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.
It’s been a long hiatus for me posting content to this blog. Been a bit preoccupied with everyday life, but getting back into the swing of things with a detailed meteorological summary of the tragic and deadly extreme flash flooding event that took place on the evening of Sept 1, 2021. Credit for this goes in part to my friend and colleague Phil Lutzak, a fellow graduate of the PSU World Campus Weather Forecasting Certificate Program.
Synopsis
In this overview of the NYC flooding event of September 1st, 2021, the main goal is to ascertain why such severe flooding occurred in light of the preceding and concurrent weather conditions for that day. While it was quite well forecast by the NHC and NWS office forecasts in terms of a significant flood threat, clearly no national office could pinpoint the areas that would suffer the worst flooding until the day of the event when it was much clearer where the heaviest rains would be falling, nor could they possibly have gotten the exact severity correct given current forecasting capabilities. In hindsight we will examine the existing conditions during and just before the most intense period of the flooding and try to determine which developing synoptic and mesoscale parameters gave the most clues as to why much of the worst flooding conditions would be directly within the New York City metropolitan area.
Forecasts Leading Up to the Event
There was a misconception after the event that the meteorological community failed to forecast the possibility of this event occurring. In fact, National Weather Service Weather Prediction Center had a solid grasp of the risks associated with the post-tropical remnants of Ida, having issued a high risk for flash flooding for areas of the Mid-Atlantic and Southern New England in the early morning hours of Wednesday, 01 Sept 2021 (4:20 AM EDT).
The forecast discussion behind this excessive rainfall outlook was chilling in its prescience, specifically citing the possibility of deadly flash flooding and 3-8” rainfall totals.
In MPD #0925, WPC forecasters referenced 2-3+” per hour rainfall rates being possible due to a combination of factors, most notably very strong low-mid level forcing via frontogenetical influences and highly efficient, deep layer warm/tropical rain processes – a characteristic of Ida’s hybrid tropical/extratropical nature.
The importance of Ida’s unique blend of tropical transitioning to extratropical character is also underscored in MPD #0923, in which WPC forecasters discuss the presence of a developing south-southwesterly low-level jet. This feature would reach peak strengths of 35-55+ knots at the height of the event, and became a critical ingredient in creating the exceptionally efficient moisture transport into the NYC area, shown in the following sections.
By 9:28 PM that evening, the worst-case scenario envisaged by forecasters leading up to the event came to fruition and the NWS OKX office issued its first ever Flash Flood Emergency for NYC, containing the emphatic “THIS IS A PARTICULARLY DANGEROUS SITUATION” wording…
Meteorological History
Surface Conditions
The following chart shows the radar representation and surface charts of the 48-hour progress of tropical depression Ida from the lower Mississippi valley into the Tennessee and Ohio River valleys and then into the mid-Atlantic and northeast regions. In the middle image it is clear that the heaviest precipitation was reduced as its inflow was becoming detached from the very moist Gulf of Mexico. The third, rightmost image shows how the tropical low, now merging with the warm front, was elongating north to south but at the same time tapping into a very moist airflow from the Atlantic Ocean, strongly enhancing the area of heaviest precipitation near the center of lowest pressure.
Low and Mid-Level Conditions
While the high precipitation producing ability of tropical depression Ida was still in evidence, the position of its southerly flow in relation to the fairly stationary warm front allowed for maximum isentropic lift to focus right over NYC and surrounding areas, with much of the convection moving in from the south still having high precipitation producing energy powered by high theta-e tropical inflow.
Here’s the MUCAPE analysis from 0200 UTC showing 1,000-2,000 J/kg positioned over NYC,
… and the following showing the extremely high 850 mb level moisture transport over the NYC area at 0200 UTC.
The 925-850 mb frontogenesis chart shows clearly where maximum frontogenesis was occurring
and the surface moisture convergence and DMC charts show, not surprisingly, that a maximum for surface and deep moist convergence was occurring over NYC and surrounding areas.
Mid to Upper Levels
This situation was one of the clearest examples of how baroclinic forcing can convert a weak or decaying tropical cyclone into an extremely prolific rainmaker. The 500 and 300 mb conditions were critical in allowing this approaching tropical low to make a fairly quick transition to a strong extratropical low. The result was the previously discussed extremely high moisture convergence right over the city.
The 300 mb chart from 8PM EDT shows the right rear entrance region of a quite strong jet streak for late summer (100-120 knots) moving into position almost directly over the low which was just southeast of the NYC area, allowing for maximum divergence above the low center as it was merging with the warm/stationary front. This allowed for very high divergence to position over an equally strong low level convergence zone.
In addition, the 500 mb analysis shows an ideal placement of the area just east of the trough base over the lower-level low circulation to allow strong upper-level divergence, resulting in intensification of the transitioning surface low.
All levels
For one final view that ties activity at the previous levels together, here’s the ARL simulated skewT diagrams for 0100 and 0200 UTC at New York City that evening. Clearly the atmosphere was saturated throughout with very high theta-e values at the lowest levels.
Conclusion
From the NY Times, September 2nd, 2021:
The rain broke records set just 11 days before by Tropical Storm Henri, underscoring warnings from climate scientists of a new normal on a warmed planet: Hotter air holds more water and allows storms to gather strength more quickly and grow ever larger.
In New York City, the dead ranged in age from a 2-year-old boy to an 86-year-old woman, the police said. Some drowned in basement apartments in Queens, where a system of makeshift and mostly illegally converted living spaces has sprung up.
Below are two dramatic images of the flooding in NYC. On the left is severe subway flooding that occurred in lower Manhattan (courtesy NY times). At right are multiple stranded vehicles on the Major Deegan Expressway in the Bronx borough of NYC (courtesy Craig Ruttle/AP).
It’s likely not possible at this time, nor in the near future, to use RAP or any of other quickest analytical tools to anticipate imminent flooding at the smallest mesoscale any more than we are currently able to. At this stage of the science, the most skilled forecasters use the best modeling tools currently available along with their own invaluable experience in watching unfolding precipitation patterns on radar loops and, combined with mesoscale graphics such as we have displayed here, anticipate where the heaviest precip is moving and whether it will intensify, weaken or remain stable.
In light of this, a critical takeaway is to encourage better education of the public about what an “Emergency” and what a “Particularly Dangerous Situation” mean in practical terms. In other words, when the public receives an EAS alert with these terms in it, they need to be acutely aware of what preventive actions to take immediately rather than just dismiss this as another alert that probably won’t affect them. One other challenge with this system is that these alerts are often only translated to only one or two other languages. This is a problem for a city with hundreds of thousands of immigrants speaking myriad languages, many of whom are not literate in English, as this renders these vital, lifesaving alerts essentially useless to a wide range of the public, with predictably tragic consequences.
A surge of warmth is coming today and late this week, with highs near or in the 60s. This will be punctuated briefly by a cooler day Wed in the mid-50s, which is still almost 10ºF above normal this time of year. Enjoy the warmth while it lasts because there will be a colder pattern next couple of weeks, starting as soon as this weekend.
Rest of today – warm and sunny with high temperatures around 60ºF. Overnight lows drop to around 40ºF with a backdoor cold front moving through overnight.
Weather Prediction Center surface forecast for 7PM Tuesday. A backdoor cold front is forecast to move through, leading to a slightly cooler day tomorrow before temperatures rebound again late in the week.
Wednesday – the backdoor cold front’s primary impact will be to make Wednesday cooler, in the mid-50s, with a good amount of sun. Overnight lows will be in the mid-60s.
Thursday – this is when the warmth really surges with the backdoor cold front returning northeast as a warm front. Behind this, south winds will lead to temperatures rising well into the mid-60s. The only cap on temperatures will be possible partly sunny cloud cover. Overnight lows in the mid-50s.
Climate Prediction Center’s 6-10 day temperature outlook for 3/14-3/18. Much of the country is likely to see colder than normal temperatures.
Climate Prediction Center’s 8-14 day temperature outlook for 3/18-3/22. The cool conditions look set to continue.
Friday– a cold front approaches the region from the west. Ahead of this, temperatures remain warm in the mid-60s. A chance of rain will accompany the passage of the front. Otherwise, expect mostly cloudy skies. Overnight lows dropping into the mid-40s. Temperatures will continue to drop through weekend.
March brings in week of great contrasts, typical of a transition into spring. Periods of rain off and on today before a plunge in temperatures going into Tuesday. Strong northwesterly winds will accompany the cold as the pressure gradient tightens around the departing low bringing rain today. Temps rebound into the upper-40s midweek but drop back towards end of week into the upper-30s.
Rest of today – periods of rain mostly before noon. Breezy with northwest winds increasing into the 15-20 mph by later in the day. Temperatures start dropping with these winds kicking in after noon bringing on strong cold air advection. Clouds clear towards the overnight when lows are expected to drop into low-20s.
GFS model 2-meter above ground level temperatures, and 10-meter above ground level winds at 7AM Tuedsay.
Tuesday – mostly sunny with high temperatures in the mid-30s. Strong northwest winds in the 20-30 mph range with gusts above 45 mph possible. Overnight lows in the low-30s.
Wednesday – high temperatures rebound quickly to near 50ºF with winds subsiding and mostly sunny skies. Overnight temperatures dropping into the mid-30s.
GFS model surface precipitation, and 1000-500 mb thickness for Thursday at 11AM. The blue thickness lines over much of the northeast indicate a return to below normal temperatures on the way.
Thursday– temperatures cooling a touch back into the mid-40s with mostly sunny skies. Overnight lows dropping back into the upper-20s.
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 significant snowstorm in store for NYC Monday into early Tuesday morning. Current trends point to 8-12″ likely for most of the city. There is uncertainty with possible mixing late Monday that could cut into this over Long Island, and if the mixing line pushes further northwest, which The European model portrays, this could lower totals in the city to more of the 6-10″ range. It is worth noting that the 850 mb set up suggests the possibility for much bigger totals closer to 18″ if the colder scenarios play out. The timing of this storm is such that the most intense snowfall should occur during the day. A narrow, intense deformation band could remain nearly stationary over some parts of the region during the daytime hours Monday. Strong northeasterly winds will accompany this storm despite relatively modest pressure falls, due to the presence of a 1034 mb high pressure center over eastern Canada creating a tight pressure gradient.
Weather Prediction Center 48 hour 10th percentile snowfall accumulations for the NYC metro region ending 1AM Wednesday
Weather Prediction Center 48 hour 90th percentile snowfall accumulations for the NYC metro region ending 1AM Wednesday
Weather Prediction Center 48 hour 50th percentile(median) snowfall accumulations for the NYC metro region ending 1AM Wednesday
Forecast Details
At the Surface
A low pressure center that tracked through the Midwest this weekend will transfer its energy as it hits the Appalachians to a secondary low offshore of Virginia tonight. The low will then slowly track to the northeast as it deepens somewhat. This isn’t a particularly strong low, and it will elongate, translating eastwards overnight into Tuesday morning (see the last image in the gallery below). The North American models (GFS, NAM) suggest a colder scenario that would see higher snow totals (2nd, 3rd imges below), while the European model (1st image) shows potential for mixing Monday evening. Strong northeasterly winds will accompany the storm.
The presence of very cold air this weekend should help lead to better chances for big totals, however, the cold air will be retreating ahead of this storm, and cold air damming will be modest.
ECMWF “Euro” model 1000-500 mb pressure, thickness, and surface precipitation/type at 7PM Monday.
GFS model 1000-500 mb pressure, thickness, and surface precipitation/type at 7PM Monday.
NAM model 1000-500 mb pressure, thickness, and surface precipitation/type at 7PM Monday.
Weather Prediction Center storm track forecast.
850 mb Level
At this level, a strong easterly low-level jet will bring plenty of moisture into the cold conveyor belt of the storm. The advancement of the warm nose of the low will be key to where the greatest potential for deformation banding and the heaviest snowfall rates set up during the day Monday. The GFS and NAM models (2nd, 3rd images below) depict this warm nose staying just offshore. This would favor the best potential for a mesoscale band setting up right over NYC and slightly north as these bands are typically situated just on the cold side warm nose of a low.
500 mb Level
Part of the reason the surface low of this storm will progress so slowly, bounce around, and elongate is due to the presence of a closed 500 mb low accompanying it. This isn’t really a “classic” set up for a big nor’easter blizzard here, however, the closed low does help keep cold air aloft and help enhance lift via increasing the lapse rate between the surface and this level.
300 mb Level
A curved jet streak should set up just north and east of the developing low during the day Monday. The entrance region of this jet streak should allow stronger divergence and enhanced lift for this low.
A long duration but light impact winter weather event is forecast to hit Tuesday and Wednesday. Since last week, the track of this storm has shifted north, resulting in warmer air present near the coast. This will result in wintry mix and little to now accumulating snow. We miss out on a more potent storm later in the week which will move well offshore of the area. Temperatures throughout the period remain below normal in the mid-30s at best, with a reinforcing blast of cold air late in the week.
Rest of today – mostly sunny with high temperatures in the upper-30s. Clouds increasing overnight with low temperatures around 30ºF.
ECMWF forecast total accumulated snowfall valid 7AM Wednesday
GFS forecast total accumulated snowfall valid 7AM Wednesday
Tuesday – mostly cloudy with high temperatures in the mid-30s. Periods of light wintry mix/snow during the day as a couple of modest low pressure centers impact the area. Light accumulations expected, probably around half an inch. Overnight lows steady in the mid-30s with rain/snow mixing possible.
Wednesday – rain/snow mix possibly extending into Wednesday morning. High temperatures in the upper-30s. Any accumulated wintry precipitation should melt rather quickly. Overnight temperatures dropping into the low-30s.
GFS model surface precipitation and 1000-500 mb thickness for 7AM Thursday. A potent storm is seen exiting east well offshore from NYC.
Thursday– another low pressure, center, much stronger than the ones associated with the early week develops and tracks well south of us. High temperatures in the mid-30s. The main impact of this storm for us will be the stiff winds it produces as it continues to deepen and the pressure gradient around it tightens. These winds will also be from the northwest, bringing in a colder air mass. Overnight lows in the low-20s as a result.
It’s been two weeks now without any appreciable precipitation in NYC and this dry stretch continues this week. A mostly zonal flow regime aloft should provide for generally calm conditions, esp. given a lack of any meaningful supply of moisture. Temperatures should trend into mid-40s with warming westerly downsloping flow modifying the air mass, eventually transitioning to a mild southwest flow later in the week.
Rest of today – mostly cloud with highs in the low-40s. Overnight lows in the low-30s.
Weather Prediction Center surface forecast for 7AM Tuesday. High pressure to our southwest should help drive westerly winds our way.
Tuesday – mostly sunny with high temperatures in the low-40s. Overnight lows in the low-30s.
Wednesday – still mostly sunny with high pressure remaining in control. High temperatures in the mid-40s. Overnight temperatures dropping into the mid-30s.
GFS model 500 mb height and vorticity for 7AM Thursday. Generally flat, zonal flow is seen over our area. However, signs of a big change are visible to the west, over the Northern Plains.
Thursday– High temperatures in the mid-40s again with mostly sunny skies. Overnight lows in the mid-30s.
