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.    

Storm System to Bring Wintry Mix to CT 12/28/2015-12/29/2015

While several locations have witnessed snow flurries or snow showers a few times during the fall/early winter, many of us will see our first wintry precipitation of the 2015-2016 season late Monday night into Tuesday as the next storm system approaches.  Unfortunately (if you're a snow lover) for the state of CT we are not looking at much in the way of snowfall.  You would have to travel further northward into central and northern New England for that.

After a several day stretch of insanely warm temperatures, including numerous records being broken, a push of cold air is working towards and into the state, although its stay will be rather brief.  A shortwave trough moving through southeastern Canada will allow for a pretty strong cold front to push through the state during the late evening/overnight hours of Sunday into Monday.  While the passage of this front will yield to clear skies, temperatures will be much colder than they had been the past several days.  In fact, temperatures will be as much as 15-20F colder with high temperatures barely above the 40F mark!

The next storm system is expected to pass well to our north and west.  As typical with these sort of storm tracks warmer air will eventually overspread the state.  However, initially there will be enough cold air in place for precipitation to began as snow across much of the state with perhaps the exception of the immediate shoreline.  The one feature responsible for this will be the area of high pressure which will slide to the east well off to our north.  The flow around the high will transport and keep colder air locked in at the surface.  However, as the high departs off to the east, we will lose the effects from the high pressure and eventually warm air will also work in at the surface and this is when the transition to plain rain will occur.  While the colder air will be initially locked in at the surface initially, warm air advection will be occurring aloft in the lower levels of the atmosphere.  This will allow for snow to transition to sleet and perhaps even some freezing rain.

 
The end result will be very little in the way of snowfall across the state with the most occurring across the NW/NE Hills, however, this doesn't mean the Tuesday AM commute will be messy.  We will be dealing with slushy roads with sleet perhaps some freezing rain falling along with plain rain.  Expect a very slow AM commute.  Below is what I'm currently thinking as far as any snow goes:

2015-2016 Remainder of Winter Outlook

December 2015 is likely going to end up as the warmest December on record for numerous climate locations across the Northeast.  Through the first 23 days of the month, the entire Northeast has not only been slightly above-average but WAY above-average.  The graphic below depicts this very well:

Looking at the image and the color scale, you can see that temperatures through the first 23 days of the month have been running as much as 6-9F to 9-12F+ above-average!!  These numbers are nothing short of impressive and come months end numerous records will be broken for warmest December on record.  While winter only officially began just a few short days ago, the winter season has not gotten off to a great start for cold or snow lovers across the Northeast.  In addition to the record warmth, numerous climate locations may also break or tie some records for least snowiest December on record (we will have to watch Monday/Tuesday (28th/29th) time frame for the potential of some winter precipitation across portions of New England).

The Northeast hasn't been the only region of the United States to experience above-average warmth this month, in fact much of the United States has seen December temperatures running near or above-average.

What was/were the causes for this anomalous December warmth and what does this mean for winter moving forward?  These questions and more will be addressed below as we highlight how this winter may play out and what we can possibly expect.

EL-Nino Southern Oscillation (ENSO)

One of the biggest drivers of the global atmospheric weather pattern is that of the EL Nino-Southern Oscillation (ENSO).  ENSO is broken down into three distinct phases; La Nina, EL Nino, and neutral ENSO conditions.  Each state is defined based upon the sea-surface temperature anomalies (SSTAs) across the equatorial Pacific across a region from about 170E to 90W latitude and 5S to 5N in longitude.  For visual reference see graphic below:

 Since about mid-to-late winter/early spring the equatorial Pacific Ocean region has been suggestive of EL Nino conditions.  EL Nino has been all over the news as of late but what exactly is EL Nino?  An EL Nino episode occurs when SSTA's are running at least +0.5C above-normal for at least five consecutive trimonthly periods.  (A few examples of trimonthly period would be December-January-February, January-February-March, February-March-April, etc.).  La Nina and EL Nino episodes are also broken down into weak events, moderate events, and strong events.  One method used to indicate the SSTA's across the ENSO regions and also indicate the strength of the ENSO event is called the Oceanic-Nino Index (ONI).  For the purposes of EL Nino, a weak EL Nino occurs when the SSTA's are between +0.5C and +0.9C, a moderate EL Nino occurs when SSTA's are between +1.0 and +1.4, and a strong EL Nino occurs when SSTA's are at or greater than +1.5C.   Below is ONI data dating back to the start of 2015.  The red text indicates the beginning of the current EL Nino episode.  With the latest ONI reading of +2.0, this indicates that this EL Nino episode is a pretty strong EL Nino.  In fact, this will go down as one of the strongest EL Nino's on record when all said and done.  (Note:  The EL Nino was officially defined with the JJA reading).

Beyond ENSO classification and strength classification, ENSO can further broken down into where the ENSO event is 'based'.  The classifications for this are west-based, east-based, and basin wide.  Where each ENSO event is situated is just as, if not more important than the actual ENSO state itself.  When determining where the ENSO event is based we can look at both the SSTA configuration across the equatorial Pacific and look at where the focus for tropical forcing is located (we will touch upon this aspect next).  Below are the SSTA's as of December 24th, 2015:

Looking at the equatorial Pacific region (black highlighted circle) the waters are exceptionally warm across the region.  Given how widespread the well above-average SST's are this is indicative of a basin wide EL Nino event.

Tropical Forcing

The next atmospheric variable we will discuss is that of tropical forcing.  When talking about tropical forcing we are looking at convection (areas of showers and thunderstorms) which develop in and around the Indian Ocean and propagate eastward across the equatorial Pacific.  When water vapor condenses to form clouds, this process releases what is called latent heat (latent meaning "hidden").  The more convection you have and the stronger the convection, the more heat that is released into the atmosphere.  This is significant because this heat which is released (especially if there is a great deal of heat released) can have a major influence on the jet stream across North America.  The strongest influences of the latent heat and subsequent ridging typically (not always) takes place anywhere from 30° to 50° east of where the tropical forcing is occurring. 

When assessing tropical forcing, one thing we can look at are outgoing longwave radiation (OLR) anomalies across the Pacific Basin.  Outgoing longwave radiation is a measure of the amount of solar radiation which is emitted back into space from the Earth's surface.  The more convection and clouds, the less in the way of radiation emitted back into space.  Assessing tropical forcing, however, can be a little tricky as over the course of time the forcing can shift across the Pacific.  Looking at OLR anomalies from December 1st through the 22nd, we can see that the majority of the tropical forcing (enhanced convection has been located between about 170W-150W.

Stratosphere/Polar Vortex/Arctic Oscillation (AO)/ Quasi-Biennial Oscillation (QBO)

Outside of the strong basin-wide EL Nino other contributions to this anomalous warmth across the east has been due to the state of the Stratosphere, the strength of the polar vortex (which we can use the Arctic Oscillation (AO) to measure), and the phase of the Quasi-Biennial Oscillation (QBO).  Through much of the fall and into the month of December, the AO has been quite positive.  A positive AO is defined by below-average height anomalies in and around the Arctic region.  These below-average height anomalies indicate a stronger than average Arctic low pressure center (polar vortex).  This is enhanced by very strong westerly winds between about 30-50mb (lower stratosphere) which is indicated by the positive phase of the QBO.  Below are graphics of the 500mb and 50mb height anomalies (left and center images respectively) along with the 50mb zonal wind anomalies (right image) from December 1st through the 22nd.  (Note the below-average height anomalies are indicated by the darker blue/purple shadings and the positive wind anomalies (indicative of westerly winds are indicated by the brighter orange shadings).  

Looking at the highlighted area on the below graphic, you can see the AO has been predominately positive with the exception of the brief period around the 15th of the month where the AO dipped slightly negative.  However, since then the AO has been extremely positive.

Connecting the strong EL Nino, the placement of the strongest tropical forcing, and the strength of the polar vortex indicated by the very positive AO, the influences on the atmospheric pattern across the United States has been for a trough across Alaska, western Canada, and down into the western United States at times and for ridging across the eastern United States.  We can reference the 500mb height anomaly graphic to see this.

With December coming to a close what can we expect for the duration of winter moving forward?  Will a pattern favoring extreme warmth and no snow in the east continue or will winter finally show its true face?  Below we will explore the signals which are in place which may be suggestive of where winter is headed moving forward.  

We will begin by viewing the December 25th 12z 500mb height anomaly charts for the 8-10 day period from the American GFS forecast model (graphic on the left) and the European forecast model (graphic on the right).  When looking at the run (and this has actually been developing over the past few runs) we notice some substantial differences within the pattern compared to what we saw for December.

The major differences here are the big ridge developing across the western-tier of the United States extending northward through western Canada and towards Alaska and the deep trough across the eastern United States.  Below are observations and ensemble forecasts for both the AO as well as the Pacific-North American teleconnection pattern (PNA).  The PNA can hold a strong influence on the atmospheric pattern across the Northern Hemisphere mid-latitudes.  The state of the PNA is classified as being either positive, negative, or if there is no clear signal, neutral.  The state of the PNA is measured by analyzing geopotential height anomalies at the 500mb level.  The positive phase of the PNA is characterized by above-average height anomalies situated across the western-tier of Canada and the western-tier of the United States and below-average height anomalies situated across the southeastern United States.  The negative phase of the PNA is a mere opposite of the positive phase with below-average heights situated across the western-tier of Canada and the western-tier of the United States and above-average height anomalies situated across the southeastern United States.  With a positive phase, this leads to ridging out across the west and a trough at least across the southeast and with a negative phase, this leads to troughing across the west and ridging across the east.  

While the ensemble spread is a bit more chaotic for the AO as opposed to the PNA, the consensus within the guidance is not only for the AO to drop but perhaps drop significantly.  This would indicate a weakening polar vortex which favors a higher likelihood for colder air to spill southward into the central/eastern United States.  The consensus for the PNA, however, is much stronger with the ensemble mean all favoring a rapid rise in the PNA.  This would promote ridging developing into the western-tier of the United States northward into western Canada, Alaska and perhaps poking into portions of the Arctic.  These signals all point to the likelihood that as we at least move through the final week of December and into the first week of the New Year, a major pattern change may take shape.  However, will this new pattern change become a fixture for the duration of winter and what will come with the pattern change?  

When looking even further down the road than just the next two weeks, we must continue to keep in mind how strong the EL Nino is along with the state of the Pacific as a whole along with the state of the lower stratosphere and the polar vortex.  Throughout the month of December, the strong EL Nino has held its dominance throughout the Pacific and one of its fixtures has been the strong vortex in the Gulf of Alaska region.  When you combine these with the strong polar vortex the result is for major warmth across much of the United States, especially in the east.  In order to alter this pattern, you need the Gulf of Alaska vortex to weaken and retreat northward and the polar vortex to weaken.  Unless the polar vortex continues to be attacked by wave propagating in the lower stratosphere/upper troposphere which would further induce weakening and unless the zonal westerlies weaken in the lower stratosphere, it will be very hard pressed to think the upcoming pattern change becomes a fixture through the remainder of winter.  What this means is after a potential pattern change over the next 10-14 days, the pattern could once again begin a transition and we see more in the way of ridging once again building into the east, however, not likely to the extent we saw during the month of December.  

The other major interest of note is the lack of colder air which will arrive if this pattern flip does indeed occur.  For the most part, temperatures across much of Canada have been running above-average.  We can see this from the image below.

  

Looking at the GFS ensembles from Friday 12/24/2015 0z run, the forecast for the 11-15 day period is continued warmth relative to average for much of Canada.  

Unless the changes which are forecasted to happen within the lower stratosphere, the polar vortex, and Gulf of Alaska region with regards to the Gulf of Alaska vortex become a constant the pattern which looks to develop moving into January may not be a permanent fixture.  This means we could see ridging become established once again across the east, however, this should not be to the degree which occurred in December unless the polar vortex were to once again restrengthen to the levels we've seen this month.  Despite the potential for more troughing to occur across the east, the lack of cold in and across Canada should limit more in the way of cold working into the central and eastern United States.  Below is my forecast for the month of January split into two parts; the first half of the month to reflect the potential upcoming pattern change and the second half to reflect the relaxation of that pattern change.

Moving forward into February if the changes discussed above headed into January don't become a constant it will be hard-pressed to find a source for major Arctic air to really work into the United States.  In fact, it is very possible warmth (although not record warmth) may once again overspread a good portion of the United States.  Below is my forecast for February.

  This forecast does not mean we will not see periods of colder temperatures or even at time some really cold temperatures, however, when these episodes occur they should be rather brief, lasting no more than a couple of days at most. 

I also provide this forecast with a low confidence rating.  If the polar vortex does indeed continue weakening (this can be aided by a weakening of the westerly QBO) and the PNA can become positive, this would promote a higher likelihood for a pattern shift towards colder in the east and mild across the west.  

As for snow lovers across the east, each scenario does not necessarily mean a poor snow winter (although once you get to New York City and points south things certainly don't look good), however, we would like to see some troughing become more present in the east and also see a more active pattern/storm track.  Thus far, the strong ridging that has been in place across the east has worked to weaken storm systems moving through the jet stream to our west.  

The winter of 2015-2016 is certainly not lost, however, big changes must occur.  There are signs for these changes to take place but the million dollar question is, will they persist?