The third major snowstorm of this winter is set to affect the area today and tonight as a deepening low pressure tracks northeast parallel to the coast, producing moderate to heavy snow with up to 12 inches expected east and south of NYC along with strong northerly winds and wind chills near -5 to -10 degrees. Cold temperatures will then return for an extended period of time, as high temperatures will mostly remain in the 10s and 20s for the next 7-9 days.
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Monday, January 20 Observations:
The first arctic cold outbreak since January 7 made its way southward through Canada, with a cold front pushing south through NY state during the day, producing areas of light snow, before reaching the area in the evening with isolated snow showers. With a southwesterly flow initially in place ahead of the front, temperatures returned to above average levels, peaking in the upper 30s inland, low 40s north/west of NYC, and in the mid to upper 40s in NYC and Long Island.
The highest temperature was 48 degrees in JFK airport, and the coolest high temperature was 38 degrees in Andover, NJ.
Today – Tuesday: Heavy Snow, Wind, Frigid
As yesterday’s morning update noted, there have been few consistent signs for a major storm to affect the region until this point, aside from a few model runs in the 156-180 hour range, which was mostly supported by the ECM which showed a significant system but with a somewhat different setup. The model guidance only fully began to trend towards a major storm early yesterday morning as they continued to slowly correct towards a sharper and stronger shortwave and vort max, which forces a low pressure to develop earlier and closer to the coast with more widespread and heavier precipitation. The trend was not over at that point, however, and the GFS and NAM have continued to trend wetter right through this morning’s 6z runs. While some small scale uncertainty remains, the third major snowstorm of the winter and the first with the heavy snow axis near the NYC area is set to affect the region today and tonight.
Impact Analysis: Since yesterday’s update, when the model guidance was still gradually correcting towards a stronger and further west low pressure, the guidance has generally come close to an agreement regarding the track and impact, with the low pressure tracking near southeast Virginia later today and briefly slows down southeast of New Jersey early tonight as the trough axis gains a negative tilt before quickly deepening and continuing to track northeast towards Atlantic Canada. Considering that the system is mostly northern stream based with little moisture from the Gulf of Mexico involved, as well as the cold air mass present north of the system that will be pulled into the region, precipitation type will be snow for most locations that observe precipitation, including far southern areas in Virginia and eastern North Carolina where some initial mixing with rain is expected. With the deepening of the low pressure and strong mid level lifting, moderate to heavy precipitation is expected to develop near and east of the I-95 corridor, supporting heavy snowfall.
Modeled precipitation amounts generally range from 0.35″ in interior western areas to 0.60″ near NYC and 0.80″ in Long Island/coastal CT. Snow to liquid ratios will be higher than the standard 10:1 ratio, however, with a thick dendritic growth zone (DGZ) with a saturated column up to 600mb, where temperatures of -12C to -18C support the formation of dendrite snow crystals and are favorable for higher ratios, which along with strong lifting within the DGZ but with strong northerly winds at 15-25 mph due to the tightening pressure gradient support ratios of at least 15:1. The strongest mid level lifting and most favorable dynamics are expected to set up between Philadelphia and central NJ and extend into NYC and Long Island, which is roughly where the heavy snow bands are expected to develop between 4-9pm, and the possibility of thundersnow cannot be ruled out under some of these bands. Later into the evening and night hours, the heavy snow bands will weaken as they shift east into Long Island and CT. Northwest of these bands into NW NJ and SE NY, steady moderate snow is expected throughout the duration of the storm. With the above factors noted, snow totals of 3-6″ are expected in NW NJ and SE NY, 7-11″ over the immediate NYC area, and 8-12″ over southern NYC into Long Island and coastal CT. There remains some uncertainty depending on the exact banding and ratios, however, with higher ratios and locations under the aforementioned banding axis capable of surpassing 12″ of snow, while locations northwest of the bands potentially seeing slightly less snow than forecast.
Forecast for NYC Area: Snow showers have already developed across northern NJ and NYC over the last 1-2 hours, and are expected to continue to steadily spread across the rest of the area by the early afternoon. Temperatures will continue to steadily fall before stalling in the low to mid 10s north and west of NYC and mid to upper 10s near and south/east of NYC for the mid to late afternoon hours. Heavy snow bands will develop near Philadelphia and central NJ early this afternoon, likely spreading into the area by 3-4pm with heavy snow focusing near NYC and Long Island/coastal CT while moderate snow falls elsewhere. Thundersnow cannot be ruled out under the heavier snow bands. By the evening and early overnight hours, a strengthening northerly wind up to 15-25 mph is expected, which along with heavy snow is expected to lead to near blizzard conditions in Long Island, although official blizzard criteria is not expected to be reached, while wind chill values fall into the 0 to -10 degree range. The snow bands will gradually shift east into the rest of Long Island and CT while weakening after 9-11pm, with snow steadily tapering off from west to east from 12am-2am west of NYC and 3-5am east of NYC.
Snow accumulations of at least 3-6″ are expected in NW NJ and SE NY, 7-11″ over the immediate NYC area, and 8-12″ over southern NYC into Long Island and coastal CT. While the model guidance has come into better agreement since yesterday’s update, despite the fact that it has taken until the night before the storm to actually reach a consensus, there remain some minor uncertainties regarding the snow totals and the ratios, with higher ratios than currently forecast leading to an increased likelihood of totals near/locally over 12 inches. The setup of the heavy snow bands will also continue to be monitored, which is currently forecast to end up from central NJ into NYC and west-central Long Island; this axis has the potential to see more snow than currently forecast, while NW NJ and SE NY may see slightly less snow than currently forecast. Live storm updates will be posted starting around 1pm and continuing through the early overnight hours.