7:45 pm EST Thursday 2-23-12:
New forecasts coming in now and still trending cooler. This means that the secondary low will develop more quickly and reach a greater intensity before being driven off by approaching high pressure that will be building in for Saturday.
Low will approach the area tonight and snow will start at around 5:30am. Little accumulation before dawn but this thin layer will set the stage for more efficient accumulations with heavy snows later. Heavy snow will come with the 2nd low forming roughly 50 miles NE of Boston. This new low will start out fairly strong and will continue to deepen though cyclogenisis is not expected at this point. The new low will start to pull in sufficient cold air starting around 11:00. Warm air advection (which is warm air interacting with cold air usually overtaking it and produces precipitation) will be halted or significantly slowed by this point due to cool air being wrapped in by this point by the secondary low.
East winds brought on by the secondary low passing south of us will draw in warmer air along the coast and we will see a change to sleet possibly mixing with rain.
Snow amounts: Southern York County: 1-3″
Coast north of Portland to 20 miles inland: 3-5″
Inland and foothills: 4-6″
3:45 pm EST Thursday 2/23/12: Snow will overspread the region Friday Morning and continue throughout the day peaking at around noon. Temps will hover near freezing or a little bit above throughout the day. Temps will sharply rise in the 500 hour when a warm front comes through. This will cause a change to rain up until maybe 5 miles from the immediate coast. This changeover will persist for an hour or 2 and then cooling takes place after dark returning snow for all. Snow will taper off and end at around 2-3am north to south. Clear skies return with blustery conditions saturday.
Friday will feature essentually a very stormy day. Rain at the immediate coast and snow in the mountains with mix in between.
Going in depth a little more… A low will intensify as it moves NE out of the Ohio valley and into New England Friday morning. Snow will overspread the region Thursday night and will stay snow across the entire forecast area untill ~8am. This is where the forecast becomes very tricky. The coast south of Portland will experiance the changeover first with rain overrunning that area and remaining locked in place as warm air pushes north. Meanwhile a secondary low undergoes cyclogenesis over Cape Cod. Depending on how strong this low gets, the warm air could stall or even retreat slightly.
There are 3 dominant senarios for the secondary low development: 1) 2nd low deepens more rapidly and pulls in significant cold air therefore resulting in more significant coastal snows. 2) 2nd low fizzles and gets absorbed by intensifying main low therefore pulling in little to no cold air resulting in minimal coastal snows and hevier upslope snow. 3) 2nd low deepens at a marginal rate resulting in a moderate amount of cold air being pulled in and causing the warm air to be bottled up resulting in a sharp coastal front with a steep temperature difference. The exact placement of this front will likely determine the rain snow line if senerio 3 plays out
Our next storm will be impacting the region Friday with rain at the coast and snow inland. The mountains will pick up a few inches of wet snow. Rain will dominate at the coast. A late weekend storm will pass far out to sea and will not impact the region.
A storm will develop along a cold front and will move NE through the day. Amounts will be light other than far east Washington county where up to 1′ of snow could fall.
Indy will be hosting the suberbowl this weekend with no weather worries. Not that that will matter much since the game will be played inside the dome. What to expect inside the dome; 68 and dry.
No need to go into detail for any of the days in the 7-day outlook. The forecast simply is sun with a few clouds highs ranging from 29-37 in southern ME and take off a few degrees and you get the temps for the north and mountains. Add a few degrees to get southern NE temps. Mid atlantic: rainy for Superbowl sunday with temps generally in the 40s through the 7-day.