Sept 28, 2011: Winter-Like Start To October

The cut off low which brought widespread clouds to the region over the last day started to drift to the east, bringing the rain bands further east along with colder temperatures and lower humidity. Most of the area saw a few showers with cloudy skies, but the western parts of the area saw an unexpected round of heavy rain this morning, with as much as 1-2.5 inches of rain falling in parts of Sussex and Orange county. High temperatures today were slightly cooler than yesterday as a result of the increased cloud cover and rain, peaking in the upper 60s to lower 70s inland, mid 70s in the immediate NYC area, and the lower to mid 70s in Long Island and southern Connecticut.

The cut off low will continue to drift to the east, bringing more widespread showers into the area for tonight into Thursday, with a period of moderate to heavy rain possible in parts of the area. As this cold front pushes to the east of the area, cloud cover will clear with drying conditions for Thursday night, but another cold front will then push through the area on Friday night. Behind this front, the coldest air mass of this fall so far will move into the region, bringing high temperatures into the 50s across most of the area for Sunday, and when combined with a low pressure, the potential is there for the first snow of the season to fall in parts of New York state and Pennsylvania.

Tomorrow’s Outlook:

As previously mentioned, the cut off low drifting east will bring widespread rain back into the area. With 850 mb temperatures similar to those of today, near 13-14 degrees celsius, along with cloudy skies and rain, temperatures will be similar to those of today but slightly warmer, peaking in the mid 70s inland, mid to upper 70s in the immediate NYC area, and in the mid 70s across most of Long Island and southern Connecticut.

Occasional showers are expected to fall throughout the day today, with light to moderate rain affecting the area. Occasionally, especially during the middle of the day, locally heavy showers may be possible from NYC and further west. No significant rain amounts like those of Friday are expected, but rainfall amounts between 1/2 and 1 inch are expected across the area, with amounts locally up to 1.5 inch from NYC and further west. Storm updates will be posted during the day tomorrow when necessary.

Friday – Weekend: Cooling Down, Some Rain Expected

The cold front will move through on Thursday night, bringing clearing skies and drier conditions, with partly cloudy skies returning by Friday. Meanwhile, another front will approach the area from the west, which will move through by Friday night. This will keep warm temperatures in place during the day on Friday, with high temperatures expected to reach the lower to mid 70s inland, mid to upper 70s in the immediate NYC area, and the mid 70s in Long Island/S CT. Isolated showers are possible, but widespread rain is not expected.
For the weekend, a much colder air mass will move in from Canada. Meanwhile, an upper level low will form over the region, which will result in a weak surface low providing widespread showers across the region while trapping the colder temperatures aloft over the Mid Atlantic into Pennsylvania and parts of New York. This will produce scattered showers for the area on Saturday potentially into Sunday, with up to 1/4 to 1/2 inch of rain likely to fall, but no significant rain is expected, and the showers are mostly expected to be scattered. With the showers moving into the area of below freezing 850 mb temperatures, however, the potential is there that the first flakes of the season may fall in the higher elevations of New York and Pennsylvania. More information will be posted on this potential over the next few days.

In the NYC area, this cold spell will bring colder than average temperatures to start October. High temperatures on Saturday will reach the lower 60s inland and the mid 60s across the rest of the area. Due to the cloud cover on Saturday night, temperatures will drop into the 40s across most of the area with lower 40s inland and lower 50s in NYC. Sunday will be the coldest day, as cloud cover, cold 850 mb temperatures near zero degrees celsius, and scattered showers will keep temperatures below the 60 degree mark across most of, if not all of the NYC area. At this time, I am expecting temperatures to peak in the mid 50s in the western parts of the area and the mid to upper 50s from the immediate NYC area and further east; this is conservative when compared to the majority of the models, which are most likely overestimating the intensity of the cold air by showing high temperatures in the upper 40s to lower 50s across most of the area.

The coldest night will be on Sunday night, when the cold air mass starts to weaken. 850 mb temperatures will remain cold, near zero degrees celsius, which combined with less cloud cover and no risk of rain, will allow for the coldest temperatures of the cold spell to affect the area. Low temperatures are expected to drop below 50 degrees across the area, including NYC, which should see lows in the mid-upper 40s, with low temperatures reaching the 30s in parts of NW NJ/SE NY. Low temperatures in the lower 40s are possible as far as the immediate north/west suburbs of NYC in the colder case scenario.

Next Week: Warm Up Or Another Cold Spell?

As the trough will push out of the region by Monday, a surge of warmth will move in from the west, bringing warmer temperatures for Monday, reaching the upper 50s to mid 60s across the area, and even warmer temperatures for Tuesday, reaching the upper 60s to lower 70s across the area, potentially slightly warmer. Afterwards, however, uncertainty increases for the middle to the end of next week as a trough from Canada approaches the region. Some models keep this trough to the north of the area while bringing warmer than average temperatures into NYC, reaching the upper 70s, while others drop the trough to cover the entire region, with temperatures returning into the lower 60s for highs. The model ensemble means have been consistent for the last 2 days with dropping this trough into the region, and some of the main models, such as the GFS and ECMWF, are trending towards this scenario as well.

At this time, I expect this trough to mostly affect the interior Northeast with the NYC area close to the southern edge of the cold air mass, with temperatures slightly dropping, potentially into the mid-upper 60s range for highs, with temperatures potentially warming up again by the end of next week as the trough is likely to exit the region. Regardless of whether the cold or warm scenario verifies, however, dry conditions with sunshine are expected for next week as a large high pressure spreads across the region. Stay tuned for more information on next week’s outlook over the next few days.

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