A low-pressure system over the Great Lakes brought a cold front across the Northeast US along with some rain and snow. At 12Z 24 February, this low-pressure system was perfectly positioned in the right jet entrance region of the jet streak, indicated by the dark pink color, shown in Figure 1.
Low pressure systems are characterized by air converging, or coming together, at the ground and then rising. The right entrance region of a jet streak is characterized by divergence, or air moving apart, at high altitudes. When stacked above each other, these conditions are optimal for the low be maintained as it moves away from the Great Lakes and across the Northeast US. Figure 2 shows how divergence and convergence are related to high- and low-pressure systems.
Figure 3 is a surface analysis showing the low and its associated cold front at 18Z 24 February. Cold fronts and low-pressure systems appear hand in hand because the cold, denser air lifts warmer, less-dense air. This rising air creates an area of low pressure that is often associated with rain and thunderstorms. Rain was present along the cold frontal boundary, but this specific front was weak enough that no severe weather impacted the area. However, snow did occur along the warm frontal boundary east of the low. While this seems like a juxtaposition, warm fronts do often produce snow in winter due to their less aggressive nature than cold fronts.
As the front continues to move across the Northeast, it continues to stay fairly weak. The temperature gradient as seen on the surface observations in Figure 3 is not super strong. This is supported by the water vapor satellite imagery show in Figure 4 and the air mass RGB in Figure 5. When looking at water vapor satellite imagery, darker colors indicate lack of moisture in the atmosphere while lighter whites represent more moisture. As you can see in Figure 4, this front is also not associated with strong moisture gradient; higher contrasts have been seen throughout history.
Drier, colder air will follow behind the frontal boundary, but it will not be highly different than the warmer, moister air in front of it as seen in Figure 5. In air mass RGB imagery, green colors represent warmer, moister air with blues and purples indicating cooler, drier air. The air following the cold frontal boundary is only slightly bluer than the green air before it. The cold front is expected to continue moving across the Northeast and into the Atlantic Ocean over the next couple days, bringing cooler temperatures to the region.
Finally, I would like to note that the lack of severe weather across the rest of the United States is due to the impressive zonal flow spanning the height of continental US and the positively tilted trough over the western US as seen in Figure 6. Positively tilted troughs produce little severe weather, and zonal flow is associated with moving storms associated with cold fronts fast across the US just like this cold front in the Northeast.