April 23, 2012: Behind Storm, Chilly Pattern Develops

Forecast Highlights:


- Mainly cloudy, chilly, occasionally rainy through next weekend
- Temperatures to remain mostly below average
- Additional rain expected on Thursday, possibly weekend


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Storm Overview:


Throughout the day yesterday and the overnight hours, the region was affected by one of the strongest storms of the entire season and the biggest storm since early December. As a low pressure moved up the coast from southeastern Virginia into NYC and north into New York state, widespread moderate to heavy rain fell, with rain totals ending up between 2.5 and 3.5 inches in Long Island and NYC, 2-4 inches in southern CT, and 1.5 to 3 inches in northern NJ/SE NY. Gusty winds were also observed, with a peak gust of 54 mph in La Guardia airport and 40-50 mph gusts across most of Long Island. The low pressure ended up noticeably to the east of the expectation, failing to track west of NYC, although the main impact in the area from this change was slightly weaker winds than expected and temperatures failing to surge into the mid-upper 50s west of NYC. Instead, temperatures today peaked in the lower to mid 50s from NYC and further west, and in the mid 50s to lower 60s in Long Island and southern CT.

Although the widespread rain moved out last night, the low pressure will continue to affect the region through tomorrow with mainly cloudy skies and isolated showers. Although the low pressure will move out by tomorrow night, widespread cloud cover, below average temperatures and occasional showers will stick around through the rest of the week and into the weekend as well as a weak low pressure moves through on Thursday, followed by another potential low pressure for the weekend.


Tomorrow's Outlook:


As the low pressure continues to slowly drift away from the region, mostly cloudy skies are expected with breezy SW winds with gusts generally reaching up to 30-35 mph. Highs are expected to reach the lower to mid 50s inland, mid to upper 50s in the immediate NYC area, and the upper 50s to lower 60s in Long Island and southern Connecticut. Isolated showers are possible at times, especially north and west of NYC.


Wednesday - Weekend: Chilly, Mostly Cloudy, Rainy At Times


With the low pressure moving out of the region, partly cloudy skies are expected for Wednesday with lighter winds, although isolated showers are still possible north and west of NYC. Temperatures will slightly warm up, reaching the mid to upper 50s inland and upper 50s to lower 60s across the rest of the area, which is still colder than average.

The brief clearing in the cloud cover won't last for long, however, as another weak low pressure moves through the region on Thursday. This low will be much weaker than yesterday's storm, with occasional showers expected throughout the day on Thursday into Thursday evening with at least 1/4 inch of rain possible. Temperatures will rise into the lower to mid 60s, possibly passing 65 degrees near the immediate NYC area. Some weak instability is shown on the models, and a few rumbles of thunder may not be out of the question when the cold front moves through in the evening.

The low pressure will then move into southeastern Canada, quickly intensifying while stalling for a short period of time. This will allow cold air to drop into the region once again, while suppressing any incoming storm tracks over the weekend so that any storm does not track too far to the north of the area. There is a general model agreement for some sort of a wave of low pressure for the weekend, although the intensity and location of the low are still uncertain, with some models showing a cold 40-45 degree rain for the area while others keep the rain south of the area. The models frequently overestimated the intensity of cold spells this season, and at this time I am siding with the northern outcomes where the storm ends up affecting the area with some rain and below average temperatures for the weekend. Currently, most models favor Sunday for rain, although the rain could also extend back into Saturday as the GFS and DGEX are showing, and the CMC is not far from. There is still some uncertainty for this time frame, however, including the location and timing of the storm potential for the weekend, with the possibility that the storm may entirely stay south of the area, and the forecast is still subject to some changes. The latest models do not show any significant warm spell approaching; should temperatures end up warming significantly, the earliest time frame possible for this would be into the first 7 days of May.