Forecast Highlights:
Friday Night Storm Forecast
Calm conditions continue across the region today with a high pressure in place. These calm conditions will not continue for long, however; there are currently two storms in the eastern half of the US, a weak low pressure near Illinois producing moderate snow across the Great Lakes, and another system producing heavy rainfall near the southeastern US. Both of these will continue to approach the region, with a strong coastal low moving up the coast tomorrow in the late afternoon, evening and overnight hours, producing the first blizzard for the area since January 2011, slightly over 2 years ago.
Storm Set-up: This storm is a result of two shortwaves phasing over the region, with a significant nor'easter tracking off the coast. Unlike the major snowstorms that affected the region over the last few years, this storm takes place under a different and much more marginal pattern; there is a trough in the western US instead of a ridge, with the ridge axis east of the typically ideal position for a major East Coast snowstorm, along with a lack of blocking near Greenland.The two aforementioned low pressures will continue to move closer to the region tonight and early tomorrow; the low near the Great Lakes will move east towards western Pennsylvania, while the southeastern US low pressure will move up the coast towards North Carolina while intensifying. As the phasing takes place, the coastal low pressure will become the dominant system and will quickly intensify, as temperatures cool down across coastal areas with rain changing to heavy snow along with strong wind gusts. The low is expected to deepen to at least 976 millibars while briefly stalling close to Cape Cod on Saturday morning before weakening and heading offshore.
Model Guidance Overview: As with other storms this year, the model guidance has not been very consistent with this storm. Signs for the major storm scenario only showed up 144 hours out on the ECMWF model; with the three blizzards in 2010-11, signs showed up of a major storm further in advance. Even then, the ECM still exaggerated the storm compared to current expectations with the low pressure tracking over the coast, not offshore. The ECM was the only model to suggest a major storm for another two days until the rest of the model guidance caught on; until that point, the rest of the models only suggested this was going to be a minor snow event for the interior Northeast, with no sign of a coastal low developing.
Today's models are still not in full agreement on a major storm for New York City; the most bullish models at this time are the NAM, ECM and SREF, which suggest at least 16-20+ inches from the immediate NYC area into Long Island and Connecitcut. The GFS, CMC and UKMET remain further east with less significant snowfall, especially after the 0z runs last night when the low pressure was modeled to be much further offshore, but have gradually been trending slightly closer to the area with each run. The NAM model showed widespread 20+ inch amounts across the area; the NAM is known to have a wet bias and its amounts on a regional scale are likely exaggerated, and for tonight's update I am siding with a solution leaning closer to the ECM/SREF models.
Regional Forecast: As the two storms approach the region, two separate areas of precipitation will develop for Friday morning; the first will be widespread light-moderate snow in the northern Northeast, and the second consisting of moderate-heavy rain in the southern Mid Atlantic from the coastal low pressure. While snow continues in the northern parts of the region, the coastal low will spread further north by the afternoon hours, with mostly rain expected south of the I-80 corridor and mostly snow to the north. By the evening hours, the coastal low pressure will become the dominant storm, with temperatures aloft and at the surface cooling down as the rain/snow line gradually shifts southeast. Heavy precipitation will expand into eastern NJ, NYC, and southern New England, with heavy snow and strong winds developing and lasting throughout the overnight hours as the storm slows down and nearly stalls close to Cape Cod. A tight precipitation gradient is expected west of about NYC or eastern NJ, with lower snow totals expected but with at least moderate snow throughout the overnight hours. The snow will gradually end on Friday as the low pressure weakens and drifts out to sea.Significant precipitation amounts are expected from this storm as it contains a lot of moisture; liquid equivalent precipitation totals of over 2 inches are likely towards Long Island into southern New England, with most, if not all of that falling as snow. Widespread significant snowfall amounts of over 12 inches are expected in New England into the NYC area and eastern New York state, with the highest totals towards southern New England into Boston with near to over 24 inches of snow expected. Strong wind gusts over 40 mph are expected as well, which will result in blizzard conditions. Thundersnow cannot be ruled out as well for parts of southern New England, including Long Island.
The latest snow forecast is for at least 8 to 16 inches of snow in northern New Jersey and SE NY, with the lower end of this accumulation range for locations further southwest and the higher end further east closer to and including NYC where totals up to 12 to 18 inches may be possible; 10 to 20 inches in Long Island; and 16 to 24 inches of snow across southern Connecticut. Depending on where the heaviest snow bands develop and stall under, which currently appears to be closer to western Connecticut, snow totals could exceed 24 inches. For the latest local forecasts, please refer to the 5-Day Forecast page, updated as of this evening.
With the storm less than 24 hours from starting, there is higher confidence on the overall forecast, although there are still some areas of minor uncertainty which will be monitored throughout the day with tomorrow's storm updates. There is still some minor uncertainty regarding exactly how far west the coastal low tracks, which has an impact especially over the immediate NYC area and northern/eastern NJ. Given the tight precipitation gradient expected in the west side of the coastal low pressure, a minor difference in the setup of the heaviest snow bands will have a larger impact on local accumulations. Should the gradient end further east than currently expected, snow totals would be lower than currently forecast, potentially ranging from 6-12 inches with parts of Long Island and Connecticut over 12-18 inches. If the gradient is further west, however, totals would need to be raised for New York City, southeastern NY and northeastern NJ to over 12-18 inches, locally over 20 inches. Taking this potential gradient into consideration, I went slightly conservative on snow totals for the western parts of the area, although this will likely need to be revised upwards; any additional revisions to this forecast will be made on Friday morning. Additionally, at least some mixing with rain is likely for parts of the area, especially along and south of the I-80 corridor. The duration of any changeover to rain and the timing of the changeover to snow will be monitored as well for some impacts on the forecast snow totals in NYC, central NJ and Long Island.
This is the final detailed storm discussion. Storm updates will be posted throughout the day on Friday and into parts of Friday night, both here and in the NYC Area Weather twitter page.
Brief Long Range Overview: The cool down behind this storm will be short lived, as temperatures quickly warm up on Monday into the upper 30s and 40s as a low pressure tracks well north of the area; this will produce rain, with the potential for some initial front end precipitation for interior parts of the area. A colder pattern will return for the rest of the week with highs back into the 30s, along with the possibility of another storm towards late next week.
Good write-up.
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