Following last night’s snow event, the cold air mass that has been over the area for the last week will continue to moderate, with high temperatures returning into the 30s by Friday and the low 40s for the weekend with rain staying mostly north of the area. Attention turns to next week and beyond, however, as a stormier pattern is likely to develop for the region, starting with a snow/rain storm next Wednesday (Image credit: PSU e-Wall).
Tuesday, January 28 Observations:
Observations are currently in progress and will be posted shortly.
Tonight – Friday: Warming Up
WPC surface analysis from 6z Wednesday (1am), depicting the low pressure off the coast of North Carolina, at the time snow began to spread into the area (image credit: WPC).
The trough that has covered the region with a widespread cold air mass over the last few days is currently lifting out of the region, but not before having produced an unusual snow and ice snowstorm in the southern US, with high ratio snowfall extending further inland than originally expected last night, producing as much as 5-7 inches of snow from Delaware into southern NJ, 2-4″ of snow in eastern-central Long Island, and 1/2 to 1 inch in NYC. With the departure of the low pressure, a high pressure will build into the region tonight into Thursday, leading to mostly sunny skies and high temperatures warming up into the 25-30 degree range for most locations. As the high pressure slides to the east with a light southwesterly flow returning on Friday, temperatures will climb above freezing for the first time since Monday, peaking in the low to mid 30s with mostly cloudy skies. A weakening frontal boundary will approach the area on Friday night, with the possibility of a few snow showers towards NW NJ.
Saturday – Monday: Some Showers Possible, Highs Back Into 40s
Several important changes in the synoptic pattern over North America are currently underway which will begin to have a more significant impact on the area beginning on Saturday. Since mid January, a strong, persistent ridge has been stationed over western North America and the northeast Pacific Ocean, leading to a meridional flow with most of the shortwaves associated with storminess in the eastern US originating from northern Canada diving southward, bringing frequent cold temperatures into the eastern half of the US. This also presented a difficulty for the model guidance to gain a proper handle on the storms given the lack of data sampling for the computer models to ingest over northern Canada; this was especially evident with the 1/21 storm which was not modeled to its full extent until only 48 hours before the onset of precipitation, and last night’s light snowfall which ended up further northwest than modeled. Over the next few days, however, the trough over the region will continue to lift out, which along with the ridging over western North America collapsing and being replaced by troughing over the southwest US, will lead to a southwesterly flow aloft from the south central US into the region as ridging returns into the southeast US.
While the above pattern will not lead to a sustained warm pattern, it will help to result in a temporary warm up over the weekend as a weak wave of low pressure tracks north of the area on Saturday into Saturday night. As of a few days ago, there was more consistent model support for this to produce rain with some snow in the area, although this has since become less likely with the latest model runs depicting a weaker and further north low. Interestingly, the ECMWF model has been the most consistent in keeping the precipitation north of the area, despite its relatively poor performance this winter. With mostly cloudy skies on Saturday and a continued SW wind, high temperatures are expected to warm up into the upper 30s to low 40s. Temperatures overnight are expected to struggle falling below the low to mid 30s, with the cold front likely to dry up as it approaches the area on Sunday with the most favorable dynamics well to the north of the area. The main uncertainty is regarding the high temperatures, depending on the timing of the front and whether any showers persist into the area; at this time, I am siding with highs peaking in the low to mid 40s during the afternoon ahead of the frontal passage with a few showers possible. For the upcoming Super Bowl on Sunday evening in Rutherford, NJ, the latest outlook is for mostly to partly cloudy skies with a breezy WNW wind at 8-16 mph, temperatures near 37 degrees at kickoff around 6:25pm, falling to 34 degrees by 10pm. Monday is expected to remain mostly cloudy with highs in the mid 30s, although the possibility of some rain and/or snow cannot be ruled out.
Tuesday – Wednesday: Storm Expected, Impacts Uncertain
A stormier pattern is expected to develop for the region into February, starting out with the first significant storm potential since last week expected to occur on Tuesday night into Wednesday. A shortwave trough is expected to enter the southwestern US around Monday, February 3, which with the southwesterly flow aloft is then expected to track ENE towards the central and northeastern US regions, while potentially interacting with a northern stream trough dropping out of Canada towards the Midwest, leading to the development of a surface low pressure over the central US which then tracks towards the eastern coast on Wednesday. The latest model guidance is remarkably consistent with the overall depiction of a storm affecting the region, having consistently shown signs of this occurring over the last few days; except for the 0z ECMWF, which kept the snow mostly south of the region, the remainder of today’s global model runs, along with the majority of their ensemble members, support a potentially significant snow and rain event affecting the region.
Model Analysis: With the overall synoptic pattern in place, the model guidance is expected to have a better handle on this time frame than with the late January pattern, when there was no consistency regarding the major snowstorm on January 21st affecting the area until just 1-2 days before the onset of precipitation. While the probability of precipitation falling in this time frame is high, with an 80% chance of precipitation included in the latest 8-day outlook, the main challenge in the forecast for NYC is how much precipitation falls and what will the precipitation type be, factors which depend on the track of the low pressure and the upper level setup. Posted to the left is the 12z ECMWF at hour 144, from the Pennsylvania State University e-Wall site, which highlights the two key features that are involved in this time frame, the southern shortwave over New Mexico and the northern stream shortwave north of North Dakota. As these features are currently in the central Pacific and northern Canada, respectively, at least another 4-5 days are expected until these energies will be better sampled, with the model guidance likely to continue shifting back and forth with the smaller details until then.
The potential track of the low pressure based on the latest indications ranges anywhere from the southeastern US to NY state; a stronger, slower and more amplified southern shortwave which has more interaction with the northern stream trough will be more likely to lead to an inland storm track that given an initial cold air damming signature with a high pressure positioned over New England would likely lead to some initial snow before warming mid level temperatures lead to a changeover to ice/rain, with the northern extent depending on whether the low pressure transfers to the coast and where this occurs. Meanwhile, a more progressive and flatter shortwave with less interaction with the northern stream would tend to stay more suppressed and likely enhance probabilities of a plain snow event in the area, but would lead to an overall weaker low pressure as well. Reviewing the latest set of model guidance, the GFS is the most progressive model, which is a typical bias, while the rest of the guidance is slower with the system. Regarding the timing, I am currently siding towards a blend of the two, as the ECMWF occasionally tends to be too slow with onset of precipitation, with the preliminary timing outlook from Tuesday evening to Wednesday evening subject to change. The next uncertainty is dependent on the aforementioned track which would influence what precipitation types the area receives; a recurring medium range model bias this winter has been to underestimate the strength and amplitude of shortwaves entering the US, and accordingly the majority of storms trended northwest from where they were positioned in the medium range. Another factor to consider, however, is the continued progressive flow in the upper levels which is likely at this time to prevent a significantly amplified storm track well to the north or west of the area.
Preliminary Forecast: With the above factors taken into consideration, while there remains a fair amount of uncertainty for an event a week away, the probability of precipitation affecting the region is high, and the potential exists for significant snow and/or rain amounts. Taking recent model trends and biases into consideration, I am currently siding closer to a scenario where the low pressure transfers to a track just along the coast, with a snow to mix/rain event during Wednesday. Considering that this is nearly a week away, however, the current outlook is only preliminary and is subject to change over the next few days. As is typical of models in the medium range, there could be a time period where the storm signal is weaker, although should this occur, it is not a final indication of the storm outcome, especially considering the recent tendency for significant changes in the outlook even within the short range. Should significant revisions end up being made to this outlook, the anticipated setup would favor a trend towards a warmer and further north storm. More information will be posted on next week’s outlook over the next few days.