April 7, 2013: May-Like Warmth This Week

Forecast Highlights:

With a ridge building into the region and a frontal boundary staying mostly north of the area, a warm pattern is expected across parts of the region for the majority of this coming week with conditions much more late spring-like as highs reach the 70s in most of the area. The warmth isn't entirely here to stay, however, as a cold front will produce rain and possible thunderstorms on Friday followed by a brief yet relatively strong cool down with sub-freezing lows possible again.

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Monday - Friday: Warm, Some Rain

After a relatively inactive pattern with a lack of storminess since the end of March, a much more active spring-like pattern is expected for this week. A strong trough is currently dropping into the western US while a low pressure develops in the central US, resulting in a widespread snowstorm to its north and a severe weather outbreak to its south. The associated frontal boundary will extend through the Great Lakes and the Northeast with an upper level low in southeast Canada preventing the warmth from extending north through the entire region but also failing to suppress it south of the area. The warmth will continue through Thursday and early Friday as the central US system moves into the region, bringing a cold front with widespread rain and thunderstorms.

Edited 4/8 Morning

Model Analysis: Over the last few days, there were significant differences with the models regarding this week's pattern with the frontal boundary the main area of uncertainty, along with the track of the central US storm; the CMC and DGEX showed the boundary far north enough for almost the entire region to warm into the 70s and 80s, while the GFS was moderately suppressed, showing the frontal boundary in New England, enough to keep the area with highs in the 70s. The ECM, meanwhile, was much more suppressed with the boundary, dropping it persistently south of the area into the central Mid Atlantic, resulting in only 1-2 days of warmth followed by clouds, rain and highs in the 40s/50s. The ECM is typically reliable, but in this case was entirely on its own with keeping the boundary south of the area, as even its own ensemble mean further north and warmer. As a result, the forecast discussions for the last few days considered the ECM to be a cold outlier and sided with the rest of the models, with highs persistently in the 60s and 70s.

The ECM trended north on 4/7, showing the frontal boundary north of the NYC area but still south of the other models which had it towards central New England. The ECM still struggled initially, showing a strong Saturday coastal low, a highly unlikely scenario which it lost with the following run. Despite these trends, with the 4/8 morning runs all of the models, including the ECM, trended towards much slower timing of the storm than initially expected, which has implications on the mid-late week forecast. Wednesday is still expected to be mild, peaking in the 70s for most of the area except for parts of coastal LI and eastern CT. By Thursday, however, with the slower timing of the storm, the frontal boundary will be able to temporarily shift more south and end up over the area on Thursday, not to the north. This will result in a sharp temperature gradient; there is some uncertainty regarding exactly where it sets up, although should it be over the area as currently modeled, temperatures in NYC and northern NJ would end up in the 60s, perhaps in the 70s in western NJ, while Long Island and CT reach the 50s. While the original ECM runs did indicate a colder Thursday, they were still too far south with the frontal boundary, with the front over the central Mid Atlantic with the NYC area seeing highs in the 40s, a scenario still unlikely.

With the slower timing of the storm, rain from the cold front is likely to last longer as well. Given the storm track over the region, the frontal boundary will struggle lifting far north of the area, with Thursday night lows closer to average. Friday's highs will depend on the location of the low pressure, still subject to some changes which will be reflected in more details in tonight's (4/8) discussion. While earlier models had rain ending by Friday morning, the latest expectation is for rain to continue through the afternoon hours, possibly the evening, before ending. A cold air mass is still scheduled to move in for the weekend. Stay tuned for more information on the updated forecast.


Forecast for NYC Area: Mostly to partly sunny skies are expected on Monday with highs generally in the upper 60s to low 70s from NYC and further north/west and the low to mid 60s east of NYC. Increased clouds are expected on Tuesday with a risk of scattered thunderstorms especially north and east of NYC in the morning hours associated with a wave of low pressure north of the area, with otherwise partly to mostly cloudy skies and highs in the mid to possibly upper 70s from NYC and further north/west and the upper 60s to low 70s east of NYC.

With the frontal boundary north of the area on Wednesday, the warmest temperatures are expected as the next wave of low pressure stays mostly north of the area. Partly to mostly cloudy skies are expected with highs similar to those of Tuesday. The frontal boundary then starts to shift south on Thursday, reaching the area. A sharp temperature gradient is likely, with southern and western areas still likely in the 60s and possibly 70s while north/eastern areas cool down into at least the 50s.

The low pressure in the central US will track through the region on Friday, producing widespread rain and likely thunderstorms, especially south and west of the area. Any severe thunderstorm risk from this cold front is likely to stay minimal and south/SW of the area at this time. Cooler temperatures are expected on Friday with the cold front moving through, likely in the upper 50s and 60s but subject to change. While confidence is higher than yesterday regarding the outlook, the temperature outlook for Wednesday and Thursday is still subject to some revisions. Stay tuned for more information on this week's outlook.


Longer Range: Cold Not Gone Yet

While the March-early April cold pattern has ended, the last of this winter's cold is not gone yet. A strong albeit brief trough is expected to drop into the region behind the cold front, providing the region with a dry and much colder weekend. There is some uncertainty regarding the exact intensity of the trough, although highs are expected to reach the 50s with overnight lows mostly in the 30s, perhaps below freezing for interior areas. This cool down is likely to be short lived, however, as temperatures warm up again by early next week. Stay tuned for more information on the longer range.