Feb 05

Feb 5, 2016 Morning Update

8:30 AM: Heavy Snow Falling Across Much Of Area

nerad21As last night’s blog post noted, a wave of low pressure previously forecast to remain offshore trended much stronger and farther west over the last two days, sufficiently enough to produce widespread moderate to heavy snow across the area. Despite an initial period of rain last night, which amounted to over 1/4 inch in some locations, a quick changeover to snow followed early this morning, with ongoing moderate to heavy snow associated with strong mid-level frontogenesis and upper-level divergence near the right entrance quadrant of a powerful jet streak. The strong synoptic forcing is supporting snow rates near 1-2 inches per hour, accompanied by thundersnow earlier this morning in northeast New Jersey.

As of 8 AM, most of the NYC area airports recorded at least 2 inches of snow, with reports of over 3 inches of snow in parts of Long Island and Connecticut. At least an additional 1 to 3 inches of snow are likely west of NYC, with another 2 to 5 inches east of NYC. As the coastal low quickly continues to track northeast, snow will gradually taper off from west to east, ending west of NYC towards 10-11 AM and east of NYC towards 11 AM to 1 PM.

Feb 04

Feb 4, 2016: Snow Expected Tonight, Tomorrow

Forecast Highlights:

total_f36Weather forecasting is not an exact science, and occasional events that unfold much differently than forecast continue to remind us such. Tonight is one of these cases, as a wave of low pressure initially forecast to remain well offshore has trended substantially stronger and closer to the coast, to the extent that widespread moderate to heavy snow is now forecast to affect much of the coastal corridor tonight into tomorrow. The peak of the snow is expected tomorrow morning, with significant impacts likely to the Friday morning commute with up to several inches of snow expected.

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Feb 04

Feb 4, 2016 Brief Update: Snow Tomorrow

1:40 PM: Snow Likely Tomorrow

total_f36Confidence is increasing for a light to moderate snow accumulation tonight into Friday morning.

A short-range trend in the model guidance, associated with a shortwave trough both deeper and slower than previously modeled, is resulting in a wave of low pressure developing close enough to the coast to produce widespread precipitation. Given that the temperatures will still be cooling down from the 50s today, some rain is likely to start, but with a period of moderate snow increasingly likely later tonight into Friday morning, possibly heavy east of NYC.

Accumulations are still uncertain at this time, although the latest trends suggest the possibility of several inches of snow over Long Island and Connecticut, with lighter accumulations near and north/west of NYC. This is especially evident in the latest model guidance, as with the 12z GFS (posted to the left). A more detailed analysis will be posted later this evening about the forecast for tomorrow.

Jan 23

Jan 23, 2016 Blizzard Updates

Frequent updates will be posted below on the blizzard and heavy snow event affecting the region today. The latest updates, along with the latest available snow reports, will be at the top of this post. Radar images are from the Pennsylvania State University e-Wall.

Links: Yesterday’s Forecast | 8-Day Forecast | Twitter | Facebook


Saturday, January 23

12:30 AM: 2nd Biggest Snowstorm in Central Park Records

1.24_0515As of 10 PM, the low pressure has become elongated off the coast, with a 987 hPa low centered southeast of Cape Cod along the triple point. This low pressure will continue to weaken and track northeast tonight into tomorrow.

As the radar to the left shows, most of the snow has tapered off across the area, except for a lingering band of moderate snow over central Long Island and scattered snow showers over NYC and eastern New Jersey. Central Park recorded a total of 26.8 inches as of 12 AM, just 0.1 inch below the largest snowstorm on record, 26.9 inches, set on February 11, 2006. Nonetheless, it is very remarkable that a storm which only 36-48 hours ago was forecast to remain mostly to the south of the tri-state area ended up producing Central Park’s second largest snowstorm on record. Some additional snow totals from airports in the area include 30 inches at JFK airport and 28 inches at LaGuardia airport.

This is the final storm update for tonight. A brief post-storm analysis, including additional snowfall reports, will be posted on Sunday morning or afternoon.





8:20 PM Update: Central Park’s 3rd Biggest Snowstorm on Record

As of 7 PM, Central Park recorded 25.1 inches of snow. This places it as the 3rd biggest snowstorm on record, behind December 1947 (26.4″) and February 2006 (26.9″). Although the storm is beginning to wind down, additional weakening snow bands will continue to rotate through NYC and western Long Island over the next hour or two before collapsing, which will bring Central Park either very close to or just slightly over the record.

Other totals in the tri-state area include 27.7″ at JFK airport, 25.7″ at Newark, NJ, and 24.5″ at LaGuardia airport.





6:40 PM: Intense Snowfall, Blizzard Conditions Continue

1.23_2245As of 4 PM, the low pressure remains stalled just off the Delmarva Peninsula, with a minimum pressure of 983 hPa. Meanwhile, a secondary low pressure is developing well to the southeast of Cape Cod near the triple point between the warm/cold fronts and the occluded front, with a minimum pressure of 985 hPa. The primary low will gradually begin to progress east over the next few hours.

The mid-upper tropospheric low is currently passing south of the tri-state area, with the strongest deformation and resulting frontogenesis shifting off to the east. Accordingly, with the strongest forcing for ascent moving offshore, precipitation is gradually decreasing in intensity across the region, but with a lingering band of heavy snow slowly moving east through southern CT into NYC and central New Jersey. The peak of the storm has largely passed in northern NJ, with the snow gradually winding down over the next 2-4 hours before tapering off from NW to SE. Farther to the east, the bands will slowly pivot through CT and Long Island while weakening, with snowfall rates gradually weakening until snow tapers off around or a little after midnight.

Snowfall reports are already approaching historic levels in parts of the tri-state area. As of 6 PM, JFK recorded 26 inches of snow, with 24 inches at LaGuardia, along with snowfall rates generally around 2-3 inches per hour. Central Park was at 19.3″ as of 4 PM, and is expected to approach and/or surpass the 24 inch mark before the storm ends, firmly placing it among the top 3 snowstorms in recorded history. Elsewhere in the area, at least 12-20 inches fell over most of Long Island and northern New Jersey, decreasing rapidly to at least 4-7″ over Orange county, NY and central Connecticut.





4:15 PM: Intense Snowfall, Blizzard Conditions Continue

nerad25aAs of 1 PM, the Weather Prediction Center (WPC) analyzed the low pressure just off the Delmarva Peninsula, with a minimum pressure of 986 hPa. The low pressure will begin to drift east later tonight as a secondary low pressure develops along the triple point south of Cape Cod.

The last several hours have not seen any new developments, besides the continued persistence of heavy snow bands over most of the tri-state area, driven by strong mid-level frontogenesis associated with deformation east of the upper level low, with snowfall rates frequently exceeding 2 inches per hour. The strong pressure gradient north of the low pressure is resulting in continued strong winds from the northeast, with gusts as high as 57 mph in Islip, NY and 48 mph at JFK airport, resulting in significant coastal flooding and blizzard conditions across much of the area.

While snowfall reports have not been updated by the National Weather Service since 1 PM, the latest observations from LaGuardia and JFK airports indicate 20 inches of snow have accumulated, and Central Park’s total of 14.7″ as of 1 PM, when accounting for continued 2 inch per hour rates, would likely be within the same vicinity. Only two storms in recorded history surpassed 2 feet of snow in Central Park; this storm is poised to become the third such storm, and approach Central Park’s record of 26.9 inches set in 2006.

Snow will continue to fall at a similar intensity until at least 6-8 PM, when the snow bands will gradually progress east of NYC with snow rates decreasing from west to east, ending for most locations by midnight. By the time this storm ends, it will likely have its place among the most significant blizzards in New York City’s recorded history, a ranking that just 18-24 hours ago did not appear to be a high likelihood.





12:40 PM: NYC Approaches Its Biggest Snowstorm On Record

1.23_1730As of 10 AM, the low pressure remains positioned off the coast of Southeast Virginia, with a minimum pressure of 987 hPa. The low pressure will remain nearly stationary through this evening as it becomes collocated with the mid-upper level low, while a secondary low begins to develop along the triple point farther offshore later tonight.

Heavy snow continues to fall throughout most of the tri-state area, as heavy snow banding associated with strong mid-level frontogenesis and deformation remains stalled overhead. The National Weather Service has yet to issue updated snow accumulations since this morning, although Newark, NJ and LaGuardia, NY have recorded 15 inches of snow depth from their latest hourly observations. Central Park has already recorded 1.26″ of liquid-equivalent precipitation, which with a typical 10:1 snow to liquid ratio would translate to 12.6 inches of snow. With the system only slowly moving off to the east, these snow bands will continue to pivot through the tri-state area through at least 6-8 PM this evening before winding down.

snowmap3Given the current snow observations, and anticipated 1-3 inch per hour snow rates through the remainder of this afternoon, the snow forecast has been increased, and over 2 feet of snow in NYC, western Long Island and northern New Jersey are within reasonable reach. Central Park’s biggest snowstorm on record is 26.9″ from February 11, 2006; this storm is currently on track to end up within Central Park’s top 3 snowstorms on record, as only 2 storms in recorded history surpassed 2 feet of snow.






10:00 AM: Heavy Snow Continues, Up To 16-24 Inches Expected

1.23_1430As of 7 AM, the coastal low pressure is positioned off the coast of Southeast Virginia, with a minimum pressure of 987 hPa. The low pressure, having developed over the North Carolina coast last night, continued to deepen last night, and is currently becoming occluded, signaling that it will slow down and stall off the coast this afternoon before a secondary low pressure develops farther offshore along the triple point.

Yesterday’s evening forecast update highlighted the challenges in determining the northward extent of the heavy snow banding, especially with the mid-upper level taking longer to close off than previously modeled, resulting in a faster progression of the system into the region and a farther northward extent of the heavy snow banding before the surface low occludes. Model runs as recently as yesterday morning depicted snow starting in NYC late this morning; in reality, however, snow already began late yesterday evening, with several inches on the ground as of this morning. An abrupt northward shift in the snow accumulations followed, which was highlighted in the evening post, with snow forecast amounts significantly increased throughout the tri-state area. While the shift in the position of the low pressure was relatively minor, that small shift in the position and timing of the storm meant a significant change in snow accumulations due to the sharp cutoff in snow totals ending up north of NYC, as opposed to over NYC.

700 hPa frontogenesis, overlapped with the radar mosaic, from the SPC Mesoanalysis, valid at 1400 UTC (9 AM EST).

frontogenesisAs the radar mosaic above depicts, a band of heavy snow currently extends from west of Washington DC into central Pennsylvania, northern NJ, NYC and Long Island. This band is associated with strong frontogenesis, or the enhancement of a temperature gradient, which corresponds with strong upward vertical motion. To the north of this band, a sharp cutoff in snowfall rates is apparent due to the resulting subsidence, or sinking air, to the north of this heavy snow band. This band slowly progressed north through the tri-state area last night and early this morning, with latest observations from the National Weather Service suggesting up to 7 to 12 inches have already accumulated over most of northern New Jersey, NYC and Long Island, decreasing to 1 to 4 inches in far northwest NJ, SE NY and southern CT.

High resolution models indicate that as the upper-level low continues to slowly drift northeast with a deformation axis setting up near the tri-state area, the heavy snow banding will stall and pivot near central NJ into NYC and Long Island through at least 6-8 PM this evening, continuing to produce heavy snowfall rates over 1-2 inches per hour and wind gusts over 35-45 mph, along with the risk of isolated thundersnow. Afterwards, the bands should weaken and shift offshore as the low pressure and forcing for ascent weaken with a secondary low developing farther to the east, with snow tapering off by 9 PM – 12 AM west of NYC, and 11 PM to 2 AM east of NYC. The latest snow forecast at this time remains for 4 to 8 inches of snow from SE NY into central Connecticut; 8 to 16 inches over northern NJ north of I-80 into coastal Connecticut and eastern Long Island; and 16 to 24 inches of snow over NJ south of I-80 into NYC and most of Long Island.

Jan 22

Jan 22, 2016: Heavy Snow, Blizzard Conditions Expected Tomorrow


Due to rapid changes in the forecast snow accumulations, this post was updated at 11 PM Friday. The new snow forecast can be found at the bottom of this post.

Forecast Highlights:

rad_1.22The first major snowstorm of the winter is currently affecting the Mid Atlantic region up to central New Jersey, with snow expected to spread into the area tonight. Heavy snow will continue to fall through Saturday, mostly near and south of NYC, with the potential for over a foot of snow and near blizzard conditions. A sharp gradient in snow totals is expected over the area, however, which results in continued higher than usual uncertainty, despite the onset of the storm being only several hours away.

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Jan 22

Jan 21, 2016 Brief Update

12:00 AM: First Snow Map Posted

Following today’s latest trends in the model guidance regarding the evolution of the storm, there is sufficient confidence to issue a preliminary snow map for the upcoming weekend snowstorm.

This map is largely based on the expectation for strong confluence downstream of the upper level low, and earlier trends for the upper level low to become cut off earlier as a result of more amplification than previously modeled, that would likely result in a low pressure track far south enough to keep the heaviest snow bands south of NYC. As yesterday’s forecast discussion noted, a strong gradient in snow accumulation is expected north of the snow banding, and in reality would likely be stronger than the map below depicts. The positioning of this gradient is somewhat uncertain, and continues to shift around with each model run; the placement shown below is preliminary, and the snow gradient is subject to slight shifts with additional updates on Friday.

Another forecast issue arising with this event is precipitation type, especially along eastern Long Island and the NJ coast, as an onshore northeasterly flow with relatively warmer ocean temperatures potentially resulting in a period of rain. Sleet is also possible, perhaps to a more widespread inland extent, as the trend towards a slower cutoff low is also indicative of less initial cold air advection into the system. During this same time frame, strong warm air advection aloft associated with a strong low-mid level easterly jet is expected, which in addition to providing sufficient moisture in conjuncture with strong ascent producing significant snowfall amounts over Virginia and Maryland, also results in a potentially above freezing mid-level warm layer. This aspect of the system will need to be further monitored, as more rain and sleet would limit snow accumulations over eastern parts of the area.

A more detailed forecast analysis will be posted on Friday morning.



Jan 20

Jan 20, 2016: Major Snowstorm Expected, Though Uncertainty Lingers

Forecast Highlights:

ne_f78The cold air mass which has been in place since the weekend has since moved out, with temperatures moderating into the mid 30s earlier this afternoon. Similar temperatures are likely to continue through Friday, when a deepening low pressure will approach the region, producing the first major snowstorm of the winter. While confidence is high regarding the potential for significant snow accumulations, specific details such as the exact positioning of heavy snow banding and the gradient in snow accumulations have yet to be resolved, which for the time being results in continued uncertainty regarding exact snow accumulations.

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Jan 18

Jan 18, 2016: Snowstorm Next Weekend – Hype Or Reality?


Given the potential for a major snowstorm, the first of this winter, frequent blog posts will be posted as long as this storm continues to pose a risk of producing significant snow accumulations.

Forecast Highlights:

gfs_mslp_pcpn_frzn_neus_20December’s record warmth gave way to a noticeably cooler but still warmer than average pattern so far this month, with Central Park having recorded its first measurable snow yesterday in association with a poorly modeled coastal low pressure. Cold temperatures will continue this week under a strong upper level low, moving out later this week ahead of an approaching shortwave trough which may produce the first major snowstorm of the winter across parts of the East Coast during the upcoming weekend.

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Jan 18

Blog Status: Post Coming Up Shortly

January 18th, 7:58 PM

A detailed blog post summarizing December and analyzing the potential for a major snowstorm next weekend is currently under progress, and will be posted by 10-11 PM tonight.


Dec 28

Dec 28, 2015: December’s Reality Sets In

Forecast Highlights:

nmmThis month so far has been dominated by warmth resembling anything but December. In fact, the December 1-27 period was warmer than 96% of all Novembers in NYC’s recorded history. A transient but strong cold air surge, however, will bring reality back into the picture, as temperatures return into the low 40s, which is still near to slightly above average, in addition to the first widespread frozen precipitation event outside of Maine, which will produce widespread sleet and freezing rain inland of NYC tomorrow, as signs of winter slowly but gradually begin to make their presence over the next month.

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