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Public Analysis: Coastal storm Saturday, improving Mothers Day, warmup next week

Good evening! We hope you had a wonderful Friday and enjoyed the weather over the past few days. It’s about to go downhill. Clouds will increase this evening as a coastal storm, which has been discussed for several days, begins developing over the Delmarva. A few isolated showers or areas of drizzle may develop overnight as low-level moisture and lift gradually increases. But mainly dry conditions are expected to stay in control. Temperatures will drop into the upper 40s to lower 50s in most areas

Rain will begin spreading from southwest to northeast throughout the region on Saturday morning. The intensity of rainfall likely become moderate to heavy by Saturday afternoon and evening, as the low pressure area moves further north to a position just off the Southern New Jersey or Delaware coast. If you have plans to go to the Yankees vs Astros game at Yankee Stadium tomorrow afternoon, it’s looks very likely you will experience delays or be rained out. Check our Sportscast page for more updates tonight and tomorrow. Temperatures with rainfall are likely to remain chilly and raw,  mostly in the upper 40s to lower 50s.

The biggest threat from this storm in terms of hazardous weather is from the potential for localized flash flooding. A strong easterly-low level jet with a plume of Atlantic moisture is forecast to develop. Strong frontogenesis from a thermal gradient will enhance lift in the atmosphere, adding support for torrential downpours that could cause some minor flooding on roadways, poor drainage and low-lying areas. Current models suggest this strongest lift will set up close to the I-95 corridor, north of Trenton, where 2” or more rain could fall. Intricate details and mesoscale dynamics are difficult for models to handle, so we will have to carefully monitor the positioning of these potentially heavier rainfall amounts. Otherwise, much of the region will likely receive at least 1” to 2” of rainfall from this storm.

NAM showing storng mid-level frontogenesis over the region tomorrow afternoon

NAM model showing strong mid-level frontogenesis over the region tomorrow afternoon

A tight pressure gradient will cause some gusty winds to push onshore as well. Sustained northeast winds between 15 to 25mph are expected with some gusts to around 40mph, especially near the coast. These onshore winds could lead to some minor coastal flooding during high tides Saturday evening  especially along the Western Long Island sound and the New Jersey shore. But a lower astronomical high tide cycle, between the full and half moon phase, is expected tomitigate coastal flooding impacts overall.

Rain will wind down and taper to showers later Saturday night as the storm begins moving further to our northeast. As a northern stream disturbance drops south out of Canada and phases with a southern stream disturbance, the low will track into the New England coastal waters. A drier northwest flow will cause clouds to mix out for more sunshine on Mother’s Day, with temperatures rising into the low/mid 60s during the early afternoon hours. It will be likely windy again due to a tighter pressure gradient behind this storm over the Gulf of Maine — with northwest winds possibly gusting over 30 mph at times.

 

3km NAM showing some scattered showers and isolated thunderstorms possible early Sunday evening

3km NAM showing some scattered showers and isolated thunderstorms possible early Sunday evening, as the coastal storm meanders over the Gulf of Maine

Another northern stream disturbance moves southeast from the Great Lakes and phases with the coastal storm as the day goes on. The atmosphere will be more unstable with cold-air aloft and daytime heating in the low levels. So a few scattered showers and isolated thunderstorms are possible later in the afternoon and early in the evening. Inverted-V model forecast soundings suggest thunderstorms might be capable of gusty winds and small hail. We will monitor this minor threat closely over the weekend, but we aren’t anticipating enough instability for any severe weather. We are also expecting festivities and the game with Derek Jeter Night to go on, with only a slight chance of a rain delay.

On Monday, the upper-level low will still be over New England. So some cool, unsettled weather could continue, with few isolated showers later in the day. A significant warming trend in temperatures is then likely later next week as deeper troughiness over the Western United States results in a stronger ridge building into the Eastern US. Temperatures, owing to west-southwest winds, could reach the well into 70s by Tuesday. Then more summer-like weather is possible between Wednesday and Friday with temperatures in the 80’s thanks to more compressed mid-level heights with ridge over Northeast and Mid-Atlantic regions. Some spots may even get to near 90 degrees!

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The GFS ensembles showing much warmer than normal temperatures over Northeast US late next week

The only fly in the ointment is that there is potential for a backdoor cold front to mitigate some of the warmth by next weekend. This occurs as some residual high-latitude blocking drops southward into Canada, possibly supporting the development of ac older high pressure to our north and temperatures falling back into the 50’s and 60’s with a maritime airmass.

Overall, however, we are likely looking at a several day stretch of warmer than normal air by the middle part of next week, with no significant rainfall events after this weekend. For more forecast updates, we encourage you to sign up for our Zone Forecasts, which include detailed updates daily and feature videos, interactives, and more — all sent to you directly in newsletter format!

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