Mar 04

Mar 4-5, 2015 Storm Updates

Occasional updates will be posted below on the snow and rain event affecting the region over the next day. 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


 

8:10 PM: Snow Tapers Off; Warmer Pattern On The Way

3.6.15_0015As the baroclinic zone continued to progress south throughout the day, snow gradually decreased in intensity by the mid to late afternoon hours, and as of 7 PM, only scattered snow showers remain with the steady snow having shifted south into Virginia. Preliminary snow accumulation reports suggest that 2 to 5 inches accumulated in southeast NY, 3 to 6 inches in northern NJ north of the I-80 corridor into coastal CT, and 4 to 8 inches in NYC and Long Island into the rest of New Jersey.

As of 4 PM, Central Park recorded 7.0 inches of snow, bringing the March snowfall to date to 13.6 inches, marking Central Park’s 12th snowiest March on record dating back to 1869, and the snowiest March since 1967. Additionally, Central Park brings its seasonal snow total to 42.0 inches, which is remarkable considering only 1.0 inch accumulated in December. Prior to this winter, in Central Park’s 145 recorded winter seasons, 43 winters had 1 inch or less in December; out of these years, only 5 winters (11.6%) recorded near or over 40″ of snow during the entire season, with the last such occurrence during 1977-78, and the average winter snowfall for Decembers with 1 or less inch of snow is only 19.8″, much lower than the 28.6″ average of all winter seasons in Central Park.

Warmth Returns: Unlike previous events, however, the latest 8-Day Forecast shows no additional snow over the next week. In fact, after another cold Friday, temperatures begin to steadily trend upwards, returning into the 40s and possibly even the low 50s in spots by next week, as the upper level flow in the northern US trends increasingly zonal. This warm trend can be partly attributed to an increase in tropical forcing over the equatorial Pacific Ocean, as convection associated with the MJO, which has been recently weak and centered near the phases 7-8 regions which are indicative of a trough and colder temperatures in the eastern US, is projected to re-emerge near Indonesia, indicating a phase 4 of the MJO which is often correlated with near to above average temperatures in the eastern US. There are, however, signs that the warmth will struggle to fully build into the region, as model guidance often exaggerates the eastward expansion of ridges in the spring, with a more pronounced northwesterly flow than modeled keeping parts of the region near the edge of the colder air masses to the east, and the longer range models continue to show occasional surges of cold temperatures beyond next week. More information on the longer range outlook will be posted with a more detailed analysis on Friday or Saturday, while daily updates to the 8-day outlook will continue in the meantime.

 

12:00 PM: Still Snowing

3.5.15_1645The baroclinic zone has continued to progress slower than modeled even as of last night, and a widespread axis of moderate to locally heavy snow remains nearly stalled from southern Pennsylvania into New Jersey and coastal New England. The persistence of strong upward vertical motion associated with the aforementioned mid-level frontogenesis continues to produce moderate to heavy snow, with the heaviest snow in the area generally over northeast NJ, NYC and Long Island, where radar reflectivity continues to depict returns over 20-25 dBZ. The high-resolution model data is accordingly trending slower with the ending time of the snow, and storm total accumulations may end up within the 4-8 inch range across NYC and Long Island and slightly lower over northeast NJ.

As previous updates have noted, the southward push in the baroclinic zone is associated with a surge of cold and dry air from the north, and locations near the northern end of the precipitation shield, particularly over northwest NJ and southeast NY, are only recording light snow with little accumulations despite the regional radar mosaic above depicting heavy snow bands overhead. As these locations are relatively far from the nearest radar sites in Upton, NY and central NJ, the radar beams only reach the higher levels of the atmosphere, where steadier snow may be falling, but is likely evaporating closer to the surface due to dry air. Based on the above and the latest available snow reports from the NWS, these locations appear to be on track with last night’s forecast at this time.

 

8:30 AM: Widespread Snow Continues Today

3.5.15_1315Since the previous forecast update, the steady moderate precipitation associated with the baroclinic zone has spread throughout the area, initially falling as rain with temperatures lingering in the mid 30s to low 40s. A gradual changeover to snow from NW to SE occurred towards 12-3am inland of NYC and 3-5am from NYC and farther south and east, with steady periods of light to moderate snow since then. Latest preliminary reports suggest at least 1 to 3 inches of snow through 7-8 AM this morning, with temperatures currently in the low 30s for most locations.

The latest regional radar imagery posted to the left depicts widespread moderate snow throughout the area, with a narrow band of heavy snow extending through central NJ into southern parts of NYC, aligned closely to the axis of maximum 700 hPa frontogenesis. As the baroclinic zone continues to gradually shift southeast, the precipitation shield will slowly follow along, with the heavy snow shifting south of the area while steady light to moderate snow continues through at least 3-6 PM before ending from north to south. Last night’s snow accumulation forecast remains unchanged at this time.

 

9:50 PM: Rain Continues This Evening, Snow Expected After Midnight

3.5.15_0430Observations: As yesterday’s update discussed, a strong baroclinic zone is setting up near the region, highlighted by a significant contrast in temperatures ranging from the 20s in central Kentucky to the 60s in western North Carolina, accompanied by a powerful upper level jet streak and approaching shortwave trough providing widespread synoptic ascent and producing widespread moderate to heavy precipitation along and north of the baroclinic zone. As the trough axis slowly approaches from the west, its associated cold air mass continues to be gradually advected eastward, with the east push of cold and dry air gradually shifting the baroclinic zone and accordingly its precipitation field to the southeast.

Even though there is no well-defined surface low pressure center, the setup is nonetheless favorable for heavy precipitation, with significant upper-tropospheric divergence due to the powerful jet streak surpassing an impressive 180 to 200 knots at the 250 hPa pressure level, as well as cyclonic vorticity advection ahead of the approaching shortwave trough, factors which both favor upward vertical motion and precipitation, with moisture from the southern US transported into the region by the strong southwesterly flow aloft along the frontal boundary. The latest regional radar imagery above depicts an elongated band of heavy snow just north of the rain/snow boundary, with steady light to moderate snow to the north and a sharp cutoff in the northern fringe of the system in Indiana and Ohio.

Following yesterday’s wintry mix event, largely forced by a strong southwesterly flow which transported a much warmer air mass into the region, temperatures peaked in the low to mid 40s throughout most of the area with localized spots of upper 40s; for parts of the area, this was the warmest day since early January, following the near historic cold pattern in February notable for its low temperatures but especially its prolonged duration. With persistent cloud cover and winds above 5 mph maintaining a mixed layer near the surface with little cold air advection occurring, however, temperatures have been very slow to cool down this evening, and remain in the upper 30s to low 40s range for most locations as of 9 PM. The rate of cooling overnight will be an important factor to determining snow accumulations later tonight.

 

Forecast Analysis: The model guidance has struggled with the handling of this system over the last few days, with minor changes in the timing and tilt of the baroclinic zone and the amplitude of the upper-level trough influencing the timing of the snow as well as precipitation types. The GFS and ECMWF ensemble members depicted a notable variety of solutions, indicating a lack of consensus, ranging from over 6 inches of snow to little accumulations in the tri-state area. A noticeable trend over the last 12-24 hours has been for a slower eastward progression of the baroclinic zone and a more amplified upper level jet than modeled, resulting in a trend towards heavier precipitation across the area tonight which gradually winds down on Thursday as the baroclinic zone shifts south with time. The latest set of model runs generally supports totals ranging from around 0.25 to 0.60 inch of liquid-equivalent precipitation north of NYC and 0.60 to 0.80 inch elsewhere. This trend towards slower timing, however, also implies a slower cooling rate of surface temperatures, which will remain above freezing for a longer period of time than modeled earlier and result in continued periods of moderate rain prior to the changeover to snow.

As previously noted, surface temperatures have been slower to cool down than modeled, and the moderate to heavy precipitation currently overhead is falling as rain. Latest observations would support the timing of the changeover from rain to snow around 1-3 AM from NYC and farther north/west into coastal Connecticut, and 3-5 AM in Long Island and central New Jersey, siding towards the slower and warmer end of the model guidance. By then, precipitation totals falling as rain are likely to amount to about 0.10 to 0.20 inch north of NYC and 0.20 to 0.40 inch elsewhere. The aforementioned dynamics are likely to support a period of moderate to locally heavy snow through the early morning hours on Thursday, before gradually winding down and progressing south throughout the day, but with the earlier rain resulting in lower snow accumulation than precipitation totals would accumulate.

Based on the latest available information, forecast snow accumulations are for 2 to 4 inches of snow over Sussex county in NJ into southeast NY and southern Connecticut; 3 to 5 inches of snow over northern NJ north of the I-80 corridor; 3 to 6 inches over NYC and Long Island; and 4 to 7 inches south of the I-80 corridor in New Jersey. This remains a very complex situation depending on the exact progression of the baroclinic zone and cooling rate, which so far has been slightly slower than modeled, and additional updates will continue to be posted tonight.

Mar 03

Mar 3, 2015: Snow, Ice Return Tonight & Thursday

Forecast Highlights:

rgemMarch continues with the cold and snowy pattern from the end of February, with several inches of snow having accumulated across the area on Sunday. Additional light to moderate snow and ice is expected this afternoon, followed by a changeover to freezing rain and rain later tonight and another wave of snow on Wednesday night. More prolonged dry conditions will return for the remainder of the week, however, with no additional snow expected.

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Mar 01

Mar 1, 2015: Spring Begins With More Snow

Notice

The previously noted technical issues have been resolved. More frequent updates will resume beginning today.

Forecast Highlights:

wrf-nmm_ref_frzn_neus_24Meteorological spring began early today, on March 1st, yet the snowy and near historic cold pattern which has dominated the past month and a half continues, albeit to a less anomalous extent. Two low pressure systems will affect the region over the next week with snow today and ice/rain on Tuesday, primarily inland of NYC where widespread freezing rain is possible, followed by a return of well below normal temperatures for the late week period.

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Feb 25

Feb 25, 2015 Morning Update

Notice

Note: Updates to the 8-Day Forecast page will resume on Saturday or Sunday.

This morning’s update will briefly review the latest forecast for several upcoming precipitation events. A more detailed analysis will be posted late tonight.

 


 

Storm #1: Wednesday Night – Thursday
Snow Mostly Stays South of NYC

6z GFS hour 30, valid at 1200 UTC Thursday, 2/26 (7am EST), depicting a sub-1000 hPa low near eastern North Carolina with widespread snow extending into Virginia. This is substantially north of where the GFS depicted the low 2 days ago as of the previous forecast update. Image from PSU e-Wall.

f30An upper level low currently over the southwest US will merge back into the southern branch of the jet stream and progress ENE towards the southeast US, where sufficient cold air is expected for an accumulating snow event. Prior runs have mostly kept precipitation south of Virginia, but as the previous forecast update noted, model guidance at that time had shown signs towards more amplification of the shortwave trough and a farther north track, which had some support from model ensembles and several recent analog cases. This trend has continued over the last two days, and as the latest 6z GFS run depicts to the left the low pressure is now forecast to track near eastern North Carolina with widespread snow extending into Virginia and the Delmarva Peninsula.

Despite the north trend, the shortwave trough remains embedded within the southern branch of the jet stream, and lacks much connection to the northern stream that would result in a more significant interaction and a much more amplified system tracking up the coast. While additional slight northward adjustments are still possible, this may not be sufficient for the snow to expand north into the tri-state area, although the possibility of snow showers mainly south of NYC cannot be ruled out on Thursday morning. Otherwise, a strong high pressure will build into the region from Friday into Sunday with temperatures remaining in the 20s for highs and in the 0-15 degree range for lows, potentially below zero inland should significant radiational cooling occur.

 


 

Storm #2: Sunday Night – Monday
Southwesterly Flow Develops, Mixed Precipitation Possible

A change in the pattern towards a more active subtropical jet stream is expected to occur towards next week as an upper level low becomes stationed near the western US with a broad southwesterly flow extending throughout the US. This southwesterly flow will advect warm and moist air into the region, which accompanied by synoptic ascent ahead of an approaching shortwave trough will likely result in a widespread precipitation event on Sunday night into Monday. The model guidance continues to struggle with the handling of the shortwave energies involved, and additional changes are still expected over the next 1-3 days before signs of a consensus emerge, although the southwesterly flow and stronger warm air advection aloft signal the potential for ice and/or rain in addition to the snow, with the possibility of colder surface temperatures than modeled as was the case with last weekend’s storm given the antecedent frigid air mass. Due to the progressive nature of the system within the strong upper level jet stream, however, no significant snow accumulations are anticipated.

 


 

Storm #3: Tuesday – Wednesday
Stronger System Possible

An active subtropical jet stream continues through the remainder of next week, and model guidance has been persistently identifying the midweek time frame for a potential widespread precipitation event as the upper level low in the southwest US gradually progresses east with an increasingly meridional flow over the eastern half of the US. As this is still a week away, there is too much spread in the model guidance and ensembles for a high confidence outlook, although regardless of the track of the low pressure, the antecedent cold air mass indicates a potential for snow or ice to occur again in the region. More details will be posted with tonight’s update.

Feb 23

Feb 23, 2015: Cold Pattern Continues This Week

Forecast Highlights:

temp22Following yesterday’s mild temperatures, yet another frigid air mass is on track to progress into the region today with daytime temperatures struggling out of the mid to upper 10s. Cold air advection will continue into tonight with lows in the single digits and below zero for most locations once again. A brief warm up is expected on Wednesday possibly accompanied by scattered snow showers, but with otherwise little relief from the cold pattern, with February on track to end up within the top 10 coldest months in NYC in recorded history.

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Feb 22

Feb 21, 2015 Night Update

12 AM Update: Snow Changes to Rain Near Coast, Ice Inland

nerad25Over the last day, a disorganized low pressure system affected the region with areas of widespread precipitation, primarily focused over the Mid Atlantic, but with areas of downsloping and subsidence resulting in a widespread dry slot over Pennsylvania, northwest New Jersey and southern NY state. Despite the low pressure track generally well to the west of the region, the sped up timing of the system relative to modeled depictions several days ago and the lingering anomalous cold air mass from the last several days resulted in sufficient antecedent cold temperatures to produce widespread snow, even down into Maryland and Virginia.

The strongest low-level warm air advection and frontogenesis were focused south of model depictions, from Maryland into central New Jersey, where over 4 to 8 inches of snow were recorded, with the I-95 corridor over New Jersey near the borderline between heavier snow to the east and lighter snow to the west, where less than 2 to 4 inches accumulated. Since about 9-10pm, warm air advection in the lower atmosphere resulted in a layer of above freezing temperatures in NYC, Long Island and central New Jersey, where a changeover to freezing rain and later plain rain occurred. Farther north, however, temperatures remain in the mid to upper 20s, with snow and sleet persisting north of the I-80 corridor in New Jersey into southeast NY and coastal Connecticut. As the latest regional radar mosaic above depicts, from the Pennsylvania State University e-Wall, most of the precipitation has progressed east of NYC, although occasional waves of light to moderate precipitation are likely to continue through early Sunday morning.

A brief warm up is expected on Sunday with increasing mixing of the lower levels following the departure of the storm, with temperatures rising into the mid 30s to near 40 degrees across the area. The cold pattern which has dominated late January and almost the entirety of February will continue, however, as yet another frigid air mass is advected into the region on Monday with high temperatures in the 10s, and overnight lows approaching the low single digits again for most locations.

Feb 20

Feb 20, 2015: Record Cold This Morning, Snow/Rain To Follow

Notice

Note: Forecast updates will remain limited in the near term due to technical difficulties. 8-day forecast will be updated less frequently until these issues are resolved.

Forecast Highlights:

rgem2Record cold temperatures were observed this morning as Central Park reached a low temperature of 2 degrees, breaking the previous daily record of 7 degrees, as well as marking the coldest temperature since January 2004 and the coldest February temperature since 1979. A widespread moderate snow event s expected on Saturday afternoon and evening with several inches of snow likely, followed by a changeover to ran overnight and another round of cold temperatures early next week.

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Feb 18

Feb 18, 2015: Cold Ending To Week; Brief Weekend Warmup

Forecast Highlights:

wrf-nmm_ref_frzn_neus_24Clear skies and calm winds provided the region with yet another frigid morning, with interior locations falling below zero again. Substantial warming is expected today to near 25-30 degrees accompanied by snow showers, but with temperatures cooling down again on Thursday and Friday. A brief weekend warm up is expected, but also potentially accompanied by rain and ice which may lead to some flooding and icing concerns in the worst case scenario.

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Feb 16

Feb 16, 2015 Evening: Light Snow Tonight

9:50 PM Forecast Update

nerad253A wave of low pressure currently over eastern Alabama is producing a wide swath of precipitation, falling as snow and ice across North Carolina and Virginia. This system is mostly expected to remain to the south of the area, however, as the strongest upper level forcing remains too far south to produce sustained moderate to heavy precipitation over the tri-state area. The latest high resolution model suggest up to 1 to 2 inches across the tri-state area, possibly less than 1/2 inch in northern areas, although latest radar imagery depicts a band of moderate snow over southern Pennsylvania which may approach southern parts of the area, in which event accumulations over 2 inches would be expected. Any snow is expected to taper off by 10-11am on Tuesday with temperatures climbing into the low to mid 20s.

Feb 15

Feb 15, 2015: Relentless Cold Pattern Continues

Forecast Highlights:

temp13An active winter pattern rages on across the northeast US, with the addition of yet another snowstorm over New England. While the highest snow accumulations have largely stayed out of the NYC tri-state area, the cold air masses have not, with temperatures tonight expected to be some of the coldest observed over the last several years as Central Park recorded its coldest February temperature in 28 years. More snow and cold are on the way for this week, with only a brief sign of relaxation of the cold by next weekend.

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