Heavy rains and Thunder Possible Overnight Wednesday into Thursday

For several days now computer forecast guidance has been extremely consistent with the potential for a rather strong and intense storm system, however, the consensus with regards to the track of the storm was up in the air.  Over the past few days a consensus has been drawn that the system will indeed pass well to our west.  With a track so far to the west we will not see snow (perhaps early AM Wednesday we would see some frozen precipitation with the first part of the storm), however, we will be dealing with the potential for some extremely heavy rainfall and even the potential for some thunderstorms. 

The graphic below is from today's (2/21) run of the GFS computer forecast model looking at the 500mb heights/winds.  What we see here is a very deep trough pushing towards the east coast of the United States associated with very intense winds at the 500mb level forecasted to be as strong as 110-120+ knots (indicated by the purple colors).  Notice at this time how the core of these winds are just to the southwest of southern New England.  This will place the region in a very favorable position for very strong and rather intense lifting which will enhance the potential for heavy rains as well as the potential for thunderstorms.   

The GFS forecast model is indicating some anomalously high precipitable water values pushing into southern New England overnight Wednesday with values as high as 1.3'', an indication that some areas could receive at least 1'' of rainfall!

Another interesting aspect of this system is the forecasted instability right now.  The GFS right now is advertising a decent surge of elevated instability (instability which occurs above the boundary layer) moving into the region overnight.  This perhaps occurs due to steepening lapse rates in the mid-levels of the atmosphere coincident with decreasing temperatures aloft while temperatures in the lower levels and the surface increase (along with moisture content):

Forecasted lapse rates overnight Wednesday into Thursday:

Forecasted MUcape overnight Wednesday into Thursday:

All in all for snow lovers this system is bad news, however, for any weather enthusiasts this will be a fun system to watch given the dynamics involved.  We will see some pretty heavy rains push through the region along with the potential for thunderstorms and strong winds.  More to come as the week progresses!

Monday, February 8th, 2016 CT snow map/discussion

Our active weather pattern continues as more snow is targeted for the state of CT as we begin a brand new work week.  However, unlike Friday where some spots saw some pretty impressive snowfall amounts (as much as 6-12''!!) this system likely won't match those totals, however, there will be some impacts to travel.  While we are about 12-15 hours away from the onset of snowfall there is still a little bit of uncertainty with exactly how far west the storm tracks and where the strongest lift traverses over.  This will ultimately determine how much snow we receive and where the highest totals occur.  With this said, I believe the storm will end up tracking a bit too far east for CT to really get into the heaviest snows, especially for any prolonged period of time.  I do believe many areas (especially the further east you are in the state) will see at least a brief period of moderate to heavy snow.

With the following graphics below we can sort of see where some of the uncertainty comes from.  The following images are a bufkit profile for over Windsor Locks, CT from both the American GFS (top graphic) and NAM (bottom graphic) computer forecast models.  The area highlighted in purple is the best snowgrowth zone.  This is indicated by the purple and yellow contours.  The area highlighted in orane is vertical velocities with the red contours indicated upward motion (great for generating precipitation!).  The more contours you have, the stronger the lift!  You want these contours to run right through the best snowgrowth zone.  If you look at the difference between the GFS and NAM you see the GFS has a -10 contour while the NAM only has a -5 contour run through this zone.  This is indicating that the GFS is forecasting stronger lift than the NAM which would result in a period of heavier snowfall and perhaps higher totals.  Other sounding locations across CT yield similar looks.  This right here is the reason for the bit of uncertainty.

Looking past this uncertainty, this is not a very long duration storm system, however, we will see on and off snow-showers through Wednesday thanks to the upper-level trough which will be associated with this coastal storm.  Given how this is not long-duration, this is another reason why totals should not be all that significant.

Early morning rush hour traffic should not be terrible as the snow may not really break out until the mid-morning hours, although light snows could break out as early as 7-8 AM.  As the morning progresses, snow rates will vary between light to moderate and perhaps even briefly heavy at times reducing visibility.  Snow should taper off by the late afternoon hours so any impacts to the evening commute should be confined to wet roadways beginning to ice over.

Below is what I am expecting:

Monday, February 8th, 2016 Storm Potential

The past few winters have featured February's which not only saw a good deal of cold here across the region but also featured numerous snow events.  February 2016 looks to continue the trend for active February's as the pattern we are entering will be quite favorable for numerous snow chances.  While we just finished with a snow event another one looms on the horizon and just a few days away.

Over the past 24-hours or so, a few of the medium/long-range computer forecast models have featured a decent shift to the north and west with what appears to be a rather significant storm system.  While there is still a great deal of uncertainty with regards to how close to the coast the system will track, the latest trends have been rather interesting.  

Below is a graphic from today's 18z run of the American GFS computer forecast model valid for Sunday evening looking at the 500mb level.  There are two areas highlighted which will be of major interest over the coming few days.  The first area of interest is the northern stream trough which is expected to dig into the United States at the end of the weekend/beginning of the upcoming work week.  How this feature develops and behaves will be extremely critical.  The second highlighted area of interest is the very strong piece of shortwave energy in the southern stream.  This will be responsible for the development of a very strong and rather intense storm which at this time is off the coast.  If this trough digs in faster and sharper (sharper meaning digging further south) it may act to pickup the storm and allow the storm to not only work further north and west but come very close to the coast, perhaps enough to give us precipitation:

The uncertainty right now exists not only because of what was just mentioned above but also due to computer forecast ensembles.  Today's 12z GFS ensembles show some individual members bringing the storm close enough to the coast to give us impacts while other members remain further east.  However, the rather interesting thing to note is how the models have come north and west over the past 24-hours or so.  In fact, even the European model had a shift to the north and west this afternoon.  Below are some of the GFS ensemble members:

As newer data becomes available and the situation should begin to become much more clear.  If overnight computer forecast models continue coming further north and west I think we definitely start having to prepare for a storm on Monday.  However, if tonight's models start going back towards the south and east the potential for impacts will likely decrease.  This will be a pretty potent system so if it does track west enough someone could end up with a quite a bit of snow.  Stay tuned!

Snow surprise! Accumulating Snow expected Friday, February 5th, 2016

Over the past couple of days computer forecast models have been insisting that an area of low pressure which develops along a cold front stalled to our south and east will track far enough to the west to bring precipitation, including snowfall into portions of southern New England.  Well over the past 12 hours or so, computer forecast models have really come further west and now we are looking at the potential for accumulating snows as far back as western CT.

The following graphic is looking at the 500mb level and 500mb vorticity.  What we are looking at is a very potent piece of shortwave energy traversing through the 500mb level.  This very strong piece of energy will be responsible for the continued development and strengthening of a surface low pressure along with low pressure centers developing at the 925mb and 850mb levels:

One of the computer forecast models, the GFS model has been quite aggressive with precipitation and lift across our area.  However, several other computer forecast models have also been either similar to the GFS or trending towards the GFS.  Below is an image from the latest 18z run of the GFS showing vertical velocity at 700mb.  The brighter colors indicate very strong and rather intense lifting.  We should see a period of very strong lift push through CT and help enhance snowfall intensity:

As far as impacts go, expect a very traitorous Friday morning commute given the timing of the snowfall with snowfall breaking out either overnight Thursday or very early AM Friday and continuing through the early to mid afternoon.  Expect poor driving conditions along with numerous delays.  Below is my snowfall forecast:

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!