Monthly Archives: January 2021

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 Weekend Weather – Jan 29, 2021

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An arctic chill with bitterly cold winds kicks off the weekend as strong high pressure moves in. Overnight lows in the teens and high temperatures in the 20s will range 10-15ºF below normal for this time of year. This cold air could set the stage for a nor’easter bringing significant snowfall to the region, with totals > 6″ possible Monday into Tuesday. As usual, track details on this storm will be pivotal, and are not clear at this time.

Rest of today – mostly clear, cold, and windy with high temperatures in the low-20s. A strong arctic high and a departing low will create a tight pressure gradient that ushers in stiff northwesterly winds 20-25 mph. Wind chills will hover around 0ºF. Overnight temperatures drop into the mid-teens with wind chills likewise dropping below zero.

Weather Prediction Center surface forecast for 7AM Saturday. A strong area of high pressure is parked over much of the Eastern US.

Saturday – winds abate with high pressure moving more directly overhead. Sunny, but still cold with high temperatures around 30ºF. Overnight lows will be in the upper-teens under increasing cloud cover.

Sunday – mostly cloudy as the next storm system starts to work in. High temperatures around 30ºF. Overnight lows in the upper-20s with the possibility of snow developing overnight into Monday morning.

  • GFS model total snowfall accumulation as of 7AM Tuesday
  • ECMWF model total snowfall accumulation as of 7AM Tuesday
  • UKMET model total snowfall accumulation as of 7AM Tuesday

Monday – stiff northeasterly winds developing along with snow. High temperatures in the low-30s. The storm possibly bringing us significant snow came ashore over the west coast yesterday and will be transiting the country the next couple days. It is eventually forecast to spawn a coastal low, bringing a nor’easter into our region. Even though cold air will precede this storm, offshore waters are still mild, in the low 40s-50s, and with the storm likely to bring southerly/northeasterly flow at the outset, we could see enough warming to mix to rain at the coast. Storm track and strength will be vital to the eventual snowfall totals. Models seem to signal a very tight banding feature bringing heavy snow – you’ve heard this before but these bands are notoriously difficult to pinpoint even a day ahead of the event. If the optimal scenario plays out, we could see a storm with similar or possibly bigger totals than the one in December. Overnight lows Monday shouldn’t budge much, in the low-30s, with some warm advection associated with portions of the storm.

NYC Weather Update – Jan 25, 2021

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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.

NYC Weekend Weather – Jan 22, 2021

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A cold and breezy start to the weekend with a cold front ushering in below average temperatures mostly in the mid-30s. High pressure builds and keeps things dry during the weekend. However, the upper-level pattern shifts to allow a shortwave trough to push through early next week, leading to a storm that could bring some accumulating snow overnight Monday into Tuesday.

Rest of today – partly cloudy with high temperatures in the low-40s. A moisture-starved cold front will work its way through the region. The main impact of this front will be to induce a shift in winds to the northwest, and trigger some decent cold air advection. This will lead to overnight temperatures plummeting into the mid-upper 20s.

Weather Prediction Center surface forecast for 7AM Saturday

Saturday – high pressure builds in behind the cold front, giving us a mostly sunny day. This high pressure and a low off to the northeast over the Canadian Maritimes will lead to a fairly tight pressure gradient, and the result should be breezy winds from the northwest, sustained in the range of 15-20 mph at least. So despite the sun, the cold start to the day will lead to temperatures in the low-30s and a much colder feel with wind chills around 20ºF. Overnight lows will be the coldest in quite some time, in the low-20s.

Sunday – windy conditions continue at least part of the day with high temperatures in the mid-30s. Once the center of the high moves over us, winds should subside. Overnight lows in the mid-20s with clouds building in.

GFS model 500 mb height and vorticity animated loop valid 7PM Sunday through 7PM Monday, showing a de-amplifying shortwave trough ejecting from the southwest towards our region.

Monday – as the high pressure eventually moves off, a shortwave trough will be progressing towards our region. The accompanying surface low will bring mostly cloudy skies. Temperatures should peak in the mid-30s. Overnight, the storm is positioned to possibly bring us some light accumulating snow. Currently, it’s hard to pin down a total, but the following images from GFS and ECMWF models suggest something on the order of 3-5″ is possible. Low temperatures in the upper-20s should support all snow during this event, so storm track will be key here.

  • GFS model 24 hour snowfall total ending 1AM Wednesday
  • ECMWF model total snowfall ending 1AM Wednesday

NYC Weekend Weather – Jan 15, 2021

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Our extended period of calm weather comes to an abrupt end this weekend. A low pressure system with its attendant vigorous cold front sweeps through overnight bringing moderate to heavy rain. We could see as much as 1-1.5″ of rain with this event. Behind this front, windy conditions prevail Sunday as the low exits but continues to deepen. Next week, we’ll see a return to normal temps around 40ºF.

Rest of today – mostly cloudy with high temperatures in the mid-40s. Rain chances increase as the storm system approaches us. Warm air advection associated with the warm front of this storm will result in little movement on overnight lows, which will hover in the mid-40s. Moderate to heavy rain is likely after 9PM tonight and into the overnight hours.

High Resolution Rapid Refresh simulated radar for 1AM Saturday.

Saturday – as the storm pulls off to the east in the morning, rain chances should decrease, ending by noon. Isolated wrap around showers are possible. Temperatures will decrease during the day with cold air advection, dropping into the low-40s. Overnight lows in the mid-30s as skies clear.

Sunday – mostly sunny with high temperatures in the low-40s. Breezy with west winds in the 15-20 mph range and stronger gusts due to a large pressure gradient around the exiting and intensifying low. Overnight lows in the mid-30s.

Weather Prediction Center surface forecast for 7AM Sunday. The low affecting us this weekend is seen in the upper right corner, with a tight clustering of isobars around it, indicating a large pressure gradient.

Monday – an upper level low will affect the area pushing a cold front through our region, but this front should be moisture starved. Partly sunny with highs around 40ºF. Overnight lows around 30ºF.

NYC Weather Update – Jan 11, 2021

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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.

NYC Weekend Weather – Jan 8, 2021

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The calm weather we enjoyed this week continues into next week. No storms are forecast through the beginning of next week. During this stretch, temperatures should be around normal at about 40ºF. Longer term, an Arctic blast may be in store next weekend, bringing much colder temperatures our way.

Rest of today – mostly sunny with high temperatures in the low-40s. Overnight lows in the upper-20s.

Weather Prediction Center’s surface forecast for 7AM Saturday, a coastal low well off to our south.

Saturday – high pressure remains in control, keeping an offshore low well away from us. Mostly sunny conditions with high temperatures around 40ºF. The pressure gradient between this low and high pressure to the west should yield some steady winds and resulting wind chill values will be in the low-20s. Overnight lows in the upper-20s to around 30ºF.

Sunday – sunny with high temperatures around 40ºF. Winds should subside a bit with high pressure moving more directly overhead. Overnight lows around 30ºF.

Monday – high pressure continues to dominate our sensible weather with sunny skies as a result and another seasonable day with highs around 40ºF. Overnight lows again around 30ºF.

Arctic chill coming?

Longer term, looking into next weekend, it’s possible that a good swath of the Midwest and parts of the Northeast could see some much colder weather. Below, you’ll see a chart that shows a highly amplified pattern at the 500 mb level for next weekend, with much above normal heights in the west (warmer than normal conditions), and correspondingly much below normal heights in the east (colder than normal). It’s still too far out to know to what degree this cold snap will affect us though.

GFS model 500 mb height anomalies next Saturday at 7PM. The blues, purples, and whites indicate much lower than normal heights. 500 mb heights can be a proxy for surface temperatures.

NYC Weather Update – Jan 4, 2021

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We’re finally getting a prolonged stretch of calmer weather to start the new year after a couple weeks with big storms to end things. Temperatures during this week should be at or above normal in the low-40s. Looking ahead, a storm is possible next weekend, though as it stands the setup would favor pushing this storm out to sea well before it impacts the region.

Rest of today – mostly to partly sunny with high temperatures in the low-40s. Overnight lows in the mid-30s.

Weather Prediction Center surface forecast for 7AM Tuesday. A departing low pressure system is visible in the top right of the frame.

Tuesday – partly sunny with high temperatures around 40ºF. Overnight lows in the low-30s.

Wednesday – mostly sunny with high pressure building in. High temperatures in the low-40s. Overnight temperatures dropping into the low-30s.

Thursday – High temperatures in the low-40s again with mostly sunny skies. Overnight lows once again in the low-30s.

  • Climate Prediction Center outlook for 1 month precipitation
  • Climate Prediction Center outlook for 1 month temperatures

Looking ahead at this weekend, a coastal storm looks like it will be shunting out to sea south of the region, although this could change in the next couple days. This month, Climate Prediction Center is assessing higher than normal chances for above average temperatures, and modestly higher chances for above average precipitation.