Another winter storm will approach the area late Sunday and Monday. This storm while not huge, can still make for tough commute to work on Monday morning.

One low will head into Ohio and a secondary low will develop near New Jersey. With an artic airmass already in place, everyone will start as snow. However, the mid-level lows including the 850mb low are gradually trending north with this storm. Including the 850mb, which almost every track into Pennsylvania. Models soundings show a warm nose between 800mb and 900mb early Monday morning. This could lead to mix and change over with sleet for parts of Northeast New Jersey, New York City metro area and Long Island. The shortwave through for this system continues to trend more amplified. This will support the primary low in Western PA before transferring to coast. The more sleet mixes in the lower end of totals we are likely to see.

If the 850mb and surface lows track farther north like the GFS and UKMET suggest today. More places quicker changeover from snow to sleet/freezing rain then plain rain. If the cold air holds out longer, and there is little mixing with sleet, higher snowfall totals may be realized. After new guidance comes in tonight, I may update this forecast, if they are any significant changes.

The National Weather Services in Upton, NY and Mt. Holly, NJ have issued blizzard warnings for Extreme Southeast NY, Northeast New Jersey, and Southern Connecticut. They are forecasting 20 to 30 inches for almost their entire forecast area. Winds are expected to gust between 55mph to 65mph. With the strongest winds being on Eastern Long Island.

A shortwave trough associated with an Alberta Clipper, is moving eastward over Mississippi River Valley now. The is trough will amplify, meaning take an extreme negative tilt, and phase with northern stream shortwave energy coming down from Central Canada tomorrow. When the northern stream shortwave energy starts phasing with the southern stream, the trough will being to close off at 500mb. All models agree on this general scenario. But slight differences in handling of shortwave energy and interaction, are causing models to show different precipitation fields.

Mid-level centers closing off just south and east of the Tri-State area. These features will help with maturation of the cold-conveyor belt or the comma-head. The closed 500mb low also captures the low before goes out to sea then slow meanders off Long Island. As this low occludes, dry air will start intruding in the storm’s circulation. This is most likely closer to the low pressure center. Further away center, near the northern fringes, features a stronger deformation zone. It hard to pin exactly where we would see the banding. So the purple area in the forecast below shows most snowfall totals in purple area.

Strong vertical velocities (lifting in the atmosphere) along deformation zone, will cause snowfall rates of 2 to 4 inches per hour. Also this a deep arctic cold airmass coming in tomorrow, with strong high over Quebec.  So snowfall ratios are likely higher then typical average of 10 to 1. Right now, I expect ratios to be near 15-20 to 1, during the height of storm, Monday night and Tuesday. Where this band or another setups, we’ll be the areas that receive locally higher snowfall totals of 30 inches. Stay tuned for more detailed analysis of model runs tonight and tomorrow, before worst of the storm arrives. My current snowfall forecast is below. This forecast will updated, if necessary.

Snowfall forecast 11:30am 1/25 Update: The model guidance has trended with faster developing trough of warm of air aloft (TROWAL) and cold-conveyor belt with this storm. This means higher totals areas further Northwest. Also the cold-conveyor belt (CCB) tracks further east tomorrow over the area. For example, the 12z NAM model show below decent vertical velocities or lifting that and boundary level temperatures cooling enough for bands moderate snow late tomorrow afternoon for much of the area. Right now, I see this making for loss snowfall accumualtion with the changeover to rain in the morning for coastal areas. But I will monitor any stronger model trends with this CCB.

 From last night:

Snowfall forecast below for Saturday’s coastal storm you probably have heard about. Precipitation should arrive early Saturday morning and continue through most of the day. As with ever potential winter storm, there number things that often need to come together for a significant snowfall in the Tri-State. Especially for New York City and coastal sections. Here are some pros and cons for this storm that I see below. Based on the today’s model guidance:

Pros for snowfall

1. Surface and 850mb lows track south and east of area of the tri-state area.

2. Enough cold air already in place.

Cons for snowfall

1. No strong, cold high pressure to the north to keep cold air or setup a thermal gradient.

2. Not enough blocking in Atlantic, to force a slower moving storm

3. Phasing with northern stream occurring late.

4. Ridge more over the Pacific instead over the West Coast of North America.

Consider there are more pros and cons here. My forecast has light to moderate snowfall totals at best. Despite the low deepening into 980-990mbs, this storm matures to late for most of our area. Over interior Central and Eastern CT, this storm will start develop enough, that some heavy rates of snow may be possible. Comeback for more updates to this forecast and some model analysis  tonight or tomorrow. As well an update for another threat for snow early next week!