Arctic cold December 1 - 10

Low pressure over the Great Lakes will pull a storm system over the southeast north through the Ohio Valley and across central New England. This will bring widespread precipitation over the northeast today through tomorrow. The precipitation began as a mix of freeezing rain and snow earlier this morning, resulting in a coating of snow and slippery roadway conditions. With warm air advection ahead of the storm, temperatures held steady through last night and have started to rise this morning. Precipitation has moved out of the area for now, but another area currently over PA will move in later this morning. With temperatures now above freezing, precipitation will be in the form of rain only. Periods of rain will continue through today. Cloud cover will keep temperatures around 40 degrees. Tonight, moisture from the southern system will reach the region resulting in locally heavy rainfall. Total accumulations in Keene will reach 1.0 to 1.3 inches. SW NH will be in the first maxima, with the south coast, subject to moisture flow off the Atlantic, will be the second maxima, reaching between 1 to 2 inches of rainfall by Tuesday morning. Rain will clear out tomorrow morning, and skies will partially clear. We will still be on the east side of the storm and therefore will reach around 45 degrees, however frontal passage Tuesday night will drive temperatures down to 21, and keep highs around 37 on Wednesday.

Further north, the storm system today and tomorrow will again be a producer of signficant snowfall reaching 5 to 10 inches.

A colder air mass from Canada with 850mb temps -3 to -6C will infiltrate the region Wednesday and will set the stage for a clipper moving west across the lakes into Thursday. This system will bring light QPF over New England and Quebec. It will tap into some of the warmth to the south, resulting in some precip type issues, but should be mainly snow in Keene. QPF on the order of .1 to .2 inches is possible. GFS is lighter than the NAM which brings up to .4 inches across the area. All in all, expecting a light 1 to 3 inch snow event Thursday.

This storm system will set up near Newfoundland (50N/50W) with a second system over the Great Lakes Saturday allowing a wedge of cold to flood the northern plains. The 50/50 low will develop ridging over Greenland and allow the cold in the midwest to continue east with only slight moderation. The ECMWF is less robust with the arctic air mass next week, however has not had great run to run consistency. For what its worth, CPC is along for the ride, indicating 70% confidence of below normal temperatures across the plains and 40% across the Northeast. 850mb temps shown by the GFS drop to near -20C by the start of next week. This will set the stage for a potential snow storm Monday through Wednesday. The GFS operational and ensemble runs have been consistent in bringing a low east from the SW over the weekend and develop it over the southeast and bring it northeast off the M/A coast, strengthening it sub 980. ECMWF does not release S/W over the southwest, resulting in a northern storm system only, with southeast ridging, and relative warmth in the east. Going by GFS, Track is still an issue, and one not to be worried about at this point. GFS has been flopping around with the track, with 00z run bringing low pressure west of New England (precip type issues) and 06z run sending it 500 miles east of the region (QPF issues).

In the long term, the one thing helping us out in terms of cold is a negative EPO. +PNA ridging is fairly consistent in the models, however contaminated by low pressure off the northwest coast. Meanwhile, there is also potential for the S/W over the southwest to be held in place (as shown by ECMWF). The main problem with this is southeast ridging would prevent the arctic air mass from making its way east. Even saying that the low kicks out of the southwest, low pressure off the PAC NW would be a nuscance by sending a strong Pacific Jet eastward, developin zonal flow and limiting arctic airmasses. The 06z GFS brings the low to the coast a little later than the past runs, resulting in a longer stay of cold air (through the second week of December). Here is what to expect for the first part of December:

• Arctic air mass starting 12/1. Temps averaging 5 to 9 degrees below average. Highs generally 25 to 35, Lows generally 5 to 20.
  
• Significant snow event 12/3-12/5. Expecting all snow. Accumulations greater than 3 inches.
  
• Cold sticks around through 12/10.
  
• Pacific Jet sends cold back north 12/10-12/17. Temps averaging 1 to 3 degrees above normal.
  
  
  
• Overall for December: Temps 1 to 3 degrees below normal. Snowfall 15 to 20 inches.