Slightly revised 4pm
Temperatures today have cooled down relative to yesterday’s warmth, but are expected to rebound back into the 40s on Monday and 50s on Tuesday with partly to mostly cloudy skies. The next storm system will affect the region on Wednesday into Wednesday night, with rain favored for the area, possibly changing to snow overnight but with the highest probability of snow to the north of NYC. A brief but strong cool down is expected for Thursday, followed by another warm up in time for next weekend.
Today – Tuesday: Warming Up Again
Posted above from left to right are the latest available surface analysis and radar composite from WPC, and the initialized GFS 500 millibar heights and vorticity from NCEP MAG; both are valid at 12z (7am). Yesterday’s cold front has shifted well offshore, with another cold air mass currently situated over the region. As of 12pm, temperatures are still in the 35-40 degree range across most of the area, but will only slowly rise through the afternoon, peaking in the upper 30s to low 40s for most locations.
Focusing on the western US, a strong jet streak is entering western North America with a strong upper level westerly flow near the US/Canada border, as depicted in the 500mb map with a strong geopotential height gradient supporting a strong westerly flow. This will allow a warmer air mass to quickly track east-ESE through the central US, passsing to the north of the closed upper level low near northwestern Mexico, which will continue to become mostly cut off from the main flow. Along with a weak area of low pressure quickly tracking east through southern Canada setting up for a surface W-SW flow on Monday and Tuesday, another quick warm up is expected. Scattered snow showers are possible early on Monday morning, possibly amounting to a coating in northern parts of the area, followed by some clearing of cloud cover with high temperatures rising into the mid-upper 40s. Even warmer temperatures are expected on Tuesday with partly sunny skies and a westerly wind at 6-12 mph supporting highs reaching the low to mid 50s, perhaps peaking in the upper 50s near NYC and NE NJ.
Wednesday – Thursday: Rain Expected, Snow Possible
The next storm system is expected to affect the region on Wednesday into Wednesday night, and this time has a higher probability of producing moderate to heavy precipitation unlike the March 2-3 storm. This storm is the result of a complex interaction of three systems; the closed upper level low over northern Mexico which will progress eastward with some interaction with the system but a full phase unlikely, a shortwave trough entering the NW US which will reach the central US, and the northern stream originating in Canada. The northern stream will dig south into the central US, with phasing of the two shortwaves likely as the surface low pressure quickly deepens, producing widespread precipitation across the region, along with snow to the north of the low pressure as another cold air mass enters the region.
12z GFS at hour 84, on 0z Thursday (7pm Weds), depicting a strong low pressure centered over Long Island with snow well to the north, later on briefly reaching interior SE NY and central-northern CT. This run is among the northernmost models for this storm (image credit: PSU e-Wall).
Since yesterday’s update, the model guidance has come into better agreement, with a well defined trend towards a stronger, sharper and more amplified northern stream disturbance digging further south, aiding in an earlier phase reflecting to a stronger, more amplified and further north surface low pressure. This trend is the opposite of what was observed with the March 2-3 storm, when during the 3-day range the models trended towards a stronger and further south polar vortex which eventually led to the significant south trend. A significantly suppressed scenario appears unlikely at this time; rather, the main bust risk at this time would be a stronger and more amplified system than currently forecast, which would support plain rain for the area and as far north as the central-northern Hudson Valley, along with warm temperatures surging into the 50s and even 60s across the area ahead of the cold front. While this scenario does not have much support, it will continue to be monitored, and the latest forecasts sides with a further north and warmer outcome than the current model consensus.
Forecast for NYC Area: Mild temperatures are expected ahead of the system, with the cold air mass coming in as the storm is ongoing rather than ahead of it, supporting rain as the initial precipitation type across the area and likely extending as far north as central NY state with the onset of precipitation around the late morning-early afternoon hours on Wednesday. Temperatures are generally likely to peak in the 40s, but the main uncertainty is the track of the low pressure which will determine how far north the warm sector extends, where temperatures are expected to surge into the 50s with a strong southerly wind; at this time, the warm sector is forecast to reach NYC and Long Island, although a slight north shift from the latest forecast would include most of the area in the warm sector for a period of time. As the low passes northeast of the area with a strong northwesterly wind at 15-25 mph, the cold air mass to the north will begin to filter into the area with temperatures dropping into the 30s in the evening and the 20s later overnight. This will support a southern shift in the rain/snow line, but with the southward extent of snow still somewhat uncertain; the latest model trends towards a stronger and further north system have decreased the probability of snow in the area, with the latest GFS and CMC runs depicting NYC with plain rain. Considering the strong cold air advection expected overnight with a very tight pressure gradient, however, enough cold air may filter in to support at least a brief period of light snow at the end. Given the aforementioned trends, the latest 8-day forecast keeps precipitation type as mainly rain except for the very end of the event for most of the area, with a more prolonged changeover to snow possible towards interior SE NY and central CT after at least 11pm but with significant accumulations unlikely.
While confidence is somewhat higher than the March 2-3 storm, some areas of uncertainty remain as previously noted, which will influence the strength and track of the low pressure and ultimately the high temperatures/wind direction on Wednesday and how much snow, if any, falls overnight. In the event that the current forecast does not verify, higher odds are placed towards a warmer and less snowy outcome than currently forecast, with plain rain across the area and highs in the 50s on Wednesday. A lower but still plausible possibility exists for a colder, weaker and further south outcome, which would favor rain to snow with at least light to moderate snow accumulations away from coastal areas. More information will be posted over the next few days.