Steven Copertino

Public Analysis: Snow Likely Friday, A Larger Threat Looms

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A cold front moved through the region early this morning and introduced some slightly cooler temperatures just ahead of another more potent front that should provide a good shot of colder air, followed by the potential for light to moderate snows on Friday. This weekend should remain quite cold and dry, but is this just the calm before the storm? We answer this with all of the meteorological details in our article below:

 

The region saw a cold front pass through the area earlier this morning with some showers passing through the area. Even though we did have this cold front passage, temperatures will remain relatively mild today and into tomorrow, due to downsloping westerly winds. With relatively clear skies this afternoon, temperatures should had no problem reaching well into the 50’s and even 60’s for southern locations. As the cold front that impacted our region continues to move off of the coast, a tight pressure gradient will set itself up over the region due to a large and intense area of low pressure over Hudson Bay in Canada, that continues to move very slowly to the east. This pressure gradient will create gusty winds of up to 35 to 45 mph this afternoon, but should gradually diminish as we head into the late afternoon hours and evening. Temperatures will be able to drop quite efficiently underneath clear skies with most of the area staying in the 30’s.

The beginnings  of an Arctic airmass will start to bleed into the region by tomorrow afternoon as another front moves through, limiting temperatures to the 40’s and low 50’s. Despite colder mid-levels from this airmass, temperatures will remain only slightly above-normal due a more south-west component to the winds and direct sun.  The Arctic airmass dropping through our area will set up a nice temperature gradient, which will set the stage for our next chance at snow.

Visible satellite imagery and current surface observations over the Northeast this afternoon (Courtesy of Simuawips.com)

Visible satellite imagery and current surface observations over the Northeast this afternoon (Courtesy of Simuawips.com)

As a potent piece of energy begins to dive southeast out of Canada on Thursday evening, the Arctic front that will be draped over our area will be the focus for low pressure development along that front. Due to the strength of this upper level system, there will be a healthy amount of lift at the surface which will help to develop precipitation just to the north of the low pressure system as it begins to take shape over the Ohio Valley. This band of precipitation should initially be on the lighter side during Thursday evening and may be in the form of a rain/snow mix to the south and along coastal sections.

As we go into Friday morning, the low pressure area should pass to the south of the metro area and be located just offshore with precipitation affecting the vast majority of the region. As this low moves offshore, upper level dynamics due to a strong jet streak located at roughly 13,000 feet will provide an enhancement to the precipitation over much of the area just as colder air to the north begins to rush in, which should promote a change to more wintry precipitation for most locations.

The snow should increase in intensity during the late morning and early afternoon hours thanks to the aforementioned dynamics at play. Snowfall accumulations across the region, will depend largely on where heavier banding develops and boundary-layer and surface temperatures for much of the event. If this low tracks further north, some areas south of the systems track will draw in warmer and drier air initially, which could reduce snowfall totals. We will try to pinpoint these snowfall totals in future updates, with a threat map likely by this evening.

Afternoon NAM model showing the potential light to moderate snow event on Friday afternoon (Courtesy of http://www.atmos.albany.edu/student/tburg)

Afternoon NAM model showing the potential light to moderate snow event on Friday afternoon (Courtesy of http://www.atmos.albany.edu/student/tburg)

The Next Snow Threat: If you have been keeping up with our forecasts over the past couple of weeks, you already know that we have been very attainment on the prospects of high-latitude blocking developing for the time period that we are now entering. Earlier this week we also mentioned that we had three potential waves all with chances of affecting the New York Metro area over the next week or so, with the first wave being the storm talked about above. Now over the past few days, the models have really backed off the second wave, which was originally forecast by the computers models to pass to our south and provide a shot at some snow this weekend. However, it was highlighted that this threat was highly dependent on whether or not an upper level low near the eastern Canadian maritime region, would act to press down on this system as it moved east and shove the low south with time.

This is exactly what has happened since our last update as all of the computer models now agree on this second wave being pushed too far south for any significant impacts to the metro area as it quickly moves east through the Southeastern states this weekend. Some may think that we’re getting off easy now that this wave is no longer a threat, but this is quite the opposite actually. This wave’s failure to organize will set the stage for possibly the single most impressive snow threat we have seen so far this winter to take shape.

This afternoon’s computer models have begun to come closer together in their solutions as high latitude blocking — in conjunction with a sharper ridge out west — really slows down the progressive/quick pattern we have been plagued by during the entire winter. As this pattern really begins to slow down, it’s looking more likely that an upper level disturbance originating from deep in the Canadian prairies will dive down into the central part of the country, which allow a deep trough to form by Monday evening. Blocking over Greenland and ridging over the Northwest US could allow for this trough to continue to deepen/amplify as it swings eastward through the Ohio Valley on Tuesday, which may lead to the development of an area of low pressure. There is even evidence of the ridge in the Northwest US connecting with the blocking over Greenland, which amplifies the blocking and forces a very strong Upper Level Low to develop and get pushed to our south, thus interacting with multiple pieces of energy and gathering plenty of moisture before it makes its way towards our latitude.

This low pressure would have to be monitored very closely as an area of Arctic high-pressure to the north and west may force it to redevelop off the Mid-Atlantic coast as we have seen many times in the past. These types of systems that redevelop off of the coast are called Miller-B systems, and tend to produce rather significant precipitation for the Northeast as they slowly move off to the east and intensify, and have heavy precipitation blossom in a short period of time, bringing numerous prolonged impacts.

500mb hieghts from this afternoons European model showing a very deep trough over the US (blue) and blocking out to the west and east (Courtesy of Accuweather Pro)

500mb heights from this afternoons European model showing a very deep trough over the US (blue) and blocking out to the west and east (Courtesy of Accuweather Pro)

While it is obviously much too early to nail down any specifics at this point in time, the clusters of models (ensembles), evidence of ridging over Greenland, and ridging over the Northwestern states all point to the possibility of at least an area of low pressure developing along the coast towards the Tuesday/Wednesday time period. Of course this can change very quickly as we have seen with the aforementioned second wave, which is why all of us at New York Metro Weather will be monitoring this potential system very closely over the next few days and will provide updates on the situation as we get closer.

For more information and posts like this one, make sure you sign up for Zone Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

 

Have a great evening!

Steve Copertino

 

Steven Copertino

Public Analysis: A Battle of Two Seasons

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After another impressive but brief shot of cold weather this past weekend, another warmup is likely tomorrow and Wednesday along with some showers. Afterwards, the high-latitude blocking that we have been discussing for a few weeks now will provide a few chances for accumulating snowfall and colder weather for the NYC metro area.

This afternoon has been a cool, but pleasant one as a large area of high pressure that is currently centered off of the Mid-Atlantic remains in control of today’s weather. Light southerly winds of around 5-10mph have warmed temperatures into the 40’s across the entire area with some light high clouds noted on visible satellite imagery. Even though the area is a good 5-10 degrees higher than what they were yesterday, temperatures are still a few degrees below normal for this time of year. This will be short-lived as a large and very intense low pressure system intensifies over the Central part of the country and introduces even stronger southerly winds courtesy of a warm front overspreading the area. These southerly winds will usher in much warmer air and increasing cloud cover this evening, so temperatures should be above normal for our low temperatures tonight. Due to the low level moisture increase, some spotty drizzle or showers may be possible by this very late this evening and into the morning tomorrow.

Latest observations, radar, and visible satellite imagery for the Northeast showing relatively quiet conditions. (Courtesy of Simuawips.com)

Latest observations, radar, and visible satellite imagery for the Northeast showing relatively quiet conditions. (Courtesy of Simuawips.com)

As we move through tomorrow morning, mostly cloudy skies should be commonplace for the entire region with some showers present as well during the morning commute hours. The strong warm front that was mentioned will continue to usher in strong low level flow from the south, which will allow temperatures to warm well into the 50’s tomorrow afternoon despite persistent cloud cover and rain. While the cold front from the large area of low pressure in the Plains continues to advance to the east, moisture will also be abundant by later tomorrow afternoon. This moisture will stream ahead of this front and create more widespread showers for the entire area that should last into the early morning hours of Wednesday.

Since the best dynamics with this cold front are off to our north in Canada, heavy rain is not likely a threat at this time. Once the actual cold front clears the area on Wednesday, temperatures should still be able to climb into the 50’s and even 60’s during the afternoon hours as any residual moisture is removed from the area and clear skies begin to take over. Late Wednesday evening and into Thursday is when the colder air arrives as the main upper level energy associated with the low pressure in the Plains passes to our north and allows for cold air to really “bleed” and overspread the metro area. This will be especially true just a few thousand feet above our heads while winds gradually shift from the Northwest.

 

Afternoon NAM showing more cold air bleeding into the region by Thursday afternoon and evening

Afternoon NAM showing more cold air bleeding into the region by Thursday afternoon and evening

As we move later into the week, a change in the large-scale pattern evolution over the Western Hemisphere, aided mostly by the development of significant high-latitude blocking, will support the return of at least some colder weather over the Northeast and Mid-Atlantic regions. Today’s latest model and ensemble guidance suggest several separate waves could bring wintry precipitation into the region this weekend and into next week. There is still much uncertainty with the track and intensity of each of system, especially with the northern stream flow being fast and zonal initially. As we have seen, the trend for disturbances to trend quicker and weaker has been something commonplace this winter, but that was mainly due to a lack of blocking.

The first potential system that we are tracking looks to take place on Thursday evening and into Friday morning. This afternoons model guidance has diverged significantly on the exact outcome, but there seems to be at least some potential for a wave of low pressure to track from the Central US underneath the strong blocking high to our north and a large upper level low in SE Canada. Depending on just how far south this upper level low pushes the wave of low pressure will determine whether or not our area sees measureable precipitation from this event. This afternoons American model showed the wave of low pressure being able to track more to the north thanks to the upper level feature in Canada not pressing down on it as much, and ultimately delivers some light to moderate snow on Friday.

GFS ensembles mean precipitation output for Friday afternoon

GFS ensembles mean precipitation output for Friday afternoon showing light to moderate snow for the area

Another Pacific disturbance comes ashore later this week, and even more questions arise with this potential threat. As the disturbance tracks to the east over the Rocky Mountains, a low pressure will likely form in the Central Plains. This area of low pressure will have an area of high pressure off of the Mid-Atlantic coast that should provide it with a very impressive moisture feed as it begins to strengthen over the Tennessee/Ohio Valley. The aforementioned blocking will provide fresh cold air for this system as it traverses a very sharp temperature gradient, but where this exact gradient establishes itself is the real question as of right now.

If the blocking to our north is too strong, then the gradient and the system will wind up suppressed to our south and the area will see little, if any impacts. If the blocking isn’t as oppressive on the system, then the low pressure will be able to take a more northerly track. If this system is able to track directly to our south, then all of the moisture that is sucked up from the record-warm Gulf will fall over the region and possibly have significant impacts. It i worth noting that this afternoons European model has trended a bit further south with no impacts for our area and very clearly represents what could happen if this system isn’t able to gain enough latitude due to the upper level feature in Canada. 

12z GFS model showing significant precipitation for the Northeast on Saturday evening due to less oppressive blocking able push the system south

12z GFS model showing significant precipitation for the Northeast on Saturday evening due to less oppressive blocking able push the system south

Finally, later next week, more pacific shortwave energy digging may lead to another storm along the East coast. However, the blocking to our north may weaken by this point to allow for track further northwest or system to phase to late with northern stream off the coast. This may result more mixed or lighter precipitation in the region.

***It should be noted that each individual threat discussed here still remains extremely uncertain. As the models begin to catch on to the pattern evolution, we may see more drastic changes with the upper-level features and evolution of individual system.

We believe the chances are pretty high for cold and snow threats with this pattern evolution — but that doesn’t mean anything is guaranteed. Stay tuned for further updates and details as we move closer.

For more information and posts like this one, make sure you sign up for Zone Forecasts — where multiple detailed articles, videos, and interactives are posted each day.

 

Have a great evening!

Steve Copertino

 

Steven Copertino

Public Analysis: Cold Front Passage, Big Warmup This Weekend

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The general theme of the winter of 2016-2017 continues this week.

Due to a lack of blocking that would normally work to slow individual pieces of energy within the jetstream down, we have once again missed out on a sizeable storm for the Northeast. As you can see down below, we have two separate pieces of energy that were quite literally just 12-18 hours away from being able to interact with one another and produce a snowstorm for the Northeast US. The computer models were in excellent agreement over the past five days that instead, these two pieces would not be able to interact in time due to the very quick flow, and would instead come together this evening to produce a low pressure system that will track to the east of the 40N/70W benchmark while rapidly strengthening and deliver sizeable snows to southern New England and portions of Maine.

500mb map highlighting the two disturbances that were able to remain just far enough apart to prevent another snowstorm for our area (Valid 4am this morning)

500mb map highlighting the two disturbances that were able to remain just far enough apart to prevent another snowstorm for our area (Valid 4am this morning)

Even though we miss out on a large storm, the northern piece of energy moving over our area today is quite vigorous and will be accompanied by a strong cold front. This cold front was located in central Pennsylvania as of 1pm this afternoon with numerous showers noted across the region. In conjunction with the strong mid level disturbance, we have strong low-level lapse rates, which are basically the change in temperature within an area from the surface to a few thousand feet above our heads. When there is a healthy difference in temperatures with increasing height, we see upward motion take place in the atmosphere which promotes shower development like we are seeing ahead, as well as behind this cold front. This afternoons short range computer models have been keying in on these showers and the associated cold front impacting the NYC region by 3pm or so.  The entire region should expect showers lasting through the evening commute, but due to the factors mentioned above, it would not be impossible for the northern sections of the area to see some graupel or even snow mixed in with these showers as the front passes and temperatures begin to drop. Those traveling should pay attention for possibly slick road conditions in the heavier rain/snow showers this afternoon and evening. As the precipitation moves out later this evening, expect gusty winds on the order of 25-35 mph from the WNW to take over and last into tomorrow due to yet another tight pressure gradient over the area associated with the strong low exiting to our east.

Current surface map showing the location of the cold front and associated showers set to move over the region this afternoon (Courtesy of Simuawips.com)

Current surface map showing the location of the cold front and associated showers set to move over the region this afternoon (Courtesy of Simuawips.com)

With temperatures this afternoon in the 30’s to middle and upper 40’s across the area, the cold front passage later today should provide a good contrast as temps fall into the low 30’s and into the 20’s for inland sections this evening. Thursday and Friday will feature a more seasonable airmass in place with highs in the middle to upper 30’s across the entire region with mostly dry weather expected for both days. As we move into the weekend, a broad area of mid level ridging will move in from the west and continue east over our area. Winds from the south/southwest will send temperatures well-above normal on both Saturday and Sunday with highs deep into the 50’s across the area. Some southern locations may possibly sneak into the 60’s by Sunday afternoon if stronger southwest winds are realized. Due to the aforementioned ridging, conditions should remain dry with mostly clear skies, so this weekend should be an excellent one to enjoy the warmer weather before things turn a bit cooler and unsettled into the work week next week.

Afternoon European model showing temperatures on Sunday possibly reaching 18-24 degrees above normal (Centered on 1pm Sunday)

Afternoon European model showing temperatures on Sunday possibly reaching 18-24 degrees above normal (Centered on 1pm Sunday)

For more information and posts like this one, make sure you sign up for Zone Forecasts — where multiple detailed articles, videos, and interactives are posted each day.

Have a great day!

 

Steven Copertino

Public Analysis: Significant Snowstorm Likely Tomorrow

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After tracking this potentially significant system over the past couple of days, we have seen some sizeable differences showing up on the computer models regarding potential impacts and accumulations, but this afternoon’s computer model guidance has come into line and it is looking quite likely that the entire New York metro area will be seeing seeing a significant amount of snow during the next 24 hours with a variety of potential impacts.

As was talked about on Monday, we have our two key pieces of energy that have to interact and come together this evening in order for our storm to take shape and really begin to intensify. If we look on the 500mb chart below, which is essentially what’s happening up in the atmosphere at roughly 18,000 feet, we can see our two distinct features highlighted in pink. Our first piece can be seen over Kansas City, Missouri this afternoon which has generated the beginnings of our storm over Arkansas and Tennessee with precipitation starting to break out all the way up into Illinois/Indiana/Ohio. As our second feature begins to dive south from its current position to the north of Bismark, North Dakota and interacts with the piece of energy in Missouri, the low pressure currently in the south will begin to speed up and track into northern Tennessee this evening. More precipitation will begin to blossom to the north of the low pressure area as time goes on. This low should steadily deepen as it tracks through Virginia by the early morning hours and bring the onset of the precipitation to the southern New Jersey by 2-3am. This area of snow and rain should gradually move up from southwest to northeast and since we have temperatures in the 50s-60s this afternoon, the initial precipitation may be in the form of a rain/snow mix due to residual warm air. As the precip starts to come down at a heavier rate, a switch to heavier snow/mix is likely for much of the area.

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