Currently, we have a large broad trough sitting over North America with a polar vortex over northern Saskatchewan. We have a very fast flow through the CONUS right now, limiting the potential for deepening waves. However, we will see a few flat waves sliding through over the next few days. One of interest will be ejecting eastward underneath Alaskan ridging by Saturday afternoon. Again, model guidance keeps the wave very weak -- barely discernable at all -- until maybe the Ohio Valley, and allows it to deepen a little once it reaches south of New England.
This midlevel shortwave will pick up a small surface reflection originating in the Gulf of Mexico, and pulls it northward, still as only a weak low pressure area. We will see increasing warm advection through Sunday, and precipitation start to spread northeast by Sunday afternoon. Expect mostly rain south of the Mass Pike, but north of the pike, we could see a light snow event, possibly up to 2" to 4" in southern New Hampshire.
|posted by Sam Lillo @ 12/11/2009 10:32:00 AM
