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NYC Nor’easter Snowstorm Update – Jan 31, 2021

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Synopsis

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.

NYC Detailed Forecast for September 6, 2019

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The forecast for tomorrow in NYC hinges largely on what happens with Hurricane Dorian’s track. Although the center of this still powerful storm is expected to pass well south of the region, its influence on wind patterns, and its outer bands of clouds and rain could still impact the city. In essence, as has been alluded to by others, Dorian’s impact on NYC will be not unlike that of a Nor’easter. This forecast, as a result, carries a fair deal of bust potential especially as it relates to precipitation totals and to some extent with the maximum sustained winds.

My Forecast
High: 71°F | Low: 63°F | Max sustained winds: 24 mph | Total precipitation: 0.02″ – verification will come from METAR data for the period between 2AM Friday and 2AM Saturday (06Z Friday to 06Z Saturday) at LGA (LaGuardia Airport), and the KLGA Daily Climate Report.

Verification
High: 69°F | Low: 60°F | Max sustained winds: 32 mph | Total precipitation: 0.03″
Surprisingly, despite personally witnessing some moderate rain bands move over Midtown on Friday, KLGA itself only picked up 0.03″ of precipitation from the outer rain bands of Dorian that hit the city. That means my precipitation forecast was almost spot-on in this respect. I was 2-3°F too warm on both high and low temperatures. Statistical models weren’t really expecting much in the way of rain. When rain did occur temperatures cooled somewhat via evaporational cooling since the atmosphere did start off on the dry side Friday and there was room for this cooling to take place. The forecast bust, as it turns out, was with the maximum sustained wind, where I fell short by 8 mph. Despite low rainfall totals, even a small bout of rain could have kicked up winds via downward momentum transfer of somewhat faster moving winds aloft. The other thing to remember is that northeast winds are climatologically most likely to produce the fastest winds in September. This wind direction also happens to have a long fetch over open water for many north-facing shores in NYC, including KLGA. That long fetch over open water would tend to reduce surface friction since water is smoother than land on average, and allow for faster winds.

  • Weather Prediction Center surface forecast for 2AM Friday at the beginning of the forecast period
  • Weather Prediction Center surface forecast for 8PM Friday
  • Current GOES satellite image of Hurricane Dorian – it’s cirrus shield has already reached NYC

Synoptic Set Up
Hurricane Dorian will be approaching from the south and the storm’s center will accelerate northeast well offshore of the NYC area during the forecast period. At the surface, high pressure will be in place early in the forecast period, but will weaken quickly. A surface trough is forecast to form and travel east while a second surface trough associated with Dorian may form late in the forecast period.

At the 500 mb level, a shortwave trough will be moving east. This will assist in continuing to accelerate Dorian off to the northeast. This interaction with Dorian will also bring some relatively strong divergence across the area later in the day, providing some enhanced lift that could be conducive to rain. Finally, at the 300 mb level, there is some evidence that we could be in a favorable exit region of a jet streak. This will server to further enhance upper level divergence and lift at these levels.

North American Model (NAM) forecast for 500 mb height and vorticity at 11PM Friday. The intense vorticity associated with Dorian is clearly evident in the bottom right, along with a fairly potent shortwave trough approaching from the west

High Temperatures
GFS, NAM, and NBM are in consensus that Friday will be a much below average day in terms of high temperatures. All three statistical models come in at 71ºF or 72ºF for high temperatures, which is about 8-9ºF below normal for this time of year. The synoptic setup for tomorrow favors northeasterly to east-northeasterly winds given the counter-clockwise flow around Dorian’s center, and similar to the situation with a passing Nor’easter. These wind directions favor onshore flow, bringing in a cooler, moist air mass off the Atlantic into the area. With sea surface temperatures hovering right around 70ºF, there’s not too much more room for cooler temperatures. This set up also favors low clouds, and this is indicated in the statistical models as well. I don’t see too many “gotchas” so I’m going with 71ºF.

Low Temperatures
Statistical models show the chance that the low temperature during this forecast period may actually occur overnight going into Saturday. The fact that GFS, NAM and NBM all converge on 63ºF as the low gives me increased confidence that this is a fine temperature to settle with. There aren’t any signs of strong temperature advection or changes in airmass to warrant a big deviation from this.

  • NAM MOS forecast
  • GFS MOS forecast

Max Sustained Winds
Even though the center of Dorian will pass well offshore of NYC, the large radius of its wind field will still result in fairly robust winds across the area. The average of GFS and NAM MOS is about 18 knots. Climatologically speaking, northeasterly winds are actually the most likely to produce winds exceeding 21 knots during September. I think it’s possible that if a rain storm related to Dorian moves through, we could see sustained winds up to about 25 mph with some downward momentum transfer possible.

Total Precipitation
This is a tricky precipitation forecast because forecast models like SREF place the probability for precipitation over 0.10″ not that far away from the city, and the gradient of probabilities increases quickly the further east you go. This makes sense, since the best conditions for rainfall will be closer to the core of Dorian. Given that the track forecast for Dorian seems to be shifting further offshore, though, it doesn’t make sense to bank on a big rainfall total from this event. The GEFS and SREF QPF plumes average is only 0.06″, hardly a big rainfall total, though the spread is anywhere from nothing to about 0.20″. The atmosphere starts of relatively dry tomorrow, and 850 mb forecasts don’t suggest any low-level jet conveying deep moisture (though Dorian can definitely provide this too). Furthermore, forecast soundings show a pretty persistent dry layer in the mid-levels of the atmosphere. So despite the fact there’s going to be some enhanced lift from divergence at the 500 mb and 300 mb levels tomorrow, I’m erring on the side of this passing storm only dealing a glancing blow. I don’t think it’ll be completely dry, though, like GFS and NAM MOS, so I’ve gone ahead with 0.02″ as a forecast for total rainfall.

  • NAM forecast for 850 mb relative humidity and winds at 11PM Fridayat
  • GFS forecast for 850 mb relative humidity and winds at 11PM Fridayat

NYC Weather Update – May 14, 2019

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After a very cool, wet start to the week, temperatures should moderate and conditions will gradually improve as we approach the weekend. A pattern change at mid and upper levels is apparent in forecast models going into this weekend. We finally break free of persistent troughing that brought the cold, rainy weather this weekend going into the beginning of this week. Instead, we’ll get to look forward to sunnier, warmer weather more in line with the calendar.

Rest of today – if we don’t reach 55°F, today will be the second day in a row we set a new record low and record low maximum at KLGA. High temperatures are forecast to be in the low-50s with lots of clouds. Needless to say, it’s been quite cold and below average for this time of year. The noreaster that brought us miserable conditions yesterday is steadily moving east. However, a surface trough and moisture is forecast to rotate around its back side as it keeps retreating east. This could result in scattered showers later in the afternoon and evening. Overnight lows are expected to be quite cool again, in the mid-40s.

Weather Prediction Center surface forecast for 2PM today

Wednesday – temperatures should rebound nicely out of the gate as we finally get some clearing skies. High temperatures should reach into the mid-60s. Chance for showers overnight going into Thursday as a cold front approaches from the north. Overnight lows much warmer in the mid-50s.

Thursday – the warm up continues despite cloud cover associated with this approaching cold front. High temperatures expected to touch 70°F for the first time in a while. This passing (and slowing) cold front could continue to touch off a couple showers going into Friday. Overnight lows slightly cooler in the low-50s.

Weather Prediction Center surface forecast for 8AM Thursday

Friday – cooler with high temperatures in the upper-60s and partly sunny skies. Overnight lows into Saturday in the mid-50s. Pattern change is coming with large scale troughing forecast for the western US while a ridge builds east, essentially the opposite of the pattern we’ve had the past few days.

NYC Weekend Weather – Mar 22, 2019

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A long duration Nor’easter slowly moves its way eastwards. Conditions improve during the second half of the weekend. A brief warmup to above average temperatures takes place. This doesn’t last, with another cold front passing through to start next week. Tomorrow, keep an eye out on the skies for a possible glimpse at the aurora borealis, typically not visible at these latitudes.

Rest of today – chance for rain shower diminishing as the center of a slow moving Nor’easter continues to progress northeast. High temperatures reaching around 50ºF. Winds will increase on the backside of this departing low overnight. Winds will shift towards the northwest as well, bringing in colder air and overnight lows in the mid-30s.

GOES East satellite loop of the storm system affecting the Northeast
Ocean Prediction Center surface analysis for the Atlantic Basin. A strong blocking high is inhibiting the forward progress of the Nor’easter impacting our area. This is leading to a long duration coastal flooding and wind event.

Saturday – decreasing clouds as the low above continues progressing northeast slowly. Winds will increase as this low continues to deepen and the pressure gradient builds between it and and area of high pressure further west. Steady winds in the 20-25 mph range with gusts as high as 40 mph are forecast. High temperatures will be a bit below normal as a result in the upper-40s. Overnight lows will be cold, in the mid-30s with clear skies.

Weather Prediction Center surface forecast for 8AM Sunday, still showing a tight pressure gradient between a high over the Ohio Valley and the departing Nor’easter

Sunday – temperatures rebound into the mid-50s as an area of high pressure builds and slides off to our southeast, and winds turn towards the southwest bringing in warmer air. Sunny skies – this will be the best day of the weekend.

Monday – another cold front approaches from the west and brings a possibility for rain. Temperatures ahead of this front should reach into the low-50s. Behind this, we’ll get another shot of cold air, with temperatures dropping overnight into the low-30s.

Northern Lights Possibly Visible from NYC

On Tuesday, The Space Weather Prediction Center (it exists!) detected a large Coronal Mass Ejection (CME) associated with a potent solar flare. As a result, they have issued a moderate geomagnetic storm watch for Saturday, March 23. Of note, the belt where the charged particles from this CME would impact the Earth’s upper atmosphere and result in an aurora quite a bit further south than where the northern lights are typically visible. In fact, they may even be visible from NYC, although it may be hard to see them due to light pollution.

NYC Snowfall Forecast – Mar 3, 2019

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A winter storm warning is in effect for NYC and the surrounding metropolitan region. This isn’t exactly how we’d all want to start March off! This storm is anticipated to bring some travel impacts to the area, however, for reasons discussed below, this won’t be a blockbuster snowmaker. Watch out for a slog of a morning commute tomorrow. This snow may also stick for a while – a frigid continental polar air mass from Canada will sweep in behind this storm bringing temperatures generally 10-15°F below normal for this time of year. High temperatures in the mid-30s should limit melting.

Headlines

Snowfall totals: I’m forecasting 4-6″ in parts of eastern Queens, southeastern Brooklyn, and lower totals further east into Long Island. Higher totals of 6-8″ are more likely to occur in Manhattan, the Bronx, and points further inland, particularly interior regions of Connecticut. Below are probabilistic forecast maps of various amounts of snow (>= 2″, >= 6″, and >= 8″).

Timing: Precipitation starting in earnest around 8PM. Starting out as a mix of rain/snow near the coast, but transitioning over to all snow later in the evening. The heaviest snow will happen overnight. Because of the fast-moving nature of this storm, precipitation is expected to end rather quickly between 4-6AM Monday morning in the city.

Uncertainties: There is still potential for a wobble in the storm track, further east and south would result in higher snow totals near the coast. Further west and closer to the coast would mean more mixing/rain at the coast and lower snow totals. There will be a rather sharp gradient of increasing snowfall totals spreading across the region (as seen in the previous probabilistic snowfall total forecasts). Mesoscale heavy snow bands will be difficult to pinpoint ahead of time. Some areas could see several inches more than neighboring areas just a few miles south and east.

Synoptic Set Up (The Big Picture)

A storm that’s currently unleashing severe storms with tornadoes across the Deep South now will slide up along the Mid-Atlantic and Northeastern coast of the US. As this storm progresses, it will move close to the 40°N/70°W benchmark, a spot that’s climatologically correlated to heavy snow events along the heavily populated I-95 corridor during the winter. This storm will continue to strengthen as it moves offshore. Snow is expected to develop ahead of the advancing warm front associated with this storm as its precipitation shield advances. Heavier snow is forecast to develop later on as strong isentropic lift associated with the warm front occurs, creating the potential for frontogenesis and some mesoscale bands of very heavy snow. The storm is expected to move quickly along the Northeast coast, such that the duration of precipitation in any one spot is expected to be less than 12 hours.

At the 500 mb level, a shortwave trough will provide positive vorticity and some additional lift/divergence, allowing the storm to continue strengthening. Finally, at the 300 mb level, the surface low will be close to the entrance region of a curved 300 mb jet streak. This will provide yet more divergence and lift, if only for a brief period.

  • Weather Prediction Center’s surface forecast for 1AM Monday morning
  • GFS model 500 mb vorticity and height for 1AM Monday
  • GFS 300 mb height, wind forecast for 1AM Monday, note the brighter red, orange, and white streak over the Northeast, indicating a jet streak.

Evolution of the Storm Track

Over the course of the last three days, forecast models have come into better agreement with this storm tracking close to the 40°N/70°W benchmark (circled in red in the images below). Note the increasingly tight clustering of storm center locations around the benchmark in progressive storm track forecasts from the Weather Prediction Center.

  • WPC storm track forecast issued 7AM Saturday, the brown spots indicate forecast storm center locations around the benchmark
  • WPC storm track forecast issued 7AM Sunday, the green spots indicate forecast storm center locations around the benchmark

The tightening clustering of these forecast storm center locations lends greater confidence to the idea that the storm will track very close to the benchmark.

Ensemble Snowfall Totals

The two primary model ensembles (GEFS and SREF) have been edging ever so slightly upwards in their forecast mean snowfall totals, while the model spread has decreased over the weekend

  • Latest GEFS ensemble plumes for snowfall totals at KLGA
  • Latest SREF ensemble plumes for snowfall totals at KLGA

These means/spreads were part of what informed my own forecast snowfall totals at the top of this post.

Factors Supporting Heavy Snow

  • Storm track over or very near the benchmark
  • Strong isentropic lift and possible frontogenesis (see images below). Strong lift is a critical ingredient for generating heavy precipitation
  • Possibility of mesoscale bands as a result of this lift, generating heavy snowfall rates
  • Temperatures probably supporting frozen precipitation through the atmosphere
  • GFS forecast for 850 mb frontogenesis
  • NAM 12km forecast for 850 mb frontogenesis and temperature advection (red shades indicate warm advection)
  • NAM forecast sounding for 1AM Monday
  • GFS sounding for 1AM Monday

Factors Suggesting Lower Snow Totals

  • Possibility still remains for storm track to shift further inland, introducing more warm air off the ocean, more rain than snow at the coast
  • Warm advection associated with the storm’s warm front possibly also affecting snow development. Note how close the overlapping temperature and dew point profiles in the forecast soundings above are to the freezing mark, the dashed blue line the middle of the image that is angled to the right at 45°. Evaporational cooling should help somewhat in staving off warming but if temperatures warm more than forecast, we could see more mixing
  • Mesoscale bands of heavy snow may not push far enough onshore
  • Surface temperatures ahead of the storm in the upper-30s near the coast, urban heat island effect could retard snow accumulation
  • Fast moving nature of the storm, total precipitation window only 12 hours
  • Small window for the best moisture support at the 850 mb level. No real evidence to suggest a low-level jet carrying a ton of moisture into the region.
NAM model forecast of 850 mb relative humidity and winds. There’s not too big of an area of completely saturated air at this level, and winds are not strong at this level either.

NYC Weather Update – Weekend Nor’easter – Oct 26, 2018

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I haven’t had time to post about the current week’s WxChallenge forecasts for Caribou, ME, which I’ll have a follow up post about Saturday or Sunday to go over my results. Instead, this week, I’m going to put the same forecast skills I’ve been applying to the upcoming nor’easter that’s going to impact NYC Saturday. I’ll provide a deterministic (exact number) forecast for high temperature, low temperature, maximum sustained wind speed, and total accumulated precipitation for the period starting 2AM Saturday and ending 2AM Sunday, with a less exact forecast for the rest of the weekend. In my later follow up post, I’ll verify my results and see just how close I got. For purposes of verification, my forecast will be for LGA. If you’re only reading this summary, just know that Saturday will be a windy, raw, rainy day, but that conditions will improve as the day goes on.

Friday – partly sunny skies with high temperatures in the low-50s. Light winds from the south-southeast.

Saturday – High temperature: 54°F. Low: 48°F. Maximum sustained winds (2-minute averaged): 34.5 mph from the east-northeast. Total precipitation: 1.25″. The bulk of the rain should end by the afternoon hours.

Sunday – mostly cloudy, high temperatures in the upper-50s with return flow from the west downsloping into the area.

Forecast Discussion

The nor’easter that’s coming to us this weekend has tropical origins as the remnants of Hurricane Willa, which originated in the Eastern Pacific and made landfall in Mexico as an intense Category 3 storm. This means that it will be able to tap to tropical moisture, bringing the potential for a heavy rainfall event. At the surface, a low pressure center will be intensifying as it slides up along the Mid-Atlantic coast. At the mid and upper levels of the atmosphere, the set up is favorable for robust divergence, which should result in to strong surface convergence and lift. At the 850 mb level, there are indications of a strong low-level jet with winds as high as 50 knots from the east to east-northeast during the Saturday morning hours ahead of the warm front attached to the nor’easter. This would enable highly efficient moisture transport and convergence in our area. The net result of this should be periods of heavy rain. This is what justifies rainfall totals over an inch, though because of the relatively fast forward speed of this storm, I don’t believe that totals above 1.50″ are likely.

These aren’t pictured below, but MOS (model output statistics), and forecast plumes (ensembles of many different iterations of the same forecast model) probabilities suggest a consensus range of 1.15″-1.24″. Short Range Ensemble Forecast (SREF) probabilities show a greater than 90% chance for rainfall totals greater than or equal to 0.50″, 70-90% chance of totals greater than or equal to 1.00″, but very low chances of totals exceed 2.00″. The record rainfall for Saturday at LGA is 1.76″, though there are higher record totals surrounding this date, so this record isn’t what we’d call particularly strong.

On the temperature front, the trajectory of the onshore flow accompanying this storm actually brings it over Atlantic waters that are warmer than the air temperatures have been this week. This should bring warmer air into the area, however, because it will also be raining and cloudy, evaporational cooling will be a concern (as it rains, some of the moisture from raindrops will evaporate, which takes heat input to achieve, lowering surrounding temperatures), and that will likely knock temperatures down a bit. Overnight lows should end up being fairly mild in comparison to previous nights because of cloud cover and the aforementioned winds over warmer waters.

The wind speeds should be quite strong tomorrow. MOS is showing winds in the 24-26 knot range. However, given that 850 mb winds will be even strong, in the 50 knot range, and it will be precipitating, meaning downward transfer of momentum by raindrops should mix some of these stronger winds to the surface, which is why I think sustained winds could be as high as 35 mph at some point in the day at LGA (which is exposed near open water, so there’s less of an impact from friction over the land). I think gusts could easily top 40-45 mph tomorrow during the most intense rain squalls.

Surface forecast from the Weather Prediction Center valid for 8AM Saturday, showing the nor’easter in question

850 mb forecast for relative humidity and wind valid 8AM Saturday. The dark blues show saturated air mass, and the wind barbs show strong onshore winds

500 mb vorticity and heights, the yellow-orange-purple shading shows progressively stronger values of positive vorticity. Without getting too technical, positive vorticity is related to divergence aloft, which helps aid upwards motion (lift). Strong upwards motion can lead to clouds and precipitation.

Shaded areas indicate strong winds at the 300 mb level. These are referred to as jet streaks. Our region is forecast to lie within the left exit region of a jet streak, an area that favors divergence and enhanced upwards motion/lift

Not surprisingly, the SREF probability forecast shows a 70-90% probability of omega (a quantitative measure of lift) exceeding -9 microbars/sec, which is considered quite strong

Update: Verification

According to the KLGA Daily Climatological Report showed the following for Saturday, October 27, 2018:

High Temperature: 53°F

Low Temperature: 45°F

Max Wind: 41 mph

Max Gust: 50 mph

Total QPF (this is taken from METAR data): 0.98″

I’ll attempt to do a post-mortem on the winds and QPF forecast where I missed pretty significantly later in the week.

NYC Spring Nor’easter Update – Mar 20, 2018

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This is a special bulletin regarding the nor’easter expected to impact the region tomorrow. This may end up being one of the biggest snowstorms ever to hit the NYC Tri-State this late in March. On to the forecast details:

Impacts: snow, heavy at times, with some thundersnow possible. Blizzard conditions possible. Steady north to north-northeasterly winds in the 20-30 mph range with gusts 35 mph+. Coastal flooding during high tide cycles with storm tides 2-3′ above normal. Widespread snowfall accumulations 8″+ in NYC, Central NJ, Lower Hudson Valley, southwestern CT. The possibility exists for more than a foot of heavy, wet snow area-wide. I think the best bet is the low-end 10″ of the official forecast for NYC that calls for anywhere between 10-18″. Expect disruptions to both commutes, in particular the PM commute. Power outages likely due to the combination of accumulating heavy wet snow and windy conditions downing trees and/or power lines.

Timing: conditions deteriorating overnight. Snow beginning early in the morning in NYC (as early as 5-6AM possibly), later in the morning north of I-287. Heaviest snow during the day, especially in afternoon hours when lift is maximized. Snowfall rates of 1-2″/hr or more possible during the afternoon. Snow tapering off overnight, probably ending by midnight.

Discussion: this storm is unlike the previous two that struck the area. The surface and near-surface is colder than what it was at the outset of the last two storms. This will aid in snow sticking quickly, despite the high sun angle this late in March. The storm track has been trending westward but right now looks to be directly over the 40°N/70°W benchmark, a track that favors heavy snow over the area. The bust potential for a snow total below 8″ is still there, but even a snowfall of 5-6″ would still be substantial for this time of the year!

Focus on the storm track of the deeper low, the one that has the orange and brown plotted storm center positions.

NY Weather Update – Mar 19, 2018

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It sounds like a broken record at this point, but another week, yet another nor’easter with a chance of snow, arriving on the second day of spring no less! As with previous storms, how much snow we get will hinge critically on the storm’s track and proximity to shore. Looking ahead past the storm, temperatures remain subdued and below normal for this time of year.

Rest of today – sunny, high temperatures in the low-40s.

Tuesday – increasing clouds, with a chance for rain snow mix later in the day. High temperatures in the upper-30s.

Wednesday – snow developing overnight and continuing through the day. Accumulating snow currently forecast to be light in the 1-3″ range. This could increase though, based on current forecast ensemble totals ranging 5-6″. The caveat is that blacktop will probably be largely snow free due to the high sun angle.

Thursday – conditions improving overnight and mostly sunny skies with highs in the mid-40s. Snow should melt quickly with the high sun angle and temperatures.

NYC Weekend Weather – Mar 16, 2018

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An uneventful, though kind of cold weekend is in store for the NYC area. Great news for those of you going out for St. Patrick’s Day festivities. Looking ahead into mid-week next week, we have the potential for yet another nor’easter impacting the region with, you guessed it, the possibility for more snow.

Rest of today – partly sunny to mostly cloudy skies with a high near 40°F.

Saturday (St. Patrick’s Day) – warmer, sunny, with a high in the mid-40s, pretty much ideal conditions for the parade.

Sunday – sunny, high in the low-40s. High pressure will be in control of the area.

Monday – mostly sunny with highs in the mid-40s.

Why Seemingly Unending Conveyor Belt of Nor’easters?

The simple answer: The Greenland Block. You may have heard the term “blocking high” mentioned in regards to the anomalously active and cold weather pattern over the Northeast this month. In essence, what’s happened is that a strong ridge of persistent high pressure has formed over Greenland this month. Very cold air over snow-covered landmasses like Greenland is often quite stable. Colder, denser air, also increases surface pressures.

Cyclonic flow around such an area of strong high pressure can wreak havoc with the polar jet stream – diverting its normal flow around the high. This can (and has in our case) lead to the polar jet diving far to the south, allowing large intrusions of Arctic air into the Eastern US. Jet streams can also enhance storms via upper level divergence, lowering surface pressures. Lastly, the blocking high can slow the normal eastward progression of storm systems, causing storms to linger over areas and extended periods of precipitation and coastal impacts in the case of nor’easters.

The Greenland Block is correlated with an index called the North Atlantic Oscillation. When values of this index are negative, it’s more likely that such a blocking pattern arises. Lucky for us, it appears that we may finally get a break in this pattern towards the end of the month.

 

 

NYC Weather Update – Mar 12, 2018

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Another week, another nor’easter! Luckily, this time around, the storm will stay outside of the notorious 40ºN 70ºW benchmark, meaning that impacts for NYC should be relatively light. On the backside of this storm, weather should be fairly innocuous and average for this time of the year.

Rest of today – increasing clouds ahead of this incoming storm. High temperatures in the mid-40s. Temperatures drop to near freezing overnight in the city, setting the stage for snow overnight as the storm approaches and rapidly strengthens.

Tuesday – lingering snow from overnight ends quickly in the morning or transitions to rain. When all is said and done, we might pick up 2-4″ of snow in the city. Temperatures will be marginal at best and the snow will probably have difficulty sticking to blacktop. There is an outside chance of more than 6″ but this probability is low. As you can see from the preceding graphics, the bulk of the storm, and its center will be tracking quite far southeast of the area. Winds will be shifting towards the northwest around 20 mph and high temperatures will only be around 40ºF due to the combination of wind, clouds, and precipitation.

Wednesday – an unsettled regime continues into Wednesday with some slight chance for a couple snow showers. Mostly cloudy with high temperature in the mid-40s.

Thursday – partly sunny, high in the mid-40s.