1st Call Snowfall Map for Saturday, January 26th, 2016 Storm

Throughout the course of the week major headlines have been made for a potentially major winter storm to impact the mid-Atlantic and Northeast states this weekend.  Since the end of last weekend (nearly a week ahead of the projected event!) computer forecast guidance has been very consistent in showing a storm impacting these regions.  The only questions were where does the biggest impacts occur and where what kind of snowfall amounts we would be looking at.  Over the past 24-hours the situation has started to become much more clear and it is looking like the biggest impacts and highest snowfall accumulations will be from NJ on south into the mid-Atlantic where the highest snowfall totals could approach 18-24''!  For us here in CT we will not see nearly as much snow or much in the way of serious impacts from this system.  

Below are graphics from the overnight run of the GFS forecast model looking at late overnight Saturday (1:00 AM EST) focusing on the 500mb, 700mb, and 850mb levels.  Highlighted are the centers of low pressures at these levels.  Those smaller closed contours within the highlighted area indicate the system is "closed off" which indicates the system has reached peaked intensity.  Given how far south of CT, this is occurring this indicates that moisture inflow from the Atlantic will be shut off from entering the system and will result in a decrease in the precipitation the storm has to offer.  These pressure centers tracking further south also indicate the strongest lifting will be well south and west of this area:

  

The below graphic is a GFS bufkit profile for Waterbury, CT also from the overnight run of the GFS.  Here we are looking at a profile of the atmosphere.  There are several highlighted areas.  

1) The circled area is the area of best snow growth.  You want this zone to be located inbetween the -12C and -18C isotherms as this is the desired range for best snowgrowth.  While I did not overlay the temperature contours (it starts to get a little messy with lots of overlays) the snowgrowth zone is located in this range which is a good thing!

2) The red contours indicate upward vertical motion (rising air) and the blue contours indicate downward vertical motion (sinking air).  What you want to see is lots of upward vertical motion within the best snowgrowth zone and you DO NOT want to see any blue contours within this zone as that would lead to sinking air and a decrease in precipitation.  Notice how within the snowgrowth zone we aren't seeing much in the way of upward vertical motion, this indicate we likely will not see much in the way of heavy snowfall rates.  

3) Also plotted are relative humidity values, the higher the relative humidity, the more saturated the air is said to be.  In this case we would like to see higher relative humidity vales than what are depicted and would also like to see values >90% (which is what is only plotted) be within the best snowgrowth zone too.  Looking at the relative humidity values there could be some dry layers in the atmosphere which could allow for some snow to evaporate before reaching the ground:

With the above said, below is what I am currently thinking as far as snowfall totals are concerned across the state:

Outside of snow we will also see some fairly strong wind gusts with this system as well with winds gusting at times to 40-50 mph.  Despite not much in the way of snowfall goes as far as totals this could yield to blizzard-like conditions at times, especially when snow is falling at a heavier rate.  We could also see some isolated power outages as well.  

Update #2 on weekend storm potential

As of Tuesday afternoon the consensus is still in place for at least some sort of impact to portions of southern New England this weekend from a rather potent coastal storm.  However, the situation is still not clear at all as to what we can expect in terms of snowfall totals.  Some pieces of guidance suggests some areas could see some significant snowfall accumulations (>8-12'') while other pieces of guidance are more moderate (~4-8'').  Given the time frame we are in it is not uncommon at all to have these questions regarding the significance of any impacts. Besides the potential significance of impacts it is also unclear as to the exact timing of everything.  In yesterday's piece we looked at several ensemble members of the American GFS forecast model, we will do the same today.  Below is from today's 12z run of the GFS:

Looking at these individual members which is valid for early Saturday afternoon, we can see continued consensus for some sort of impact.

As we continue to go through the next few days the main area of focus will be on a rather strong piece of energy which is just entering the Pacific Northwest will slide southeastward through the southern Plains into the southeast then swing northward through the Carolina's and off the New England coast.  The image below is also from today's 12z run of the GFS and is looking at 500mb vorticity valid for very early AM Friday morning:

As this energy then begins the northward turn towards the Carolina's and continues moving north this is what we will really have to pay attention to because how this energy and the storm evolve will ultimately determine the impacts we receive.

Looking at today's run for overnight Saturday we notice that the GFS is suggesting the system will "close off" at 500mb well to the south of New England.  Typically when a system is closed off at 500mb, or begins to close off, this is a tell tale sign that the system is at maximum intensity and will shortly begin to weaken.  This process leads to occlusion which essentially shuts off the moisture inflow to the system:

Something else to notice is also how far south the GFS closes off the system at 500mb.  If this would occur then the majority of the heaviest of the snows would remain well to the south of New England with the highest amounts across the mid-Atlantic to NJ.  For us to receive the maximum amounts we would want that to close off just south of Long Island,  The tracks and path of the 700mb and 850mb lows will also be critical because the heaviest banding of snow occurs just to the north and west of these tracks.  Some other computer models, including the European model (which I can't post graphics) also are fairly similar with the 500m depiction and where the system closes off.    

As we go through the next few days we will pay extremely close attention to how the computer forecast models handle the 500mb level and how the pieces of above evolve.  While confidence is high on some sort of impact, confidence remains rather low as to how extreme these impacts will be.  By late Thursday afternoon we should have a much more clear idea of what kind of impacts we are looking at.

Storm to Impact Southern New England Saturday, January 23rd, 2016?

Snow lovers rejoice as there may be some excellent news for you on the horizon.  After a near historic slow start in the snowfall department for many locations, as we move into the fourth weekend of January computer forecast models are showing some very interesting solutions with regards to a potentially strong coastal storm sometime early on this upcoming weekend.  At this point in time it is way too early to discuss details or get into specifics, however, we will take a look at the potential synoptic setup and determine the likelihood of a storm and potentially how big of a storm.

When looking at the medium/early long-range for a potential storm system the one piece of guidance that is extremely important to look at are the model ensemble means.  Model ensembles provide different "members" with each "member" providing a solution.  Ensembles are extremely useful in this range because they can provide a certain confidence level for the forecaster interpreting them.  If the different members are providing various solutions this would decrease the confidence a forecaster may have on a hit.  However, if the different members are more similar to one another, this would provide a much higher confidence level for the forecaster.  With this said, we will take a look at some of the ensemble members for the American GFS forecast model from the 12z run on January 18th valid for early morning on Saturday the 23rd:

The GFS ensemble members (the members being each individual panel showing a potential solution) are actually in fairly decent agreement of a storm track close enough to the coast to provide impacts to southern New England (and perhaps some major impacts).  Given how consistent the ensemble members are this gives a heightened sense of confidence that indeed we may see a storm at some point this weekend, perhaps very late Friday into Saturday.

As we move through the week the focus will be on a piece of energy which is expected to enter the United States from the Pacific-Northwest late tomorrow.  The piece of energy is expected to dive southeast into the southern plains, through the southeast and then work up the eastern sea-board where it may interact with some energy moving through the northern branch of the jet stream:

As we head towards the weekend the situation should continue to become more and more clear and a major focus will be placed on the 500mb level (which is shown in the graphic above).  This level is where the key pieces of energy are located and where interactions with the jet stream and energy would occur.  At this point in time its still too early to really go into great detail about what to expect, however, the potential certainly exists for not only a storm to impact southern New England but for a fairly big storm.  Stay tuned for further updates!

Storm System to Impact southern New England 1/16/2016

If you're a huge snow fan living here in southern New England the winter of 2015-2016 has been nothing sort of depressing.  After the warmest December on record across many locations we finally have more frequent cold outbreaks transpire across the region, however, the cold has come without any meaningful snow.  Unfortunately this trend will continue this weekend as the next major storm system is set to bring predominately rain to much of the region with perhaps some snow mixed across higher elevations and the further north into New England you go.

When looking at the track of Saturday's storm system we see a track which brings the surface low pressure just to the south and east of southern New England.  Typically, especially this time of year a storm track like this would be yielding not only snows but some hefty snowfall totals for someone:

If the storm track is favorable for snow then what's the problem?

Re-posting the same graphic above, however, looking at the continental United States as a whole, there are three key pieces to note:

1) The primary low pressure system moving northward through the Great Lakes.  When certain conditions are in place, these primary areas of low pressures can "transfer" their energy to just off the east coast of the United States.  When this process occurs and when the primary low pressure weakens, the secondary low begins to take dominance and this can help to bring down colder air from Canada (the flow around the low coming from the N to NE brings down colder air).

2) The secondary low pressure development and track just to the south and east of southern New England.  Unfortunately with this weekend, the secondary low pressure development is just going to occur too late and the primary low stays way too strong.  The end result is warmer air advecting into southern New England from the south and southwest.

3) The lack of a high pressure system to our north.  A good chunk of our snowstorms, especially bigger snow producing snow events all have an area of high pressure to our north.  What this does is reinforce colder air into the region from Canada.  Unfortunately, with a lack of high pressure to our north, there is nothing to reinforce cold air and nothing to prevent warmer air from working northward.

Unfortunately this system is going to produce precipitation mainly in the liquid form, however, higher elevations areas and central/northern MA will mix in some snow.  We are looking at 1-2'' of rainfall region wide with some areas picking up 3'' of rain.  Flash flooding will be an issue in the typical flood prone locations.  As this system departs another surge of Arctic air will arrive, perhaps even with some snow squalls later in the day on Sunday.

Record Warmth With a Sunday Washout (1/10/2016)

An area of strong low pressure will be passing well to the west of southern New England on Sunday and this track will allow for a warm front to push through much of southern New England.  With the passage of the warm front will come a highly unseasonably warm/moist air mass as temperatures and dewpoints will climb well into the 50's.  In fact, a few areas, could even get close to 60F.  This warmth will indeed set some records in some spots.

With the warmth, however, comes rain...and quite a bit of rain.  Some areas will pick up as much as 1-2'' of rain with a few locations perhaps picking up as much as 3-4'' of rainfall.  Given how the ground is partially frozen (especially the top layer) this could create some issues with puddles and localized flooding.  Below is a graphic from the January 9th 12z GFS computer forecast model showing Precipitable Water Values "PWATS" for early Sunday afternoon.  We see PWAT values around 1.1'' to 1.3'' which is pretty impressive for this time of year and suggestive of the heavy rain potential we will be seeing:

 

We will also see the potential for thunderstorms as well embedded in the heavy rainfall as some weak instability pushes in thanks in part to the warm/moist low-level airmass advecting in.  Its within any thunderstorms that some areas could pick up the 3-4'' of rainfall.  The thunderstorms could arrive in what is called a forced line of low topped convection.  Unlike warm-season thunderstorms which are formed mainly due to strong instability, these thunderstorms are formed from very strong wind dynamics aloft which forces air to rise upwards, hence the term "forced convection".

Below we see the forecast from the January 9th 12z GFS computer forecast model for 500mb winds (winds about 18,000ft off the ground) during the early afternoon hours on Sunday.  The mid-level jet streak modeled is about 80 knots or so and arrives from the SW.  Notice the area over CT/MA where the color shading goes from yellow to red.  At the edge of this boundary we call this the nose of the jet.  This provides a good focal area for enhanced lift (stronger winds arriving) and it is along this boundary we could see a forced line of convection develop.

With winds just above the surface fairly strong it is also possible some of these stronger winds are transported down to the surface, thus it could be fairly gusty at times.  If any convection does form or push into the region, this will also enhance the potential for some stronger winds mixing down to the surface.  All in all we could see winds gust as high as 40-50 mph across the region with the small potential for a gust or two reaching 60 mph.  Isolated to widely scattered power outages will be a possibility, however, they should not be a major issue.

After the passage of this storm system we will see the beginning of a drastic pattern change towards much colder weather and yes perhaps even some snow chances...but we'll talk about this in a few days.