Occasional updates will be posted below on the heavy rain, wind and snow event affecting the area on March 29-31. Radar images are from the Pennsylvania State University e-Wall.
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Current storm rain totals in NYC: (Updated 7am)
Central Park – 2.78″ | LaGuardia – 2.23″ | JFK Airport – 3.10″
Monday, March 31
10:20 AM: Heavy Snow Unexpectedly Persists Over LI, CT
The deformation snow band has persisted longer than expected over CT into LI and has failed to weaken as forecast, which along with a pocket of cold air aloft supporting snow with the bursts of heavier precipitation is leading to a narrow and nearly stationary band of heavy snow extending from New Haven county in south CT into western Suffolk county in Long Island. Locations under this narrow band are likely to continue observing heavy snow for the next 1-2 hours before gradually ending, with localized snow totals up to 4-6 inches expected. Outside of this narrow band of heavy snow, lighter snow rates are expected, mixing with sleet/rain, with up to/less than 1 inch of snow in other parts of central Long Island and southern CT.
7:55 AM: Rain, Snow, Sleet To Gradually End
Over the last few hours, the deformation band over Pennsylvania slowly collapsed as another round of heavy precipitation entered southern New England, later pivoting through western New England and extending southward into the area and eastern NJ. The pocket of cold air aloft, while having moderated, has continued to extend further south and east with continued cold air advection last night, and with the aid of heavier precipitation rates has produced snow and sleet under the bursts of heavier precipitation near the area. This can be seen in the regional precipitation type radar to the left (take note that there is an error with exaggerated reflectivity values over New Jersey), with a narrow axis of snow under the higher reflectivity values from central MA into CT and the NYC area. As the low pressure continues to track eastward, precipitation will generally end over the next 2-3 hours with clearing skies expected late today. Gradual warming is expected through Wednesday, when highs will peak in the upper 50s to low 60s.
The next forecast update will be posted late today.
Sunday, March 30
10:10 PM: Light Rain Continues Tonight
The low pressure continues to slowly drift east, while slow moving bands of precipitation in association with the upper level low continue to pivot through the area. A well defined deformation band has set up from central NY into east-central PA and eastern Maryland since the late morning and remains nearly stationary, continuing to produce heavy snow under a pocket of colder air in the low-mid levels. As the storm continues to drift east, the bands will weaken as they shift east through the area, with enough cold air possibly filtering in to allow for a changeover to light wet snow in the early morning with little to no accumulations forecast. Clearing skies are expected late on Monday with highs reaching the upper 40s to low 50s from NYC and further north/west and the mid-upper 40s further east.
This is the final storm update for tonight. The next forecast discussion will be posted on Monday.
6:30 PM: Second Round Beginning
With the cyclone having cut off from the main flow, the progression of the upper level low and the precipitation shield northwest of the low has nearly stalled, with bands of heavy precipitation training over central NY into east-central PA and Maryland over the last several hours. With a narrow pocket of low-mid level cold, heavy snow and sleet is currently falling under this band, with localized reports of as much as 4-6 inches of snow and sleet.
As the storm continues to slowly drift east, the primary banding over Pennsylvania will gradually weaken and dissipate as another area of nearly stationary banding sets up around NJ into the NYC area, lower Hudson Valley and western New England, likely developing after 8-11pm and continuing through early Monday morning before tapering off. The pocket of cold air will accordingly shift east, but will gradually moderate, which along with lighter precipitation rates relative to Pennsylvania will support occasional periods of light to moderate rain tonight, especially from NYC and further north/west, which may mix with light sleet and wet snow towards the late overnight hours and Monday morning; the highest probability of mixing is towards NW NJ/SE NY and southern CT, but may extend closer to the north/west suburbs of NYC with little to no accumulations likely.
11:00 AM: Second Round Slowly Approaching
Since the evening update, rain intensified and continued to affect the area through at least 1-3am, when the heavy rainfall mostly shifted northeast of the area except for another round of heavy rain which affected central-eastern Long Island and SE CT between 4-7am. Due to this additional area of heavy rainfall late last night, the highest storm total rain amounts so far have been found in this area, with totals as high as 4-5 inches of rain; Westhampton Beach, NY (Suffolk) has had a total of 4.48″ so far. Further west, storm totals so far decrease from east to west to about 3″ near western LI into south central CT; 2.5 inches near NYC; 2 inches near north central NJ; and 1.5 inch towards western New Jersey.
As the latest regional radar above shows, the first round of rain associated with the strong warm air advection is now near northern New England, with heavy snow affecting central and northern Maine. Meanwhile, as the low pressure nearly stalls southeast of New Jersey later today into tonight, the upper level low will slowly continue to track northeast as well with the second round of precipitation currently near the central Mid Atlantic region to continue tracking NE closer to the area, with steady rain expected to redevelop after at least 3-6pm. The heaviest rain is likely to set up over eastern Pennsylvania and possibly western New Jersey, where another 3/4 to 1.25 inch of rain with locally higher amounts is expected, decreasing further east with 1/2 to 1 inch north and west of NYC and less than 1/2 inch from NYC and further east. Rain will gradually decrease in intensity later tonight, ending mostly by Monday morning; cold air advection is expected today and tonight with stronger northerly winds up to 10-20 mph, gusting up to 30-35 mph, which may lead to a changeover to wet snow by early Monday morning mainly towards the Hudson Valley and interior CT but possibly closer to the north/west suburbs of NYC as well with little to no accumulations expected.
Saturday, March 29
9:05 PM: Heavy Rain Tonight
Drier mid level air is present near Virginia and will continue to advance NE, which along with the strongest forcing for heavy precipitation gradually shifting northeast will support a few more hours of heavy rain, until at least 1-2am, before the back end of the heavy rain moves through the area from SW to NE. Afterwards, scattered showers are expected to persist through Sunday morning. The rest of the forecast for Sunday into Sunday night remains unchanged at this time.
Forecast Update – Warm Up Scaled Back: With the low pressure likely to take longer to depart the region than previously forecast, which also partially results in a more amplified trailing shortwave on Wednesday pushing the frontal boundary further south than earlier forecast, the forecast warmth surge for the early-mid week has been scaled back compared with earlier predictions. Yesterday’s outlook for Monday, with morning rain and otherwise mostly cloudy skies and highs in the mid 40s-low 50s, sided with the colder end of yesterday’s model guidance and remains unchanged based on the latest data. Tuesday is still expected to warm up into the 50s at least from NYC and further west, perhaps reaching western Long Island and SW CT, but with Wednesday appearing less likely to at least significantly surpass 60 degrees with a further south forecast placement of the frontal boundary, with latest thinking for highs in the upper 50s-low 60s. Rain is still expected for the late week time frame but with uncertainty regarding the exact timing and rain totals.
6:15 PM: Rain Continues To Intensify
Over the last few hours, the low pressure continued to slowly intensify with the aid of positive vorticity advection ahead of an amplifying shortwave and upper level divergence near the right entrance quadrant of a strong jet streak, which additionally is leading to a stronger pressure gradient and thus stronger winds surrounding the cyclone. The strengthening southerly flow to the east of the low pressure is leading to increasing advection of warm and moist air along with stronger frontogenetic forcing as the temperature gradient strengthens north of the warm front, factors which all support the continued development of widespread moderate to heavy rain over the next few hours, especially north of central NJ.
The continued development of rain can be seen when comparing the latest regional radar imagery with that of the early afternoon, as moderate rain over eastern parts of the region has become more widespread and continues to slowly spread further north. Heavier rain will develop especially after 8pm, continuing through about 1-3am when drier air in the mid levels entering the system along with the strongest forcing for precipitation shifting northeast of the area, will lead to a period of drier conditions through Sunday morning with scattered showers. The main uncertainty is the placement of the heavier rain on Sunday evening and early overnight hours, with increasing indications that the higher rain totals may be west of the area, with the rain bands weakening as they shift east overnight. The forecast at this time remains for 2-3 inches of rain.
1:55 PM: Rain Developing
As of 1pm, the low pressure was positioned near NE Tennessee. Minimum pressure is near 1007 hPa, and the low is steadily tracking NE. The low pressure will slow down as it tracks through Virginia tonight, stalling near southern New Jersey on Sunday evening before slowly progressing offshore.
Rain associated with warm air advection has began to affect the area earlier than forecast, as a strengthening southerly low level jet advects warm and moist air into the eastern parts of the region. The current round will produce light to moderate periods of rain through at least 4-6pm, when a brief decrease in rainfall rates is anticipated. As discussed last night, heavier rain will develop this evening, mainly between 8pm and 1-3am, as the increasing southerly winds east of the cyclone continue to advect warm and moist air into the area, which will be forced to rise aloft as surface northeasterly winds keep colder and denser air near the surface; this strong upward vertical motion, along with increasing frontogenetic forcing, will thus result in a widespread area of moderate to heavy rain early tonight, with at least 1 to 2 inches of rain expected, locally higher especially north and NE of NYC.
Drier air will enter in the mid levels behind tonight’s rain, leading to scattered showers for the rest of the overnight hours through Sunday morning with temperatures in the mid 40s to low 50s. As the cyclone detaches from the main flow, the surface low pressure will slow down and briefly stall just off the southern NJ coast, with a strong pressure gradient leading to an increasing northerly wind up to 10-20 mph, gusting up to 30-35 mph. As the low pressure stalls, additional rain bands will continue to rotate through the area and into SE New York, New Jersey, and eastern Pennsylvania, mainly from Sunday afternoon through the overnight hours as the rain gradually decreases in intensity and coverage area, mostly ending by late Monday morning. Another 1/2 to 1 inch of rain is expected in this time frame, with the higher totals north and west of NYC. The northerly winds will lead to cold air advection overnight, but the temperature profile is not expected to cool down sufficiently to allow for snow except for perhaps interior northern areas by early Monday morning.
Latest thinking at this time remains for 2 to 3 inches of rain across the area, locally higher up to 4″. Additional updates will continue to be posted through today and tomorrow as the slow moving storm continues to affect the region.