Active pattern continues; Fast moving system late Sunday through first part of Tuesday

The active weather pattern looks to continue as we move into the beginning of the work week as a fast moving storm system is expected to slide just south of the state.  Unlike the big blizzard several days ago, this system will be moving at a much quicker rate with the duration expected to be less than 12-hours in total.  In fact, the heaviest if the activity will only occur in a 6-8 hour window. 

Computer forecast guidance suggests as this system slides south of the state it will slowly begin to intensify.  With winds in the lower levels of the atmosphere coming from the southeast, this will contribute quite a bit of Atlantic moisture into the system.  With sufficient lift in place, we will see a fairly large precipitation shield develop and with temperatures at all levels cold enough, at least initially, we will see snow break out. 

The first flakes could begin between the hours of 11:00 PM Sunday night and 1:00 AM Monday morning.  By 3:00 AM to 4:00 AM, periods of moderate to heavy snowfall will be occurring across the state and snowfall rates in the heaviest echos will approach 1’’ to 1.5’’ per hour.  We will continue to see moderate to heavy bursts of snow continue up until about 10:00 to 11:00 AM before the snow begins to taper down.  Across southern CT, computer forecast hints at warmer air working in the lower levels of the atmosphere.  This will allow for a transition from snow to sleet and perhaps some freezing rain or even plain rain during the early morning hours, thus cutting down snowfall totals across this portion of the state. 

Due to the timing of the system and the heaviest of the precipitation rates, morning travel will be extremely messy with significant impacts.  Expect numerous delays on the roads and very slow travel.  School closings are highly likely across many towns and cities.

While my snowfall forecast is a bit less than what many others are suggesting, to me there are a few flags which is inhibiting me from going any higher;

1)       The speed of the system.  When looking for snowfall totals approaching amounts such as 8’’…12’’ or higher, one of the main factors to take into account is the speed of the storm.  If you have a storm system moving as fast as this one, you have to ask yourself, how long is the heaviest precipitation expected to last?  What are the projected snowfall rates during this time?  What kind of snow growth are we looking at?  What type of lift are we dealing with? 

2)       There is no established mid-level circulation.  Below is a graphic from today’s run of the 12z GFS.  While I am using the GFS to give a visual, all other significant models are similar.  Having no established mid-level low can make for some not so great lift, especially in the mid-levels.  One way to get excellent snow growth and subsequent ratios is to have the presence of very strong mid-level lift. 

3)       Looking at bufkit profile for Windsor Locks, CT there are some definite flags to me here.  There isn’t a ton of omega (the red contours) and much of the highest values remain outside of the area of best snow growth zone (area highlighted by the yellow contours).  What this says to me is that much of the best lift is all mainly in the lower-levels of the atmosphere and not within the area of best snow growth.  This indicates that overall we will be looking at fairly poor snow growth and snowflakes that won’t be very large in nature…small flakes take longer to accumulate.  This will also lead to some poor snowfall ratios.  However, with this said, some of the low-level lift is rather impressive and this will lead to a very narrow zone of extremely heavy snowfall with much better snow growth and ratios.  Within this zone snowfall totals up to 10’’ will be possible and a 12’’ amount can’t be ruled out. 

With this said, below is my snowfall forecast:

Forecast Busts...Because They Happen!

     While my forecast certainly wasn't the only one that "busted" with regards to the blizzard of 2015, the focus on this piece will be from my perspective, my experiences, and giving a little insight into how forecasts are composed and why they can be so challenging.

     While a busted forecast absolutely sucks, especially when numerous people depend on what you have to say as they pretty much work their lives around what's going to happen with regards to the weather, the most important thing to know when it comes to weather forecasting is that it is an imperfect science.  What does this mean?  In simple terms it just means there is no way to get every forecast 100% right 100% of the time.  There are just too many variables involved within our atmosphere which is incredibly, incredibly complex and these processes don't always work out the way it appears they will.  In some instances, forecasts busts have a positive side to them.  Forecasts busts allow the forecaster to look deeper into what went wrong and hopefully find some clues which can be used in the future.  This is actually one of the most important things in forecasting and one of the key ways a forecaster can better him or herself.

     My Forecast

     Below are the two forecasts maps I created for this storm.  The map on the left was made early Sunday afternoon with the final map, on the right, made late Monday afternoon:

     My thoughts were that very heavy and intense banding would traverse over much of CT with extreme western fringes receiving a tad less and the far southeastern part of the state.  I was thinking the system would track a bit further west than what actually occurred and based on my thinking that would have allowed for that very intense narrow band, called a deformation band, to setup somewhere in western or central CT.  It was the area under this banding which had potential to receive 24-36'' and as you can see last night my thinking was that would be through much of central CT.  Well the system ended up tracking a little further east and this allowed for the heavier banding to not work any further west than the I-91 corridor.  This led to the heaviest snowfall totals occurring across eastern CT with central CT receiving much less and western CT much, much less.  In a nutshell this is how the forecast worked:

 
     Below is a screen shot of the radar taken at 3:18 AM this morning.  The circled area is where the heaviest snowfall and the heaviest banding setup during the overnight hours.  The much heavier more intense snows never really made it west of I-91 and remained just east of a Hartford to New Britain to Bridgeport line.  Once the snow shield hit this corridor it came to a halting stop and overtime slowly eroded to the south and west:

     West of this line we still had moderate to even heavy snow falling, however, snowfall rates weren't much more than 1'' to maybe 1.5'' per hour while across eastern CT, snowfall rates of 2'' to 3''...even 4'' per hour were quite common.  

     All in all a slight track further east than expected meant a further eastward placement of the heavier snow bands and subsequent snowfall totals.  

     The slight track further east also reduced the magnitude of the winds, particularly the further inland you worked.  While too my knowledge I don't believe any official CT reporting station reached official blizzard criteria (official blizzard criteria is sustained winds 35 mph or greater and visibility 1/4 of a mile or less for 3-consecutive hours) blizzard conditions were present.  

What To Take With These Potentially Large Storms

     Any time storms of this magnitude are forecasted the one thing to remember is there will always be a "screw zone"...there is always going to be an area which receives much less snow than forecasted.  As mentioned in a previous post, deformation bands are associated with rapidly rising air which is enhancing precipitation and precipitation rates.  However, this will also lead to an area of rapidly sinking air which works to eat away at precipitation.  Forecasting in advance where both these zones are axes will occur is simply beyond challenging.  Since these bands are very narrow in nature and depend heavily on mesoscale factors, computer forecast models simply aren't precise enough to accurately forecast or predict where these bands will setup.  Usually you just have to wait until the event is ongoing such as last night when it wasn't under after 2:00 to 3:00 AM when it became obvious where the banding would sit and pivot over.  

What Can Be Done Differently In the Future?

     There really isn't a right or wrong answer here.  Each situation is quite unique and brings about its own special challenges.  In the case of this system, there was a great deal of model consistency on a slightly west track meaning much heavier precipitation working well into western CT.  However, at the last minute, guidance began to track slightly east and the track slightly east was just enough to move the heaviest snow into eastern CT.  

     In these situations it can be very difficult to relay information to the general public because people want precise details and they don't want to hear "maybe's" "if this happens"...they want exacts and unfortunately this is a field where you can't always give exacts.  In my opinion, its just best to be as honest as possible, even if it means you're sounding unsure or contradictory or presenting ideas which seem to be from both sides of the table but that's a facet that comes with forecasting.  

     I know when I am looking at computer models and reviewing data and I'm looking at a situation in which it seems possible we could be looking at 12''+ of snowfall I get a little nervous...now imagine a situation like this where numerous data is indicating as much as 24"+...the nerves go crazy.  This is because all it takes is one little thing to go wrong or one slight shift to completely mess up a forecast as a whole.  

     Too conclude, while many across central and western CT did not receive anything close to what was forecasted, many others did.  Going beyond CT, even back across NYC and into NJ the forecast was busted heavily, however, extending into RI and eastern MA, the forecasts were nearly perfect...both with regards to snowfall accumulations, winds, and impacts.  While the goal is to be as accurate and correct as possible for every individual person, sometimes forecasts involve more than just what someone got in their own backyard...the bigger picture can provide a much more telling story.  So while your area may not have had much, there are many who were pounded hard and are dealing with much more in the way if impacts.  Forecasts busts are awful and make a forecaster feel awful, however, at the end of the day that is part of the field and it always will be.  All you can do is keep your head held high and continue to learn as much as possible through experiences and any resulting studies which are done.    

  

Historic Blizzard Underway...CT forecast/discussion update

Just to reiterate from yesterday, this storm is NOT historic in nature because this isn't something we've never seen before, this storm is historic in nature due to the fact of what it will produce, and that's widespread snowfall totals ranging from 1' to 2' throughout New England and extending back through NYC and into portions of NJ...so we are looking at an extremely large geographical area receiving feet of snow.  In fact, some areas, may even close in on 3' of snow!!!

Currently the storm is evolving beautifully!  The circulation is beginning to deepen rather rapidly just off the coast of the Carolina's and you can see there is already an immense amount of moisture available and working into this system:

We have already seen light to even moderate bursts of snow across this state which started in the late morning and early afternoon hours.  These bursts of light to moderate snow bands will continue through the remainder of the evening before snowfall rates substantially begin to pick up after 11:00 PM or so.  Winds have also started to increase and will become an issue overnight as well.  

This will be a very long duration storm with periods of light to moderate snows continuing throughout the afternoon tomorrow along with strong wind gusts.  

What To Expect

Statewide, I am expecting an average of 18-24'' of snowfall..this is an average meaning some locations will end up with more than 24'' and some locations could perhaps end up with less than 18'' (but still more than 12'').  Why is this?  Well when you have these very intense systems you get what is called a deformation band...these bands are notorious for producing very heavy snowfall rates and dropping alot of snow in a very short amount of time.  These bands can be a complicated mess when it comes to forecasting.  The exact placement of them is something that isn't particularly modeled very well and also these bands can sometimes sit over a general area an pivot for hours...this is a situation in where areas can get upwards of 30"+ of snow.  When taking to gauge where this banding may setup we typically look at the 850/700mb levels and look at their low pressure tracks along with vertical velocities.  We will just highlight the 700mb level for time constraints:

The above image is taken from just one of the computer forecast models used for forecast guidance.  However, the consensus is we will see a favorable enough low track to get the deformation band to pivot across CT, however, the question is does that occur across western and central CT or central and eastern CT?  Something we won't 100% know until it gets going, however, at this time I'm leaning more towards the area highlighted in red on the snow map below as the highest likelihood of getting under the banding.  

Another issue the deformation bands present is they also produce something called a subsidence zone...or what we weather weenies call "screw zones".  As Newton once said, "what goes up, must come down" and that's pretty much what this is.  Remember, the very strong lift describe above...that is air rising vigorously...well in response air must sink vigorously.  So typically just to the north and west of this band will be an area of sinking air...this sinking air shuts off or lessens the rate of the precipitation falling...so while several locations are getting creamed, others are getting screwed.  All this means that is there will be some areas that probably receive less than 18-20'' of snow and there is no way to tell where that will happen.  

With this piece of info out of the way let's look at what to expect:

• Snowfall rates pick up as the evening and overnight progresses
• Snowfall rates will approach 2-3' per hour' at times and under the deformation band could approach 3-5'' per hour
• Thunder/lighting possible (also helping to enhance snow rates locally)
• Winds pick up...gusts along the coast approaching 60-70 mph.  Further inland 45-55 mph
• Blizzard conditions expected tonight and tomorrow morning
• Numerous power outages likely due to strong winds and downed trees and utility poles
• Heaviest of the snow occurring between the hours of 11:00 PM and 9:00 AM tomorrow

Below is an updated map.  Keep in mind the 24-36'' possibilities could be shifted depending on the deformation band...where it sets-up, where it pivots, and the duration the band sits over certain areas.

Historic snowstorm Looking Likely 1/26/15 - 1/27/15 Across CT

     A historic snowstorm is set to impact the state of Connecticut beginning on Monday and lasting through at least the first part of Tuesday.  First off, let's briefly discuss what will make this historic.  Snowstorms producing snowfall amounts of this magnitude certainly aren't unheard of around these parts, and while over the past several years we have seen more than a few, getting snowstorms to produce such widespread amounts greater than 12'' and even 18'' over a large geographic area don't happen very often.  Cities such as Boston, Providence, Hartford, and New York City could all be looking at over a foot-and-a-half of snow when all said and done and that's what makes this historic...how such a large area is expected to receive such massive totals.

     We are looking at a very long duration snowstorm to impact the state beginning on Monday and lasting through much of the day on Tuesday.  As the system begins to develop just to the south of CT and slowly sort of slide northeast, the system will stall out.  During this process, the system will undergo rapid cyclogenesis (strengthening), with a great deal of thanks to a strong thermal (temperature) gradient that will be in place in the lower levels of the atmosphere and at the surface.  A strong area of high pressure to the north will continue to pump in very cold air aloft over the state (and this high will also work to keep the storm movement very slow) and warm and moist air working into the storm will setup this gradient.  As the system strengthens rather rapidly, the precipitation field will begin to blossom rather quickly and precipitation rates will rapidly begin to increase.

     The first flakes are expected to break out across the state perhaps as early as noon Monday afternoon.  As the afternoon progresses, light snows will begin to overspread the state, however, snowfall rates should remain on the lighter side.  As afternoon progresses towards evening, we will begin to see more in the way of moderate bands of snowfall begin to work into the state.  As the evening progresses, we will begin to see periods of moderate to heavy snowfall become much more common across the state.  In addition to snowfall rates intensifying, the winds will begin to pick up as well.  The heaviest of the snowfall rates are expected to occur between the hours of 11:00 PM Monday night and 9:00 AM Tuesday morning.  During these hours is when the majority of the snowfall accumulations will occur.  Snowfall rates could approach 2-3'' per hour with snowfall rates up to 4-5'' per hour possible in any bands containing thunder and lightning.  Winds during this time will also become sustained between 25-35 mph gusts as high as 45-55 mph possible.  In fact, coastal CT, especially SE CT, could see gusts as high as 65 mph!  The combination of very strong winds will lead to blizzard conditions at times and will also cause numerous power outages due to downed trees and utility poles.  

   
     While snowfall intensities and rates will be decreasing during the morning hours of Tuesday, periods of light to even moderate pockets of snow will continue into the early evening hours.  Winds will also remain rather strong through much of the day on Tuesday before beginning to subside in the late afternoon hours.

     Snowfall totals may be lower across the southeastern part of the state and far northwestern CT and back in Fairfield county towards New York City.  Across southeastern CT, there may be a pocket of dry air which works in aloft, but this depends on the exact track of the 700mb low.  This pocket of dry air could cut-off snow for a period across this area leading to lower totals.  Back across northwestern CT and southwestern CT, there may be an area of subsidence (sinking air) which cuts off precipitation.  This will occur just to the northwest and west of the heaviest banding that will set-up known as a cold conveyor belt (CCB).  In fact, where this band sets-up and pivots is where the highest snowfall totals will occur and these totals could approach two-and-a-half to three feet.  However, at this time it's very difficult, if not impossible, to determine where this band will setup and we may not 100% know until the event is on-going.  This is due to the fact that they are typically very narrow in nature and our computer forecast models aren't coarse enough to accurately depict where they will setup.  However, as we get closer we can zero in on a specific area and can have a general idea of where the highest totals may occur.

Below is the first call snow map and expect another updated map tomorrow evening, and with a little more detail of where perhaps the heaviest banding will occur.

Messy Saturday in Store Across CT on Saturday

A messy Saturday is in store across the state as a coastal storm is set to bring a mixture of snowfall, sleet, some freezing rain and even rain to the state.  Given how we will be dealing with multiple varieties of precipitation, this will certainly yield to quite a complex forecast, especially with regards to how much snows and where the highest snowfall totals will be across the state.  Let's get into this!

Brief Meteorological Background:

The below image shows the 500mb level (chart on the left) and sea-level pressure (chart on the right).  These two images come from today's 12z run of the GFS and there are 3 highlighted areas;

1.  This area is what is responsible for the development of the low pressure.  Strong energy associated with the mid-level trough is leading to the development of the surface low which you can see in the chart on the right where the 3rd highlighted area is.

2.  This highlighted area is a weaker piece of energy embedded in the northern stream moving into the northern-tier of the country.  This energy will sort of combine with the southern stream energy, or "phase" and this will help the coastal storm to become a little bit stronger and also keep it a bit closer to the coast.

3.  This highlighted area is the surface low pressure.

We will now fast-forward and look 24-hours down the road and the projected 500mb pattern and sea-level pressure chart:

1.  With the first highlighted area, we can now see the trough and associated energy draped right along the east coast now.  The trough here has a negatively-tilted component to it and this is something that will also favor the storm track to be closer to the coast.

2.  The second highlighted area is our surface low pressure or our coastal storm.  The system here is shown stronger than what it was just 24-hours prior and the system will continue to strengthen throughout the day on Saturday as it passes just to our south and east.

3.  For the third highlighted area there is a blue circle here.  One thing to notice is the lack of a surface high pressure in and around this region.  Having an area of surface high pressure in this general region is a great way to keep colder air in the lower levels locked in place and this high can also prevent a storm track too close to the coast.  Unfortunately, with no high pressure here and a storm track just off the coast, this will allow for warmer air to work in both at the surface and within the lowest 10,000ft of the atmosphere and that will be the reason why for multiple precipitation types.

With all this said what can we expect?

Forecast:

• Everyone will start off as snowfall with precipitation breaking out across the state between 4:00 AM and 6:00 AM with southern portions of the state beginning closer to 4:00 AM.  While there is a big of dry air in place aloft, forecast soundings indicate the airmass should begin to saturate rather quickly.  
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• As the morning progresses snowfall will begin to fall more moderately to heavy at times.  Snowfall rates may approach as much as 1'' to 1.5'' per hour at times during the heaviest bursts of snow.  
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• As the morning also progresses and the system works its way northward, warmer air will begin to work in the state in the lowest 10,000ft of the atmosphere.  As this warmer air work in, precipitation across the state will begin to transition over from snow to sleet, freezing rain, and even rain, especially across southeastern CT.  While some freezing rain is expected this is not expected to be a major issue, however, there may be enough to provide a coating of glaze across some communities.  
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• The system is expected to be a quick mover with the precipitation begin to wind down during the later half of the afternoon and be out by 7:00 PM, however, some light precipitation may linger, especially across the northeastern portion of the state.  
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• The heaviest of the precipitation will fall between about 12:00 PM noon and 4:00 PM.  Much of the snowfall accumulations, however, should occur prior to noon as this is when we will begin to see the changeover process occur.  
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• The highest snowfall totals should be confined to the northwest hills and northeastern CT where cold air may stay in place a bit longer.  
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• Anyone traveling should take it extremely slow and expect numerous delays.  Travel is not advised unless absolutely necessary.  

Below is the projected snowfall forecast:

Major Blast of Arctic Cold Set to Arrive...But How Long Does it Last?

     The first week of 2015 looks to be quite cold across Connecticut as a major blast of Arctic air is pushing towards the state.  An upper-level trough which was responsible for the messy storm system this weekend, is continuing to push through the central-tier of the United States.  As the trough and attendant cold front slide east it will usher in much colder air into the state.  In fact, we may be looking at our coldest temperatures of the 2014-2015 winter season later in the week.

     Right now it appears the worst of the cold will occur between Wednesday and Friday.  This is when computer forecast guidance suggests that the core of the coldest low-level airmass will slide overhead.  During this time, daytime temperatures will only get into the teens with nighttime lows falling close to and even below-zero in the typically colder spots.

     With a much colder airmass becoming established across the state this week, the million dollar question is, will see see any decent snowstorms or snow threats?  The answer to this question is a big fat NO.  The weather pattern this upcoming week is nothing sort of brutal cold and dry.  While there does look to be a developing area of weak low pressure to the south of CT late Tuesday, moisture looks rather starved and the system pretty weak so nothing significant is expected.  Some snow showers can't be ruled out but this may be more likely across far SE MA.

     Looking beyond this upcoming week and next weekend, there are some signals that the pattern will begin to relax a bit and we will see temperatures much closer to average return and perhaps even some days of above-average temperatures.  8-10 day progs from the GFS and ECMWF computer forecast models all suggest that we will see more in the way of ridging developing across the eastern United States and into our area.

Until then, however, it's nothing but brutal cold and dry with no storms expected this week at this time...how boring!