Second forecast for 3/1 - 3/3

A major winter storm will affect central and northern New England Thursday Night through Saturday Morning. Precipitation will begin as snow for all of SNE Thursday Night. Snow will continue past dawn in SW NH and NW MA, however will quickly change to sleet and freezing rain south of the Mass Pike as mid level temperatures rise above freezing. Snow accumulation of 1 - 2 inches will still be possible before the change-over in parts of CT, RI and SE MA. Here in Keene, the heavy accumulation once hyped for Thursday Night is now not looking as extreme. The warming of the mid levels could present some dry slotting complications. We may avoid this, but it is a short term forecasting factor that can only be speculated right now. At this point, accumulations of 2 to 4 inches will still be possible by Friday morning in Keene. A change-over will occur later in the morning to freezing rain and sleet. Right now, I think that we wont have to deal with any plain rain mixing in. Temperatures at the surface will be right around freezing Friday afternoon, so all precipitation will stay in frozen form. Precipitation will change back to snow and sleet Friday evening, and light snow will taper off by midnight Saturday. Additional accumulation of 2 to 3 inches is possible.

As for total snow accumulation, MOS data has decreased the accumulation forecast significantly down to 2 to 3 inches. I'm going to stay up in the range because higher accumulations based on high QPF supported by the GFS, NAM, and EURO. The NWS is also going with 4 to 8 inches.

Ice accumulation at least up to advisory level is possible Friday afternoon. Freezing rain and sleet will fall steady from 10am through 4pm and could accumulation up to a quarter inch of ice accretion.
NWS is discussing the issuance of winter storm watches for NW zones of SNE. I think we can be expecting watches issued by the evening shift today.

12z Model discussion:
The EURO and the GFS are both in the same camp with this storm: on the east side. The GFS has less QPF forecasted (1.50" to 1.75") than the NAM maxing out at 2.50" to 3.00". However, the NAM is about 100 miles further west with the low and takes it north up the CT River Valley. This puts 850mb 0C about 50 miles north of the GFS which draws the line along the NH/MA border.

Short term discussion:
The low pressure responsible for the moisture transfer to the coast is currently located in Kansas. The low will move northeast through tomorrow. A disturbance out of Canada will interact with the low and enhance the precipitation associated with the system. The low will center itself over Lake Michigan by tomorrow evening. While the low stalls, precipitation will continue to slowly inch eastward. Secondary development over the Delmarva peninsula will move north-northeast toward the region Friday morning. The track of this low will determine the type of precipitation that falls during this storm. The track will be influenced by the amount of energy that is transfered from the primary low over the Great Lakes. If the pressure falls along the coast are greater, then a more eastward track could occur, but otherwise we could see the coastal track north through CT. Right now the NWS is expecting a track across I-95 in SE Mass. Nowcasting time starts tomorrow afternoon as we can start watching the pressure falls. The HPC isnt expecting a low to form until 12z Friday. I'll post the latest HPC discussion right after this.

Storm snow accumulation forecast map for New England:

(Map correction: "valid: 12z Thursday 3/1 - 12z Saturday 3/3")

Snow accumulation forecast for Keene, NH for 12 Thursday 3/1 through 12z Saturday 3/3 (Issued at 0830 2/28/07): 4" - 7"
Ice accumulation forecast for Keene, NH for 12 Thursday 3/1 through 12z Saturday 3/3 (Issued at 0830 2/28/07): .1" - .3"