A major winter storm is expected to hit the Northeast primarily Saturday with a strong nor’easter developing and deepening as it tracks offshore. This will bring a swath of > 8″ accumulations from NYC through points north and east, with the bullseye likely over southern New England where snowfall totals could exceed 2 feet locally. Gusty north winds will accompany this storm, leading to some blowing and drifting snow. In line with most other forecasts this morning, my own forecast is for 7-10″ of snowfall in NYC but with the potential for a sharp gradient possibly cutting through the city itself, where the western part of the city could see below 6″ while eastern sections see closer to 10″ or more.
As with the last round of accumulating snow we had, antecedent conditions support enough cold air in place to result in an all snow event. With a storm track offshore enough so there should be no mixing, the primary uncertainty in snow totals arises from storm track. Model runs today should help us determine if the storm will track on/near the 40ºN 70ºW benchmark (more snow), or to the east (less snow). Overnight, model consensus has shifted west, supporting higher snow totals than were forecast at this time yesterday. If we see some consistency across runs today supporting this solution, confidence will grow in a significant snowfall for NYC. Mesoscale banding will bring bouts of intense snow with this storm, and the exact placement / duration of these features will determine where the highest snow totals occur.
GEFS ensemble plumes for total snow accumulation at LGA. The mean here is about 7″ with a significant spread between 3″-14″ between ensemble members.SREF ensemble plumes for total snow accumulation at KLGA. The mean here is much higher than GEFS, 18″, with similarly large ensemble spread between 2-35″!NWS Blend of Models total snowfall forecast ending 1 AM Sunday, showing about 11″ for NYC.NAM model total snowfall forecast ending 1 AM Sunday, showing 8″ for NYC.GFS model total snowfall forecast ending 1 AM Sunday, showing 7″ for NYC.ECMWF model total snowfall forecast ending 1 AM Sunday, showing 12″.WPC probabilities of > 6″ of snow accumulation by 1 AM SundayWPC probabilities of > 12″ of snow accumulation by 1 AM SundayNWS New York Office official forecast as of this morning, mainly calling for 6-10″ in the city proper.
Forecast Details
At the Surface
Models are projecting a couple shortwaves merging and developing as a coastal low off of the Carolinas later today and tonight. This storm is forecast to intensify and track a little east of the 40ºN 70ºW benchmark overnight, a position that historically signals the best snowmaking potential for NYC during coastal winter storms. The forward speed of this storm has picked up in model runs recently, but it is expected to be a strong storm with minimum pressures falling to the 960s by Sunday. A tight pressure gradient is expected between the intensifying low and high pressure to the north, which should cause gusty north winds to help advect cold air down to the coast.
Weather Prediction Center surface forecast valid for 7 AM SaturdayWeather Prediction Center storm track forecast.ECMWF “Euro” model surface forecast for 7 AM SaturdayGFS model surface forecast for 7 AM Saturday
850 mb – 700 mb Level
A robust 850 mb low-level jet flowing onshore from the northeast is forecast. This should provide the storm with good moisture content, aiding the formation of snow. Strong 850 mb and 700 mb temperature advection and frontogenesis is also evident in all models, occuring during the morning Saturday. This should induce heavy snow bands to develop for a few hours early on Saturday. These bands could produce 1-3″ per hour snowfall rates, and as always, areas where these bands set up and persist the longest will ultimately pick up the higher end totals.
GFS model 850 mb relative humidity & winds at 7 AM Saturday. A strong LLJ flowing onshore from the northeast is visible.GFS moidel 700 mb temperature advection at 7 AM Saturday.ECMWF “Euro” model 500 mb height and vorticity at 11 AM SaturdayECMWF “Euro” model 300 mb winds. Two jet streaks are evident in the vicinity of this storm, north and south of the storm’s projected center.
500 mb Level
This storm will benefit from a deep, synoptic scale trough that will acquire a slight negative tilt. This trough will eventually form a closed low at this level. This will aid the low in intensifying by increasing divergence at this level, facilitating upward movement of air over the surface low, leading to lower surface pressures.
300 mb Level
The storm’s center is expected to lie downstream of an exit region of a jet streak, and also upstream of an entrance region of another jet streak to its north. This is ideal placement for maximizing divergence at this level of the atmosphere over/near the low’s center, and supports the development of a strong surface low.
A relatively fast moving offshore low is expected to bring this winter’s first round of accumulating snow in NYC. Fairly good agreement among different models suggests decent confidence of totals NYC in the range of 3-5″, and it is worth noting that trends have been towards a higher total in overnight model runs. In fact, both the Euro and GFS agree on about 5″ of snow for NYC by the end of this event, and I tend to agree with this end of the forecast range at this time.
Antecedent conditions with a shallow but decently cold air mass in place means the primary uncertainty arises from storm track. Subsequent model runs should help us determine if the storm will track on/near the 40ºN 70ºW benchmark, slightly inside (more snow), or to the east (less snow). The timing of the snow during the overnight hours into the early AM rush will help boost totals since we will have enough cold air in place. Moderate and potentially heavy snow is likely during a 3-4 hour window starting around 4 AM.
GEFS ensemble plumes for total snow accumulation at LGA. The mean here is about 3.2″ with a significant spread among ensemble members both higher and lower than this.SREF ensemble plumes for total snow accumulation at KLGA. The mean is also about 3.2″, with similarly large ensemble spread..NWS New York Office official forecast as of this morning, mainly calling for 4″ in the city proper.
Forecast Details
At the Surface
Models are projecting a storm to develop off of Cape Hatteras and move close to the 40ºN 70ºW benchmark overnight, a position that historically signals the best snowmaking potential for NYC during coastal winter storms. This storm isn’t projected to be particularly strong, perhaps only dipping to 996-998 mb at its closest approach to the city, and it will be a relatively fast moving storm, both of which are factors that limit its potential to deliver large snowfall totals.
Weather Prediction Center surface forecast valid for 7 AM FridayWeather Prediction Center storm track forecast.ECMWF “Euro” model snowfall total for NYC from this event.GFS model snowfall total for NYC from this event.High resolution rapid refresh simulated radar valid at 4 AM Friday, depicting the strengthening storm hitting a swath of the Mid-Atlantic (including areas already walloped by this weekend’s major storm) and New England with a band of potentially heavy snow.
850 mb Level
There isn’t a strong sign of a robust 850 mb low-level jet with this storm. That’s in line with the profile of a weaker storm with less intense precipitation. However, most models are depicting strong 850 mb and 700 mb temperature advection and frontogenesis occurring for a few hours just south of the city, which could signal the possibility for some heavy snow bands to develop for a few hours overnight. It’s within these bands that we could see up to 1″ per hour snowfall rates, and as always, areas where these bands set up and persist the longest will ultimately pick up the higher end totals.
GFS model 850 mb temperature advection and frotogenesis as modeled by GFS valid at 4 AM Friday.GFS model 500 mb height & vorticity at 4 AM FridayECMWF “Euro” model 300 mb height and wind at 10 PM Thursday
500 mb Level
Another supporting factor for a decent round of snow with this storm is that there will be a negatively tilted 500 mb through developing upstream of the surface low. This should aid the low in intensifying, though as stated above, it still won’t be a particularly potent one at the surface when it’s nearest to us.
300 mb Level
The 300 mb level shows a an exit region upstream of the surface cyclone preceding the event. The WPC does discuss a coupled jet scenario with the jet streak at this level eventually helping induce a lower-level jet which would boost snowfall totals, but the this might happen after the storm really impacts us.
A very active weather pattern this month brings yet another chance for decent accumulations of snow in NYC. This storm will be on the weaker side, and will slow down as it tracks offshore of the region. The result should be a long duration but likely a generally light to moderate snowfall event. Snowfall totals around NYC will probably be in the range of 4-6″, though with every storm this season, some potential exists for both higher and lower totals. If colder scenarios and better lift are realized, we could see > 8″. A warmer scenario would see more mixing and totals below 4″. Light snow should spread over NYC during the afternoon hours with periods of moderate and potentially heavy snow in the early evening. Mixing with sleet and rain even is possible during the early overnight hours. Snow and sleet could continue into the early afternoon hours Friday.
Weather Prediction Center 48 hour median snowfall accumulations for the NYC metro region ending 7PM Friday. This is showing about 4-6″.
Weather Prediction Center 48 hour 90th percentile snowfall accumulations for the NYC metro region ending 7PM Friday, showing 6-8″.
GEFS ensemble plumes for total snow accumulation at KLGA. The mean here is about 7″ with a significant spread among ensemble members both higher and lower than this.
SREF ensemble plumes for total snow accumulation at KLGA. The mean is about 5.5″, with similarly large ensemble spread..
Forecast Details
At the Surface
Deep arctic air precedes this storm, which will form along a frontal boundary stretching from the Gulf Coast to offshore of the Mid-Atlantic. This low will be on the weak side, only hitting around 1012-1000 mb. For reference, the last couple storms that hit us were about 10-15 mb deeper. Over the course of the week, models have trended colder with the storm, pushing its trajectory further offshore, close to or outside of the 40ºN 70ºW benchmark that signals the best snowmaking potential for NYC during coastal winter storms. It is important to note that even with the track trending colder, mixing is still likely at some point during the storm, and significant mixing would lower overall totals. If we have an overall colder scenario, we may see closer to 8″ by this time Friday.
ECMWF “Euro” model surface precipitation/type at 1PM Thursday.
GFS model 1000-500 mb pressure, thickness, and surface precipitation/type at 7PM Thursday.
NAM model 1000-500 mb pressure, thickness, and surface precipitation/type 1PM Thursday.
Weather Prediction Center storm track forecast.
850 mb Level
There isn’t a strong sign of a robust 850 mb low-level jet with this storm. That’s in line with the profile of a weaker storm with less intense precipitation. However, most models do show the 850 mb warm nose setting up just south of the city, which would favor the strongest precipitation occurring as mostly snow over the city during the Thursday afternoon-early evening time frame.
NAM model 850 mb winds and relative humidity at 1PM Thursday.
GFS model 850 mb temperature, height, wind at 1PM Thursday
ECMWF “Euro” model 500 mb height & vorticity at 1PM Thursday
500 mb Level
A longwave trough that reflects the very cold air over the central part of the US will be in place upstream of this low. There will not be any negatively tilted trough at this level providing enhanced lift for this low, thus explaining the weaker profile of this storm.
300 mb Level
Similarly, the best support for strong lift at this level of the atmosphere won’t come until late in this storm’s evolution. There are no clear entrance or exit regions co-located with the storm early on, signifying an absence of enhanced lift from divergence at this level.
Another accumulating snow event is possible during the day Sunday this weekend, with accumulations somewhere in the 2-4″ range currently most likely. If this storm tracks a bit closer to shore, we could see totals more in the 4-6″ range. The timing of this storm is much faster than the previous one, with onset of snow early in the day Sunday, lasting potentially through the early afternoon hours. As a weaker system, without as strong a high pressure system downstream, winds should also not be as robust as with the Monday storm.
Weather Prediction Center 48 hour 50th percentile snowfall accumulations for the NYC metro region ending 1AM Wednesday
Weather Prediction Center 48 hour 90th percentile(median) snowfall accumulations for the NYC metro region ending 1AM Wednesday
GEFS ensemble plumes for total snow accumulation at KLGA. The mean here is about 4″ with a significant number of ensemble members showing lower amounts.
SREF ensemble plumes for total snow accumulation at KLGA. The mean is about 2″, with similarly large numbers of ensemble members showing lower amounts.
Forecast Details
At the Surface
Low pressure developing over the Southern Plains will emerge offshore of the Carolinas later tonight. This surface low will strengthen modestly as it tracks quickly northeast. Current thinking is that the storm track takes it outside of the classic 40ºN/70ºW benchmark that leads to maximized snowfall for nor’easter type systems in this area.
ECMWF “Euro” model 1000-500 mb pressure, thickness, and surface precipitation/type at 1PM Sunday.
GFS model 1000-500 mb pressure, thickness, and surface precipitation/type at 1PM Sunday.
NAM model 1000-500 mb pressure, thickness, and surface precipitation/type 1PM Sunday.
Weather Prediction Center storm track forecast.
850 mb Level
At this level of the atmosphere, it’s apparent that this storm is much less of a headline maker than Monday’s snowstorm. It’s evident from various models that while there should be enough moisture to sustain precipitation, the winds at this level are not forecast to be anywhere near as strong as on Monday. The lack of a truly robust low-level jet will make for an overall slightly drier scenario.
ECMWF “Euro” model 850 mb winds and relative humidity at 1PM Sunday.
GFS model 850 mb winds and relative humidity at 1PM Sunday.
NAM model 850 mb winds and relative humidity at 1PM Sunday.
500 mb Level
Unlike the last storm, the 500 mb level flow for this upcoming storm is more progressive. This will lead to the storm moving faster through the area. One notable factor contributing to the potential for a decent storm this time is that there will be a negatively tilted trough at this level, indicative of a maturing and deepening low. This feature will serve to enhance divergence at this level and induce surface lift in response.
300 mb Level
As was the case with Monday’s storm, a curved jet streak should set up just north and east of this storm’s surface low. The entrance region of this jet streak should allow stronger divergence and enhanced lift as a result.
A quick hitting storm passes south of the city today bringing some rain and mixed precipitation, with no accumulating snow expected. Colder temperatures then take hold in the mid-30s behind this storm Tuesday as a strong area of high pressure builds over Quebec. This sets the stage for a potentially significant snowstorm developing Wednesday into Thursday with 8″+ totals possible along the I-95 corridor (with higher amounts north and west). However, there is still a good deal of uncertainty with the eventual track of this storm that could result in large differences in outcomes.
Rest of today – temperatures dropping through the low-40s into the 30s with mostly cloudy skies and a steady, chilly rain, possibly mixing with some wintry precipitation. No accumulation is expected. Overnight lows around the freezing mark with precipitation ending as high pressure begins building in.
Weather Prediction Center surface forecast for 1PM Monday. An area of low pressure is seen exiting the east coast, bringing us a period of rain and possible mixed precipitation, with snow further inland.
Tuesday – proverbial calm before the storm as high pressure dominates, giving us a mostly sunny day with high temperatures around 40ºF. Overnight lows again in the upper-20s with cold northerly winds flowing around the east side of this high.
Wednesday – high pressure yields to a developing coastal storm. Partly sunny to start with increasing clouds. High temperatures in the mid-30s. Overnight lows drop into the mid-20s. The big story is the potential for a significant snowstorm with accumulations possibly over 8″. GFS and the Euro model have come into agreement for much higher totals, 14-15″. However, NAM shows a warmer scenario with warmer air working further north, thus cutting into overall totals (only 7″). It’s also possible that the low tracks close enough to shore that we end up with a good deal of rain mixing in at the coast, cutting snow totals even further.
Part of the energy fueling this storm is coming all the way from a shortwave with origins over the Pacific Ocean. This has only just made landfall in the US today. As this energy gets sampled by upstream soundings (weather balloon launches) and other means, the forecast models should get a better sense for how this storm will evolve. At this time, there’s enough uncertainty in the forecast to still not buy into any specific totals. If you look below, you can see there’s a lot of spread in the models in terms of the track of this storm. This then translates to a wide range in ensemble forecast totals. In addition, with a coastal storm like this, where there’s a lack of deep, Arctic cold air ahead of the storm, there’s a sharp gradient between areas where the event would be all snow vs. a mixed event. If you see the 24 hour probabilities of > 8″ accumulation, you can see that a 50 mile shift in the storm track further south and east would give us much higher chances for big snowfall totals, while a shift the other way could result in a bust on snow totals. Suffice to say, this storm will bear close monitoring today and tomorrow as more data comes in and models have a chance to digest it.
ECMWF “Euro” model surface pressure, precipitation and type for 1AM Thursday
ECMWF total snow accumulation at 7AM Thursday, showing 14″ of snow in NYC.
GFS model surface pressure, precipitation and type for 1AM Thursday
GFS total snow accumulation at 7AM Thursday, showing 15″ of snow in NYC.
NAM model surface pressure, precipitation and type for 1AM Thursday
NAM total snow accumulation at 7AM Thursday, showing 7″ of snow in NYC.
Weather Prediction Center probabilities of > 8″ total accumulation in 24 hours leading up to 7AM Thursday
Weather Prediction Center storm track forecasts, note the cluster of blue crosses associated with a surface low near the Delmarva Peninsula. This is the storm that could bring us snow.
GEFs ensemble model plumes showing a huge range of possible snowfall totals at LGA during this storm. The mean is 7.83″.
Thursday– depending on the speed and track of the storm, we could see precipitation lingering into the morning hours, with additional accumulation possible. Highs should hover around the freezing mark. Overnight lows drop into the mid-20s with reinforcing cold air advection on the backside of the departing storm.
A major news story unfolded over the weekend as the Southeastern US got slammed with a snowstorm that dropped uncommon snow totals over the area, causing widespread travel disruptions. This region of the country is not accustomed to snowstorms of this scale and many municipalities were not prepared for it. Making matters worse, there was a major forecast bust in this storm, which shared key characteristics with a similar forecast bust that led to a high impact snowstorm hitting NYC a few weeks ago on November 15th (and may have prompted the ouster of the director of NYC Office of Emergency Management). For example, Richmond, VA had a forecast going into Sunday for only 1″ of accumulating snow, but in fact received 11.5″ when all was said and done – a near record-breaking storm.
Below, I’ll provide a “post-mortem” analysis of why forecasters missed the mark so badly in this case. The overall lesson here underscores the difficulty of forecasting snow when temperatures are expected to be hovering close to freezing, especially in coastal storms where the precipitation gradient can be quite sharp.
Dry air at the outset of the storm
Soundings from KWAL (Wallops Island NASA Launch Facility, which we can use as a reasonable proxy for areas in Virginia heavily impacted by snow) at the outset of this storm showed very dry air at the low levels of the atmosphere. This is indicated by the large gap between dew points (green line) and the environmental temperature (red line) on the Skew-T diagram below.
Since I think most people reading this are probably not familiar with Skew-Ts, let me provide a brief exposition. These charts are densely packed with data and can be difficult to read. To orient yourself, know that the y axis on these represents pressure levels from the surface (~1000 mb) all the way up to almost the very limit of the atmosphere at 100 mb. Pressure levels are also related to altitude, though this relationship is not linear because it depends on temperature. The x axis on these charts shows temperature in degrees Celsius. However, note that the lines of temperature are actually slanted at a 45 degree angle and not straight up. The dotted blue line to the right marks the 0 degree mark, critical for determining whether precipitation is frozen or not.
So back to the Skew-T at hand – notice that above the 700 mb layer, the dew point (green) and environmental temperature (red) lines were essentially overlapping. This indicates a layer of air that’s reached saturation since by definition, dew point is the temperature to which the air would need to be cooled to be saturated. When you see a thick layer of dew points and temperatures meeting, it generally indicates ongoing precipitation (thinner layers like this can indicate clouds). In this case, what’s happening is that precipitation is falling from about 400 mb down, but from 700 mb and below, the air is very dry.
With this set up in place, we have excellent conditions for evaporational cooling. As precipitation from above starts to saturate the layers below (some of the precipitation evaporates into the dry layer), the temperature actually cools because evaporation is a phase change of water that requires an input of energy (heat). This is exactly the same mechanism that occurs when you exercise and sweat, or when you step out of a shower (even a cold one) and feel cooler. The net effect of the evaporational cooling in this case, like in the storm that hit NYC in November, was to keep environmental temperatures below freezing for longer than expected (shifting the red environmental temperature line to the left on a Skew-T), allowing snow to fall and accumulate for a longer period as well.
The issue for forecasters here, and for NYC on November 15, was that the models were not all in agreement about how dry the low levels of the atmosphere would be at the outset of the storm. Forecasters are trained not to rely solely on just one model’s depiction of upcoming events, even though in this case, some models had what turned out to be a much more accurate take on dry air. As we’ve seen, the difference of a degree or two when temperatures in the atmosphere are close to the freezing line can have serious consequences for tangible weather impacts.
Frontogenesis and mesoscale (localized) banding
When coastal storms form off the East Coast during the winter, the temperature differential between the warmer air south of the storm’s core and the colder air to the north can lead to frontogenesis, which is the process of the formation of a frontal boundary. In these storms, the result is a coastal front. During this process, a mesoscale circulation forms as atmospheric dynamics attempt to restore equilibrium between cold and warm airmasses. This circulation can greatly enhance lift, a critical ingredient for heavy precipitation, as well as helping cool the air columns. For coastal storms during the winter, the result of strong frontogenesis is the development of narrow, but intense localized bands of heavy precipitation. The difference between an area impacted by a band like this can easily be more than 0.50″ of liquid equivalent, which if you convert to snow using a standard 10:1 snow-to-liquid ratio is 5″! The trouble with these mesoscale features, as is the case with thunderstorms, is that even the most advanced forecast models do not have sufficient resolution to accurately capture features on these scales. That means it’s often difficult to know for certain if/where/when one of these bands sets up and for how long – a critical, high impact detail that can make or break any forecast.
Analysis of frontogensis at 1PM on Sunday – the blue-green hues over Virginia indicate areas of strong frontogenesis
As it happened, with this storm, stronger frontogenesis than forecast took shape. The North American Model (NAM) actually had a pretty good handle on this, but as with the NYC storm, forecasters didn’t put all their eggs in one basket and side with this solution.
NAM’s forecast for frontogenesis valid at 3PM Sunday – the very tightly packed purple lines are an indication of intense frontogenesis
Cold air damming
Along the Eastern Seaboard, certain orientations of high pressure systems can lead to an effect known as cold air damming. This occurs when high pressure centers of Canadian origin set up northeast of the mid-Atlantic and Southeast. Anti-cyclonic clockwise flow around these highs brings cold air around the core of this high into the East Coast with easterly winds. At some point, these winds start to hit the eastern flank of the Appalachian mountains. Because cold air has higher density, the mountains provide an effective barrier to the westward (and upward) progress of this cold air. This then leads the air to gradually turn to the left (south) and progress further south than would otherwise be possible without the cold air damming effect. This is visible from the following surface analysis where you can see surface isobars linked to the high pressure center “sagging” south along the eastern edge of the Appalachians. This phenomenon can provide a critical shot of cold air in advance of a storm that can tip the balance from a rain event to a snow/mixed/frozen event. Forecasters probably did have a decent handle on this, but I mention it because it would have helped in keeping cold air in place prior to and during the beginning of the event.
Given that this scenario has unfolded twice this season, a key takeaway for forecasters should be to have heightened awareness of snowfall totals exceeding model consensus when one or more of those models is indicating the possibility for both strong frontogenesis with a coastal storm like this and very dry air preceding such a storm. Ideally, forecasters and emergency managers should be in close communication about probabilities of exceeding forecast totals as soon as evidence and observations show a colder scenario unfolding. If possible, these details should be passed on to the general public by highlighting the uncertainty that exists and probabilities, even if they’re not high, of exceeding forecast totals dramatically. Municipalities should have a fallback plan for fast mobilization of personnel and equipment for snow removal in the event that a forecast bust of this magnitude starts to look more likely during the early onset of a storm when we can verify things like dew points, and observe trends of mesoscale bands on radar.
Classic major nor’easter to bring blizzard conditions to a large swath of the Northeast Tuesday just days from the official start of spring. Areas in and around NYC likely to see snowfall accumulations of over 1 foot, locally higher. This may end up being one of the biggest snowstorms/blizzards in history for the month of March in NYC.
Rest of today – the proverbial calm before the storm. Mostly sunny, cold, with high temperatures in the low-30s.
Tuesday – a major late season nor’easter will bring heavy snow and blizzard conditions to the area. Blizzard warning in effect for the entirety of Tuesday. Snow starts falling overnight into Tuesday. Heaviest snows forecast to begin around the morning rush and continue through most of the day. Blizzard conditions expected on the coast with steady north to northeast winds 30-35mph and gusts over 45mph. Visibility near zero at times. High temperatures at or below freezing. Widespread accumulations over 1 foot and approaching or exceeding 18″ expected around the NYC metro area. Details on the storm at the end of this post.
Wednesday – lingering chance for snow showers early with wrap around moisture on the backside of the departing nor’easter. Mostly cloudy with a high near freezing.
Thursday – skies clearing, high temperatures in the low-mid 30s.
Major Blizzard to Impact the NYC Region
Winter Storm Stella, as the Weather Channel refers to it, is set to bring widespread heavy snow to the area beginning overnight Monday and continuing throughout the day Tuesday.
Impacts – Snow accumulations over 1 foot, in many cases approaching 18″. Locally higher amounts, with some areas possibly approaching 2 feet. Heavy snow and blowing snow during the day Tuesday. Snowfall rates 2-4″ per hour and possibly higher in the heaviest snow bands possible. Thundersnow may accompany the strongest snow bands. Blowing and drifting snow with steady northeast winds 30-35mph and gusts 45-50mph will contribute to blizzard conditions with near zero visibility at times. East and northeast facing shorelines may experience moderate coastal flooding during high tide cycles. Heavy, wet snow at the coast combined with high winds may lead to power outages. Hazardous travel conditions, severe disruptions to aviation likely. High confidence in storm total snowfall at this point, but there is still uncertainty about whether and where mixing could occur.
Timing – Snow begins early in the overnight hours Tuesday. Light accumulations of 2-4″ possible by daybreak. Heavy snow likely beginning during the morning rush hour and continuing through most of the work day, as well as into the evening rush hour. Winds quickly intensifying from the morning and staying steady through the evening hours. Heaviest snow tapers off in the early evening hours, but snow showers could continue overnight. Winds remain strong overnight into Wednesday. Conditions improve going into the morning Wednesday.
Discussion – an area of low pressure that had its origins in the Pacific has made its way across the northern US, impacting the Northern Plains and Upper Midwest with snow. This storm system will phase with a secondary, coastal low pressure system that is currently moving up the coast from the Southeast. As these storms merge, the coastal low will undergo rapid intensification and cyclogenesis, becoming a strong Nor’easter. This storm will be drawing on subtropical moisture, and will encounter an airmass that will be quite cold due to the presence of an Arctic high pressure system prior to the storm’s passage. These ingredients will set the stage for a classic major blizzard for the Northeast late in the winter season, only days from spring.
As always, uncertainty remains about the exact location of the heaviest snow bands with this storm. Areas that are impacted by these bands can easily rack up several more inches than surrounding areas that are spared. The storm is expected to track west of the 40°N/70°W benchmark. However, during the last model runs, the storm track has trended north and west, increasing the chances for the city itself to see the heaviest snow, in addition to areas north and west. If this track shifts west some more, warmer air off the ocean wrapping into the core of the storm from the south could induce mixed precipitation with rain cutting down on totals in the city and Long Island. If the track shifts east, heavier snow would fall over points east of the city.
Above average temperatures today give way to accumulating snow Friday. Very cold air then rushes in for the weekend, much along the lines of last weekend. This time around, cold air will persist, as a polar vortex is set to take hold of the East Coast. With this cold air in place, there is potential for a significant snowstorm in the form of a Nor’easter/coastal storm early to mid-week next week.
Rest of today – quite warm still with high temperatures remaining steady around the mid-50s. Breezy with west wind between 15-20mph under clear skies. Increasing clouds towards nightfall.
Friday – a rain/snow mix is anticipated to begin falling overnight, steadily transitioning to all snow by daybreak. This looks to be a messy commute. A cold front slides south of the area and a strengthening low pressure center moves along this frontal boundary, bringing us this snow. Due to warm temperatures in preceding days, snow will have a hard time sticking at first, but temperatures will remain cold enough throughout this event to yield likely snow accumulations of 3-5″.
Saturday – temperatures will remain well below normal as winds shift to the northwest following the passage of the cold front and storm system above. Breezy with winds around 15-20mph and decreasing clouds. High temperatures will struggle to hit freezing. Overnight lows leading into Saturday and then overnight into Sunday only in the teens.
Sunday – cold, sunny, with high temperature again barely at or above freezing. Spring forward occurs early Sunday, set your clocks ahead and get ready for more sunshine late in the day (not that it’ll help make things warmer right now).
Winter Not Giving Up – Possible Snowstorm Next Week
The predominant weather pattern thus far this winter has been one in which the jet stream has taken on an orientation that favors above average warmth over the eastern half of the US. Just as we turn the corner towards spring, it appears we are about to get slammed with a polar vortex and weather pattern more typical of February. While the cold itself will be enough to put a damper on spring, the real headline is the possibility for a significant late-season snowstorm in the form of a Nor’easter some time early to mid-week next week. Will keep you all updated on this as more data becomes available in the coming days.
An eventful week of weather continues into the weekend, though not to the same degree of intensity. We will see another chance for snow, as well as rain this weekend. Temperatures rebound back to around or slightly above normal for the weekend. Looking ahead, there are some signals at another possible strong storm a couple weeks out, but it’s much to early to be certain.
Rest of today – cold, windy, sunny with areas of blowing snow. High temperatures below normal around 30ºF. Wind chills in the teens. Overnight tonight, we could pick up a light coating of fresh snow from a fast moving, and relatively weak storm system.
Below are some reported snowfall totals from yesterday’s coastal storm. As you’ll see, there was a fairly sharp cutoff between areas that received 9″ or more of snow. Long Island, Connecticut, and parts of the Hudson Valley got the largest totals. This was largely due to the fact that the most intense bands of heavy snow spent more time parked over these areas than it did in the city.
Saturday – conditions improving, along with warmer temperatures in the mid-40s under mostly cloudy skies.
Sunday – another storm system moves in from the Ohio Valley. This will bring a mixture of precipitation to the Northeast. Luckily, with high temperatures in the low-40s, we will see all rain.
Monday – winds pick up behind the departure of the storm system above, and skies should clear up as well. Temperatures should again be in the low-40s.
We’re in for a wild ride over the course of the next 24 hours as our weather goes from possibly record-breaking warmth to what is expected to be the most significant winter storm so far this season. Significant snow accumulations over 6″ and possibly as much as a foot are expected across the region, resulting in a winter storm warning for all of the NYC metro region.
Timing
Judging by the amount of sun we’re getting, temperatures will likely hit record-breaking levels in the low-60s in the city today. They will drop steadily to around 50ºF by the evening commute as a cold front pushes through and Arctic air flows in from the north. Overnight, temperatures will continue falling rapidly to around freezing. Precipitation is expected to begin around 3-4AM Thursday here in the city and continue through the early afternoon. Unfortunately, the timing of the heaviest precipitation does look to bring significant impacts to the morning commute.
North American High Resolution simulated radar 1km resolution, tomorrow at 8AM.
Impacts
Rain/snow mix to start, but by the morning rush, expecting all snow through the region. Heavy snow at times possibly reaching 1-2″/hr. Some thundersnow could occur. Hazardous travel conditions during the morning rush as plows will have trouble keeping roads clear with traffic and the moderate to heavy snow. Gusty winds could produce near-blizzard conditions with low visibility.
Snowfall Totals
Here are some graphics for snowfall totals from our local National Weather Service Forecast office. The general forecast calls for 6″-12″ in the city. The exact extent of totals will depend, as is generally the case with this type of storm, on where the heaviest snow bands set up and for how long they sit over an any given area.
Probabilities for 4″+ and 6″+ of snow respectively
Discussion
An shortwave that’s made its way rapidly across the country from the Pacific will move along the cold front that is pushing through today. As it does so, it will spawn a secondary low off the Mid-Atlantic that will strengthen rapidly as it moves over open water. At the same time, plenty of cold air will wrap around the deepening coastal low with high pressure to the west. This will put in place all the ingredients for a classic coastal winter storm for this area. The only thing keeping this storm from being a major blizzard with snowfall totals exceeding 2 feet is the fairly quick pace that it’s expected to move at.
This coastal storm will drive the expected heavy snows tomorrow. Its track is expected to take it just outside the 40ºN 70ºW benchmark, a spot that from a climatological perspective has translated to heavy snow storms for this region.
