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.