NYC Weekend Weather – Nor’easter Update – Jan 23, 2015

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The details are starting to come together for tomorrow’s Nor’easter. Over the past day, forecast models have been pointing to a faster moving system, such that the onset of precipitation is expected to begin overnight tonight, with the bulk of the precipitation ending by early afternoon tomorrow. This storm is expected to throw a little bit of everything our way tomorrow, making for a nasty day overall, with snow changing over to freezing rain or sleet, then perhaps a period of plain rain, followed by a possibility of a rain snow mix.

What to Expect

Snow, moderate to heavy at times, beginning overnight tonight. Winds picking up from southeast, then eventually moving to the northeast and north during the day Saturday. Snow transitioning to a period of possibly freezing rain or sleet during the morning hours, then a period of rain around midday and a possible rain/snow mix towards late afternoon before precipitation gradually tapers off later in the evening. High temperature right around or slightly above freezing.

Forecast Storm Track

Forecast models are in generally good agreement that the center of this Nor’easter will be passing just inside the 40ºN 70ºW benchmark sometime in the late afternoon Saturday (approx 4-5PM).

Without a high pressure center to the north supplying cold air to the area, this setup will allow for enough warm, moist air to circulate around the eastern side of the low pressure center to give us a mix of precipitation throughout the day. The extent to which snow can be sustained will be strongly dependent on dynamical cooling, and how quickly cold air can be pulled in on the western side of the low pressure center.

Storm track forecast from the Weather Prediction Center, with clusters indicating forecast positions of individual ensemble members.
Storm track forecast from the Weather Prediction Center, with clusters indicating forecast positions of individual ensemble members.

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Snowfall Forecast

As you can see below, the probability of more than 4″ of snow is quite low for coastal areas, especially Eastern Long Island, where mainly rain is forecast. The heaviest totals (no more than 5″, most likely) will be concentrated well north and east of NYC where temperatures are expected to be cold enough to sustain all snow for longer. Because the forward speed of the storm is now predicted to be faster, the chances of NYC getting any significant snowfall (even 2″) is considerably lower. Most of the city is in a swath of between 30-40% chance of getting more than 2″ of snow.

Probability of greater than 2" of snowfall
Probability of greater than 2″ of snowfall
Probability of greater than 4" of snowfall
Probability of greater than 4″ of snowfall

Ice Accumulation

The probability of us receiving a trace, but a measurable amount of ice from freezing rain is quite a bit higher than the probability of receiving snow, with most of the city in the 40-60% range.

Probability of ice accumulation greater than .01"
Probability of ice accumulation greater than .01″

Sunday – the storm will be long gone by Sunday, and we’re expecting to hit highs in the mid-upper 30s.

Monday – there is some potential for a round of all snow on Monday, but forecast models have not been in good consensus on how this will play out. A clipper system is expected to pass through, though it is unclear whether this system will spawn a secondary low offshore. In the latter case, we could see some significant snow, while if it’s just a clipper, we probably won’t see more than a couple inches.

NYC Weekend Weather – Jan 22, 2015 – Nor’easter Coming

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All eyes turn towards the imminent Nor’easter that will be bringing significant winter weather impacts to the NYC metro region. Many variables remain unresolved that could affect the eventual outcome, but at this time, it looks like we’re in for a nasty combination of freezing rain, rain, and snow during the day Saturday. At present, forecasts call for somewhere between 2-4″ of snow in the city along with some ice accumulation. Precipitation should fall as all snow north and west of NYC, however, overall accumulation should be slightly less than in the city itself since the most intense precipitation will remain near coastal areas.

Friday – we get a pleasant, sunny, and slightly above average day with high temperatures in the mid-upper 30s.

Saturday – a tricky forecast for Saturday. What we know for sure, with different forecast models in relatively close agreement, is that an area of low pressure now forming over the Texas Gulf Coast will track over the Southeast, and then offshore of North Carolina by Friday night/early Saturday. Once the low moves offshore, it will rapidly intensify, and then track right on or very close to the 40ºN 70ºW benchmark by Saturday afternoon/early evening.

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The uncertain part about this scenario has to do with the thermal profiles in place. With no high pressure over us or to the north pumping in cold Canadian air, the depth of cold (sub-freezing) air will be relatively shallow.

As the Nor’easter approaches us, the cyclonic flow around its center will wrap in some relatively warmer air in from the ocean and points south. This makes for a complicated picture – with warmer air aloft (see animation below) during parts of the day, and below freezing air nearer to the surface throughout points in the day, the recipe is set for at least some periods of freezing rain – precipitation that falls as rain, and then freezes on contact with a sub-freezing surface.

During the middle portion of the day, temperatures should be warm enough at the surface to support plain rain for some time, before transitioning back into freezing rain, rain/snow mix, perhaps with a period of all snow before tapering off Saturday evening.

output_QGEuaq
NAM output of temperature profiles at about 4,800 feet between 10AM and 7PM Saturday. Notice the light pink indicating temperatures between 0ºC and 10ºC, which only gives way to below freezing temperatures (light blue, indicating 0ºC to -10ºC) later in the time frame. The center of the Nor’easter is located within the middle of the set of concentric rings you see near NYC.

nam-hires_namer_057_925_temp_htDeviations in the storm track to the east would result in more cold air being pulled in from the action of northerly winds on the western side of the low pressure center’s cyclonic flow (less freezing rain/rain, more snow), while deviations of the track west would result in warmer air being in place (less snow, more rain). So, even a slight adjustment in the storm track could alter the thermal profiles, and subsequently what kind of precipitation we see.

Sunday – temperatures overnight Saturday will be below freezing, which would allow anything that fell and melted to refreeze. Things do clear up Sunday, with highs about average in the mid-30s, and with clouds diminishing.

Monday – there is a chance for yet another round of mainly snow, potentially heavy, as another coastal storm is possible. Highs will be close to the freezing mark, making this an all snow event if it should pan out.

 

NYC Weather Update – Jan 20, 2015

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NYC gets brushed by a fast-moving Alberta Clipper system, with the potential for some light accumulating snow across the area Wednesday afternoon and evening. High pressure builds behind the clipper system Thursday and Friday, with high temperatures about average for this time of year. There’s some potential for a coastal storm approaching on Saturday/Saturday night, but with considerable uncertainty at this time, it remains to be seen if this scenario pans out, and if it results in snow or rain or a mix of wintry precipitation.

Wednesday – clouds increasing through the day with high temperatures in the mid-30s. Flurries may develop in the afternoon, however, the bulk of any snow is more likely to occur later in the evening and overnight. Max accumulations of 2″ in the city (1″ is more likely).

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NAM model showing precipitation over the area Wednesday, as a clipper system transfers its energy over to a coastal low which will remain well offshore.

 

Thursday – mostly cloudy day with some snow flurries possibly lingering into the morning. High temperatures around the mid-30s.

Friday – high pressure continues to build over the region with skies clearing and high temperatures again in the mid-30s.

Saturday – forecast models are hinting at a coastal storm for Saturday. Right now, it appears as though the storm track brings the center of the low slightly to the east of the 40ºN 70ºW benchmark. Temperature profiles in the area also appear to be around the freezing mark. This will bear monitoring, as a slight westward jog of the storm track and a cooler temperature profile could result in some significant snow.

NYC Weekend Weather – Jan 15, 2014

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We end this week off with a windy day Friday, followed by an intrusion of cold air on Saturday before a warmup Sunday that should be accompanied by some rain during the day, then possibly a mix of rain and snow Sunday night. Some chance of snow persists into early Monday.

Friday – a cold front dropping from Canada will tighten the pressure gradient ahead of it, bringing with it breezy west-northwest winds between 15-25mph during the day tomorrow. High temperatures will be about normal in the upper 30s, but with wind chill values only in the 20s.

Saturday – subsequent to the passage of that cold front, we get another shot of cold, arctic air, with temperatures on Saturday struggling to even reach 30 in the city, and only in the 20s elsewhere.

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Sunday – a low pressure system will be moving steadily northeast into Quebec by Sunday. This storm system will have a trailing cold front as well as a preceding warm front. We should enter the warm sector behind the warm front passing over us Sunday. This will allow for temperatures to rise into the mid-40s (possibly higher in a few spots). There will be a transfer of energy to a secondary low pressure center which is forecast to form off the Mid-Atlantic coast. This will result in the chance for us to get a few periods of moderate-heavy rain on Sunday, especially in the afternoon hours. As the coastal low moves off to the northeast, rain should taper down during the overnight hours into Monday, and temperatures will be cold enough to support a chance of rain/snow mix.gfs_namer_087_1000_850_thick

Monday – snow showers should end early Monday. High temperatures will be about average for this time of year, in the upper 30s.

NYC Weather Update – Jan 12, 2015

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We start this week with a mixed bag of precipitation, currently rain, but eventually back to a wintry mix before ending. The rest of the week will be dry, with colder days on tap for the mid-week period before another warming trend to end things off.

Tuesday – once the storm system that’s responsible for today’s rain and mixed precipitation moves away, a cold front will usher in a strong area of high pressure that will dominate our weather for the mid-week period. This high pressure area will allow cold Canadian air to flow into the area from the north. High temperatures will struggle to reach the freezing mark, while a steady north wind will ensure wind chills in the teens.gfs_namer_033_1000_850_thick

Wednesday – will be similar to Tuesday in terms of sensible weather with highs in the low 30s, and partly sunny skies.

Thursday – another partly sunny day, but with slightly warmer temperatures in the mid-upper 30s, near normal.

Friday – should be essentially the same as Thursday with highs again in the mid-upper 30s. Doesn’t look like we’ll get any chance for precipitation throughout the end of the week and weekend.

NYC Weekend Weather – Jan 9, 2014

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This first full week of the new year has featured the coldest temperatures all winter and first noticeable snow accumulations for NYC. This weekend will see a slight warming trend, with some rain possible by Monday. Looking ahead towards the end of next week, we could get hit with a coastal storm, which may bring a mix of precipitation types to the region.

Saturday – strong high pressure builds over the area, so expect a clear day, but still quite cold with highs in the low 20s and wind chills in the teens.

Check out that high pressure over the Ohio Valley at 1036mb
Check out that high pressure over the Ohio Valley at 1036mb

Sunday – as the high pressure area moves east, winds on the backside of the high will shift towards the southwest. This will favor a rebound in temperatures to slightly below seasonal highs in the mid 30s. Cloud cover will also increase ahead of an area of low pressure approaching from the southwest.

Monday – the aforementioned broad area of low pressure will pass through on with winds persisting from the southwest. This will allow temperatures to continue climbing into the upper 30s, meaning this will primarily be a rain event, although some mixed precipitation is possible early.

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Tuesday – immediately following this low, temperatures will plunge back into the upper 20s with strong Arctic high pressure moving in behind the low.

NYC New Years Weather Update – Dec 29, 2014

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2015 is right around the corner, and I’m happy to report that weather conditions will be dry, though on the cold side for New Year’s Eve festivities and for New Year’s Day (we’re talking lows in the upper 20s in the city, daytime highs in the mid-30s). This cold but fair weather pattern holds through the week, with a slight warmup ahead of a storm system moving in Saturday & Sunday.

Tuesday – partly sunny day with highs in the upper 30s. However, north winds will yield wind chill values closer to 30.

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Wednesday (New Year’s Eve) – with high pressure building to our west, and a low pressure system well to our north, things will stay dry and mostly sunny for your New Year’s Eve outings. The downside is that winds will remain moderate and push wind chill values into the 20s with daytime highs in the mid-30s. Overnight lows New Year’s Eve will be in the mid 20s, with wind chills in the teens.

Thursday – basically a repeat of Wednesday, with high temperatures hovering in the mid-30s and mostly sunny skies.

Friday – still cold, with highs in the upper 30s, though winds should abate slightly.

This weekend, we’ll see a storm system approach from the southwest and track to the Great Lakes region. The storm system should allow for some slightly warmer air to enter the region ahead of it, but we’re still only talking high temperatures only in the mid 40s. Best chance of rain will be Sunday.

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NYC Christmas Weather Update – Dec 24, 2014

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A foggy start to the busy travel day for many will feature periods of locally heavy rain and gusty winds later this morning into the early afternoon. Near record warmth with high temperatures in the low 60s today will give way to cooler but calmer weather going into the holiday weekend before another round of unsettled weather early-mid next week.

Today – foggy conditions will be a prelude to a stormy Christmas Eve. An approaching warm front will move through shortly and allow for a surge of warm air to raise temperatures into the low 60s. Along with this, there looks to be a period of widespread showers in the late morning and early afternoon hours. Afterwards, there should be a lull in the rain before a second round of showers and possibly scattered thunderstorms associated with this storm system’s trailing cold front moves in. Winds will pick up ahead of and then behind this cold front. If you are traveling either by air or car, the latter part of the day could see some weather related disruptions and delays. Overnight lows will be very mild near 50.

Plenty of fog on the Whitestone Bridge
Plenty of fog on the Whitestone Bridge
NAM model stimulated radar image for 2PM EST, 12/24/2014
NAM model stimulated radar image for 2PM EST, 12/24/2014

Christmas Day – conditions improve dramatically during the day in the wake of the cold front. Any lingering showers should end early in the morning with rapidly clearing skies accompanied by a gusty west wind. High temperatures in the mid-50s will actually be set early in the morning with temperatures dropping steadily during the day to the upper 40s later in the afternoon.

Friday – fair weather continues as an area of high pressure builds over the Eastern US. Partly cloudy with a mild high near 50.

Saturday – much the same as Friday with high pressure still in control. High again near 50.

Sunday – mostly cloudy with a chance of rain, slightly cooler with highs in the mid-40s. A frontal boundary may stall just south of us, setting up conditions for an extended period of unsettled weather next week.

NYC Weekend Weather Update – Dec 19, 2014

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This weekend will feature about normal temperatures for mid-December, with a small chance of rain/snow on Sunday. Relatively quiet weather during the weekend will give way to an active weather pattern for the first half of next week, with a robust storm system arriving Christmas Eve (all rain, sadly, so no white Christmas for us here in NYC).

Saturday – high pressure currently in control of the weather will erode as it moves east. Clouds cover will increase with high temperatures around 40.

Sunday – easterly winds off the ocean in the wake of high pressure centered over Atlantic Canada will bring some slight chance for precipitation. The lower atmosphere is fairly dry, and is not primed with moisture for precipitation. If precipitation does materialize, temperature profiles are low enough that some snow flakes could be seen, but the overall impact will be negligible. High temperatures will be in the low 40s with cloudy skies.

GFS model output for Sunday
GFS model output for Sunday, 12/21/2014

Monday – a significant storm system will be approaching our region from the Central Plains. Forecast models point to a primary low pressure center over the interior of the country while a secondary low forms along the coast. Ahead of this storm system, some scattered showers could pass over the area Monday. Otherwise, expect a mostly cloudy day with high temperatures in the mid-40s.

Tuesday – coverage of precipitation will increase on Tuesday as that secondary low pressure center draws closer to the area. Warmer, marine air will be in place before a warm front passes over. This should ensure that temperature profiles remain warm enough to preclude the possibility of snow. Temperatures may rise to as high as the 50 degree mark Tuesday.

This early-mid week storm will cause some travel headaches for Christmas, but fortunately, it does appear the majority of precipitation will be in the form of rain.

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Tropical Weather Update | Typhoon Hagupit – Dec 5, 2014

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A potent and massive typhoon is taking aim at the northern Philippines, in particular, Samar Island. Some of these areas were devastated by Category 5 Super Typhoon Haiyan less than one year ago, which broke the record for strongest landfalling tropical cyclone with wind speeds measured in Tacloban of 190mph. If you have friends or family in the Northern Philippines, Hagupit certainly bears keeping an eye on. Luckily for Tacloban, the current forecast track should take the center and northern semicircle (the stronger portion) of the storm north of the area, which should spare the area worst hit by Haiyan from another direct hit and the worst effects of a typhoon.

wp201422_sat
Infrared satellite imagery of Typhoon Hagupit – note the symmetrical appearance of the inner portion of the storm, along with a well-defined eye (classic signs of a very strong storm).

Forecast Track

From the image below, you’ll see that Hagupit is currently forecast to move slowly west-northwestwards over the next 48 hours. Due to the strength of the storm, and the uncertainty surrounding the steering mechanisms in place (a subtropical ridge – high pressure area to the north weakening, and a frontal boundary), there is a low degree of confidence over the overall track forecast. However, it does appear, even with the uncertainty factored in that the storm center will pass to the north of Leyte Island and Tacloban, which was devastated by Super Typhoon Haiyan. That’s good news, since this would mean the weaker, southern semicircle of Hagupit would pass over the Leyte Gulf area. This would significantly reduce the effect of a devastating storm surge, since the winds from the storm would not have the best fetch (distance over open water) to build up a storm surge. In effect, with the current track, the strongest winds would be deflected by the terrain of Samar Island, sparing Leyte Island.

It is worth noting, based on this current track, that Legazpi City in extreme southeastern Luzon Island would bear the worst of the storm, including what could be a devastating storm surge. The bay east of Legazpi could serve to funnel storm surge westward under the right conditions, amplifying the effect of the surge in a similar (though less intense) manner as Leyte Gulf and San Pedro and San Pablo Bay did for Tacloban in Haiyan.

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Haiyan_2013_track
For comparison, the track of Super Typhoon Haiyan in November 2013. Dots indicate position of the center of the storm every 6 hours, the colors indicate strength, with red indicating Category 5.

Intensity Forecast

Typhoon Hagupit has well-established outflow in the northern quadrant, as you can see from the satellite image above (white streaks fanning out from the center of the storm). It is being affected by easterly vertical wind shear, hence the absence of the same outflow bands in that sector of the storm. Hagupit has already weakened from a Category 5 Super Typhoon, but is still forecast to approach the Philippines as either a strong Category 3 or weak Category 4 storm, which would mean wind speeds likely in the range of 110-120mph. After landfall, Hagupit should weaken dramatically as interaction with the mountainous terrain of the Philippines disrupts the typhoon’s dynamics.