A major winter storm is set to bring immediate impacts to the entire Tri-State region with a mixed bag of wintry precipitation ranging from snow to sleet, freezing rain, and rain. Coastal flooding and even urban street flooding could be a concern. Temperatures will plummet in the wake of this storm, with Arctic winds blowing from the northwest bringing the coldest air of the season and the potential for a flash freeze. The track of this storm has bounced around a bit throughout the week, though at the time of this writing, a warmer scenario with a storm track further north closer to the coast looks more likely.

My Forecast
High: 48°F | Low: 17°F | Max sustained winds: 35 mph | Total QPF: 1.40″ | Total snow accumulation: 1.00″ – verification for temperatures and precipitation will come from METAR data for the period between 1AM Sunday and 1AM Monday (06Z Sunday to 06Z Monday) at LGA. Wind speed verification will draw on the daily climate summary from the National Weather Service.

Verification
High: 40°F | Low: 15°F | Max sustained wind: 38 mph | Total precipitation: 0.80″ | Total snow: 0.00″ – Decent job of handling max sustained wind and the low, however, I missed the mark on high temperatures and overall precipitation by a large margin. I’ll post a more in-depth post-mortem analysis on this later this weekend. However, I do want to provide an initial assessment of the reasons behind my forecast bust on high temperatures and precipitation. These both have to do with the progression of the coastal and warm fronts associated with this storm. The warm front never made it further north than offshore of Long Island. As a result, we didn’t really get into the warm sector as I thought we would. This resulted in more northeasterly flow, keeping temperatures suppressed. The timing of the heaviest precipitation happened to be in the immediate six hour period preceding the start of my forecast window, when another 0.64″ of precipitation fell. I’ll look a bit more into this in the post-mortem, but I suspect the storm progressed a bit faster than forecast model data suggested on Saturday afternoon.

Synoptic Set Up
A large scale storm system with origins from the Pacific has been marching through the Ohio Valley and will eventually move offshore right in our vicinity. As this surface low continues to intensify, a warm front will first push into the coastal areas of the region. Ahead of this, snow should develop late Saturday, heavy at times. Eventually, as the warm front moves north of us, we’ll experience a transition over to rain. As the surface low progresses east, precipitation will end in the afternoon Sunday. This low will then continue to deepen, causing strengthening winds from the northwest to usher in an Arctic airmass and the coldest temperatures of the year.

High Temperatures
National Weather Service only recently released a warmer forecast in the mid-40s, before which they were showing highs in the mid-30s. However, most other sources are suggesting a substantially warmer high temperature in the upper-40s to near 50°F. In this case, I tend to agree with the consensus shaping up on the warmer side, with MOS guidance being on this warm side, and the generally reliable National Blend of Models similarly warm. The current most likely storm track places the area in the warm sector of this low, with MOS guidance showing an extended period of east-southeasterly winds veering to the south and southwest and blowing at a good clip, I can buy into the idea there will be decent warm advection and a surge of warm air to push temperatures up in to the upper-40s. Furthermore, I don’t see a lot of potential for evaporational cooling occurring, since the atmosphere will start off saturated during the morning hours (it’ll be raining).

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Low Temperatures
With strong northwest winds expected to develop on the cold flank of the surface low as it exits the area, low temperatures are likely to actually occur late overnight going into Monday. This is because warm advection will proceed the bulk of the rain Sunday morning. I’m siding with a blend of low temperatures from NAM, GFS MOS, and National Blend of Models.

Max Sustained Winds
Strong northwest winds are expected to develop behind the exiting low. A well-mixed layer is visible in forecast soundings, and this suggests the potential for the strong winds aloft at 850 mb to mix down. Sustained wind speeds could easily be in the 25-30 mph range with higher gusts. The intensifying low should also lead to an isallobaric component (winds becoming stronger in response to a deepening low) to the wind, which I think could push wind speeds to 35 mph. I believe the strongest winds of the day are actually coming after the precipitation since there’s going to be a warm nose above the surface, putting an inversion in place that would diminish downward momentum transfer while rain is coming down.

Total Precipitation
Several of the key ingredients needed for a heavy precipitation look to be coming together for this storm. This includes several strong vorticity maxima at 500 mb moving through. At the 300 mb level, a jet streak is forecast to be in the vicinity, but I don’t see this area sitting under a favorable jet streak quadrant that would support additional lift. Most of the lift here I think will come from the combination of 500 mb vorticity maxima and 850 mb isentropic lift depicted above. I actually see some low potential for elevated convection that could spur bouts of this heavy precipitation to fall. Moisture looks robust, with an 850 mb low-level jet forecast to develop as well. This should support deep moisture and lends further credence to the potential for heavy rain. Given the temperature profiles, it appears the risk of freezing rain and sleet is low at the coast, though more significant north of the city.