Afternoon All Zones: Significant snowfall increasingly likely Thursday
Forecast models have trended in favor of a stronger, more impactful storm system moving through the Mid Atlantic states on Thursday, and confidence is increasing in a significant snowstorm for a large majority of the forecast area. The potential exists for 9-12″ of snow in parts of the area, and higher amounts cannot be ruled out where bands of heavier snow develop.
The story of the storm system begins over the Midwest states, where a disturbance in the mid levels of the atmosphere develops on Wednesday. This energy moves eastwards from the Midwest through the Ohio Valley, and eventually to a position off the Mid Atlantic Coast. As it does so, interaction with a disturbance in the northern jet stream will cause the energy to deepen.
Evolution of the storm system on the GFS model
The response to this disturbance at the surface (where we are) is the development of a low pressure area. This low pressure center shifts from the Mid Atlantic states to the Delmarva Coast, and eventually a position south of New England. This places much of the Northern Mid Atlantic and New England in a prime location for heavy snow, to the northwest of the low pressure area.
The exact track and intensity of the storm remain somewhat uncertain, but forecast models today have all trended northwestward and stronger with the surface low itself. The storm system being closer to the coast means that more intense dynamics associated with the storm would move through parts of Pennsylvania, New Jersey, NYC, and into New England.
These dynamics in the atmosphere are a very critical component of the forecast. A well positioned upper level jet stream will allow precipitation to expand westwards from the low pressure area. But intense low pressure areas closing off in the mid levels the atmosphere will also enhanced lift for precipitation. Along temperature and wind gradients, this lift, know as frontogenesis, will create bands of very intense snowfall on Thursday.
The NAM model depicts intense frontogenesis (black area) and lift creating very heavy snowfall.
Within these bands, snowfall rates of 1-2″ per hour will be possible. Forecast models have wavered a bit on the bands location, but most of them agree that they will traverse the areas from Southeast PA through NJ, into NYC/LI and Southern New England.
Conditions are likely to be particularly poor on Thursday as the storm passes by. Significant snowfall accumulation with low visibility and gutsy winds now appears likely. Travel will be limited and significantly impacted, both in the air and on the area roads. Emergency crews and snow plow services should prepare to up crews from Wednesday night through Thursday in anticipation of snowfall accumulation.
Stay tuned for further updates and videos with more details on timing and other important information as well.
