Oct 11, 2011: Warmth Won’t Last For Long

With the large ridge slowly weakening, today brought colder temperatures into the region, with high temperatures staying in the 70s across the area today, unlike yesterday and two days ago when temperatures surged well into the 80s, breaking record high temperatures across the area. As a low pressure moves up the coast, tomorrow will bring rain and colder temperatures, peaking in the 60s across most of the area. Even though temperatures will warm up again by the late week with showers and thunderstorms on Friday, a cold front will bring a stronger cold air mass into the region. While this cold air mass will not be strong and persistent, it is a step towards what may be a colder ending to October.

Tomorrow’s Outlook: Rain Returns

Rain currently over the southern Mid Atlantic will spread north tomorrow as a low pressure moves up the coast. A few showers are possible in the morning hours with more widespread showers developing after 4 PM, but unlike the expectation from last night’s update, it appears that the rain should be focused further west than first thought, over Pennsylvania, with less rain falling over the immediate NYC area. At this time, I am expecting 1/2 to 1 inch of rain to fall across most of the area, with locally higher amounts up to 1.25-1.5 inch possible west of NYC. If necessary, storm updates may be posted tomorrow afternoon and evening.

Due to the cloud cover, rain and an east wind, high temperatures will be colder tomorrow, peaking in the upper 50s to lower 60s inland and the lower to mid 60s in the immediate NYC area, Long Island and southern Connecticut. As the low pressure moves north, it will bring a warmer air mass further north as well, and with warming temperatures aloft, temperatures will remain steady during the overnight hours, if not slightly rise towards the early morning hours.

Thursday – Weekend: Rainy Ending To Week, Chilly Weekend

As the wave of rain moves to the north of the area on Thursday, mainly cloudy skies are expected with a few showers. High temperatures will be warmer due to the warmer temperatures aloft, reaching 12-14 degrees celsius, peaking in the upper 60s to lower 70s inland, lower to mid 70s in the immediate NYC area, and the upper 60s to lower 70s in Long Island/S CT. Temperatures may reach the 75 degree mark in the immediate NYC area if there are breaks in the cloud cover.
On Thursday night, cloudy skies will return as a cold front approaches the area. A negatively tilted low pressure will bring a line of rain and potentially thunderstorms through the Mid Atlantic on Thursday night, moving from the southwest to the northeast . Showers and potentially thunderstorms are expected to affect the area on Friday afternoon into the early evening hours, with the rain potentially heavy at times. The thunderstorms will end around Friday evening, with high temperatures slightly colder than those of Thursday. More information on Friday’s event will be posted with tomorrow night’s update.
Next Weekend – Early Next Week: Chilly, Dry

As the graphic above shows, a colder air mass will move in behind Friday’s cold front. With the low pressure stalling close to the region, windy conditions are expected for Friday night and Saturday, with winds potentially gusting up to 30-40 mph at times across most of the area. With the colder air mass moving in, temperatures will drop into the mid to upper 40s inland, and the upper 40s to mid 50s across the rest of the area. Saturday will bring partly sunny skies and windy conditions, and with 850 mb temperatures near 2-4 degrees celsius, high temperatures will peak in the upper 50s to lower 60s inland and the lower to mid 60s across the rest of the area.

The cold air mass is expected to weaken by Sunday, but it no longer appears that a significant ridge could build into the region. The potential was uncertain from the start, and now it appears that the cold air mass will remain stuck over southern Canada, with the NYC area near the edge of the colder temperatures to the north and warmer temperatures to south. Due to this boundary, there is some uncertainty with the high temperatures for Sunday through Tuesday. At this time, I am expecting temperatures to reach the upper 50s to mid 60s across the area for these days with a slight risk of showers on Monday and Tuesday, but this forecast could change. Stay tuned for more information on the outlook for early next week.

Longer Range: Winter-Like Ending To October?

By the middle of next week, however, much more interesting scenarios are starting to show up on the latest models. My October outlook, posted at the start of this month, hinted at the potential for more frequent cold spells during the last 7-10 days of the month. The latest teleconnections are starting to support this idea, with a negative NAO and a positive PNA developing. This combination results in a ridge in the West Coast, which in return causes a trough over the East Coast, and if the set up is right, this combination can lead to coastal snowstorms during the winter. While it’s still too early to talk about snowstorms for the East Coast, it’s the time of the year when we start to see stronger cold spells dropping into the United States, and if the latest overall idea on the pattern verifies, next weekend may bring a stronger cold spell into the region.

The latest models are surprisingly in an agreement with showing this strong cold spell, despite the time range. As this is still over a week away, there is uncertainty with the solution and changes are possible, but with the set up developing, next weekend may begin what may be a colder ending to October and start to November across the region. Regardless of whether we see more cold or persisting warmth, a storm is expected to affect the region around Wednesday-Thursday, the 19-20th of the month. Stay tuned for more information on the longer range, including the potential late week storm and the cold potential.

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