Dec 21, 2012: Winter Begins With 2 Snow Potentials

Forecast Highlights:

While the start to winter has been delayed, unlike last year winter has not been denied; the heavy rain and wind event today marks the transition to an actual wintry pattern, starting off with snow showers and strong winds across the region tonight and tomorrow, followed by chilly temperatures. The effects of this change will become even more noticeable next week, with two snowstorm potentials expected for the region, one which may result in a white Christmas for parts of the area.

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Tonight - Monday: Chilly, Windy Weekend

Early this morning, a strong cold front moved through the area, with heavy rain observed along with strong wind gusts up to 45-60 mph. Behind this cold front, a colder air mass will settle over the region for the next several days, with no sign of warmth within the foreseeable future. There have been gradual changes in the pattern until now, most notably including the strong polar vortex moving out of North America along with above normal 500mb heights near Greenland and Canada, but so far these changes have failed to produce sustained cold and snow for the region. This will gradually change in this time period, with the low pressure that resulted in the heavy rain today becoming an upper level low keeping a cold air mass in the region for the next few days.

Partly cloudy, windy and cold conditions are expected for Saturday. The low pressure from this morning's event will begin to move into Canada, with a strong WNW wind expected, at least 20-35 mph sustained with gusts up to 40-50 mph. Isolated flurries are possible especially for the interior parts of the area. Highs will be colder as well, only reaching the mid to upper 30s inland and low 40s for the rest of the area. Overnight lows will reach the low to mid 20s inland and mid 20s to low 30s elsewhere. For more location specific forecasts, please refer to the 5-Day Forecast page, to be updated tonight for the entire area. These temperatures will continue through Sunday and Monday with lighter winds.


Monday Night - Tuesday: White Christmas Possible

The first snow potential during this winter, excluding the two snow events in November, is expected just in time for Christmas eve. A weak low pressure in the Southeast will reach the region, producing light precipitation across parts of the region on Monday night into early Tuesday. Despite this being a weak system, it has potential to produce a white Christmas for at least parts of the area. Surface temperatures are likely to be an issue further south and east, especially towards the coast, where mostly rain is currently expected. At this time, most models show northern NJ and SE NY with the heavier snow from this storm with at least 2-4 inches, but there has been a small trend towards a more amplified and potentially further north storm. At this time, I am siding in between the more suppressed GFS and amplified ECM/CMC, with mostly rain for coastal areas and light snow north and west of NYC, perhaps mixing with some rain, with at least 2 to 4 inches of snow possible, but this could still slightly change. More information on this event will be posted over the next few days.


Wednesday - Thursday: Significant Storm Potential

The second and larger storm is set to affect the region on Wednesday and Thursday. The model guidance was originally showing this storm well to the west of the region, but after several changes in the large scale setup, including a block near Alaska moving east towards central Canada, the latest model guidance is showing this producing a snowstorm in the Northeast US. The models have been more variable regarding the exact outcome in the NYC area, with some of the earlier runs, such as the 6z GFS, showing more of a warm outcome with a rain/wintry mix event, while the latest runs, including the 18z GFS, are further east with a significant snowstorm for the area. The latest 0z GFS, shown to the left from the NCEP Model Analysis and Guidance site, is warmer than the 18z run, showing rain NYC and east, snow to sleet in the north/west suburbs, and a significant snowstorm for interior parts of the area. The ECM is further west and does change most of the area over to rain, but not before at least 6-12 inches of snow fall north and west of NYC.

While there have been several medium-long range snow potentials earlier this year and last year as well that failed to verify, this is the first widespread moderate-significant snow potential for the region within the December-February time frame, excluding the early season snowstorms, since January 21 this year, and before that since late January 2011. There is very high confidence that the storm will affect the area, and at least some snow is likely in parts of the area as well. The main question at this time is regarding the impact of the storm, including the intensity, track, timing and precipitation types/amounts. At this time, I am expecting an interior start as the storm initially starts to track west of the Appalachians, followed by a transfer to a secondary low pressure just off the coast, with a moderate-significant snowstorm potential for the Northeast, including the interior NW parts of the area, and a wintry mix event for the immediate NYC area, with some accumulations especially north/west of NYC but with more rain as well, especially for NYC and coastal locations. As previously mentioned, there is still time for this to change, however, and it is possible that the storm ends further east than currently expected, which would result in more snow for the area. The exact timing of the storm is still uncertain considering the time range, but overall looks to focus around the second half of Wednesday into Thursday, although still possible to minor revisions. Stay tuned for more information on this storm as details become clearer.


Longer Range: Colder Pattern, More Storm Potentials

Following the aforementioned changes in the pattern, there is no warm spell in sight within the foreseeable range. Cold temperatures are expected following this storm, with an overall colder pattern expected to last through the end of the month and into early January as well. The increased activity in the pattern will continue with several storms into early January, which some of these storms along with the colder pattern could end up as snowstorms for the area; the next pattern outlook to be posted tomorrow will discuss the late December-early January pattern in more details. There could be a storm towards December 30-31, although this one is more uncertain with some models not showing any storm at all, and such it is too early to determine the specific impacts of this storm, if one even takes place.