Mar 6-8, 2013 Storm Updates

Below, updates will be posted on the rain, snow and wind event affecting the region from Wednesday through Friday. The blog will remain in storm update mode through this time period; the next forecast discussion will be posted on Saturday.

Twitter updates are archived in the NYC Area Weather twitter page.

Blog Updates:

Friday, March 8

1:15 PM: Snow continued to fall throughout the last few hours, although temperatures are slightly warming up, already above freezing in parts of the area which could result in some more difficulty for the snow to accumulate compared to last night and this morning. The snow bands continue to hold steady over Massachusetts and interior Connecticut, where the storm significantly exceeded all expectations with 20-24 inches of snow possible in some locations, although snow is starting to weaken further west over NYC and NJ. Snow will continue falling through the mid afternoon hours, gradually mixing with light rain in some areas as it ends, with additional light accumulations expected mainly over NE NJ, Connecticut and parts of Long Island.

The next forecast discussion will be posted on Saturday, along with an overview of this storm and what went wrong with both forecasts, for the coastal low when less snow than expected fell, and the inverted trough when much more snow than expected fell.

10:50 AM: Steady light to moderate snow continues to fall across the area, locally heavy over northeastern NJ and parts of Connecticut. As of 10 AM, more widespread totals of over 10 inches have been reported across southern CT and SE NY according to the National Weather Service. With at least a few more hours of snow left, which for southern and western parts of the area may mix with rain as the storm ends, additional accumulations are expected, with totals in northern parts of the area locally as high as 12-16 inches. Totals remain lower in parts of New Jersey, NYC and Long Island, with totals near 1-3 inches generally reported in Manhattan, the lowest across the area.


8:25 AM: As of this morning, snow continues to fall across most of the region. The snow remains generally moderate, locally heavy in some spots and especially towards New England. Unlike the coastal low, when less snow than expected fell, snow totals so far exceeded the forecast, in some cases significantly so, across many parts of the region. The highest total so far is 13 inches in Hortontown, NY (Putnam), with totals of 10″ in Armonk, NY (Westchester), Harriman, NY (Orange), and Danbury, CT. Totals locally as high as 6-9 inches have also been reported in Long Island and northern NJ. Not all of the area overperformed, however, with parts of Long Island and NYC still at 1-4 inches so far.

Many models showed a general 2-5 inch snowfall across the region with totals locally over 5 inches north of the area; the NAM was the most bullish, suggesting widespread 12-18 inches across northern New Jersey into eastern NY state. While the NAM’s totals are still overdone even compared to the current observations, it was correct with heavier banding over New England into the area with more snow than what most of the models indicated. In this case, however, the NAM’s scenario originally appeared to be more of an outlier than usual, especially considering that just 24 hours ago it had a major bust with the coastal storm, showing 1/2 to 1 inch of precipitation near and west of NYC where hardly anything fell.

Snow will continue to fall through the early afternoon hours, gradually mixing with rain and ending by the early-mid afternoon. Additional light to locally moderate accumulations are expected through then, although snow rates could decrease by the end of the storm especially as temperatures slightly increase. Clearing skies and lighter winds are expected tonight giving way to sunny and mild conditions for the weekend as temperatures climb to nearly 50 degrees, which should result in a quick melting of today’s snowfall. Total accumulations are likely to end up between 6 and 14 inches across southern CT and SE NY, 3 to 9 inches in northern NJ and Long Island, and 2 to 6 inches in NYC. Totals may be locally lower in some areas and locally higher in other areas.

12:45 AM: Moderate to locally heavy snow continues to fall across most of Connecticut, northern NJ, with heavier snow bands expected to spread into southeastern New York soon. Totals in some locations have already reached the forecast range, with snow expected to continue through the early-mid morning hours. Under these locations in southern CT, SE NY and parts of NE NJ, totals are increasingly likely to reach and locally exceed 6-8 inches. Elsewhere across the area, light to moderate snow continues to fall, with accumulations of at least 2 to 4 inches expected for most.




Thursday, March 7

11:20 PM: Through the evening and early night hours, steady light to moderate snow continued to fall across most of the area, mixing with rain at times in some locations, with the heaviest snow bands so far over the Hartford to New Haven, CT corridor, extending into parts of Long Island.Accumulations have been reported in SE NY, southern CT, and parts of Long Island and northern NJ, with totals locally as high as 3-5 inches already reported in parts of SE NY.

The moderate to heavy snow bands remain over Connecticut and western Long Island, slowly shifting west towards the Hudson Valley into the immediate NYC area. Additional snow is expected to fall through the overnight into the morning hours, with snow gradually mixing with rain and then ending by the late morning to early afternoon hours. Totals are still expected to end up between 3-6 inches in SE NY, southern CT and parts of Long Island, with 2-4 inches elsewhere, locally lower near NYC and western NJ. Given the current snow accumulations, the potential is there for totals to end up locally higher than 6 inches in SE NY and southern CT.

7:15 PM: Steady rain and snow showers have continued to fall throughout the day, and steadily intensified this evening as an inverted trough continues to take shape across the region. Precipitation type earlier was generally rain or non-accumulating snow, although with the time of the day and cooling temperatures, precipitation type is changing over to more widespread snow which is starting to accumulate in parts of northern NJ, SE NY and southern CT.

Light to moderate snow, locally heavy, is generally expected to continue focusing over southern New England, the Hudson Valley, and parts of the area through Friday in the late morning hours. The heaviest snow totals are expected into southern CT and eastern parts of SE NY, with 3 to 6 inches of snow; totals locally above 6 inches are possible in Connecticut. Long Island is expected to see 2 to 5 inches of snow, with 2 to 4 inches for the rest of the area, with amounts below 2 inches in some spots such as NYC and western NJ.

11:30 AM: Since last night’s update, the low pressure continued to gradually drift to the east, although precipitation continues to expand northwest into New England and the area. From NYC and further north and west, the forecast last night for the coastal busted on the high side with precipitation failing to spread as far north as expected, with little to no accumulations observed. Some snow is currently falling in these areas, but is struggling to accumulate due to warm surface temperatures and snow rates not heavy enough. East of NYC into most of southern Connecticut, light to moderate snow still fell; amounts busted on the high side as well compared to the original forecast, instead ending up closer to the revised forecast last night for up to 2 inches, locally higher, as totals above 1 inch have been reported across parts of Long Island with amounts locally near/slightly over 2 inches further east where heavier snow fell last night. Rain/snow showers continue to fall in Long Island and CT as of this morning.

Forecast Update: Scattered rain/snow showers are expected to continue today with minimal accumulations considering the warmer surface temperatures and lack of heavy precipitation rates. The next round of the storm is expected tonight as an inverted trough sets up, producing more snow across the region, but north of the coastal low. The focus of tonight’s snow is expected north of the area, into New England and eastern NY state, with moderate snow expected over southern CT and possibly Long Island. The main uncertainty at this time is how far west the snow spreads. Last night’s update mentioned one bust potential would be if precipitation stays too far north/east for the area to receive widespread moderate accumulations. Some of this morning’s models are showing this scenario, keeping accumulations over 3 inches north and east of NYC, with lower totals for NYC, northern NJ and southeastern NY.

The current forecast for tonight is 1 to 3 inches of snow in NYC and northern NJ, with similar totals in Long Island but locally higher, 2 to 4 inches in southeast NY, and 3 to 6 inches in southern CT. These totals are still subject to minor revisions, and more information will be posted throughout the day.



Wednesday, March 6

11:00 PM: As of 10 PM, there is a broad low pressure south of Long Island and east of southeastern VA. The minimum pressure is approximately 994mb, and the system is generally drifting east.

Since this afternoon’s update, precipitation has still failed to spread north into most of northern New Jersey, and aside from an earlier period of light snow mixed with some rain, it appears most locations north and west of NYC will fail to see more than scattered light precipitation tonight with less than 1 inch of snow. Last night’s update mentioned that only a small difference with the northern end of the heavier precipitation would have a larger impact on the area, and so far this is setting up south of the expectation even from earlier today, resulting in the forecast busting on the high side with snow totals across the area tonight. Locations east of NYC are currently observing rain/snow and are expected to continue seeing light to moderate precipitation through the early-mid overnight hours, with snow accumulations generally up to 1-2 inches. From NYC and north/west, little to no accumulations are expected tonight.

Tonight’s bust is unlikely to repeat in a similar style tomorrow night, however. After scattered precipitation through the day on Thursday, generally in the form of light rain/snow, an inverted trough is expected to develop as an upper level low drops southeast through the region, later on phasing with the coastal low once both systems are well offshore. While tonight’s forecast had a larger bust potential, there is high confidence on widespread snow on Thursday night with additional accumulations expected. The main uncertainty at this time is exactly how much snow accumulates. The NAM is still being disregarded as an extreme wet outlier, and overall thinking at this time is for 2 to 4 inches of snow along/south of the I-80 corridor into NYC and Long Island, locally lower, with 3 to 5 inches of snow generally north of I-80 into southern Connecticut. Totals especially towards parts of the Hudson Valley and the Catskills may be locally above 5 inches. Some changes are still possible to this forecast, with more information to be posted with the next update on Thursday morning. One possible outcome which would result in less snow is if snow from the inverted trough focuses too far north for widespread moderate snow accumulations in the area, and this possibility will be monitored.

4:10 PM: As of 3 PM, there is a broad area of low pressure located south of NYC and east of southeastern VA. The minimum pressure is approximately 993mb, and the low is generally drifting east.

Since the update earlier today, surface temperatures across the Mid Atlantic have warmed up enough that only portions of central Virginia remain with plain snow, while other areas are generally seeing rain or mixing with some snow/sleet. Strong winds are occurring across coastal areas, with widespread gusts above 40 mph across New Jersey and Long Island. Gusts up to or locally over 60 mph have been reported along the immediate coastal areas in New Jersey.

Update – this map is no longer valid. Refer to the update above for more information.

Precipitation from the coastal low is struggling to expand north, is already verifying south of what the NAM had – the 12z NAM, which showed approximately 0.50″ of liquid equivalent precipitation from the coastal low tonight in NYC, already had widespread light to moderate precipitation covering all of NYC and northern NJ by 4 PM with 0.10″ of precipitation accumulated by NYC, which as can be seen on the radar posted above, is missing. The NAM is still adjusting south with the precipitation from the coastal low tonight, as its earlier runs significantly exaggerated the precipitation totals in the area. At this time, a general 1-4 inches of snow are expected tonight in the immediate NYC area into Long Island and southern CT, with the high end of this range towards Long Island and southeastern CT. Scattered rain/snow showers are then expected on Thursday.

Thursday Night Update: The main snow event is still expected to take place on Thursday night into Friday morning with an inverted trough. As the coastal low continues to drift more to the east, widespread light to moderate snow is expected to develop over New York state and northern New England towards Thursday evening. Throughout the overnight hours, this band of moderate snow will continue to expand west into east central NY state, then drop south through the area, with moderate snow expected on Friday morning for most of the area especially from the immediate NYC area and further north, including western CT. As the mid levels begin to warm along with surface temperatures, a changeover to sleet/rain is possible from NE to SW on Friday morning precipitation weakens and shifts south of the area, marking the end of the storm by early Friday afternoon with clearing skies and lighter winds just in time for the weekend.

There is some uncertainty regarding exact accumulations, with most models suggesting a light to moderate event while the NAM is the most bullish. Given the NAM’s wet bias and performance with today’s storm, I am disregarding the NAM as a wet outlier, although snow is expected to fall across the area considering precipitation associated with the inverted trough is expected to be widespread. At this time, I am generally expecting a 2-5 inch event, with the heaviest totals locally over 5 inches likely to end up north of NYC into the Hudson Valley region. These amounts are still subject to minor changes, however. More information on this will be posted with later updates.


12:00 PM: As of 11 AM, the low pressure was located south of New Jersey and east of the southern tip of the Delmarva Peninsula. The minimum pressure is approximately 992mb, and the low is intensifying while tracking to the ENE.

Throughout late last night and this morning, moderate to heavy precipitation spread into the Mid Atlantic region. Initially, this fell as widespread snow, although temperatures warmed up this morning with many locations outside of western Virginia and Maryland changing over to a mix or rain. Later into the early-mid afternoon hours, precipitation is expected to start spreading into the area as well. This will generally be light rain or a rain/snow mix, which will gradually change over to snow towards the evening hours as surface temperatures cool down.

Coastal Low Update: Last night’s forecast discussion noted there was still uncertainty regarding how far north the heavy precipitation from the coastal low extends, with minor differences resulting in more significant changes to the forecast. The more bullish models as of last night, the NAM and SREF, have gradually backed to the south, but remain wetter than most other models with near to slightly over 0.50″ liquid equivalent precipitation near NYC. Taking the mild surface temperatures and generally moderate snow rates into consideration, such precipitation amounts will not translate to 5 inches of snow as they typically would under normal 10:1 liquid to snow ratios, but generally lighter amounts.

Northwestern parts of the area are expected to be in the edge of the coastal low, and are generally expected to see 2 inches or less. Towards the immediate NYC area and western Long Island/SW CT, a period of moderate snow is likely tonight followed by the snow becoming lighter after about 2 AM. Amounts are generally likely to end up between 1 and 3 inches, locally up to 4 inches. The highest amounts are expected towards central-eastern Long Island and SE CT, where 2 to 5 inches are expected.

Thursday Night Update: After scattered rain/snow showers on Thursday, the second and more significant part of the storm is expected for Thursday night, as an inverted trough takes shape over New York state, later dropping south into the area, producing additional moderate precipitation. Initially, this is expected to be snow across most of the area, but as mid level warming takes place, starting in New England and expanding southwest, snow will gradually mix with and change over to sleet/rain from northeast to southwest towards Friday morning. The storm is finally expected to end on Friday afternoon, with clearing skies towards the evening hours.

How much snow falls and accumulates partially depends on the mid level warming, as the NAM is currently the most bullish with this while the GFS and RGEM keep temperatures cold enough for plain snow. At this time, I sided with a mostly snow approach but with mixed precipitation late overnight into Friday morning, with additional snowfall of 2 to 4 inches likely across most of the area, especially from NYC and further north/west and into western CT. This part of the forecast is still subject to minor revisions.

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