A high pressure remained stationed over the region today, keeping mostly sunny skies and temperatures slightly cooler than average. A significant heat wave is developing in the central US, however, and while the sustained heat will not reach the area, warmer temperatures and noticeably more humidity is expected especially for the first half of this week along with several rounds of heavy thunderstorms, possibly strong-severe, focusing on Monday evening and Wednesday, followed by a temporary late week cool down and a possible return of heat for early September.
Saturday, August 24 Observations:
Clouds from a cold front that moved through on Thursday night cleared the area early in the morning hours after a mid level shortwave triggered an isolated thunderstorm in coastal New Jersey. Throughout the rest of the day, a strong high pressure entered the region from the northwest, giving way to mainly sunny skies across the area, north winds, and temperatures slightly cooler than average, peaking in the upper 70s to low 80s for most. The highest temperature was 81 degrees in Somerset, NJ, and the coolest high temperature was 74 degrees in Montauk, NY.
[notice]Today’s discussion is more in-depth than usual. For those looking for a quick forecast, a simplified summary of the forecast discussion updated daily can be found in the 5-Day Forecast page.[/notice]
Tonight – Wednesday: Stormy, Warmer, More Humid
For the first time this summer, a strong stationary ridge is setting up over the central US, pulling a warm air mass from the Rockies into the central US with widespread 850 millibar temperatures over 20C, resulting in widespread high temperatures in the 90s and 100s, making it one of the most widespread heat waves of the year despite occurring at the end of meteorological summer. The region will remain in between the ridging to the west and troughing to the northeast, with a NW flow aloft bringing several mid level shortwaves through in the early-mid week period, triggering showers and thunderstorms, possibly strong/severe. The main uncertainty with the early-mid week outlook is regarding the exact timing and location of the shortwaves and the thunderstorms/MCS, with today’s discussion focusing on the timing but with some changes possible to the outlook.
Monday: Tomorrow’s outlook is a slightly complicated one with two clusters of thunderstorms/potential MCS complexes moving through the region. Latest observations show a cluster of thunderstorms in southern Canada, which is likely to move through New York State while weakening tonight into Monday morning while producing locally heavy rain and thunder. These storms are likely to stay north of the area, with cloud cover spreading in towards the early afternoon. This MCS will be accompanied by a mid level warm front tracking southeast through the area, bringing a much more moist air mass from the north as precipitable water values increase to 2 inches by the afternoon and evening. With this anticipated setup, partly cloudy skies are expected on Monday afternoon with highs rising into the low to mid 80s as dew points begin to climb into the 60s. By the evening, another and stronger shortwave will move through the region, likely triggering a cluster of thunderstorms tracking through SE NY and the area towards the evening hours. Some of the short range models indicate a potential MCS, although this potential is uncertain at this time and will be watched more closely tomorrow. Severe weather parameters are marginal, given low bulk shear and marginal instability, although storms will be capable of producing heavy rainfall.
Tuesday-Wednesday: Partly sunny skies are expected for Tuesday with highs climbing into the mid to upper 80s, along with more humidity as dew points likely reach the mid 60s. Another shortwave currently in the southwest US associated with tropical storm Ivo in the Pacific Ocean will track around the northern end of the ridge, reaching the Great Lakes and western Pennsylvania towards Tuesday night, potentially triggering another MCS which reaches the region, including the NYC area, on Wednesday, producing another round of thunderstorms and possibly strong-severe thunderstorms. This shortwave will be accompanied by a surface low pressure, likely to move through the area on Wednesday. There is some uncertainty regarding the timing of the storms, with some models bringing the storms in the morning to early afternoon hours, while others show a slower scenario with thunderstorms throughout the afternoon. At this time I am leaning towards a compromise with thunderstorms through the mid afternoon hours, although the timing is subject to change. Unlike Monday, more instability will be present, and some of the storms could be strong or severe. Due to the cloud cover and storms, cooler high temperatures are forecast, back in the low-mid 80s, but may be lower depending on the exact timing of the storms. Storms are likely to clear the area by the late evening-night hours.