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Light Snow Friday Morning, All Eyes on This Weekend

January 16, 2019/1 Comment/by Steven Copertino

Good Evening!

Today has been another calm and relatively cool day across much of the Northeast as high pressure remains in control of our sensible weather. Partly cloudy skies and mid-level flow coming out of the west allowed for temperatures to rise into the upper 30’s to lower 40’s for much of the NYC metro area, which is slightly above-normal for this time of year. A weak cold front is currently situated over portions of New York and Pennsylvania and has been gradually moving to the southeast during the course of the day. This cold front is expected to arrive later this evening, which will usher in a fresh batch of cold air into the region. There really isn’t much in the way of moisture associated with this front, so this will likely be another dry and cold night. Occasionally breezy conditions will set up behind the front with clearing skies from northwest to southeast tonight.

With a fresh cold air mass in place and clearing skies, radiational cooling will take over tonight, allowing temperatures to fall into the lower 20’s in and around the city, with teens possible for locations off to the north and west.

This evenings current radar and surface observations

Light Snow Likely Tomorrow Night and Into Friday Morning

Tomorrow (Thursday) will likely start off quite chilly with temperatures in the lower 20’s for the immediate New York City metro area. Continued breezy conditions will yield wind chills in the teens for the entire area tomorrow morning, so it’s definitely going to feel quite cold for the morning commute. High pressure will remain in place for the majority of the day which will allow for partly sunny skies and gradually diminishing winds into the afternoon hours. Highs will likely be hard-pressed to rise above-freezing tomorrow afternoon, with locations to the north and west of the city likely staying in the middle to upper 20’s.

By the early afternoon hours, our attention will shift to the west over the Ohio Valley. A weak and disorganized mid-level wave will be quickly heading to the east during the day with an associated area of light snow. This system will continue to gradually move into our area tomorrow evening, with increasing clouds towards sunset. Cloudiness will continue to increase during the overnight hours as moisture to our south begins to overspread the area. Light snow will quickly move into the NYC metro area, likely around 2am or so. The entire forecast area will likely stay snow for the first couple of hours, but as moisture continues to trickle in from the south, warmer air will also be on the rise. Coastal locations will likely change over to a mix of rain and snow by 6am Friday, with locations to the north and west of NYC likely staying as light snow. Precipitation will quickly head off to our east by 8-10 am, with some residual spotty snow/rain showers remaining for the rest of the afternoon.

Due to the progressive nature of this system, marginal amounts of forcing, minimal precip amounts (.1″ to .25″ of liquid), and increasing surfaces temperatures, snow totals are expected to be low. At this time, a quick coating to an inch of snow will be possible in and around the immediate NYC area, especially on colder surfaces. Once we head off to the north and west, mainly 1-3″ of snow is expected–especially for elevated locations over NW NJ and SNY.

Due to the timing of this light snow event, it seems possible that some delayed openings may be called for portions of NW NJ and SNY.

High resolution NAM simulated reflectivity showing the evolution of the light snow event tomorrow night and into Friday morning

Potentially Impactful System Shaping Up for the Weekend

The overall setup for this weekends potential system has not changed much since our last update. A large and energetic system that is currently located off the California coast will move into the Rocky Mountains by Friday morning, producing an area of low pressure over the Southern Plains at the surface. As this energetic system begins to head east during throughout Friday and into Saturday morning, another large upper-level system located over Canada will begin to shift to the south. This large system over Canada will help to inject a massive amount of cold air into the Central US, leading to a large area of moderate to heavy snow developing over the Midwest on Saturday afternoon. Things become a little more hazy later in the day on Saturday as the western edge of the Canadian system tries to interact or phase with the shortwave over the Southern Plains/Midwest. This potential interaction will be absolutely crucial for the overall impact for much of the Northeast.

As of right now there are two main solution on the table:

The system over Canada DOES interact and phases with the shortwave to its south late Saturday and into Sunday morning. This causes the surface low to gradually strengthen and track from the Southeast and eventually moves to the west of our area. While an initial thump of moderate to heavy snow would be possible for locations to the north and west of NYC, precipitation would then quickly flip to rain for the remainder of this storm. This solution would have a rather limited impact for our area, with heavy rains likely during the day on Sunday.
The system over Canada DOES NOT interact with the southern stream system and misses the phase. This would allow for the surface low to move to the south and east of our area, bringing in much colder temperatures into the Northeast. A thump of moderate to heavy snow would be likely for most of the Northeast late Saturday night and into Sunday morning. Snow would potentially change to sleet and freezing rain from south to north during the day on Sunday as warmer air in the mid levels of the atmosphere moves over temperatures that are still below-freezing at the surface. This would create a potentially hazardous situation for the immediate NYC area, with a thick layer of ice on top of snow. In this scenario, locations to the north and west would have a good shot at staying mostly snow as cold air from the north rushes into the area. This solution would obviously have a much higher impact for all locations outside of the immediate coast.

This afternoons model guidance did trend towards a solution with less interaction between the Canadian system and the main shortwave, which allowed for some more cold solutions to show up. Additionally, the models have been advertising that the magnitude of cold air just to our north will be quite impressive Saturday night and into Sunday. This cold air will be very dense, and computer models usually tend to move this cold air out of the Northeast much too quickly, leading to an underestimate of frozen precip.

At this time we feel that the trends towards a less-phased system have merit, and there will likely be a period of moderate to heavy snow late Saturday and into Sunday. While there is a high amount of uncertainty regarding what happens after that point, snow could gradually flip over to freezing rain and rain during the day on Sunday for much of the area, which would open the potential for a hazardous solution. This scenario would have the majority of the impacts mainly to the north and west of the city.

**It is important to note that this system is still a couple days away and we will still likely see some significant changes in that time. We will continue to closely monitor the progress of this system and provide updates as new data becomes available!

Impact map for this weekends system

Have a great night!

Steve Copertino

Watching Two Snow Threats Later This Week and Into the Weekend

January 14, 2019/2 Comments/by Steven Copertino

Good Evening!

Today has been quite cold and calm across much of the Mid-Atlantic and Northeast as the storm system that impacted much of the Central US to the Mid-Atlantic moved offshore very early this morning. High pressure has now begun to build in from the west in this system’s wake, ushering in colder mid-level temperatures from the Northwest. With cold mid-levels and mainly clear conditions in place today, highs were able to only reach into the upper 20’s to lower 30’s across much of the New York metro area-which is just slightly below-normal for this time of year.

Continued clear skies, cold mid-levels, and light winds will aid in the development of decent radiational cooling during the overnight hours. Low temperatures should drop steeply into the middle teens to lower 20’s across much of the forecast area tonight, with single-digit readings possible for elevated locations well off to the north and west of the city.

This evenings high-resolution regional radar and surface observations showing a cold, but very calm evening in place for much of the Northeast (Simuawips)

Cold and Clear Through Midweek

High pressure will remain in control for much of the day on Tuesday before a very weak and moisture-starved system begins to approach the Northeast from Canada. As this system approaches the area, lower to mid-level winds will shift from northwesterly to more westerly, allowing for only slightly “warmer” air to move in. This system may also have a chance to briefly increase cloudiness over the Northeast during the afternoon hours. Some slightly increased cloudiness and westerly flow aloft will likely allow for highs tomorrow to head into the middle 30’s to lower 40’s across much of the forecast area. While these temperatures are slightly warmer than today’s highs, they will still be right around normal for this time of year. As this weak system moves through moves through tomorrow afternoon/evening, there may be some light snow showers over portions of New York State and Northern Pennsylvania, but the entire New York metro area should remain dry. Once this system moves on through the area, a weak cold front will then quickly move from west to east, eliminating any remaining clouds in the area. With a relatively more mild airmass overhead tomorrow night, highs will likely only be slightly warmer than this evening’s, with readings in the upper teens to middle 20’s likely.

Wednesday will start off much like Tuesday with calm, clear, and cold conditions in place for the morning commute. Temperatures will be rather cold, with lower to middle 20’s likely for much of the immediate metro area. Another weak mid-level system will be moving very quickly well to our north on Wednesday afternoon, with the potential for some increased cloudiness over the area. Highs will reach the middle to upper 30’s, with lower 40’s likely closer to the coast.

The potential will exist for some light snow snow showers off to the north and west of the city on Wednesday afternoon/evening, but it is highly unlikely that these snow showers are able to make their way south into portions of New Jersey and New York City due to the best dynamics remaining well off to our north. As the evening continues on, another weak cold front will move through during the evening and overnight areas, bringing in another reinforcement of drier conditions. Wednesday night will likely be another cold and mostly clear night for the area, with lows dropping down into the lower to middle 20’s.

~Updated Weekly Planner for the NYC area~

Watching Two Potential Snow Threats Later This Week and Into the Weekend

Conditions will likely remain quite calm and cold through the middle of the week and into the first half of Thursday. However that looks to quickly change as we shift our attention towards the Ohio Valley. A weak northern stream disturbance will be moving quickly from west to east, with just enough moisture moving up from the south to produce a swath of light precipitation. Additionally, an area of high pressure will be located over New England, which should help this system continue on eastward towards the New York City area by Thursday evening. Light precipitation should move into the metro area by 7-9 pm, with most of the area starting as light snow. Initially, the aforementioned high pressure area should help the entire forecast area stay as mostly snow, with locations over Southern New Jersey possibly experiencing some mixing issues.

As we head deeper into the overnight hours, warmer air may continue to work its way into the immediate New York City area, causing a mix or change to rain. Precipitation will likely continue into the AM commute on Friday before quickly tapering off from west to east. At this time it does appear that this system could drop a quick coating to an inch or two across portions of the NYC metro area, with some locally higher amounts for elevated locations off to our north and west. The exact amount of snow/rain will be highly reliant on the track of this system, and we will have an update tomorrow as more data becomes available!

This evenings GFS model showing a weak disturbance producing an area of light snow over the Northeast late Thursday night and into Friday morning

Lastly, we mentioned the possibility of a “larger” system that could impact the East Coast this upcoming weekend all the way back on Friday. Since that time, the reliable computer model guidance has shifted away somewhat from a significant/pure-snowstorm, to more of a “thump” of moderate to heavy snow-along with a mix of sleet, freezing rain, and plain rain for much of the forecast area.

At this time we feel that the mostly likely scenario based on all available data is that another large storm system will develop over the Midwestern states on Friday night, with a large swath of moderate to heavy snow extending along the northern edge of the precipitation shield. This system will then have the potential to interact with a much larger mid-level system over Canada on Saturday, which will likely cause it to strengthen a bit as it tracks over the Southeast. A large and expansive upper level jet streak will help to “vent” this system out, allowing for precipitation to expand into the Northeast by Saturday afternoon. Thermal profiles appear to be cold enough for precipitation to start and stay as mostly snow for the NYC area during the afternoon and early evening hours. There is the potential that the snow could eventually change to a mix of sleet, freezing rain, or even plain rain by the overnight hours of Saturday or early Sunday, but this is where the models begin to diverge significantly. Depending on just how much this system interacts with the large tropospheric polar vortex over Canada will dictate just how much cold air can get involved and where exactly this system will track.

There is still quite a bit of time to track this system, and we could still see a shift towards either side (colder with more snow or warmer with more rain) over the next few days, so make sure to check back for updates!

This afternoons ECMWF model showing a large area of wintry precipitation breaking out over the East Coast on Sunday

Have a great night!

-Steve Copertino

Light Mix Moves Through, Watching This Weekend

January 7, 2019/0 Comments/by Steven Copertino

Good evening!

Today has been a rather cold and clear day over the entire Northeast, especially when compared to the past week or so. Stout northwesterly flow has ushered in a much more cold and dry continental Arctic airmass over the entire area, which has kept high temperatures in the upper 20’s to lower 30’s-with some mid 30’s over SNJ and Long Island.

The large, but disorganized mid-level system that we have been going over for the past week has begun to gradually edge into the Northeast this afternoon and has been producing some very light sleet and snow across portions of Pennsylvania and New York. This area of precipitation looks rather impressive on radar, but surface observations confirm that there has been barely any precipitation reaching the surface-even under the heaviest of radar echoes. This is mainly due to the very dry and dense Arctic airmass still in place through the lowest ~500 feet of the atmosphere. As the snow falls towards the ground it is evaporating in addition to transitioning to sleet. Since radar beams gradually increase with height the further out from the radar site you go, these beams are hitting this area of transitioning precipitation, causing the precip to look more intense than whats being observed at the surface.

Regardless, the narrow band of mixed precipitation will continue to gradually head east over the next few hours–likely impacting the metro area just in time for the evening commute. Due to the very unimpressive forcing and low level dry air in place, mainly sleet and freezing rain is expected for the immediate metro area with a few broken flakes mixing in at times. As we head into the NW suburbs and into portions of SNY, there could be more of a snow/sleet mix, with some very light accumulations on colder surfaces.

This evenings latest hi-res radar showing an area of light mixed precip working its way into the area

Light Mix Lingers Into Tuesday Morning

Continue light mixed precipitation mainly in the form of sleet, freezing rain, and rain will be possible as we head into the late evening and overnight hours of Tuesday as the area of high pressure currently situated over New England shifts offshore. This will cause low level winds to become more southerly in nature and will lead to an increase in available moisture. As always, a shift to more southerly winds also means an increase in surface temperatures over the entire area.

Locations over SNJ will be the first to really feel the effects temps rising above freezing, which will cause a changeover to all rain before 5 am. Since this current airmass has been rather stubborn, it may take some time for the warmer air to make its way north of NYC, but the changeover will continue through the overnight hours and into the very early morning hours tomorrow. At this time, locations north and west of the New York City area have the best chance at seeing prolonged periods of light sleet and freezing rain lasting through 5 am. Any accumulations with this system will be quite minimal, with the potential for some slippery roads by the time we reach the AM commute.

Temperatures will then quickly rise to above-freezing for the entire area around 8 am tomorrow morning as the last of the precipitation swings through. Though some dry air is expected to develop aloft as the main upper level system moves through tomorrow afternoon, skies should remain mostly cloudy with a chance at some light rain showers or drizzle lasting into the evening hours. Highs will likely reach into the lower to middle 40’s for the entire forecast area as cloudy conditions and mild low-level temps take over.

Things get a little more interesting towards the overnight hours of Tuesday as strong mid-level energy and residual moisture move through the Northeast with an associated cold front. This will create the potential for some increased precipitation to breakout after midnight. Given the steep changes in temperature with height and weak instability, there may even be some heavy spots of sleet and graupel that develop over portions of Pennsylvania and New Jersey. Otherwise, tomorrow night will be another mild night, with lows only getting down into the upper 30’s to lower 40’s with winds picking up significantly after the cold front moves through.

This evenings HRRR model showing the light area of mixed precipitation impacting our area later this evening and into the overnight hours

Attention Turns Towards This Weekend

Mainly calm and cold conditions will remain in place across much of the east for the rest of this week and lasting into this weekend. Northwesterly flow will be in place during this time, leading to below-normal temperatures and mainly dry weather. However, there are signs that we may have to watch a system coming out of the Southern Plains by Friday afternoon. The past few runs of the reliable computer models and their ensembles have shown that this piece of energy may try to interact with an incoming strong piece of energy from Canada. As of right now there are two scenarios being shown with this setup:

–The first (and least likely as of now) is that the shortwave trough over the Plains will phase with the incoming Canadian shortwave trough on Saturday. This would cause a large area of heavy snow to develop from the Midwest to the East Coast on Saturday/Sunday with significant impacts.

–The second (and most likely as of now) is that the shortwave over the South is not able to cleanly phase/interact with the incoming shortwave over Canada. Instead, the Canadian shortwave acts to suppress this system and the vast majority of the precipitation stays to the south of the NYC area, causing little to no impacts.

It is very important to note that we are still quite a while out, and significant changes are likely to occur between now and Friday. The overall evolution of this system will depend on the exact timing and location of each system and we will have to watch how these systems behave over the next four days.

This mornings GFS model which was the most aggressive model at the time. This model was phasing both the feature over the Plains and over Canada to produce a large snowstorm for the Northeast

Thanks for reading and have a great night! We’ll have an update on Wednesday!

-Steve Copertino

Saturday Soaker, Light Mix Monday?

January 4, 2019/0 Comments/by Steven Copertino

Good evening and Happy Friday!

Today has been another gloomy and cool Friday across much of the Mid-Atlantic and Northeast as out next system gradually approaches from the south. Increasing mid-level flow from the southwest has lead to a warmer and more moist air working its way into the region, with clouds on a steady increase during the afternoon hours. Despite the increasing cloudiness, temperatures have been able to reach into the middle to upper 40’s across the entire New York metro area. This is anywhere from 10-12 degrees above-normal for early January.

Clouds will continue to thicken during the evening and overnight hours as more moist air begins to stream northward ahead of a large cut-off low over the Southeastern states. It appears that any showers for the metro area should hold off until the early morning hours of Saturday, but southern portions of New Jersey could see some light to moderate rain begin to overspread the area by 11pm-1am. With thickening clouds, a mild mid-level airmass, and an approaching storm system, temperatures will only fall just a bit after sunset. Lows will only be able to reach back down into the middle to upper 30’s before southerly winds begin to cause an increase in temperatures overnight into the upper 30’s and lower 40’s.

This evenings regional radar mosaic showing a large upper level low approaching the Mid-Atlantic this evening

Soaker of a Saturday Incoming, Improving Conditions on Sunday

As the large upper level low located to our south begins to slightly become more organized Friday night and into Saturday, a surface low pressure system will begin to develop near Norfolk, Virginia. As this low begins solidify, a large area of steady rain should begin to overspread the entire New York metro area by 5-7am. The surface low pressure located to our south will help to direct a deep moisture feed directly into the area, likely causing a heavier batch of rain to move through around 8-10 am. While dynamics aren’t too impressive with this system overall, we could still see some localized areas of very heavy rainfalls with even a rumble of thunder mixed in–especially over portions of Long Island. As we head into the late morning and early afternoon hours on Saturday, the surface low pressure should then track off of the Southern New Jersey coast pushing the vast majority of the remaining heavy rainfall off the Mid-Atlantic coast. Additionally, highs will be once again be stuck in the lower to middle 40’s across much of the area, with upper 40’s possible along the coast.

Due to less-than-impressive dynamics and the potential for some dry air to get involved at the mid-levels of the atmosphere, the remaining precipitation on the western edge of the low should be more “showery” in nature-with drizzle possible as well. While occasional light to moderate rainfall is likely into the afternoon hours, the overall intensity should be greatly reduced when compared to the morning. These dreary conditions should last well into the evening hours, with the chance at some breaks in the precipitation before the main area of low pressure heads off to the north and east. The rain will finally tapper off from west to east Saturday night, with conditions quickly improving as this system pulls away. Expect breezy conditions and temperatures falling back down into the lower to middle 30’s for much of the area.

Sunday will be much more calm, with stout northwesterly flow overspreading the entire Northeast. Breezy and cool conditions are to be expected for much of the day as an area of high pressure begins to push southeastward from Canada. Additionally, high temperatures will also reach back into lower to middle 40’s, with middle to upper 30’s off to the north and west of the city. Calm conditions and clearing skies will last well into the evening and overnight hours as high pressure continues to build into the area. Conditions will be quite ripe for radiational cooling to take place Sunday night, with lows dropping into the lower to middle 20’s for the majority of the metro area, with teens even possible for NW NJ and SNY.

This evenings hi-res NAM model showing the evolution of the storm system later this evening and into Saturday night

Light Mix Possible Monday Night, Above-Normal Temps Continue Into Next Week

A large mid-level ridge will be over much of the East Coast on Monday, leading to cooler temps and relatively calm conditions, however our next system will not be far behind.

Another large, but disorganized area of energy will be over the Northern Plains by Monday afternoon, likely resulting in a sizable amount of mixed precipitation breaking out over the Midwest. Model guidance over the past day or so has become less organized with this upper level system, leading to a weaker surface reflection and much less precipitation overall. As this system likely begins to move through the Ohio Valley on Monday night and into the very early morning hours of Tuesday, the area of high pressure over the Northeast will begin to move offshore. As of right now there is a strong chance that the initial precipitation that moves through the Northeast will come in as a mix of snow, sleet, and freezing rain due to the residual cold air from the departing high pressure system. As we get into the day on Tuesday, all leftover precipitation should change to plain rain as warmer air from the south pushes into our area. At this time, chances of any significant impacts from wintry weather appear quite low.

Most of the reliable computer model guidance have the upper level system responsible for this system lingering over the Northeast through Wednesday, potentially producing another batch of light mixed precipitation over the Northeast, but it is much too early to talk about any specifics at this time.

We’ll continue to update you on both potential system over the coming days!

This afternoons ECMWF model showing the potential for some light mixed precip entering the Northeast on Monday night

Have a great weekend!

Steven Copertino

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