Early December Storm/Pattern through Mid-December

[Dave C]

Good point about late intensifacation limiting changeover factor. I was just reading the latest NWS discussion and they are definately gun-shy about this one. They mention 1 model deepening storm considerably near Cape May while another is much less aggressive. Here's the link, it's an amusing discussion due to this uncertainty
http://www.erh.noaa.gov/box/products/BOSAFDBOX
Nothing like winter storm forecasting!

[donsutherland1]

The 12/7 18z NAM's soundings show a dramatic warming in the lower levels of the atmosphere. However, just as I advised last night, at this time I believe the NAM remains an outlier.

Hence, I don't expect anywhere near as long a period of rain as might be implied by the NAM. Instead, I continue to believe that an ECMWF-GFS compromise is the way to go.

This would produce only a short period of mixing north and east of the central NJ coast and parts of Long Island. Nantucket and Cape Cod would be impacted. However, most or all of the precipitation that would fall in the big cities--Philadelphia, Newark, New York, Providence, and Boston--would be snow.

Moreover, cities such as Providence would also benefit from dynamic cooling as vertical velocities exceed 25 (-ub/second).

Finally, the 18z GFS is now out to 54 hours and also remains in very good agreement with the ECMWF. So, overall I have sufficient confidence that my preliminary ideas remain on track.

Allentown: 3”-7”
Babylon: 4”-8”
Baltimore: 4”-8”
Boston: 5”-9”
Bridgeport: 4”-8”
Harrisburg: 3”-6”
Hartford: 4”-8”
New York City: 4”-8”
Newark: 4”-8”
Philadelphia: 4”-8”
Pittsburgh: 2”-5”
Providence: 5”-9”
Washington, DC: DCA 3”-6”/IAD: 3"-6"
White Plains: 4”-8”
Wilmington: 3”-7”

[donsutherland1]

Corrected...

I accidentally left the previous forecast for BDR unchanged. It should read: 2"-5"

After having reviewed the 12z guidance, it appears that there will be a changeover in the big cities. However, the changeover in places such as IAD, BWI, and PHL should come sufficiently late that the storm is mostly snow. NYC might begin and end as snow, but a changeover could push to the north and west of White Plains for a brief time. Should the low rapidly intensify, there would be the danger of a period of heavy snow from roughly Newark north and eastward.

As for Long Island, unfortunately, it appears that the changeover will be sufficiently quick to dramatically trim what I had been expecting in Islip (previously 4”-8”; now 1”-3”). Before the changeover, Providence and Boston could be thumped. Hence, I’ve only slightly lowered my expected accumulations there.

Albany: 3”-7”
Allentown: 3”-7”
Babylon: 1”-3”
Baltimore: 3”-7”
Boston: 3”-7”
Bridgeport: 2”-5”
Harrisburg: 4”-8”
Hartford: 5”-10”
New York City: 3”-7”
Newark: 4”-8”
Philadelphia: 4”-8”
Pittsburgh: 3”-7”
Providence: 3”-7”
Washington, DC: DCA 2”-5”/IAD: 3"-6"
White Plains: 3”-7”
Wilmington: 3”-7”

[donsutherland1]

December 9-10, 1786 saw a powerful nor'easter bury parts of the interior Mid-Atlantic and New England. Morristown, NJ picked up 15" snow and New Haven received 17".

Tonight and tomorrow will see a fast-moving storm bring a significant snowfall to interior sections of the Mid-Atlantic and Northeast. Even the big cities from Baltimore to Boston will likely pick up 4" or more snowfall. IAD has a good chance, as well. DCA will be harder-pressed. But with somewhat colder solutions in the recent guidance, bust potential might exist.

For what it is worth, record daily snowfall for December 9 for select cities follows:

Boston: 4.6", 1978
Hartford: 4.2", 1995
New York City: 2.4", 1942
Newark: 3.4", 1958
Providence: 3.0", 1995
Worcester: 8.0", 1903

Many of those records should be toppled. AccuWeather's Joe Bastardi might even be smiling with the storm's timing that coincides with daily record snowfalls in Hartford and Providence in 1995.

Given the 0z guidance, I'll leave my forecast as it currently stands. There is upward bust potential and a delayed changeover or deformation zone could lead to such busts. I venture a guess that such busts would be happier than those in which snowfall would fail to reach targeted accumulations.

Final Estimates:

Albany: 3”-7”
Allentown: 3”-7”
Babylon: 1”-3”
Baltimore: 3”-7”
Boston: 3”-7”
Bridgeport: 2”-5”
Harrisburg: 4”-8”
Hartford: 5”-10”
New York City: 3”-7”
Newark: 4”-8”
Philadelphia: 4”-8”
Pittsburgh: 3”-7”
Providence: 3”-7”
Washington, DC: DCA 2”-5”/IAD: 3"-6"
White Plains: 3”-7”
Wilmington: 3”-7”

[roebear]

Don,
Harrisburg is reporting 7.5" with close by local areas to 8.5, much of area from Penn State East had around those amounts with some higher in mountains. I had 9.5" and I am about 25 miles away, very nice storm while it lasted, had fun 4WD early in the morning

[wxwatcher91]

I got literally no snow at all from that first nor easter.

the snow ended just an hour ago from the storm today and on the ground lies 16 inches. (Im at 1000ft in Keene, NH)

[donsutherland1]

Verification:
December 8-9, 2005 Snowstorm

Overall, I am not very happy with the outcomes. While I correctly noted warmer air intrusions, I was not aggressive enough in cutting back totals for PHL and southward.

Worst was in New England where I trimmed amounts for warm air and didn't give adequate weight to the potential for heavy snow on the backside of the storm. I noted on December 7, "Estimates, particularly from northern New Jersey north and eastward might need upward revision should precipitation develop explosively. Greatest chance of that happening is probably across central and eastern New England, including the Providence and Boston Metro areas." In subsequent posts, I also repeatedly mentioned the threat that heavy snowfall could follow particularly from interior New England eastward.

So, all said, an unsatisfactory performance from my perspective.

From December 7, 2005 1:00 pm
Allentown: 3”-7”; Actual: 9.1"; Error: 2.1"
Babylon: 4”-8”; Actual: 0.2"; Error: 3.8"
Baltimore: 4”-8”; Actual: 2.2"; Error: 1.8"
Boston: 5”-9”; Actual: 8.6"; Within range
Bridgeport: 4”-8”; Actual: 6.0"; Within range
Harrisburg: 3”-6”; Actual: 8.4"; Error: 2.4"
Hartford: 4”-8”; Actual: 10.5"; Error: 2.5"
New York City: 4”-8”; Actual: 5.8"; Within range
Newark: 4”-8”; Actual: 6.0"; Within range
Philadelphia: 4”-8”; Actual: 2.2"; Error: 1.8"
Pittsburgh: 2”-5”; Actual: 3.7"; Within range
Providence: 5”-9”'; Actual: 3.8"; Error: 1.2"
Washington, DC: 3”-6”; Actual: DCA: 1.6"/IAD: 2.0"; Errors: 1.4" and 1.0"
White Plains: 4”-8”; Actual: 8.0"; Within range
Wilmington: 3”-7”

From December 8, 2005 12:30 pm
Albany: 3”-7”; Actual: 2.7"; Error: 0.3"
Allentown: 3”-7”; Actual: 9.1"; Error: 2.1"
Babylon: 1”-3”; Actual: 0.2"; Error: 0.8"
Baltimore: 3”-7”; Actual: 2.2"; Error: 0.8"
Boston: 3”-7”; Actual: 8.6"; Error: 1.6"
Bridgeport: 2”-5”; Actual: 6.0"; Error: 1.0"
Harrisburg: 4”-8”; Actual: 8.4"; Error: 0.4"
Hartford: 5”-10”; Actual: 10.5"; Error: 0.5"
New York City: 3”-7”; Actual: 5.8"; Within range
Newark: 4”-8”; Actual: 6.0"; Within range
Philadelphia: 4”-8”; Actual: 2.2"; Error: 1.8"
Pittsburgh: 3”-7”; Actual: 3.8"; Within range
Providence: 3”-7”; Actual: 3.8"; Within range
Washington, DC: DCA 2”-5”/IAD: 3"-6"; Actual: DCA 1.6"/IAD 2.0"; Errors: 0.4" and 1.0"
White Plains: 3”-7”; Actual: 8.0"; Error: 1.0"
Wilmington: 3”-7”; Actual: 2.6"; Error: 0.4"

[donsutherland1]

Roebear and Wxwatcher91,

This was a good storm. Parts of New England really got rocked in the end.

[donsutherland1]

At the beginning of this thread on November 30, I set an important benchmark that would, at least for my thinking, help determine the course not just of this pattern discussion, but the one that followed. Then, I noted: Beyond the first week in December, a generally colder-than-normal regime should prevail through at least mid-December and possibly beyond. The December 8-15 period could be especially cold, with minimum temperatures possibly falling into the teens on one or more days in the Mid-Atlantic and Northeast (from at least RIC to BOS).


This morning, temperatures fell into the teens in Philadelphia, Newark, New York City, Providence, and Boston. Baltimore just missed with a low of 20°. Tomorrow morning should be even colder in some of these cities. Thus, I have increased confidence in the pattern discussion I posted yesterday given that my read on the overall pattern and its evolution still appears on course, both in terms of events and their timing.

[donsutherland1]

Verification:

∙ I would not yet write off the prospect of at least some precipitation, including snow, affecting the East Coast early next week[Week of December 4-10] via closer storm development and a closer track.

December 4, 2005 Snowfall Totals:
Boston: 1.9”
Hartford: 2.2”
New York City: 2.5”
Newark: 3.6”
Philadelphia: 1.6”
Providence: 1.6”

∙ I would be surprised if the December 1-15 period sees no measurable snowfall from DCA to BOS… The overall pattern should result in measurable snow (and in this case, more than a trace, particularly from PHL to BOS in the December 1-15 timeframe). DCA and RIC could also see measurable snow during this period.

Total Snowfall for December 1-15:
Baltimore: 6.0”
Boston: 10.5”
New York City: 9.3”
Newark: 10.8”
Philadelphia: 7.0”
Providence: 6.6”
Richmond: 4.4”
Washington, DC: DCA: 4.8”; IAD: 5.7”

∙ A strong Arctic outbreak is possible in the period beginning late in the first week in December to shortly afterward… Beyond the first week in December, a generally colder-than-normal regime should prevail through at least mid-December and possibly beyond. The December 8-15 period could be especially cold, with minimum temperatures possibly falling into the teens on one or more days in the Mid-Atlantic and Northeast (from at least RIC to BOS).

Lowest Minimum Temperature:
Baltimore: 15°, 12/14 (4 lows < 20°)
Boston: 10°, 12/14 (4 lows < 20°)
New York City: 14°, 12/14 (3 lows < 20°)
Newark: 11°, 12/14 (3 lows < 20°)
Philadelphia: 15°, 12/14 (3 lows < 20°)
Providence: 10°, 12/14-15 (4 lows < 20°)
Richmond: 19°, 12/14
Washington, DC: DCA: 19°, 12/14; IAD: 13°, 12/14 ((4 lows < 20°)

Departures from Normal 12/8-15:
Baltimore: -8.5°
Boston: -8.8°
New York City: -8.9°
Newark: -10.9°
Philadelphia: -10.1°
Providence: -8.6°
Richmond: -6.3°
Washington, DC: DCA: -9.3°; IAD: -8.8°