Sept 26, 2011: Cloudy/Wet Pattern To Continue

Note: The 5-Day Forecast page was updated tonight for the immediate NYC area. On Tuesday, the page will be updated for the rest of the area as well.


The cut off low which previously affected the region with rain remained stationary over the western Ohio Valley, producing rain over that region, while a high pressure over the region kept mostly cloudy skies and a warm/humid air mass in place. High temperatures were warmer than average once again, reaching the lower 80s inland, lower to mid 80s in the immediate NYC area, and the upper 70s to lower 80s in Long Island and southern Connecticut.

As the cut off low begins to drift east, rain will return into the area for Wednesday and Thursday, with up to an additional inch of rain expected across the area. As the cut off low phases with another storm in Canada, a colder air mass will drop into the region for the weekend, but with an upper level low in place, however, rain chances may continue through the weekend as well.

Tomorrow’s Outlook:

With the high pressure sticking over the region, tomorrow will bring mostly cloudy skies once again to the area with a SE wind. 850 mb temperatures will remain around where they were today, near 14-15 degrees celsius, but more cloud cover than today is expected with a slight risk of an isolated shower in the western half of the area. With the factors above, temperatures will be slightly cooler than they were today, reaching the upper 70s inland, upper 70s to lower 80s in the immediate NYC area, and the upper 70s across most of Long Island and southern Connecticut.

Wednesday – Friday: Clouds Persist, Rain Returns

Over the last few days, the cut off low was well to our west, keeping the area dry, but as the storm will begin to slowly drift further east, rain chances will begin to increase by Tuesday night. The cut off low’s cold front will approach the area on Wednesday before moving through on Thursday, which will spread the rain further east, from the Ohio Valley into the Northeast. This scenario will bring rain back into the area. Occasional showers will develop on Wednesday, and will become more widespread by Wednesday night into Thursday, with heavier rainfall amounts expected. By the time that this round of rain ends around Thursday night, an additional 1/2 to 1.25 inch of rain is expected across the area, with locally higher amounts possible north/west of NYC.

By Friday, the cut off low will merge with another low pressure in Canada, which will help to pull a strong cold air mass into the north central US. This will bring another cold front through the area. This cold front is expected to be drier, bringing mostly cloudy skies to the area with isolated showers. High temperatures will be slightly cooler, peaking in the upper 60s to mid 70s across the area.

Next Weekend – Next Week: Cold, Then Warming Up

As the front pushes to the east of the area, a colder air mass will move in, with 850 mb temperatures dropping below zero degrees celsius in the Great Lakes, Ohio Valley, and parts of the Northeast. Unlike yesterday, when most models showed a high pressure moving in with dry conditions, however, the latest trend has been to show an upper level low slowing down over the region during the weekend. The models continue to differ with the scenario at the surface, ranging from the CMC showing a fully developed cut off low over the US, to the GFS with a moderate coastal low near New England, to the ECMWF with no well defined surface low.

Given the recent trends we have seen and the current pattern we are in, I am currently expecting a scenario where the upper level low moves over the region with a weak surface low, producing partly to mostly cloudy skies and scattered showers from the NYC area and further north and east, but widespread moderate-heavy rain is not expected at this time. This will keep the coldest temperatures to the west of the area, with places such as Washington DC potentially ending up colder than places further east such as NYC/Boston. Regardless of the storm, colder temperatures are expected for the weekend, with high temperatures likely to peak in the 50s across parts of, if not most of the area on Sunday. Stay tuned for more information on the cool down and potential storm for next weekend.

By next week, the cold air mass will be driven out of the region as a warmer air mass from the western US spreads further east. As this is in the longer range, there is more uncertainty, but the latest teleconnections as well as the pattern suggest that the potential may be there for another widespread warm up across the region next week. More information will be posted as details become clearer.

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