April 5, 2013: Warmer Start, Stormier Ending Next Week

Forecast Highlights:

A coastal low passed southeast of the area this morning, which was followed by clearing skies and warmer temperatures, reaching the 50s across most of the area. A gradual warm up is expected to continue, with highs reaching the 60s for Sunday through Tuesday, possibly slightly cooling down but remaining generally mild as rain affects the area by the end of next week.

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Tonight - Saturday: Briefly Cooling Down

As of this evening, the setup consists of a developing coastal low pressure off the coast of New England, headed towards Atlantic Canada, with a trough dropping into the region as a high pressure currently near the Midwest dropping southeast through the region. This trough will briefly bring colder temperatures, with decreasing winds and mostly clear skies expected tonight as temperatures drop into the 20s outside of the immediate NYC area which is expected to remain in the low 30s. For more localized forecasts, refer to the 5-Day Forecast page. Tonight is expected to be the last widespread sub-freezing night for a while, possibly until next winter, with a lack of strong cold air masses showing up in the foreseeable range.

With a high pressure overhead, mainly sunny skies are expected for Saturday with highs in the low to mid 50s from NYC and further north/west, and the upper 40s to low 50s in Long Island and southern CT. Light winds are expected, shifting from the NW in the morning to the SW by the mid afternoon and south by the evening. Overnight lows are expected to end up in the low to mid 30s inland and the mid to upper 30s for the rest of the area with increasing cloud cover as a low pressure approaches the region from the west.


Next Week: Active Spring Pattern Expected

Pattern Analysis: As mentioned over the last few days, an active spring weather pattern is expected to develop next week with building ridging in the eastern half of the US as a trough drops into the western states, with a significant low pressure developing in the central regions. When combined with a widespread warm and moist air mass to the south/east and a cold air mass to the north, this setup is expected to result in a severe weather outbreak in the early-mid week, especially towards Kansas, Oklahoma and Arkansas, with a late season snowstorm to the north.

Across the East, less storminess is expected early in the week, with widespread warmth expected especially from NJ/PA and further south as temperatures climb into the 70s, but with the main uncertainty around how far north the warmth extends, depending on the northern US/southern Canada flow aloft and where the frontal boundary sets up. The ECM is noticeably stronger than the rest of the models with an upper level low in southeastern Canada, which results in a stronger cold air mass returning into the Northeast following a brief surge of warmth on Monday-Tuesday, while the midweek storm is suppressed, tracking through the Ohio Valley with a secondary low over the region. The GFS and CMC handle the upper level low differently, taking it into central Canada while a stronger trough develops in the Atlantic Ocean unlike the ECM, resulting in an amplified ridge over the eastern US as the low pressure tracks well to the north, through the Midwest and into the Hudson Bay in central Canada. As is typical of medium range setups, run-to-run consistency is not solid yet; yesterday's 12z ECM had a widespread snowstorm in the region, a highly unlikely scenario, while earlier GFS runs alternated between a strong back door cold front pushing deep into Pennsylvania and the frontal boundary staying north with persistent highs in the 70s for the majority of the region.

Looking at the ensembles, the ECM mean, while more similar to the operational run in terms of the storm track which is different than the rest of the models, is noticeably warmer than the operational run, with the trough failing to drop into the region; the 850 millibar freezing line is near northern New England, compared to central NJ on the operational run. The GFS ensemble mean, meanwhile, is less amplified than the operational run. At this time, regarding the temperatures I am siding closer to the ECM through Tuesday, and for the rest of next week with warmer temperatures than the ECM, closer to the GFS but with a less amplified setup and a further south storm track remaining over the US/southern Canada as opposed to moving due NNE into Canada, with rain spreading in towards the second half of Thursday and Friday as the storm from the central US moves in, producing widespread rain and possibly thunderstorms across the region. This part of the outlook is still subject to changes over the next few days, especially regarding the temperatures for the second half of next week and the timing of the storm.


Forecast for NYC area: A warm front will move through the region on Sunday morning, with partly to mostly cloudy skies for the rest of the day as temperatures quickly warm from the 30s in the morning into the low to mid 60s from NYC and further north/west, and the mid to upper 50s in Long Island and southern CT. Scattered showers are possible for NW parts of the area. Similar conditions are expected for Monday with warmer temperatures, but a more pronounced sea breeze for coastal areas. Highs are expected to reach the mid to possibly upper 60s from NYC and further north/west, with mid 50s to near 60 degrees in Long Island and southern CT. Immediate coastal areas in southern Long Island are likely to struggle warming past the low 50s on both days.

Mild overnight lows are expected, struggling to fall below 50 degrees for parts of the area, followed by a weak low pressure tracking north of the area as its cold front approaches. Mostly cloudy skies are expected on Tuesday with widespread highs in the 60s, perhaps reaching the low to mid 70s near the immediate NYC area in the warmer case scenario. As the low pressure in the central US continues to gradually track east, a back door cold front is likely to move through at least parts of the region on Wednesday with highs possibly slightly cooling down but remaining in the 60s and possibly low 70s, with increasing temperatures from NE to SW. Another brief warm up is likely on Thursday and/or Friday as the low pressure tracks through the region, producing widespread rain and possibly thunderstorms, with temporarily cooler temperatures and drier conditions likely by next weekend.

As parts of this outlook are nearly a week away, additional changes are still possible in the forecast. One possible change is for less of a cool down in the mid week period and continued temperatures in the 70s. Stay tuned for more information on next week's outlook.