Overrunning

We have a wintry week ahead of us that is similar in some respects to last winter. With a frontal boundary draped from SW to NE south of the region tomorrow, waves of low pressure will travel up along the boundary into the region. With high pressure to our north, boundary layer cold temperatures will be locked in place. The frontal boundary will oscillate north and south with the waves with warm air advection occuring in the mid levels. This act of warm air moving in over an established cold air mass at the surface is refered to as overrunning and can trigger steady precipitation. The exact positioning of the front and magnitude of the warm air advection dictates the precipitation type, however these set ups are often conducive to ice events.

Currently, there are two events to be watched this week: Wednesday and Friday.

On Wednesday a weak low pressure system will redevelop south of New England with some light to moderate precipitation overspreading the region. Temperatures will be cold enough to support all snow at least north of route 2, while icing becomes an issue further south. Water equivalents will range between .2" and .4" in the north with up to .6" over CT and RI (closer to the front). The main time period of snow here in Keene will be between 10am and 6pm, although the exact timing still needs to be ironed out a little. Total accumulations of 2 to 3 inches will be possible with this storm.

On Friday, a much stronger storm system will move across the Great Lakes region. With high pressure intact to our north, cold air reinforcement will keep precipitation in the form of snow at the onset, then changing to sleet and freezing rain during the day on Friday. Water equivalents could be much higher with this system and offer a potentially significant winter storm.

In addition to these separate events, clouds and light precipitation could be ongoing through Thursday as well as the front remains near the region.

More details later...