August 21: Rain Returns Tomorrow Night

Yesterday was mainly sunny across the area, with high temperatures in the mid 80s inland, with upper 80s to lower 90s for the immediate NYC area. As of 4 AM, with a chilly air mass currently over the area, temperatures are dropping quickly, and for this morning, are expected to reach the upper 40s to lower 50s inland, mid to upper 50s north and west of NYC, and in the mid 60s for New York City. Temperatures will also reach the upper 50s to lower 60s for Long Island, and the lower to mid 50s for southern Connecticut.

The area is still expected to be dry today, however this won’t last for long, as a storm approaching the area will bring another chance of rain for Sunday night and Monday.

Today’s Outlook:

Today (Saturday) will be a nice day across the area with partly cloudy skies expected and an onshore SE wind. High temperatures will reach the lower 80s inland, mid 80s for the immediate NYC area, and the upper 70s to lower 80s for Long Island and S CT.

Most of the region will also stay dry today, with the exception of western Pennsylvania and New York where a few showers and thunderstorms are possible, but this rain will continue to spread east overnight, reaching the area by Sunday.

Sunday And Monday: Rain, Potentially Heavy

Since my last update, the models were consistent in showing the heavy rain towards northern New England and southern Canada, however south of that area, there is still a lot of uncertainty, with some models such as the GFS only showing 1/4 inch, the NAM showing 3/4 inch, and the GGEM is showing nearly 2 inches for a large part of the area, though the GGEM is likely an outlier.

The models agree on a line of moderate to locally heavy rain moving through between Sunday late afternoon and Monday early morning, with rainfall amounts likely to be in the range of 1/4 to 3/4 inch across the area, the highest amounts towards the northern parts of the area. Precipitable water values are over 2 inches, and this should lead to locally heavy rainfall, with amounts locally up to 1.25 inch. These amounts may still change though, and an afternoon update may be posted to update these rainfall amounts.

Afterwards, the models have significant differences, with the GGEM forming a low pressure to our southeast with another round of heavy rain, the NAM stalls the heavy rain to our east while forming a low pressure off the SE coast, which would likely continue to move up the coast and bring a round of heavy rain to the eastern parts of the area, and the GFS simply moves the storm offshore with no additional development, though the GFS is not very good in its longer range. There is support from several models for the second low pressure offshore, however, and this scenario needs to be watched. Stay tuned for more details on this potential.

The next update that will be posted, either this afternoon or tomorrow morning, will include more details about this storm and the longer range beyond this storm.

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