12/19-21/2007 Snowfall: Initial Estimates

[donsutherland1]

A system that will track into the New England waters and then rapidly intensify on Thursday will likely produce precipitation that will linger into Friday in parts of Maine. The heaviest precipitation appears likely to be focused on portions of New Hampshire and Downeast Maine. Questions still exist as to where the inverted trough will be established.

Right now, it appears that serious boundary layer issues will likely exist for coastal locations. In my opinion, the good run-to-run continuity that has highlighted warmer air aloft suggests that these issues will be a genuine concern. As a result, in spite of some juicy qpf, I am reluctant to offer huge snowfall amounts, as snowfall prospects could well be inhibited in those areas with boundary layer issues. Nevertheless, there is some uncertainty as to whether the intensifying system's dynamics could overcome precipitation type issues in Boston and Portland. Model consistency on snowfall amounts for those two cities has varied wildly across runs.

At this point, I believe Boston has a realistic shot at picking up the 0.4" snow it needs to bring December snowfall to 20". Since 1891, that has occurred 7 times:

1902: 22.8"
1926: 24.2"
1945: 24.6"
1947: 26.8"
1970: 27.9"
1995: 24.1"
2003: 21.5"

My initial snowfall estimates are as follows:

Albany: 1" or less
Boston: 0.5"-1.5"
Burlington: 2"-4"
Caribou: 1"-3"
Concord: 3"-6"
Hartford: 1" or less
Montreal: 2"-4" (5.1 cm-10.2 cm)
Portland: 2"-4"
Providence: 1" or less
Worcester: 1"-3"

[donsutherland1]

The 12z GFS provided a much colder solution than its previous runs. In fact, it brings all snow to Portland (15.1" according to Bufkit's Zone Omega algorithm). The NAM, consistent with earlier runs continues to indicate boundary level issues along the coast. Given the dramatic differences that have opened up in the guidance with respect to eastern Maine, I will take a compromise of the warmer NAM and colder GFS solutions for that area.

The remainder of the initial ideas remain in reasonably good shape.

My final snowfall estimates are as follows:

Albany: 1" or less
Boston: 0.5"-1.5"
Burlington: 2"-4"
Caribou: 1"-3"
Concord: 3"-6"
Hartford: 1" or less
Montreal: 2"-4" (5.1 cm-10.2 cm)
Portland: 4"-8"
Providence: 1" or less
Worcester: 1"-3"

[donsutherland1]

Verification

"Mega bust" does not even begin to describe what happened at Boston and Concord. Happily, snowfall proved much greater than anticipated, not the other way around. Although 6/10 (60%) of the cities saw snowfall amounts within the forecast range, both Boston (5.8" error) and Concord (5.5" error) had errors in excess of 5". The average error for cities with snowfall amounts outside the forecast range came to 3.3".

From 12/19/2007 12:43 am:
Albany: 1" or less; Actual: 2.2"; Error: 1.2"
Boston: 0.5"-1.5"; Actual: 7.3"; Error: 5.8"
Burlington: 2"-4"; Actual: 3.7"; Within range
Caribou: 1"-3"; Actual: 1.9"; Within range
Concord: 3"-6"; Actual: 11.5"; Error: 5.5"
Hartford: 1" or less; Actual: Trace; Within range
Montreal: 2"-4" (5.1 cm-10.2 cm); Actual: 3.2" (8.2 cm); Within range
Portland: 2"-4"; Actual: 5.7"; Error: 1.7"
Providence: 1" or less; Actual: 0.2"; Within range
Worcester: 1"-3"; Actual: 3.7"; Error: 0.7"

From 12/19/2007 12:46 pm:
Albany: 1" or less; Actual: 2.2"; Error: 1.2"
Boston: 0.5"-1.5"; Actual: 7.3"; Error: 5.8"
Burlington: 2"-4"; Actual: 3.7"; Within range
Caribou: 1"-3"; Actual: 1.9"; Within range
Concord: 3"-6"; Actual: 11.5"; Error: 5.5"
Hartford: 1" or less; Actual: Trace; Within range
Montreal: 2"-4" (5.1 cm-10.2 cm); Actual: 3.2" (8.2 cm); Within range
Portland: 4"-8"; Actual: 5.7"; Within range
Providence: 1" or less; Actual: 0.2"; Within range
Worcester: 1"-3"; Actual: 3.7"; Error: 0.7"