Oct 1, 2011: Clouds/Rain To Finally End This Week

As a cold front approached the area yesterday, September ended on a warm note across the area. With mostly sunny skies, temperatures surged into the mid to upper 70s across most of the area with a few 80 degree readings in the immediate NYC area. With the front moving over the area and a wave of low pressure developing off the coast, widespread light to moderate rain and thunderstorms affected the area, with most places seeing around 1/4 inch of rain. The heaviest amounts of rain were in the immediate NYC area, where 1/2 inch of rain fell. Due to the position of the low pressure today, there was a noticeable temperature gradient across the area, with highs peaking in the lower 60s inland, mid to upper 60s in the immediate NYC area, and the upper 60s to lower 70s in Long Island and southern CT.

The pattern since September 1st across the eastern half of the US has been mostly dominated by upper level lows producing cutoff systems sticking over the region for days. In early September, Tropical Storm Lee’s remnants merged with a cold front, sticking over the region for several days. After a nearly 10-day break from the rain, another front approached, and an upper level low sat over the Ohio Valley for over a week, keeping unsettled conditions over the region. After mostly sunny skies across the area on Friday, the most amount of sunshine since the middle of September, yet another cutoff low has formed, which will only extend the period of unsettled conditions over the region.

The current cutoff low is to the east of last week’s system, which will keep chilly temperatures in the NYC area with clouds and scattered showers lasting through Tuesday. With the cutoff low merging back into the main flow, a strong trough will move into the region for Tuesday night into Wednesday, but fortunately, there will be no upper level low over the Northeast associated with this; as a result, a strong high pressure will move into the region, bringing a much needed break from the rain and clouds with mostly sunny and dry conditions lasting through this coming week.

Tomorrow’s Outlook:

As yesterday’s discussion mentioned, due to the position of the cutoff low pressure, which will stall over Pennsylvania, the area will experience a SSE/SE wind. This will bring in a mild air mass from offshore into the NYC area and southern New England, while the rest of the region sees chilly high temperatures, in the 40s and 50s, even in places such as Washington DC and Virginia, which will be several degrees colder than places further north, such as NYC and Boston.

With cloudy skies and scattered showers expected, high temperatures will be chilly once again. Long Island and southern Connecticut will see the warmest temperatures in the area, reaching the mid to upper 60s. There is more uncertainty for the immediate NYC area and further west, however, which depends on the exact placement of the occluded front and the low pressure. At this time, I’m going with a slightly cooler scenario with upper 50s to lower 60s inland and lower to mid 60s in the immediate NYC area, but temperatures may be warmer than currently expected by a few degrees.

Monday – Thursday: Cutoff Low Exits, More Cold Enters

With the upper level low still stuck over the region, the cutoff low pressure, although weaker, will remain stationary over Pennsylvania, producing more clouds and scattered showers across the region. The leftovers of the cold air mass will drift closer to the area, with 850 mb temperatures expected to end up near 2-4 degrees celsius. This will bring slightly cooler high temperatures for Monday, peaking in the upper 50s inland, lower 60s in the immediate NYC area, and the lower to mid 60s in Long Island and southern Connecticut.

By Tuesday, however, the cutoff low will finally begin to drift away. As the upper level low begins to merge into the main flow, the low pressure will drift east towards the coast of southern New England, keeping the unsettled conditions in place for one last day. Mostly cloudy skies with isolated showers are expected over the area, with high temperatures only slightly warming up, reaching the lower 60s inland and the mid 60s across the rest of the area.

As the upper level low merges into the main flow, the low pressure near New England will quickly intensify as a trough moves towards the region, with the storm moving into Nova Scotia and Newfoundland. Due to a strong Canadian high pressure moving into the Northeast, however, the storm will stay over the Newfoundland area, and no upper level low will form over the Northeast this time. The position of the storm will bring a strong cold spell into the Northeast US, focusing over New England, and into SE Canada, placing the NYC area on the edge of the cold spell. The latest trends on the models have been to take this storm further west, and this trend would only bring colder temperatures to the area. As a result of the high pressure, clearing skies will take place by Wednesday, with mostly sunny skies and dry conditions expected for the mid-late week.

The temperature outlook is a little more uncertain, and depends on the location of the Canadian storm and the cold spell. At this time, I am going with a solution placing the cold slightly to the west of the latest model solutions, bringing high temperatures into the lower to mid 60s across the area for Wednesday and Thursday. Low temperatures would be in the lower to upper 40s across the area, with upper 30s possible inland in the colder case scenario. Stay tuned for more information on the potential cold for next week.

Friday – Next Weekend: Warmth Returns

When the cutoff low was not expected to develop over the area for this weekend, the cold spell was expected to quickly exit and be replaced by a strong warm spell by the middle of this week. Instead, the cutoff low is keeping the cool air mass in place, and will help pull the mid-week cold spell into the region, keeping the warmth stuck further west. This time, however, there is no cutoff low to keep the cold stuck over the region, and with a strong high pressure over the Mid Atlantic bringing a west flow into the region, the warm air mass from the central US will gradually spread into the region by the end of next week.

There is some uncertainty with how fast the warmth reaches the region, ranging from the faster GFS model bringing the warmth by Friday, to the slower ECMWF delaying the warmth until at least Sunday. Over the last two weeks, the models were usually too fast with pushing out the cutoff lows and the troughs, and trended slower with time. Some of the models may be once again too fast with pushing the cold air mass out, and at this time, I am going with the slower solutions, expecting temperatures to slowly warm up on Friday/Saturday bringing high temperatures into the lower 70s, with more significant warmth by Sunday into early next week. This warmth will not reach the region at its peak, with the warmest temperatures staying to the west of the region, but temperatures have the potential to warm up well into the 70s during this time frame, and if the warmer case scenario verifies, may even break the 80 degree mark. Stay tuned for more information on the potential warm spell.

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