFS, and European computer forecast models all agree that a weak area of surface low pressure will develop and pass just to the south of CT, there is disagreement with a potential feature called an inverted trough.  Typically, in the northern hemisphere, troughs are characterized by a southerly "bulge" or dip in the jet stream or height contours.  An inverted trough is characterized by a northerly bulge in the jet stream or height contours associated with a low pressure system or when height contours have a westward kink in them.  The NAM computer forecast model is a bit more more prominent than the GFS computer forecast model and much more prominent than the Euro computer forecast model and thus indicates a higher likelihood for a longer duration of moderate snowfall:

 With this system being on the weaker side we will not see a fully mature system develop and with this the degree of mid-level lift will not be all that intense.  The majority of the lift will be due to low-level processes with the main contributor coming from surface and low-level convergence.  One factor that will preclude the potential for heavy snowfall and higher accumulations will be the lack of solid snow growth.  Taking a look at the 12z NAM and GFS computer forecast model bufkit profiles for over Waterbury, CT we can see that the dendritic snowgrowth zone is not between the optimal height levels of 12,000' and 18,000'.  In fact, the zone is between about 8,000' and 13,000'.  While the NAM computer forecast model shows some pretty decent upward vertical motion (suggestive of good lift) and this vertical motion intersecting the dendritic snowgrowth zone (the GFS isn't as impressive with the degree of upward vertical motion) along with the -15C temperature contour dissecting this zone, the fact that the dendritic snowgrowth zone is so shallow will preclude the giant snowflakes which accumulate quickly from developing in the upper atmosphere.  This means we will see snowflakes which are mainly on the smaller side.  Snowgrowth is optimized when the dendritic snowgrowth zone is positioned between 12,000' and 18,000' and strong upward vertical motion is present within this zone with the -15C isotherm dissecting through this zone:

What can we expect tomorrow?  Light snows should begin to breakout sometime during the early afternoon hours with intensity beginning to vary between light and moderate through the rest of the afternoon hours into mid-evening.  While snowfall rates should not be all that heavy (at most 0.5'/hr) the timing of the snows will still yield to a slow afternoon and rush hour commute leading to delays.  Snowfall amounts should generally range between 1-2'' state wide (perhaps some mixing with sleet or rain along the immediate shoreline if the system tracks a little further north) if the inverted trough feature becomes as established as the NAM suggests and/or the system tracks further northward, some areas could pick up as much as 3-4'' of snow.  This will have to be watched closely over the next 24-hours.  Below is my snowfall map:

Nor'easter to Impact Connecticut Tonight into Tomorrow

Quite the complex forecast for later this evening through the overnight hours as a potent nor'easter will bring some heavy rains, including some snow/sleet and perhaps freezing rain for interior CT and especially the extreme western portion of the state and NW hills.  In addition to rain and wintry precipitation, there will be a period of strong to perhaps even damaging wind gusts, especially along the CT coast along with some coastal flooding as well.

As of 7:00 AM EST this morning, a potent piece of shortwave energy was located down across the southeastern United States and was beginning to work northeastward along the eastern seaboard.  This piece of shortwave is quite potent and that is indicated by the closed-off nature of the low (indicated by the highlighted circles (height level of the 500mb level):

Leading up towards today, computer forecast models somewhat varied as to what exactly would happen with this piece of energy as it moved up the east coast towards southern New England.  A few computer forecast models actually began to weaken the energy allowing it to not be closed off anymore (called an open wave).  Over the past day or so, computer forecast models have actually come into better agreement that this will not actually happen and the energy will remain closed off (albeit begin to slowly weaken) as it passes just to the south and east of southern New England.  This will in fact work to keep the system a bit stronger for a longer duration and enhance the likelihood for heavier precipitation to build into CT along with potential for stronger winds as well.

One of the biggest concerns and questions with regards to this system will be the temperature of the thermal profile throughout the atmospheric column.  Even as off midday Monday, there are still some disagreements within the computer forecast models as to the strength of the warm air advection which will occur.  This issue, however, is likely more of a concern for areas north and west of I-84.  This also includes much of interior Farifled county, all of Litchfield county, and Hartford county for points north and west of Hartford.  Too illustrate, let's take a look at a bufkit profile for Windsor Locks, CT from this mornings runs of the NAM and GFS computer forecast models.  The NAM bufkit is plotted for midnight tonight while the GFS is plotted for 11:00 PM.  Notice how there are several MAJOR differences with the thermal profile throughout the atmospheric column:

This right here could be the difference between say about 2-3'' of snow for parts of northern CT and the difference between very little to no accumulations and mostly rain.  When looking at the two models and the differences, however, we can try and use some meteorological knowledge to decipher which model may be hedging towards the right direction.  For one thing, it is not very common to see the NAM forecast model actually being not only warmer but a solid deal warmer than the GFS computer forecast model but that is the case here.  There are some signals, however, which may suggest that the GFS computer model may sniff this one out and we will explore that below.

With the system still relatively strong at 500mb the response will be for the strengthening of the lows at 925mb, 850mb, and 700mb as the system works just south of CT.  Looking at the 850mb level we see the low beginning to close off east of NJ later this evening.  As long as this strengthening occurs and continues to occur dynamic cooling will be present within the middle and lower levels of the atmosphere and this will help to keep temperatures cooler and support more in the way of wintry precipitation, especially initially for inland and western CT.  However, with the track of the low expected to be close to the CT coast this will eventually usher in milder air and a transition to rain will occur.  It is certainly possible, however, that extreme NW CT could remain mostly all snow for the duration:

Associated with this system will be some very intense lift and this is evident by looking at 700mb vertical velocity values.  The shadings of yellows and reds indicate some very strong lift will move over the state during the late evening and early overnight hours and this will coincide with the heaviest of the precipitation:

This degree of lift is something we need to watch as well for the northwestern part of the state where there is more of a likelihood for accumulating snow and perhaps several inches.  A bufkit sounding from this mornings run of the GFS forecast model for a station in the NW corner of MA (right along MA border) shows excellent snowgrowth (you want the purple/yellow contours to be between 12,000' and 18,000') and decent upward vertical motion (red contours) intersecting this zone which indicates sufficient lift into this zone to produce dendrites (the type of snowflakes that accumulate the most quickly).  The issue of course will be whether the thermal profile remains cold enough to support all snow here and if so several inches of snow across the NW corner is definitely plausible:

As we head into the evening hours we have seen some light pockets of snow/sleet mix work into the state and this will be the theme over the next 3-4 hours before steadier and more heavy precipitation begins to work into the state.  Expect the heaviest of the precipitation to occur anywhere between 10:00 PM tonight and 4:00 AM tomorrow morning.  In addition, winds will continue to remain gust through the rest of the evening and overnight hours with winds of 25-35 mph and gusts upwards of 45-50 mph inland and as high as 55-60 mph along the immediate coastline.  This could yield pockets of isolated power outages.  The system departs off to our northeast tomorrow, however, we will be left with residual clouds and spotty showers.  Below is what I am thinking in terms of snow/sleet accumulation:  

Thursday Storm Update

Yesterday I had made a snowfall forecast and I'm just going to be flat out wrong, especially down across CT.  I jumped the gun too quickly and should have never made an initial forecast with snowfall amounts that high.  It was virtually irresponsible thinking on my part and knowing the red flags I should have been more conservative with my amounts.  Typically when going on the heftier side of amounts, I like to see a tremendous amount of consistency and agreement within the data and that was not the case.  With this said I will be reducing what I am expecting in terms of totals.  

When composing my initial forecast I thought there was credibility that we would see the system really strengthen off the NJ coast and continue to do so as it pushed up to the north and east.  While this would have initially pumped in some warmer air, the rapid strengthening would have led to dynamic cooling which would have quickly cooled the atmosphere and we would see a quick change back to snow and heavy snow.  This scenario, however, does not look like it will happen.  Instead, what we will see if the system strengthen as it's moving up along the SE MA coast and this will mean a massive snow event for a good part of northern New England.  

The highest snowfall totals look to occur across western portions of MA, perhaps down into extreme NW CT.  This is where the latest NAM and GFS computer forecast models indicate this is where the most intense lift will occur.  In this area during the height of the storm, snowfall rates could approach 1.5''/HR and perhaps even as much as 2'' per hour:

Down across the state of CT with the system tracking very close to the coast and no high pressure to the north to secure cold air in the lower levels of the atmosphere and down at the surface we will see warm air quickly surge into CT.  Colder air will remain in place a bit longer across NW CT and the hills of NE CT and this is where the higher totals will occur in the state.  

As the main surface low passes pretty much over CT and tracks northeast, it will begin to strengthen and a closed off circulation develops over the state of RI, this track will mean warmer air also surges northward into east-central and eastern MA so these areas will begin to transition over to rain as well.  West-central and western MA should remain mainly, if not, all snow and this area will receive the higher amounts.  

Down across CT, precipitation will begin between 9:30 AM and 10:30 AM and outside of the southern part of the state, precipitation will start off as snow and quickly change over to rain.  Expect precipitation to begin across RI and MA in the late morning to very early afternoon hours (developing from the SW first and working NE).  Winds will also become strong as well, especially across MA and perhaps RI as well where gusts of 45-55 mph will be possible leading to isolated pockets of power outages.  The precipitation begins to taper off across CT during the early evening hours and it is possible that the precipitation may even end as snow across parts of northern CT.  This could lead to an additional inch or two across some parts.  Across RI and MA everything begins to taper down during the mid-to-late evening hours.    

Below is my updated snowfall map...yes a far cry from what I was expecting yesterday afternoon:

Major Storm Expected on Thursday

We are tracking yet another storm system to impact southern New England during the day on Thursday lasting well into the overnight hours but there continues to be some uncertainties within the computer forecast models and that does lead to a challenging forecast at this time.  A couple of our computer forecast models are in agreement that as the system works up just off the coast that it will undergo rapid cyclogenesis (strengthening) and become quite a powerful storm.  Meanwhile, some other computer forecast models aren't as impressive with the system and have a much weaker and faster system.  If this isn't tough enough there will be a bit of uncertainty as to exactly where the rain/snow transition line pivots and this is critical because it could mean the difference between only maybe 1-2'' of snow and perhaps as much as 6-7'' of snow.  These details should be ironed out over the next 24-36 hours.

Both the NAM and European computer forecast models are actually in fairly good agreement with each other on a rapidly intensifying storm system just off the coast.  Unfortunately I am not able to post Euro images, however, I can go ahead and post some graphics from the NAM.  The 12z run of the NAM from the 27th of December shows a very strong piece of shortwave energy just south of southern New England by 7:00 PM EST Thursday evening:

The forecast is for this piece of shortwave energy to continue pushing to the northeast and undergoing further and rapid strengthening.  The image below is a forecast for 1:00 AM Friday morning:

This will allow the entire system t rapidly strengthen so the response will be a rapidly deepening surface low pressure and closed off circulations at 925mb, 850mb, and 700mb:

In comparison, the GFS computer forecast model valid for the same forecast time shows a weaker system than the NAM and Euro and actually doesn't really begin to strengthen the system until it reaches the Gulf of Maine. Also note how much quicker the GFS is than both the other models:

Each of these forecasts presents a different set of solutions that we could potentially see.  The GFS forecast model also tracks the system pretty much over southern New England.  What this does is allow much warmer air to work into much of the region within the lowest 3,000-4,000' of the atmosphere.  This would eventually lead from a transition from snow to sleet/rain across many locations, particularly south and east of the MA Pike.  The NAM, on then other hand, also brings in some warmth ahead of the system.  This is due to the fact that it rapidly strengthens the system well to our south and since the track is tucked closer to the coast warm air floods in ahead of the system.  However, as the system rapidly intensifies and develops those closed off circulations (and the track is just to our south and east), this induces what is called dynamic cooling and will help to rapidly cool off the lower levels of the atmosphere.  This would mean MUCH more snow for a larger chunk of the region (with the exception of the south coast where the track would still drive in warmer air here).  This is what we need to watch over the next 24-36 hours.

One thing presented on all models is the possibility for a period of moderate to heavy precipitation (whether it be snow or rain).  The GFS has a much shorter window for this probability than the NAM or Euro.  Taking a look at some bufkit profile soundings from the 12z NAM for a few select locations across southern New England we see

1) Snnowgrowth zone positioned right between 12,000 and 18,000' (purple/yellow contours)
2) Strong upwards vertical motion present within this zone (the red contours with negative values)
3) -15C temperature contour crossing through this zone (thin yellow line running horizontally)
4) High relative humidity values within this zone (not shown below as it would look too "messy")

All four of these combined indicate that the potential exists for moderate snowfall accumulations to occur for any areas that remain all or mainly snow.  The NAM shows INCREDIBLE upwards vertical motion across eastern portions of southern New England including the Boston area:

If the NAM/European computer forecast models are correct we would see a very intense band of snow setup just to the northwest of the tracks of the 925/850/700mb lows and this is where the axis of the highest snowfall totals would occur.  Snowfall rates could approach 1.5'' per hour and we would also be looking at the potential for strong winds as well with gusts as high as 40-50 mph.  Given the degree of lift and even some weak instability thanks to presence of steep mid-level lapse rates, some thundersnow can't be ruled out wither which would locally enhance snowfall rates as well.  If the GFS is correct we would be looking at a much weaker system across southern New England with not as much impacts.  Northeastern MA into northern New England would now see the higher impact as the system strengthens as it moves into the Gulf of Maine.

As of right now, given the consistency of the Euro/NAM thus far and the GFS has seemed to trend a bit in the direction of the Euro/NAM, I am leaning more towards a solution depicted by the NAM/Euro.  This of course can easily change as if they are too quick with the strengthening of the system we see higher likelihood for warmer air to invade.  So this what I'm expecting:

• Snow begins in the mid-to late morning hours, especially across CT and parts of RI and early afternoon the further north into MA one goes.  
• Snow may transition over to rain briefly, especially the south coast, as warmer air initially moves in ahead of the strengthening system
• Rain will then begin to transition back over to snow as the system strengthens and dynamic cooling cools the atmosphere aloft.  The coast, however, will remain more rain
• There will be a zone through the system as well in which snow transitions between sleet and perhaps some freezing rain.  This will be the cutoff between the higher and lower snow totals
• During the height of the storm winds could increase to 40-50 mph causing isolated pockets of power outages
• Snowfall rates could approach 1.5'' per hour and perhaps as high as 2'' per hour if there is any embedded thundersnow 
• The precipitation begins to taper off during the overnight hours of Thursday into Friday.
• Thursday rush hour commute looks to be very bad so expect a very slow commute with numerous delays.  

Below is my initial snow map but there is not a high amount of confidence with this due to concerns mentioned above.  Typically I would be more shy than not in going with lower snowfall totals, however, when the NAM and Euro tend to be in agreement more times than not that is a very good indication of what will verify.  This doesn't always work but as of right now I would lean this way:

Active Weather Period Over the Next 96-Hours

We are in store for one helluva roller-coaster ride weather wise over the next 96-hours and that ride begins well as I speak.  A powerful Arctic cold front is set to push through southern New England later on this evening and as this front plows through temperatures will really bottom out as lows tonight will be in the single digits to around 0 and even maybe slightly below-zero in some spots and that's without the wind chill.  While it has been quite gusty today the core of the strongest winds have yet to arrive.  There are some differences within the NAM computer forecast model and GFS forecast model as to what the higher end of the wind spectrum may be, however, both models are very impressive with the maximum wind gust potential.  Looking at some bufkit soundings from the latest afternoon run of the 4km NAM model across some selected locations across southern New England (Windsor Locks, CT, Worcester, MA, and Chatham, MA) the 4km NAM is suggesting that the maximum wind gust potential could be as high as 70-80 mph late this evening.  With this range we are talking about minimal category one hurricane-force gusts.  The NAM also has the profile mixing nearly dry adiabatically up to about 9,000' (~700mb) which is incredibly impressive.  Given how this may be a tad overdone and we have to consider friction, the extend of these winds are possibly a bit too high, however, 65-75 mph wind gusts are certainly possible and this is what the GFS model indicates for highest gust potential:

(NOTE:  I only showed 18z NAM bufkit soundings...even though the winds atop mixing layer are probably overdone b/c this was latest data available as 18z GFS bufkit was not out)

With winds increasing further this will not only set the stage for the possibility of scattered to numerous wind damage (downed trees/limbs and power lines) but with temperatures dropping further we will be looking at very dangerous wind chill values which could be as low as -10F to -20F.  Values these low can lead to frostbite in a short amount of time for any exposed skin.

While high temperatures on Friday will be much colder than today (not getting out of the teens in many locations) the winds will not be as strong as today, however, gusts could still get into the 20 mph range and we will once again deal with near dangerous wind chill values (as low as -10F).

One other note of interest with this brutal Arctic airmass is how close to the ground the stratosphere will be.  This point-and-click forecast sounding for a location in western MA for about 10:00 PM tonight morning shows the tropopause (layer which separates the troposphere from the stratosphere) being only around 9,000'-10,000ft off the ground...very impressive for these parts:

This brutal Arctic cold blast will be quite short lived, however, as late Friday night into the early part of Saturday our next weather system begins to impact the region.  Like with last Sunday into Monday we will once again see a developing storm system track well off to our north and west and this means we will eventually warm things up (and actually quite substantially) but before that happens we will have to deal with quite the wintry mess.  We are looking at accumulating snows for pretty much everyone (with the further north you go into southern New England the higher the potential totals) before everyone eventually transitions over to some sleet, freezing rain, and then some rain and then temperatures begin spiking up all the way into the 40's, 50's, and maybe even near 60F in some spots before the cold front pushes through Sunday night and some much colder air filters back in.

Given the extent of the airmass we will have in place it will take some time to really get the surge of warmer air into the region, thus we will begin as snow.  As always with these setups, the biggest question is how quickly does the warm air move in and how much precipitation falls as snow?  By 7:00 AM EST Saturday morning some shortwave energy moving through the jet stream aloft will be just off to our west which will help enhance the degree of atmospheric lift.  At the same time we'll have the main surface low pressure well off to our west across the Ohio Valley region:

  Due to the fact there will be no amplification of the jet stream/short wave energy (the short wave energy is also not really consolidated and compact) the system isn't expected to strengthen all that much and most of it's strength will really be from the influx of warmer/moist air from the Atlantic Ocean and cold dry air working around the backside of the system (creating a good thermal gradient which helps these systems intensify) so we aren't really looking at a powerful system.  In fact, the system may begin to weaken which will ultimately shut down the influx of warmer/moist air into the storm and the precipitation will begin to "shut off" and the axis of heavier precipitation moves off the coast:

Region wide temperatures will be certainly cold enough for precipitation to begin as snow and the first flakes should begin to fall during the overnight hours of Friday into Saturday (between 1:00 AM and 4:00 AM).  There will be some dry air in place initially, however, the profile will begin to saturate rather quickly.  As we move through the early part of Saturday morning some stronger atmospheric lift will push into the region and with this we will see periods of moderate to perhaps even some heavy snows.  At the highest snowfall rates may approach 1'' per hour and given we are looking at snowfall rations perhaps as much as 15:1 the snow will be quite fluffy and will accumulate rather quickly.  Looking at some bufkit profiles for a few locations across southern New England, initially snow growth may not be the greatest but they quickly become better (you want the yellow contours to be right between about 12,000-18,000ft with the -15C isotherm running through it ).  This is great for developing those fluffy flakes.  The next thing you want is to be able to lift parcels/moisture into this region and for that we look for those thin red contours (omega) which indicate vertical lift.  The more contours (and negative the number) the greater the lift.  Looking at these soundings we do have some red contours intersecting this great snow growth zone, however, not a great deal of red contours.  While lift will not be extremely heavy (this will preclude rates exceeding 1'' per hour) it will be sufficient for a period of moderate to perhaps heavy snow:

By early afternoon, however, much warmer air begins to filter into the region and as this warming occurs we will see a transition from snow to sleet/freezing rain, then rain beginning from south to north:

With all this said this is what I am expecting for snow.  Keep in mind that mainly everyone south of the MA Pike (and even a bit north of the Pike) will eventually transition over from snow to rain.  While some areas will see some freezing rain this should be be a major concern as the stay will be brief:

We aren't done just yet!  As Saturday progresses, we will continue to see a very strong push of warm-air advection, both at the surface and in the lower-levels of the atmosphere.  In fact, overnight Saturday into Sunday temperatures about 5,000' off the ground will be approaching the 50F mark and we will feel this warmth at the surface as well with temperatures rising into the 40's/50's and maybe near 60F in spots by 7:00 AM EST Sunday morning:

This warmth arrives just ahead of another cold front which will push through sometime mid-to-late afternoon.  With the warmth, however, just ahead of the cold front we will deal with yet another period of moderate to perhaps even heavy rain and we can't even rule of a thunderstorm as well, especially if some low-level instability develops thanks to the surge of warmth/moisture in the lower-levels of the atmosphere.  Once the cold front passes through we are back towards cold temperatures with overnight lows Sunday into Monday back into the teens/20's and high's on Monday only into the 20's.  This is certainly going to be a roller-coaster of a ride and certainly some active and very interesting weather!

Active Weather Pattern Continues With Arctic Blast

We have certainly entered a much more active weather pattern as of late and this looks to continue.  As we move through the next week not only will the weather pattern remain quite active but it will be rather bumpy with some pretty significant temperature trends.

First off, we will have a weak storm system which will affect southern New England tonight.  An area of low pressure will be developing off the coast of the mid-Atlantic and slide to our south and east.  At the same time an upper-level shortwave trough will be passing by off to our northwest.  This scenario will set the stage for some light snow showers, especially down across CT during the evening/overnight hours.  No accumulations are expected, however, some areas could get a coating of snow, especially if the low tracks a little further north.

Perhaps the biggest story over the next several days outside of the storm potential on Saturday will be extreme cold for this time of year.  An arctic cold front is expected to pass through southern New England late Wednesday evening and may be accompanied by some snow showers.  This will usher in some more cold air.  However, on Thursday a much stronger secondary cold front pushes through the region and this will usher in some extreme cold for this time of year.  While Wednesday night and Thursday will be quite cold, we feel the brunt of the cold Thursday night, Friday, and Friday night ahead of the next storm system.  In fact, computer forecast models are forecasting temperatures at 850mb (around 4500-5000') to be around -20C to -30C 7:00 AM EST Friday morning.  That is quite exceptional for this time of year:

This will yield overnight lows Thursday into Friday down into the single digits and perhaps even below-zero across the typical coldest locations.  Highs on Friday may even struggle to get out of the low 20's across many places and some spots could fail to reach 20F.  In addition to this cold we will have to deal with some pretty strong winds as well so windchill values will make it feel like it is well below-zero at times.  By Saturday things begin to change ahead of our next weather system and that looks to pose a bit of a mess, perhaps similar to what we dealt with Sunday night into Monday.

An area of surface low pressure associated with some shortwave energy will be tracking across the Great Lakes late Friday into Friday night.  As this occurs, a warm front will begin pushing northward towards southern New England.  As the warm front approaches we will see an increase in isentrpic lift associated with the warm front.  There are questions, however, with how much moisture we will have in place as the airmass will be quite dry, however, computer forecast models do show some saturation of the atmospheric profile so we may see a period of light snows develop overnight Friday.  Given how cold the airmass and ground will be snow will have zero problem sticking.  Given how the snows will be low-level produced the flakes should be tiny and we won't see heavy snowfall rates so these won't produce any big totals (maybe 1-2'').  The initial surge of warm-air advection at the surface may be rather slow through the first part of Saturday.  This is due to the possibility of a wave of low-pressure developing along the warm front:

Given how extreme the cold will be in the lower-levels of the atmosphere the warm-air advection early on will be rather weak as well until the low-level jet begins to increase and that will really accelerate the northward progression of much warmer air.  This is huge because this means a much longer time of the atmospheric profile being cold enough ti support snow.  With this in mind, while it is too early to throw out snowfall totals, many areas may be able to pick up at least 3-4'' of snow before we begin seeing a transition to sleet, freezing rain, and then plain rain.  Areas north of CT into MA have a much higher potential to pick up at least several inches of snow.  By early afternoon the low-level jet at 850mb is expected to reach 50-60 knots and this will vastly work to usher in much warmer air, both at the surface and in the lower-levels of the atmosphere:

 

As we move into Sunday things are looking rather interested ahead of the cold front associated with the low pressure system tracking across the Great Lakes  The surge of warmth ahead of the cold front looks quite impressive and temperatures could soar into the 50's to perhaps near 60F overnight Saturday into Sunday.  Computer forecast models suggest temperatures at 850mb will approach +10C very early Sunday morning:

 
This warmth will be very short lasting, however, as the cold front begins moving through during the late morning/early afternoon hours.  With the approach of the cold front we could see a period of heavy rainfall and perhaps even some thunder.  Once the cold front passes through temperatures will fall back very quickly as lows Sunday night into Monday will only be in the teens across the region.

We will certainly be experiencing some pretty drastic swings in the weather over the next week, especially with regards to temperatures.  For snow lovers, its very unfortunate the cold isn't producing snow, however, this is due to the fact that all the storms are tracking well west of us and that is allowing for warmer air to move in ahead of the storms.

Looking long-term there are growing signs that as we approach the Christmas holiday and first part of 2017 we will see a major shift in the overall hemispheric weather pattern and we may enter an average to even much-above average regime temperature wise.  This doesn't mean we won't see any sporadic cold shots but does mean overall we will be much warmer.  This certainly won't be good news for snow lovers.

Over the next few days as we approach the weekend we should be able to pin down details as to what to expect snowfall wise, whether we'll have issues with freezing rain, and when things transition over to rain.

Quick Storm Analysis

I will say I am pleasantly shocked that some snow has already began to fall across parts of CT and started as early as 2-3 PM.  Granted it was very light snow and tiny flakes but still indeed snow.  My main concern was the dryness of the atmosphere and how long it would take for the atmosphere to saturate .  Taking a look at a forecast sounding from the 4:00 PM EST (21z) run of the RAP computer forecast model timed for about 7:00 PM EST the atmosphere certainly becomes quite close to saturated from about 525mb down to the surface (note how the dewpoint (green) line and temperature (red) line are pretty much touching:

The snow that has been falling is related to the system, however, it's not necessarily from the system.  I say this because the focus of lift is completely different.  The snow which has fallen thus far has been the product of at least these two factors; 1) warm-air advection in the lowest levels of the atmosphere and 2) enhanced low-level lift from the nose of the 850mb jet:

Thanks to a very cold airmass in place and quite the cold ground, despite the fact the snow is falling very lightly and the flake size is very tiny (this is more like snow grains!) it is sticking.  In fact, some areas have a coating on the ground, including at Westside Campus at Western Connecticut State in Danbury, CT!  If there was more in the way of mid-level lift to lift parcels into the mid-levels of the atmosphere we would be seeing beautiful dendrites and big fluffy snow flakes.  Looking at the same 21z RAP we see very good dendritic snowgrowth right in the favorable area for snowgrowth (between -12C and -18C) with the -15C isotherm running right through this zone.  When you have these ingredients in place you get your perfect snowflakes which are big in size and these are the ones that accumulate quickly.  The only issue is there is no lift in this zone.  For upward vertical motion we want to see red contours but we do not have those present into this zone thus we aren't lifting air parcels or moisture into this zone so the end result is these little tiny snowflakes:

Currently the area of surface low pressure which is the main aspect of the system is still well off to our  west over the Ohio Valley region.  This low pressure will continue to strengthen but slide off to our north and west and with this track we will continue to see warm-air advection occur and warmer temperatures filter in.  Until then we will continue to see some snow and later on this evening/early overnight the flake size should increase as stronger mid-level lift slides in.  However, the timeframe for this bigger flake size and heavier snow rates will be brief (especially in CT) and snow totals will be down here.  I see no reason to make any changes to my map fro Friday night: