May 23, 2013: Rainy Through Saturday, Dry Memorial Day

Forecast Highlights:

A slow moving cold front is currently approaching the region, with occasional showers and thunderstorms expected for today and Friday. A cutoff low will develop and slowly drift through the region, prolonging the shower activity through Saturday, or Sunday for eastern locations, replacing the warm and humid air mass from the last few days with well below average temperatures, struggling to approach 60 degrees for highs. This strong cool air mass will be relatively short lasting, however, with a warming trend towards the longer range.

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Note: Due to the upcoming stormy weather, storm updates will be posted later today and through Friday and Saturday.


Today - Friday: Rain, Thunderstorms, Heavy At Times

As of 10 AM, according to the latest regional radar, shower activity remains limited over the region. With a marine layer over southern CT and Long Island, conditions remain cloudy with fog and temperatures in the low-mid 60s, while NYC, northern NJ and SE NY have already warmed into the mid-upper 70s with heat index values near 80 degrees. With increasing instability and bulk shear, thunderstorms are expected to develop especially from NYC and north/west mainly after 12-2 PM, some which could be strong/severe with heavy rain, strong wind gusts and small hail. With the cold front approaching, widespread showers and thunderstorms will spread into the eastern half of the area by the evening as well, with showers expected to continue throughout the overnight hours across the area, producing locally heavy rain. Temperatures overnight will remain steady in the low-mid 60s for most of the area.

By Friday morning, the cold front will be located near the immediate NYC area and tracking east. As a result, a gradient in temperatures should set up, with highs peaking early in the afternoon in the upper 60s to low 70s in Long Island/S CT and NYC, while steadily falling throughout the day in north NJ and SE NY from the mid 60s in the morning to the mid-upper 50s by the evening. Occasional showers will continue throughout the day, especially east of NYC with the possibility for a period of dry conditions west of NYC in the afternoon and evening. Overall rain totals through Friday are expected to end up between 1/2 and 1.5 inch across the area, with the lowest amounts east of NYC and the highest amounts north and west of NYC.


Memorial Day Weekend: Cold/Rainy Start, Dry Ending

Yesterday's update mentioned the possibility for a cutoff low pressure to develop, prolonging the rain through the weekend, which now appears increasingly likely. A low pressure is expected to develop along the slow moving cold front on Friday, becoming a cutoff low overnight into Saturday while slowly drifting northeast just off the coast, which as with other late season coastal lows will produce widespread rain to its north and west along with unseasonably cold temperatures, only reaching the 40s and 50s for highs. Temperatures may even be cold enough for some snow in the higher elevations of the Northeast. The main uncertainty remains the timing and placement of the cutoff low, with model scenarios including the ECM with a slower low pressure, keeping cloudy skies and showers through Sunday, the GFS which takes the rain out of the area by Saturday evening, and the NAM which shows most of, if not all of the rain from the cutoff low staying to the east.

At this time, I sided with a blend of the GFS/ECM, with a breezy north wind and steady light-moderate rain from Friday night through Saturday night, generally amounting to at least 1/2 to 1 inch, with highs on Saturday well below average, only reaching the 50s for highs, with conditions gradually clearing out on Sunday with highs slightly warmer than those of Saturday but still well below average. There remains some uncertainty with this outlook, especially given the lower predictability of the timing and location of the cutoff low; a sharp gradient is likely to the west of the precipitation shield, with more sunshine and highs easily reaching the 60s. Regardless of the weekend outlook, however, the coastal low is expected to exit with a high pressure building into the region in time for a sunnier and warmer Memorial Day, with highs likely to approach 70 degrees again. Stay tuned for more information on the weekend outlook.


Next Week: Gradually Warming

The high pressure that builds into the region around Memorial Day will continue to slide southeast, settling off the coast. Looking at the mid-upper level pattern, troughing is expected to continue over the western US, with the ridge axis gradually shifting east towards the central or eastern US, a setup typically favorable for a warmer air mass to move in from the west/SW. Meanwhile, lower heights aloft are expected to continue over southeast Canada, acting to prevent the warm air mass from bypassing to the north of the region, instead likely directing it into the region. As this is at least a week away, there is still some uncertainty regarding the specific details in the setup, although the pattern supports a gradual warm up in temperatures throughout next week, returning to average by the mid week and above average by the late week. Stay tuned for more information on next week's outlook.