Dec 19, 2012: Rain Thurs Night, Then Cold

*Correction: The headline was edited to fix a typo expecting rain tonight instead of Thursday night.

Forecast Highlights:

Following heavy rain and even some thunderstorms on Monday night into Tuesday, conditions are briefly drying up across the region for Wednesday and Thursday. This period of calm weather will be short lasting, as a stronger storm affects the region on Friday with heavy rain, wind and isolated flurries while a cold air mass settles over the region until about Christmas or the day afterwards, when the next storm is set to affect the region.

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Wednesday - Thursday: Calm Weather Continues

The low pressure responsible for the stormy weather for the last few days is now making its way out of the region, moving out into the Atlantic, although snow will continue over Maine for the next two days. A broad weak high pressure will move through the region, with cooler but still warmer than average temperatures expected for Wednesday and Thursday, peaking in the mid 40s-low 50s on Wednesday and the low-upper 40s on Thursday. More localized forecasts can be found in the 5-Day Page, updated for most of the area except for Long Island/S CT tonight - full updates will resume for the entire area starting on Friday. Mostly sunny skies with a breezy NW wind is expected on Wednesday, with light winds but increasing clouds on Thursday ahead of the next storm.


Thursday Night - Tuesday (Christmas): Stormy, Then Cold

The active pattern observed this week will end with a major storm on Thursday night and Friday, which is currently in the SW US and is set to affect Nebraska, Iowa and Wisconsin with a major snowstorm over the next two days. The low pressure will track towards the Great Lakes but will fail to progress northeast of there as the trough becomes negatively tilted with a secondary low pressure forming near the Mid Atlantic, moving into the Northeast where it will stall with a strong upper level low on top of the region. While the storm will not produce snow for the area, it will be more notable for its rain and wind impact, with heavy rain and possibly thunder expected from the cold front passage.

Rain will develop for the area after at least 1-3 AM with heavy rain and thunder expected to peak around 6-10 AM, ending by noon west of NYC and by the mid afternoon hours east of NYC. Up to 1 inch of rain is expected across most of the area, with locally higher totals possible. With a strong low level jet, wind gusts from the SE of near and above 40 mph are expected across most of the area ahead of the cold front towards late Thursday night and Friday morning, with localized gusts above 50 mph possible. Temperatures will initially start out in the low to mid 30s inland and the upper 30s to low 40s elsewhere, but will quickly rise as the rain approaches, peaking in the low to possibly mid 50s in the immediate NYC area into Long Island and parts of southern Connecticut on Friday morning. Behind the cold front, temperatures will quickly drop back into the 30s west of NYC and the low to mid 40s from NYC and further east for the afternoon hours; it is not out of the question that especially inland, showers change over to light snow in the late morning as the cold front exits. Snow showers will then develop across much of the western Northeast region, and isolated flurries are expected especially towards NW NJ through the early overnight hours.

The upper level low will be slow to move out with ridging extending into the Davis Strait, with a cold air mass expected to persist through at least Monday or Tuesday. During this time period starting on Saturday, high temperatures will generally be in the mid to upper 30s inland and the upper 30s to low 40s for the rest of the area; while this is not significantly below average, this is much closer to average than what has been observed so far this month, with only 2 days colder than average so far in Central Park. Overnight lows will be in the low to mid 20s inland and the mid 20s to low 30s for the rest of the area. Dry conditions will persist for the weekend and early week, with windy conditions returning on Saturday followed by lighter winds on Sunday and Monday.


Next Week: Storminess Returns

The increasingly active pattern will continue, with more storminess expected towards mid to late next week. While Christmas day is expected to be chilly, precipitation chances are somewhat uncertain as the latest GFS and CMC solutions support at least some light rain, possibly snow inland, while until this point no model has shown such a solution. At this time, I am expecting generally dry and chilly conditions for Christmas, although the risk of light precipitation cannot be ruled out at this time.

A more significant system is likely to set up for the eastern half of the US in the several days afterwards. The model guidance remains inconsistent with the specific details regarding this time frame, although based on the set up for this time period, an overall inland track is favored as opposed to a coastal track; while frozen precipitation cannot be ruled out for the area, especially inland, rain is expected to be involved during this time period, with perhaps significant amounts. Stay tuned for more information on this time period.



Longer Range: The next pattern outlook will be posted on Friday, focusing on the pattern for the rest of the month into early January.