Despite meteorological spring beginning in just two days, a January-like pattern continues regardless of the calendar date; as a strong piece of the polar vortex approaches the region, near record cold is expected tonight along with wind chill values below zero, with highs on Friday over 20 degrees below average. The cold will slightly moderate by the weekend but with widespread snow and possibly mixed precipitation expected to affect the region on Sunday night into Monday, followed by another round of cold temperatures for next week (image credit: NCEP MAG).
Today – Saturday: Very Cold, Windy; Isolated Snow Showers Today
Posted above from left to right are the latest surface analysis and radar composite from WPC, and the initialized NAM 500 millibar heights and vorticity from NCEP MAG; the radar is valid at 9z (4am), and the 500mb heights are valid at 12z (7am). After a gradual cool down in temperatures so far, a strong piece of the polar vortex rapidly surged southward from Canada with the aid of a strong upper level northerly flow, with a strong shortwave associated with this upper level low currently positioned near Michigan. This aided in the development of a relatively strong but moisture starved low pressure near southern Canada, which will progress ENE today and producing scattered snow squalls across the northeast US later this afternoon, mostly north of the area but with some snow showers possible as well near and north of NYC. The southerly flow ahead of this low pressure will lead to high temperatures mostly reaching the low 30s, a significant warm up from this morning when temperatures fell to near zero in NW NJ/SE NY and the Long Island Pine Barrens with the aid of strong radiational cooling.
As the low pressure departs, a tightening pressure gradient will lead to strong northwesterly winds at the surface, up to 15-25 mph with gusts up to 40 mph possible, which will also result in strong cold air advection as the frigid temperatures over southeast Canada brush the region while the core of the cold air mass remains north. While these frigid air masses can originate from different parts of the polar regions, in this case the core of the cold aloft surged southward almost directly from the north pole, taking only four days to transverse through Canada and reach the Great Lakes, with less time for the air mass to moderate. With Lake Erie frozen over, preventing a significant moderation in temperatures, well below average temperatures are expected tonight across the region, in some cases approaching and/or breaking record lows. Lows tonight are expected to fall into the low 10s near NYC and the immediate coast, mid-upper 0s in the suburbs of NYC and most of Long Island/coastal CT, low-mid 0s further inland, and near/below zero in interior NW NJ/SE NY. While Central Park’s record low of 5 degrees will not be broken, additional record lows in LaGuardia/JFK in the low 10s, including Islip and Bridgeport, are likely to be challenged. Along with the strong winds in the evening, wind chill values of at least 0 to -10 degrees are expected overnight into Friday morning.
Cold temperatures will continue into Friday as well with decreasing winds, mostly sunny skies and high temperatures peaking in the upper 10s-low 20s inland and the low-mid 20s elsewhere. For comparison purposes, the average high temperature for Friday in Central Park is 44 degrees, with an average low of 31 degrees. As the polar vortex becomes elongated over southern Canada, the frigid temperatures will lift from the region on Saturday, with highs reaching the low-mid 30s with mostly cloudy skies.
Sunday – Monday: Another Snowstorm Expected
As the near-record cold temperatures begin to depart the region on Friday, attention turns to the West Coast, where a significant storm system will produce widespread heavy rainfall and strong winds in California, which has been affected by a severe drought with little storminess this winter. Weak ridging is expected to become positioned over the southeast US behind a weak shortwave trough currently racing eastward through the southern US, setting up an upper level southwesterly flow aiding to carry the California shortwave trough ENE towards the central US, while the elongated polar vortex over southern Canada will aid to suppress geopotential heights and prevent significant amplification of the shortwave and a track too far north. Along with a cold air mass remaining close to the northeast US, the system will affect the region on Sunday into Monday with widespread precipitation, including yet another snowstorm despite the time of the year.
0z run of the GFS at hour 114, at 18z Monday (1pm), depicting the moderate snowfall affecting the region (image credit: PSU e-Wall).
As this is still several days away, there remain uncertainties with the more specific details in the synoptic setup which will ultimately determine the exact precipitation types and amounts for the area. Since yesterday’s runs, the GFS has trended towards less shearing of the southern stream shortwave as it enters the US, siding closer to the ECM/CMC with a more consolidated event from Sunday night through Monday night, rather than a flatter and longer lasting event through Tuesday. The main uncertainty at this stage remains the exact strength and timing of the southern shortwave, as well as the strength and position of the polar vortex over Canada and its interaction with the southern shortwave. The GFS has been somewhat consistent with the outcome over the region but with some run-to-run differences, such as the 6z run which was more suppressed with the polar vortex and slower with the southern shortwave, aiding in a colder and further south scenario, although it currently appears to be too cold and too far south with the frontal boundary on Sunday. The ECMWF remains the northern outlier, especially its 12z run yesterday which kept most of the snow north of NYC, although it slightly trended south with its 0z run last night. These details cannot be nailed down with high confidence at this time, and thus it is too early to put out a high confidence snow forecast, although the overall synoptic setup supports a potential axis of moderate to significant snow accumulations but with its exact placement and the maximum totals to be determined, with a possible range from southern Pennsylvania and New Jersey into central New England.
Preliminary thinking at this time is for high temperatures on Sunday to peak in the low to mid 30s, falling overnight into the 20s as light snow/sleet/rain showers develop on Sunday evening, gradually changing over to snow as colder air from the north enters the system. The steadier precipitation is expected to fall from Sunday night through Monday evening, generally ending by the mid overnight hours. At this time, the peak of the storm is likely to fall as snow, and the 8-day forecast has been adjusted to reflect this, although the possibility of mixed precipitation cannot be ruled out in the event the storm ends up further north/warmer than currently forecast. A more detailed analysis will be posted on Friday as the model guidance gradually begins to gain a better handle on the system.